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Transition metal intermediates bearing M−X σ‐bonds are ubiquitous in metal‐mediated C−X bond transformations. Thermodynamic knowledge of M−X bond cleavage is crucial to explore relevant reactions; but little was accumulated till present due to lack of suitable determination methods. We here report the first systematic study of the Pd−X bond homolysis dissociation free energies [BDFE(Pd−X)] of representative [(tmeda)Pd(4‐F−C6H4)X] (tmeda=N,N,N′,N′‐tetramethylethylenediamine, X=OR or NHAr) in DMSO on the basis of reliable measurement of their bond heterolysis energies (ΔGhet(Pd−X)). Despite ΔGhet(Pd−O)s of palladium‐phenoxides are generally found about 8 kcal/mol smaller than ΔGhet(Pd−N)s of palladium‐amidos, their BDFE(Pd−X)s are observed comparable. The structure‐property relationship was investigated to disclose an enhancement effect of electron‐withdrawing groups on BDFE(Pd−X)s. Linear free energy relationship analysis revealed that Pd−X bonds are more sensitive than X−H bonds to structural variation. The energetic propensity of reductive elimination from arylpalladium complexes was evaluated by combinatorial use of BDFE(Pd−X)s and BDFE(C−X)s, indicating an overall thermodynamic bias to C−N bond formation. [ABSTRACT FROM AUTHOR]

Examines equilibrium acidities and homolytic bond dissociation enthalpies of the acidic C-H bonds in As-substituted triphenylarsonium and related cations. Examination of the effects of a-triphenylarsonium groups on the equilibrium acidities; Results and discussion of the findings.

Reports on the comparison between free radicals and carbenium ions as hydride ion acceptors. Hydride affinities of free radicals obtained from thermochemical cycle; Difference in free energy changes; Estimation of absolute values for the hydride affinities of several models.

Studies the hydride affinities of carbenium ions in acetonitrile and dimethyl sulfoxide solution. Use of equations derived from thermochemical cycles; Errors associated with the determination of the reversible electrode potentials; Stable carbenium ion in dimethyl sulfoxide solution; Cancellation of errors due to kinetic shifts of the experimental potentials from the reversible values.

Presents information pertaining to the formal hydride transfer reactions regarding the reduced nicotinamide adenine dinucleotide (NADH) models, referencing to various cations and quinones. Possibility of a hybrid mechanism; How reduction potentials were obtained;Evaluation of the bond dissociation free energy of the 9-C-H bond in N-methylacridinium ion (AcrH+).

Studies the free energy hydride affinities of quinones in dimethyl sulfoxide solution. Use of thermochemical cycle; Determination of the pKa of hydroquinone monoanions; Observation of the values of deltaGhydride(Q)DMSO.

Introduction of the trifluoromethyl (CF3) group into organic compounds has garnered substantial interest because of its significant role in pharmaceuticals and agrochemicals. Here, we report a hydroxylamine‐mediated radical process for C(sp2)−H trifluoromethylation of terminal alkenes. The reaction shows good reactivity, impressive E/Z selectivity (up to >20 : 1), and broad functional group compatibility. Expansion of this approach to perfluoroalkylation and late‐stage trifluoromethylation of bioactive molecules demonstrates its promising application potential. Mechanistic studies suggest that the reaction follows a radical addition and subsequent elimination pathway. [ABSTRACT FROM AUTHOR]

N-heterocyclic phosphines (NHPs) have recently emerged as a new group of promising catalysts for metal-free reductions, owing to their unique hydridic reactivity. The excellent hydricity of NHPs, which rivals or even exceeds those of many metal-based hydrides, is the result of hyperconjugative interactions between the lone-pair electrons on N atoms and the adjacent σ*(P–H) orbital. Compared with the conventional protic reactivity of phosphines, this umpolung P–H reactivity leads to hydridic selectivity in NHP-mediated reductions. This reactivity has therefore found many applications in the catalytic reduction of polar unsaturated bonds and in the hydroboration of pyridines. This review summarizes recent progress in studies of the reactivity and synthetic applications of these phosphorus-based hydrides, with the aim of providing practical information to enable exploitation of their synthetically useful chemistry. [ABSTRACT FROM AUTHOR]

This account summarizes our recent work on the p K a scales of some frequently used organocatalysts, especially those of hydrogen-bond-donor catalysts and stronger Brønsted acid catalysts. Most of these p K a values were obtained by the Bordwell overlapping indicator method, which is known to provide high accuracy. Linear free-energy relationships associated with p K a values are discussed in relation to understanding of reaction mechanisms. 1 Introduction 2 Single Hydrogen-Bonding Donors 2.1 Proline-Type Organocatalysts 2.2 Cinchona Alkaloids Bearing a Hydrogen-Bonding Donor in the 6′-Position 3 Double-Hydrogen-Bonding Donors 3.1 Thioureas 3.2 Squaramides 3.3 BINOLs 4 Stronger Brønsted Acids 5 N-Heterocyclic Carbenes 6 Summary and Outlook [ABSTRACT FROM AUTHOR]

The past decade has witnessed a booming growth of research activity in catalytic imine reduction, due to the ongoing motivation to find more efficient conversions of the rather unreactive C=N bonds to the desired C–N segments found in many pharmaceuticals. While several timely reviews have well documented various C=N reduction methodologies with respect to the type of catalyst (acid, base, or transition metal), a detailed discussion of the core role of thermodynamic driving forces in governing these catalyses is still lacking, however. Hence, this tutorial review describes some of the most practical considerations for adjusting reduction thermodynamics by choosing appropriate catalytic strategies, in order to make the target reduction energetically feasible. The combined use of relevant thermodynamic parameters of the substrate imines, hydrogen donors, and catalysts in realizing such a goal is demonstrated on the basis of the energetics of the possible elementary paths. Experimental observations from the literature that are in line with the present energetics-based analyses are exemplified. [ABSTRACT FROM AUTHOR]

Nucleophilicity parameters (N, sN) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the Mayr equation log k2=sN(N+E). The N scale covers over ten N units, ranging from the most reactive hydride donor (N=25.5) to the least of the scale (N=13.5). This discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported for neutral transition‐metal‐free hydride donors and implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other nucleophiles such as the C−H, B−H, Si−H and transition‐metal M−H hydride donors. Structure–reactivity analysis reveals that the outstanding hydricity of 2‐H‐1,3,2‐diazaphospholene benefits from the unsaturated skeleton. [ABSTRACT FROM AUTHOR]

Nucleophilicity parameters (N, sN) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the Mayr equation log k2=sN(N+E). The N scale covers over ten N units, ranging from the most reactive hydride donor (N=25.5) to the least of the scale (N=13.5). This discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported for neutral transition‐metal‐free hydride donors and implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other nucleophiles such as the C−H, B−H, Si−H and transition‐metal M−H hydride donors. Structure–reactivity analysis reveals that the outstanding hydricity of 2‐H‐1,3,2‐diazaphospholene benefits from the unsaturated skeleton. P−H superhydrides: The unexpected philicity of P−H bonds in diazaphospholenes has made their applications to catalytic reductions a burgeoning field. A three‐parameter kinetic equation was used to evaluate their nucleophilicity parameters (N), which cover over ten N units. Kinetic studies imply their much superior hydricity over commonly used hydrides, with 2‐H‐1,3,2‐diazaphospholene being the strongest nucleophilic donor ever quantified by the Mayr equation. [ABSTRACT FROM AUTHOR]

Presents information on a study on the connection of the radical-stabilizing effects of the alpha-dialkylsulfonium groups with the free lone pair electrons of the sulfur atom. Equilibrium acidity of the S-phenacyldimethylsulfonium cation; Findings on irreversible oxidation potentials; Result of the synthesis of two S-(para-substituted benzyl)dimethylsulfonium cations.

The bench-stable cyclic hypervalent fluoroiodane reagent ( 1 ) is receiving increasing attention in fluorine chemistry because of its completely new reactivity. Fluorination mediated by reagent 1 generally requires activation by an exogenous Lewis acid. A more complete understanding of the Lewis acid activation model is thus paramount for the development of new strategies involving this reagent. Density functional theory (DFT) calculations herein demonstrate the generality of the “F-coordination” activation mechanism for reagent 1 that we recently showed to be favored over the commonly accepted “O-coordination” activation mechanism. [ABSTRACT FROM AUTHOR]

The unique heterocyclic skeletons of N-heterocyclic phosphines (NHPs) endow them with excellent hydridic reactivity, which has enabled NHPs to be applied in a great array of catalytic hydrogenations of unsaturated substrates in the past few decades. Recently, applications of NHPs in radical reductions, especially in a catalytic fashion, have emerged as a promising forefront area. This new reaction pattern, distinctive from but complementary to the well-established hydride pathway, can greatly expand the reaction scope to σ-bond scission. Herein, we briefly summarized some representative examples of synthetic applications of NHPs in both hydridic and radical reductions with an emphasis on their radical reactivity, including the structural and property studies of NHP radicals and their precursors as well as their applications in radical processes. [ABSTRACT FROM AUTHOR]

An efficient asymmetric allylic alkylation reaction with respect to 3-alkylidene oxindoles and racemic Morita–Baylis–Hillman carbonate has been achieved by using a chiral biscinchona alkaloid catalyst, which delivers the γ-substituted alkylideneoxindoles with a chiral tertiary center in moderate to good yields (up to 92%) and very good enantioselectivities (up to ＞99% ee). [ABSTRACT FROM AUTHOR]

The chiral benzofuranone structural motif is a prominent feature in many natural products, which exhibit a broad range of biological and pharmaceutical activities. In the past few years, a survey of chiral benzofuranone derivatives based on asymmetric catalysis reveals an increasing number of papers, which reflects the latest achievements to facilitate the synthesis of sufficient quantities of related compounds as potential medicinal agents and biological probes. Recent advances in this area are summarized and classified according to the structure of the starting substrate. [ABSTRACT FROM AUTHOR]

A simple, efficient, and highly atom economic haloamidation of simple alkenes has been developed, using AgBF4or InBr3/AgBF4(1:3) as catalyst and N-halophthalimide as both nitrogen and halogen source. A broad range of olefins can be applied to afford vicinal haloamines in good yields and with high regioselectivity and diastereoselectivity. [ABSTRACT FROM AUTHOR]

A polyethylene glycol (PEG)-supported NADH model as a novel organic reductant was designed and synthesized. The reductions of various α, β-unsaturated ketones by the PEG-supported NADH model were examined, and the results showed that the reductions completely and quickly proceed with no catalyst at ambient temperature. The main advantages of this liquid-like PEG-supported NADH model are easy workup, and an optimal potential for recycling use and solvent-free for use in reactions. [ABSTRACT FROM AUTHOR]

A series of primary-tertiary diamine catalysts were designed and synthesized from primary natural amino acids. Application of these new chiral catalysts in direct aldol reactions of a-hydroxyketones showed very good catalytic activity (up to 97% yield) and high syn selectivity (up to synl anti = 30:1, 99% ee). [ABSTRACT FROM AUTHOR]

The enantioselective aza‐Diels–Alder reaction is efficient for constructing chiral tetrahydropyridines, but the catalytic asymmetric aza‐Diels–Alder reaction of ketimines with unactivated dienes is still a challenging topic. Herein, guided by computational screening, a highly enantioselective aza‐Diels–Alder reaction of 2‐aryl‐3H‐indol‐3‐ones with unactivated dienes was realized by using a B(C6F5)3/chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza‐Diels–Alder reaction partners and hence offers rapid access to an array of tetrahydropyridine derivatives with pretty outcomes (up to 99 % yield, >20:1 dr and 98:2 er). The reaction is very efficient: lowering catalyst loadings for the model reaction to 0.1 mol %, enantioselectivity is still maintained. The synthetic utility was confirmed by transformations of the products. DFT calculations provide convincing evidence for the interpretation of stereoselection. [ABSTRACT FROM AUTHOR]

The enantioselective aza‐Diels–Alder reaction is efficient for constructing chiral tetrahydropyridines, but the catalytic asymmetric aza‐Diels–Alder reaction of ketimines with unactivated dienes is still a challenging topic. Herein, guided by computational screening, a highly enantioselective aza‐Diels–Alder reaction of 2‐aryl‐3H‐indol‐3‐ones with unactivated dienes was realized by using a B(C6F5)3/chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza‐Diels–Alder reaction partners and hence offers rapid access to an array of tetrahydropyridine derivatives with pretty outcomes (up to 99 % yield, >20:1 dr and 98:2 er). The reaction is very efficient: lowering catalyst loadings for the model reaction to 0.1 mol %, enantioselectivity is still maintained. The synthetic utility was confirmed by transformations of the products. DFT calculations provide convincing evidence for the interpretation of stereoselection. [ABSTRACT FROM AUTHOR]

The enantioselective aza‐Diels–Alder reaction is efficient for constructing chiral tetrahydropyridines, but the catalytic asymmetric aza‐Diels–Alder reaction of ketimines with unactivated dienes is still a challenging topic. Herein, guided by computational screening, a highly enantioselective aza‐Diels–Alder reaction of 2‐aryl‐3H‐indol‐3‐ones with unactivated dienes was realized by using a B(C6F5)3/chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza‐Diels–Alder reaction partners and hence offers rapid access to an array of tetrahydropyridine derivatives with pretty outcomes (up to 99 % yield, >20:1 dr and 98:2 er). The reaction is very efficient: lowering catalyst loadings for the model reaction to 0.1 mol %, enantioselectivity is still maintained. The synthetic utility was confirmed by transformations of the products. DFT calculations provide convincing evidence for the interpretation of stereoselection. [ABSTRACT FROM AUTHOR]

Fluorine incorporation into organic molecules is expected to lower the pKa of neighboring functionality via its strong electron‐withdrawing effect, and this strategy has been widely exploited in diverse disciplines. Herein, we report a striking anomalous α‐fluorine substitution effect on the α‐Csp3‐H acidity. We have experimentally measured the pKa values of a series of popular nucleophilic monofluoromethylating reagents α‐fluoro(phenylsulfonyl)methane derivatives as well as their C‐H analogues by Bordwell's overlapping indicator method in dimethyl sulfoxide solution. Contrary to expectations, we found that α‐fluorine substituent does not generally enhance but rather weaken the α‐Csp3‐H acidity of most (phenylsulfonyl)methane derivatives. DFT computations reproduce and provide insight into the anomalous α‐fluorine effect. A correlation was identified between the C‐H pKa of (phenylsulfonyl)methane derivatives and Mayr's nucleophilicity parameter (N) of the corresponding carbanions. [ABSTRACT FROM AUTHOR]

Fluorine incorporation into organic molecules is expected to lower the pKa of neighboring functionality via its strong electron‐withdrawing effect, and this strategy has been widely exploited in diverse disciplines. Herein, we report a striking anomalous α‐fluorine substitution effect on the α‐Csp3‐H acidity. We have experimentally measured the pKa values of a series of popular nucleophilic monofluoromethylating reagents α‐fluoro(phenylsulfonyl)methane derivatives as well as their C‐H analogues by Bordwell's overlapping indicator method in dimethyl sulfoxide solution. Contrary to expectations, we found that α‐fluorine substituent does not generally enhance but rather weaken the α‐Csp3‐H acidity of most (phenylsulfonyl)methane derivatives. DFT computations reproduce and provide insight into the anomalous α‐fluorine effect. A correlation was identified between the C‐H pKa of (phenylsulfonyl)methane derivatives and Mayr's nucleophilicity parameter (N) of the corresponding carbanions. [ABSTRACT FROM AUTHOR]

Fluorine incorporation into organic molecules is expected to lower the pKa of neighboring functionality via its strong electron‐withdrawing effect, and this strategy has been widely exploited in diverse disciplines. Herein, we report a striking anomalous α‐fluorine substitution effect on the α‐Csp3‐H acidity. We have experimentally measured the pKa values of a series of popular nucleophilic monofluoromethylating reagents α‐fluoro(phenylsulfonyl)methane derivatives as well as their C‐H analogues by Bordwell's overlapping indicator method in dimethyl sulfoxide solution. Contrary to expectations, we found that α‐fluorine substituent does not generally enhance but rather weaken the α‐Csp3‐H acidity of most (phenylsulfonyl)methane derivatives. DFT computations reproduce and provide insight into the anomalous α‐fluorine effect. A correlation was identified between the C‐H pKa of (phenylsulfonyl)methane derivatives and Mayr's nucleophilicity parameter (N) of the corresponding carbanions. [ABSTRACT FROM AUTHOR]

Thermodynamic knowledge of the metal–ligand (M−L) σ‐bond strength is crucial to understanding metal‐mediated transformations. Here, we developed a method for determining the Pd−X (X=OR and NHAr) bond heterolysis energies (ΔGhet(Pd−X)) in DMSO taking [(tmeda)PdArX] (tmeda=N,N,N′,N′‐tetramethylethylenediamine) as the model complexes. The ΔGhet(Pd−X) scales span a range of 2.6–9.0 kcal mol−1 for ΔGhet(Pd−O) values and of 14.5–19.5 kcal mol−1 for ΔGhet(Pd−N) values, respectively, implying a facile heterolytic detachment of the Pd ligands. Structure‐reactivity analyses of a modeling Pd‐mediated X−H bond activation reveal that the M−X bond metathesis is dominated by differences of the X−H and Pd−X bond strengths, the former being more influential. The ΔGhet(Pd−X) and pKa(X−H) parameters enable regulation of reaction thermodynamics and chemoselectivity and diagnosing the probability of aniline activation with Pd−X complexes. [ABSTRACT FROM AUTHOR]

Thermodynamic knowledge of the metal–ligand (M−L) σ‐bond strength is crucial to understanding metal‐mediated transformations. Here, we developed a method for determining the Pd−X (X=OR and NHAr) bond heterolysis energies (ΔGhet(Pd−X)) in DMSO taking [(tmeda)PdArX] (tmeda=N,N,N′,N′‐tetramethylethylenediamine) as the model complexes. The ΔGhet(Pd−X) scales span a range of 2.6–9.0 kcal mol−1 for ΔGhet(Pd−O) values and of 14.5–19.5 kcal mol−1 for ΔGhet(Pd−N) values, respectively, implying a facile heterolytic detachment of the Pd ligands. Structure‐reactivity analyses of a modeling Pd‐mediated X−H bond activation reveal that the M−X bond metathesis is dominated by differences of the X−H and Pd−X bond strengths, the former being more influential. The ΔGhet(Pd−X) and pKa(X−H) parameters enable regulation of reaction thermodynamics and chemoselectivity and diagnosing the probability of aniline activation with Pd−X complexes. [ABSTRACT FROM AUTHOR]

An efficient asymmetric allylation reaction of allylboronates with seven-membered cyclic imines, dibenzo[b,f][1,4]oxazepines, is described. The reaction, which is catalyzed by a Bi(OAc)3/CPA system, gives a range of chiral nitrogen-containing heterocycle structures in high yields and with good enantioselectivities. The conversion of these products to nitrogen-containing heterocycles is also demonstrated. [ABSTRACT FROM AUTHOR]

While many approaches to predict aqueous pKa values exist, the fast and accurate prediction of non‐aqueous pKa values is still challenging. Based on the iBonD experimental pKa database (39 solvents), a holistic pKa prediction model was established using machine learning. Structural and physical‐organic‐parameter‐based descriptors (SPOC) were introduced to represent the electronic and structural features of the molecules. The models trained with a neural network or the XGBoost algorithm showed the best prediction performance with a low MAE value of 0.87 pKa units. The approach allows a comprehensive mapping of all possible pKa correlations between different solvents and it was validated by predicting the aqueous pKa and micro‐pKa of pharmaceutical molecules and pKa values of organocatalysts in DMSO and MeCN with high accuracy. An online prediction platform was constructed based on the current model, which can provide pKa prediction for different types of X−H acidity in the most commonly used solvents. [ABSTRACT FROM AUTHOR]

While many approaches to predict aqueous pKa values exist, the fast and accurate prediction of non‐aqueous pKa values is still challenging. Based on the iBonD experimental pKa database (39 solvents), a holistic pKa prediction model was established using machine learning. Structural and physical‐organic‐parameter‐based descriptors (SPOC) were introduced to represent the electronic and structural features of the molecules. The models trained with a neural network or the XGBoost algorithm showed the best prediction performance with a low MAE value of 0.87 pKa units. The approach allows a comprehensive mapping of all possible pKa correlations between different solvents and it was validated by predicting the aqueous pKa and micro‐pKa of pharmaceutical molecules and pKa values of organocatalysts in DMSO and MeCN with high accuracy. An online prediction platform was constructed based on the current model, which can provide pKa prediction for different types of X−H acidity in the most commonly used solvents. [ABSTRACT FROM AUTHOR]

An efficient asymmetric aza-Friedel–Crafts reaction of phenols with isatin-derived ketimines is described. The reaction, which was promoted by a Bi(OH)3/CPA system, gave a series of chiral 3-amino-2-oxindoles with high yields (up to 99%), excellent enantioselectivities (up to 99%) and moderate to very good regioselectivities (up to 25/1). [ABSTRACT FROM AUTHOR]

Kinetik und Stereochemie der Reaktionen von aus Zimtaldehyden und MacMillans Imidazolidinonen erzeugten Iminiumionen mit Diphenyldiazomethan und Aryldiazomethanen wurden experimentell und mit Hilfe von DFT‐Rechnungen untersucht. Die Reaktionen von Diphenyldiazomethan mit von MacMillans Katalysatoren der 2. Generation abgeleiteten Iminium‐Ionen ergaben 3‐Aryl‐2,2‐diphenylcyclopropancarbaldehyde in >90 % Ausbeute und Enantiomerenverhältnissen ≥90:10. Überwiegend 2:1‐Produkte erhielt man bei den entsprechenden Reaktionen mit Monoaryldiazomethanen. Die gemessenen Geschwindigkeitskonstanten stehen in Einklang mit den aus den Einzentren‐Nucleophilie‐Parametern N und sN der Diazomethane und den Einzentren‐Elektrophilie‐Parametern E der Iminium‐Ionen berechneten Geschwindigkeitskonstanten sowie mit quantenchemisch berechneten Aktivierungsenergien. [ABSTRACT FROM AUTHOR]

The enantioselective ketimine–ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine–ene reactions of 2‐aryl‐3H‐indol‐3‐ones with α‐methylstyrenes were achieved by utilizing a B(C6F5)3/chiral phosphoric acid (CPA) catalyst. These ketimine–ene reactions proceed well with low catalyst loading (B(C6F5)3/CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2‐allyl‐indolin‐3‐ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C6F5)3 significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen‐bonding interactions, especially the enhanced N−H⋅⋅⋅O hydrogen‐bonding interaction, differentiates the free energy of the transition states of CPA and B(C6F5)3/CPA, thereby inducing the improvement of stereoselectivity. [ABSTRACT FROM AUTHOR]

The enantioselective ketimine–ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine–ene reactions of 2‐aryl‐3H‐indol‐3‐ones with α‐methylstyrenes were achieved by utilizing a B(C6F5)3/chiral phosphoric acid (CPA) catalyst. These ketimine–ene reactions proceed well with low catalyst loading (B(C6F5)3/CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2‐allyl‐indolin‐3‐ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C6F5)3 significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen‐bonding interactions, especially the enhanced N−H⋅⋅⋅O hydrogen‐bonding interaction, differentiates the free energy of the transition states of CPA and B(C6F5)3/CPA, thereby inducing the improvement of stereoselectivity. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: Electrophilic trifluoromethylthiolation has emerged as an important and efficient methodology for installing the SCF3 moiety onto an array of organic molecules. Due to the low reactivities of trifluoromethylthiolating reagents, these transformations often require activation through an exogenous Lewis/Brønsted acid. We report herein the quantification of the activation capabilities of Lewis/Brønsted acids for trifluoromethylthiolating reagents through computing the difference in trifluoromethylthio cation donor ability (Tt+DA) between the "activated" and "unactivated" reagent. A moderate correlation is found to exist between the activation capability and Lewis acidity. [ABSTRACT FROM AUTHOR]

Herein, we disclosed an efficient protocol for the construction of chiral 3-allyl-3-hydroxyoxindoles via the enantioselective allylation reaction of isatins and allylboronates catalyzed by a simple binary acid Bi(OAc)3/CPA system under mild conditions. The synthetic utility of this strategy has been demonstrated through the formal synthesis of ent-CPC-1. [ABSTRACT FROM AUTHOR]

The electrophilicity parameters (E) of some trifluoromethylthiolating and difluoromethylthiolating reagents were determined by following the kinetics of their reactions with a series of enamines and carbanions with known nucleophilicity parameters (N, sN), using the linear free‐energy relationship log k2=sN(N+E). The electrophilic reactivities of these reagents cover a range of 17 orders of magnitude, with Shen and Lu's reagent 1 a being the most reactive and Billard's reagent 1 h being the least reactive electrophile. While the observed electrophilic reactivities (E) of the amido‐derived trifluoromethylthiolating reagents correlate well with the calculated Gibbs energies for heterolytic cleavage of the X−SCF3 bonds (Tt+DA), the cumol‐derived reagents 1 f and 1 g are more reactive than expected from the thermodynamics of the O−S cleavage. The E parameters of the tri/difluoromethylthiolating reagents derived in this work provide an ordering principle for their use in synthesis. [ABSTRACT FROM AUTHOR]

Abstract: The electrophilicity parameters (E) of some trifluoromethylthiolating and difluoromethylthiolating reagents were determined by following the kinetics of their reactions with a series of enamines and carbanions with known nucleophilicity parameters (N, sN), using the linear free‐energy relationship log k2=sN(N+E). The electrophilic reactivities of these reagents cover a range of 17 orders of magnitude, with Shen and Lu's reagent 1 a being the most reactive and Billard's reagent 1 h being the least reactive electrophile. While the observed electrophilic reactivities (E) of the amido‐derived trifluoromethylthiolating reagents correlate well with the calculated Gibbs energies for heterolytic cleavage of the X−SCF3 bonds (Tt+DA), the cumol‐derived reagents 1 f and 1 g are more reactive than expected from the thermodynamics of the O−S cleavage. The E parameters of the tri/difluoromethylthiolating reagents derived in this work provide an ordering principle for their use in synthesis. [ABSTRACT FROM AUTHOR]

Electrophilic fluorination and fluoroalkylation are one of the most promising and efficient strategies in the synthesis of organofluorine compounds. The rapid progress of this field has been made possible by the emergence of a wide variety of power-variable, readily prepared, and easy-to-handle electrophilic fluorinating and fluoroalkylating reagents. Understanding the relative power of these reagents is thus vital for their use in synthetic transformations. This digest will outline some recent efforts to quantitatively ordering the relative power of electrophilic fluorinating, trifluoromethylating, and trifluoromethylthiolating reagents. [ABSTRACT FROM AUTHOR]

The most fundamental concepts in chemistry are structure, energetics, reactivity and their inter-relationships, which are indispensable for promoting chemistry into a rational science. In this regard, bond energy, the intrinsic determinant directly related to structure and reactivity, should be most essential in serving as a quantitative basis for the design and understanding of organic transformations. Although C-H activation/functionalization have drawn tremendous research attention and flourished during the past decades, understanding the governing rules of bond energetics in these processes is still fragmentary and seems applicable only to limited cases, such as metal-oxo-mediated hydrogen atom abstraction. Despite the complexity of C-H activation/functionalization and the difficulties in measuring bond energies both for the substrates and intermediates, this is definitely a very important issue that should be more generally contemplated. To this end, this review is rooted in the energetic aspects of C-H activation/functionalization, which were previously rarely discussed in detail. Starting with a concise but necessary introduction of various classical methods for measuring heterolytic and homolytic energies for C-H bonds, the present review provides examples that applied the concept and values of C-H bond energy in rationalizing the observations associated with reactivity and/or selectivity in C-H activation/functionalization. [ABSTRACT FROM AUTHOR]

Free energy relationship (FER) studies to correlate steric parameters with the enantiocatalytic performance of bifunctional tertiary-amine hydrogen-bonding catalysts, including ( S, S)-cyclohexane-1,2-diamine-derived thioureas, Cinchona alkaloid derived thioureas, and ( S, S)-cyclohexane-1,2-diamine-derived squaramides, in Michael reactions revealed that the reactions are much favored by catalysts with less bulky N-substituents. The observed FERs are independent of the chiral scaffold and hydrogen-bond donor, and deepen the understanding of current bifunctional hydrogen-bonding catalysts. Moreover, DFT calculations were performed to interpret the observed high reactivities of thioureas with less bulky substituents. In particular, the computations demonstrated the advantage of a benzyl thiourea catalyst, in which an extra CH ⋅⋅⋅π interaction between catalyst and substrate is the key factor. [ABSTRACT FROM AUTHOR]

The recent discovery of the radical reactivity of a few traditionally electrophilic N-F reagents has sparked a renaissance of radical fluorination. A knowledge of the N-F bond dissociation enthalpies (BDE) of electrophilic N-F reagents is essential for understanding of their reactivities. However, a thorough literature survey revealed that such information is extremely sparse. This prompted us to carry out the first systematic computation on the N-F BDEs of electrophilic N-F reagents. The calculated N-F BDE scale of 88 electrophilic N-F reagents ranges from 49.3 to 80.0 kcal mol-1 in acetonitrile. The large variety of N-F reagents and wide span of N-F BDEs make the scale a useful tool not only for the future rational design of novel reagents but also for judicious selection of appropriate ones to explore new radical fluorinations. [ABSTRACT FROM AUTHOR]

A highly predictive model to correlate the steric and electronic parameters of tertiary amine thiourea catalysts with the stereoselectivity of Michael reactions of 3-substituted benzofuranones and alkyl 2-phthalimidoacrylates is described. As predicted, new 3,5-bis(trifluoromethyl)benzyl- and methyl-substituted tertiary amine thioureas turned out to be highly suitable catalysts for this reaction and enabled the synthesis of enantioenriched α-amino acid derivatives with 1,3-nonadjacent stereogenic centers. [ABSTRACT FROM AUTHOR]

A highly predictive model to correlate the steric and electronic parameters of tertiary amine thiourea catalysts with the stereoselectivity of Michael reactions of 3-substituted benzofuranones and alkyl 2-phthalimidoacrylates is described. As predicted, new 3,5-bis(trifluoromethyl)benzyl- and methyl-substituted tertiary amine thioureas turned out to be highly suitable catalysts for this reaction and enabled the synthesis of enantioenriched α-amino acid derivatives with 1,3-nonadjacent stereogenic centers. [ABSTRACT FROM AUTHOR]

An asymmetric 1,6-conjugate addition of thioacetic acid with para-quinone methides has been developed by using chiral phosphoric acid catalysis in the presence of water. A series of sulfur-containing compounds were thus obtained in high yields with good to excellent enantioselectivities. Theoretical studies indicated that the water-bridged proton transfer is a potentially favorable reaction pathway. An unprecedented O−H⋅⋅⋅π interaction between water and the aromatic nucleus of chiral phosphoric acid was discovered to contribute significantly to the stereocontrol in the catalysis. [ABSTRACT FROM AUTHOR]

An asymmetric 1,6-conjugate addition of thioacetic acid with para-quinone methides has been developed by using chiral phosphoric acid catalysis in the presence of water. A series of sulfur-containing compounds were thus obtained in high yields with good to excellent enantioselectivities. Theoretical studies indicated that the water-bridged proton transfer is a potentially favorable reaction pathway. An unprecedented O−H⋅⋅⋅π interaction between water and the aromatic nucleus of chiral phosphoric acid was discovered to contribute significantly to the stereocontrol in the catalysis. [ABSTRACT FROM AUTHOR]

A visible-light-mediated, organic photocatalytic stereoselective radical cascade cyclization of polyprenoids is described. The desired cascade cyclization products are achieved in good yields and high stereoselectivities with eosin Y as photocatalyst in hexafluoro-2-propanol. The catalyst system is also suitable for 1,3-dicarbonyl compounds, which require only catalytic amounts of LiBr to promote the formation of the corresponding enols. [ABSTRACT FROM AUTHOR]