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The Grubbs G-I or G-II catalyst gives the ruthenium ethoxy carbene complex, which catalyzes ring-opening cross metathesis (ROCM) of a strained cyclic alkene to give a diene where one of the two alkene moieties in the product contains an ethoxy substituent. No polymeric products are detected. Hydrocarbons such as parent norbornene or substituted cyclopropenes can proceed with the reaction smoothly. Tertiary amines, N-alkylimides, esters, and aryl or alkyl bromides remain intact under the reaction conditions. In addition to vinyl ethers, vinylic esters can also be used. The time required to reach a 50% yield of the ROCM product t50 varies from 0.01 to 140 h depending on the strain and nucleophilicity of the double bond. Anchimeric participation of an electron-rich group would result in significant enhancement of the reactivity, and the t50 could be as short as several minutes. A similar substrate without such a neighboring group shows a much slower rate. An exo-norborne derivative reacts much faster than the corresponding endo-isomer. Alkenes with poor nucleophilicity are less favored for the ROCM process, so is less strained cyclooctene.

The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and no external oxidant is required. A rate constant for the addition of a primary radical to N-methoxylepidinium >107 M−1 s−1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radicals to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction has been used for the preparation of unique pyridinylated terpenoids and was extended to a three-component carbopyridinylation of electron-rich alkenes including enol esters, enol ethers and enamides., N-Methoxypyridinium salts are exceptionally reactive radical traps that can be used in efficient radical chain reactions with organoboranes.

A copper-catalyzed conjugate silylation of various cyclobutenone derivatives with Me2 PhSiZnCl ⋅ 2LiCl or (Me2 PhSi)2 Zn ⋅ xLiCl (x≤4) to generate β-silylated cyclobutanones is reported. Trapping the intermediate enolate with ClP(O)(OPh)2 affords silylated enol phosphates that can be further engaged in Kumada cross-coupling reactions to yield silylated cyclobutene derivatives.

The tricyclic azepino[1,2-a]indole acetates 7, readily accessible by visible-light-driven catalytic photooxygenation of cyclohepta[b]indoles 1, are convenient precursors to novel and uncommon cyclic C,N-diacyliminium ions 3. We report here the first Lewis acid-catalyzed C-C bond forming reactions of these species with TMSCN and silyl enol ethers as nucleophiles and utilizing TIPSOTf as well as Sc(OTf)3 as catalysts. Employing Sc(OTf)3/pybox complexes as a chiral catalyst system, regio- and enantioselective asymmetric alkylations with silyl enol ethers were achieved.

The reaction mechanisms of cyclic 1,3-diketones with trialkyl orthoformates and trimethyl orthoacetate in the absence of activators were theoretically and experimentally studied. The reactions proceed via C-C-coupling of the ionized forms of the reactants giving dialkyl acetals, which further transform into vinyl ethers. The reactions of the latter with ortho esters afford aldehydes (ketones). Related 2-acetylcyclopentanone reacts with trimethyl orthoacetate under argon to form a mixture of methyl enol ethers, whereas in the presence of air oxygen dimethyl glutarate is formed.

A catalyst-controlled, chemodivergent reaction of pyrrolyl-α-diazo-β-ketoesters with enol ethers is reported. While Cu(II) catalysts selectively promoted a [3 + 2] cycloaddition to provide pyrrolyl-substituted 2,3-dihydrofuran (DHF) acetals, dimeric Rh(II) catalysts afforded 6-hydroxyindole-7-carboxylates via an unreported [4 + 2] benzannulation. The choice of enol ether proved to be crucial in determining both regioselectivity and yield of the respective products (up to 91% yield for Cu(II) and 82% for Rh(II) catalysis). Furthermore, the DHF acetals were shown to serve as precursors to 7-hydroxyindole-6-carboxylates (isomeric to the indoles formed from Rh) and highly substituted furans in the presence of Lewis acids. Thus, from a common pyrrolyl-α-diazo-β-ketoester, up to three unique heterocyclic scaffolds can be achieved based on catalyst selection.

A set of rhenium-catalyzed arylation-acyl cyclizations between (hetero)arylmagnesium halides and enol lactones through a cascade C(sp2 )-C(sp2 )/C(sp2 )-C(sp2 ) bond formation under mild reaction conditions has been developed. Indeed, a wide range of functional groups on both organomagnesium halides and enol lactones is well tolerated by the simple rhenium catalysis, thus furnishing polyfunctionalized indenones in one-pot fashion and with complete control of the regioselectivity. Moreover, this approach also provides a straightforward synthetic route to neolignan and (iso)pauciflorol F. Mechanistic studies demonstrated that the reaction involves a sequence of syn-carborhenation and intramolecular nucleophilic addition.

This study demonstrates that chiral‐at‐iron complexes, in which all coordinated ligands are achiral and the overall chirality the consequence of a stereogenic iron center, are capable of catalyzing asymmetric transformations with very high enantioselectivities. The catalyst is based on a previously reported design (J. Am. Chem. Soc. 2017, 139, 4322), in which iron(II) is surrounded by two configurationally inert achiral bidentate N‐(2‐pyridyl)‐substituted N‐heterocyclic carbenes in a C 2‐symmetric fashion and complemented by two labile acetonitriles. By replacing mesityl with more bulky 2,6‐diisopropylphenyl substituents at the NHC ligands, the steric hindrance at the catalytic site was increased, thereby providing a markedly improved asymmetric induction. The new chiral‐at‐iron catalyst was applied to the inverse electron demand hetero‐Diels‐Alder reaction between β,γ‐unsaturated α‐ketoester and enol ethers provide 3,4‐dihydro‐2H‐pyrans in high yields with excellent diastereoselectivities (up to 99 : 1 dr) and excellent enantioselectivities (up to 98 % ee). Other electron rich dienophiles are also suitable as demonstrated for a reaction with a vinyl azide., A chiral‐at‐iron complex, in which all coordinated ligands are achiral and the overall chirality is exclusively due to a stereogenic iron center, catalyzes hetero‐Diels‐Alder reactions with high diastereoselectivities (up to 99 : 1 dr) and enantioselectivities (up to 98 % ee). Key for this excellent stereocontrol are bulky 2,6‐diisopropylphenyl substituents at the N‐heterocyclic carbene ligands which increase the steric hindrance at the catalytic site.

Facile and modular access to stereodefined disubstituted aldehyde-derived silyl enol ethers allowed their successful application in a stereoselective aldol reaction affording the products with excellent yields and diastereomeric ratios. The counter-intuitive stereochemical behavior of this Mukaiyama-aldol reaction is accounted for by a non-classical open transition state.

Malonate enol ethers are afforded in one step by condensation of cyclic ketones with α-diazomalonates under [CpRu(CH3CN)3][BArF] catalysis. The dual reactivity of these 2-vinyloxymalonates can be used to expand the classical range of cyclizations derived from carbonyl ylide intermediates.

Little‐explored hydrosilylation of ketenes promoted by main‐group catalysts is reported. The boron Lewis acid tris(pentafluorophenyl)borane accelerates the slow uncatalyzed reaction of ketenes and hydrosilanes, thereby providing a convenient access to the new class of β,β‐di‐ and β‐monoaryl‐substituted aldehyde‐derived silyl enol ethers. Yields are moderate to high, and Z configuration is preferred. The corresponding silyl bis‐enol ethers are also available when using dihydrosilanes. The related trityl‐cation‐initiated hydrosilylation involving self‐regeneration of silylium ions is far less effective., β,β‐Di‐ and β‐monoaryl‐substituted silyl enol ethers derived from aldehydes are difficult to prepare. This rare class of compounds has been made accessible by a transition‐metal‐free hydrosilylation of ketenes with B(C6F5)3 as catalyst and Et3SiH as stoichiometric reductant. The substrate scope is decent, and the stereoselectivity moderate to good in selected cases.

A phosphorus(III)-mediated dearomatization of ortho-substituted dianiline squaraine dyes results in an unusual skeletal rearrangement to provide exotic, highly conjugated benzofuranone and oxindole scaffolds bearing a C3 side chain comprised of a linear conflagration of an enol, a phosphorus ylide, and 2,4-disubstituted aniline. Employing experimental and computational analysis, a mechanistic evaluation revealed a striking dependence on the acidity of the aniline ortho substituent. Notably, the rearrangement adducts underwent rapid and complete reversion to the parent squaraine in the presence of a Brønsted acid.

Density functional theory (DFT) has been employed to study the structure, stability and reactivity of curcumin and some of its important analogues by computing HOMO-LUMO energy gap (H-L gap), ionization potential (IP), electron affinity (EA), chemical potential (μ), chemical hardness (η), electrophilicity index (ω) and density of states (DOS). In this study, curcumin is found to be more reactive in dimethyl sulfoxide (DMSO) solvent than in the gas phase in both of its enol and keto isomeric forms. Next, reactivities of the keto-based curcumin analogues are found to follow the order of 1,5-bis(3,4-dimethoxyphenyl)penta-1,4-dien-3-one (GO-035) > 1,5-bis(3,4,5-trimethoxyphenyl)penta-1,4-dien-3-one (GO-Y016) > 1,5-bis[3,5-bis(methoxymethoxy)phenyl]penta-1,4-dien-3-one (GO-Y031) > 1,5-bis[3,5-dimethoxy-4-(methoxymethoxy)phenyl]penta-1,4-dien-3-one (GO-Y030) > dibenzalacetone (DBA) in both gas and DMSO solvent phases. However, there is enhancement in reactivities of the complexes in DMSO solvent from those in the gas phase. The reactivity order is observed on the basis of H-L gap, IP, μ, η and DOS analyses. Moreover, GO-Y030, GO-Y031 and DBA possess similar electrophilic behaviours as indicated by their comparable EA and ω values, while GO-Y016 and GO-035 behave as the strongest and the weakest electrophiles. Furthermore, the nature of the reactive sites in the curcumin analogues has been identified via local reactivity descriptors and the molecular electrostatic potential (MEP) maps, results of which are consistent with the molecular orbital analyses.

Spiroaxillarone A, a novel and unique spirocyclic dinaphthalene natural product with significant antimalarial activity, was regioselectively synthesized from tetrahydrocurcumin in five steps with an overall 10% yield. Key features of the synthesis involved an oxidized free radical cycloaddition to build the spiro ring central skeleton and an oxidized dehydrogenation to introduce two double bonds via enol silicon ether from diketones.

A formal enone α-arylation is described. This metal-free transformation relies on the I(III)-mediated skeletal reorganization of silyl enol ethers and features mild conditions, good yields, and high stereoselectivities for β-substituted enones.

A new and general Sc(OTf)3-catalyzed C-C bond-forming reaction of 3-(2-methoxyethoxy)-endoperoxy ketals with silyl ketene acetals, silyl enol ethers, allyltrimethylsilane, and trimethylsilyl cyanide has been developed via the reactive peroxycarbenium ions, affording a wide range of complicated 3,3,6,6-tetrasubstituted 1,2-dioxenes bearing adjacent quaternary carbons and 3-acetyl/allyl/cyano functional groups in good yields at room temperature. Notably, the resultant 1,2-dioxenes are structurally stable, which can be facially transformed into another important 1,2-dioxane endoperoxide under conventional hydrogenation conditions without deconstructing the weak O-O bond.

Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N‐heterocyclic carbene (NHC)‐catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge‐tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin‐2‐ylidenes, 1,2,4‐triazolin‐5‐ylidenes, thiazolin‐2‐ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI‐MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin‐2‐ylidene‐derived BI indeed exists as a diamino enol, while both 1,2,4‐triazolin‐5‐ylidenes and thiazolin‐2‐ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto–enol equilibria., Breslow intermediates in the gas phase: In N‐heterocyclic carbene (NHC)‐catalyzed Umpolung, the reaction of the substrate aldehyde with the NHC gives the Breslow intermediate (BI) as pivotal species. The combination of IR ion spectroscopy with quantum chemical computations can determine whether the BI exists as a nucleophilic amino enol or as its keto tautomer in the gas phase, which is decisive for its reactivity both in enzymatic catalysis and in organocatalysis.

A thermal O-to-C [1,3]-rearrangement of α-hydroxy acid derived enol ethers was achieved under mild conditions. The 2-aminothiophenol protection of carboxylic acids facilitates formation of the [1,3] precursor and its thermal rearrangement via stabilization of a radical intermediate. Experimental and theoretical evidence for dissociative radical pair formation, its captodative stability via aminothiophenol, and a unique solvent effect are presented. The aminothiophenol was deprotected from rearrangement products as well as after derivatization to useful synthons.

Decarboxylative homo-Nazarov cyclization catalyzed by a Lewis acid was achieved using a cyclic enol carbonate bearing a cyclopropane moiety as a substrate. Various substrates were converted into the corresponding multi-substituted cyclohexenones in good yields via decarboxylation, followed by 6-membered ring formation involving cyclopropane-ring-opening.

Enamides and silyl enol ethers were alkylated to deliver products of N-acyl imines and ketones in the presence of a catalytic amount of N-tetrabutylammonium iodide (TBAI) under irradiation with purple light-emitting diodes (427 nm) at room temperature. A broad scope of tertiary, secondary, and primary alkylation products was achieved with good yields and tolerance of a variety of functional groups. The reactions proceed through the photoactivation of a transiently assembled electron donor–acceptor complex formed between iodide and N-(acyloxy)phthalimide to generate alkyl radicals. The simplicity and low-cost nature of these methods without using metal catalysts demonstrate the practicality of the use of alkyl carboxylates as alkyl sources in organic synthesis.

Herein we describe a nickel-catalyzed remote hydrosilylation of unconjugated enones with bulky triphenylsilane. A range of Z-silyl enol ethers are obtained as major isomers due to the process of nickel triggered alkene isomerization. Notably, some specific alkyl silyl enol ethers can be prepared from this protocol, which are not easily accessed by the traditional strategy using a strong base and chlorosilane. This reaction features 100% atom economy, simple reaction conditions, and good yields.

A novel synthetic strategy for highly enantioenriched cis-3,5-disubstituted γ-lactones has been developed by the AgOTf-promoted nucleophilic substitution of α-bromoacetates with silyl enol ethers and subsequent reductive lactonization. The utility of this synthetic method was further demonstrated through the concise stereodivergent synthesis of cis- and trans-2,4-disubstituted tetrahydrofurans.

We report here a practical strategy to access enantioenriched cyclobutenes via chiral lithium amide mediated deprotonation of 3-substituted cyclobutanones. Furthermore, this strategy has been applied to access protoilludane analogues via a sequential Negishi coupling of enol phosphates and Diels–Alder reaction.

Breslow intermediates are the key species in N-heterocyclic carbene-catalyzed reactions to promote the C–C bond formation. As the fragmentation and rearrangement of Breslow intermediates terminate the catalytic cycle of N-heterocyclic carbene, two mechanisms under debate have been proposed, in terms of the radical channel and the ionic route. Theoretical calculations demonstrate herein that ionic and radical characters can coexist, depending on the protonation state of the hydroxyl group in Breslow intermediates: radicals are merely generated in the enol system, while both of ionic and radical species exist in the enolate system with a lower barrier. Complete pathways for thiamin analogue and N-allyl benzothiazole Breslow intermediates are exclusively constructed considering experimental conditions. The growing population of the enolate under higher pH value rationalizes the increased rate of the fragmentation of thiamin. The fragmentation products of thiamin, namely pyrimidine and ketone, are the thermodynamic products, while the tertiary alcohol is both of the kinetic and thermodynamic product for N-allyl benzothiazole Breslow intermediate via a Claisen-like rearrangement. Other NHCs used to synthesize tertiary alcohol could form the enolate due to the base, followed by the production of the stable radicals and the recombination to form tertiary alcohols. It is concluded that specific protonation states and chemical structure of NHCs account for the distinct mechanisms.

Herein, we explore the use of β-diketones for CO2 fixation and utilization based on their dual Bronsted acid/Lewis base character upon activation by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and zinc bromide (ZnBr2), respectively. The effect of tautomerization on the chemical fixation of CO2 was investigated using different β-diketone compounds, namely, acetylacetone (ACAC), dibenzoylmethane (DBM) and dimedone (DMD) dissolved in dimethyl sulfoxide and activated by DBU. Spectroscopic data demonstrated that the activated ACAC can capture atmospheric CO2 through the formation of both keto- and enol-carboxylated adducts, with the ability to evolve the enol form of the ionic organic carbonate adduct upon direct exposure to CO2. Meanwhile activated DBM and DMD showed the exclusive formation of the enol-organic carbonate adducts once bubbled with CO2. Volumetric uptake measurements indicated that the chemisorption capacities of ACAC and DBM (2.38 mmol CO2 per g sorbent) were higher than DMD (1.59 mmol CO2 per g sorbent). Additionally, the chemical fixation of CO2 into cyclic carbonates (CCs) was achieved by in situ complexation of the investigated β-diketones with a zinc ion. The catalytic systems were able to catalyze the transformation of several terminal oxiranes into the corresponding CCs under atmospheric CO2 pressure with excellent conversions. Interestingly, the catalytic system showed the ability to convert the naturally occurring pinene oxide into dimeric pinene carbonate.

A novel hydrogen-bond-assisted sequential reaction of silyl glyoxylates is described. This method provides an efficient strategy for the synthesis of silyl enol ethers with high selectivity. In these transformations, hydrogen bonds from 2-nitroethanol and its derivatives are critical to the stereochemical outcome. Both E- and Z-isomers are achieved via Henry reaction/Brook rearrangement/elimination and Henry reaction/Brook rearrangement/retro-Henry reaction/elimination processes, respectively (up to 99:1 Z-selectivity, and 9.2:1 E-selectivity).

Aim. To synthesize 4-cyanoindolo[2,3-c]pyrilium salts and examine their reactivity towards N-nucleophiles. Results and discussion. The acylation reaction of 2-(indolyl-3)-2-aroylacetonitriles under acid catalysis conditions was studied. 4-Cyanoindolo[2,3-c]pyrillium borofluorides were obtained, and ketonitrile enolacylates were isolated as by-products of the reaction. Treatment of the 4-cyanoindolo[2,3-c]pyrilium salts with ammonia led to 4-cyano-β-carbolines while the interaction of the salts with hydrazine hydrate resulted in formation of pyrazolo[3’,4’:5,6]pyrido[3,4‑b]indoles – derivatives of a new heterocyclic system. The latter are formed via recyclization involving the pyran ring and the cyano group. Experimental part. Upon the treatment of 2-(indolyl-3)-2-aroylacetonitriles with acetic anhydride/tetrafluoroboric acid mixture, the acylation of the indole fragment in position 2 was followed by cyclization, resulting in formation of 4-сyanoindolo[2,3-c]pyrilium salts. The reactivity of the pyrylium salts was studied on the examples of their interaction with N-nucleophiles – ammonia and hydrazine hydrate. The structure of the compounds synthesized was confirmed by 1H NMR, IR spectroscopy and elemental analysis. Conclusions. It has been found that moderate yields of 4-сyanoindolo[2,3-c]pyrilium salts are the result of competing acylation of the hydroxyl group of enol ketonitrile, which blocks the pyran ring formation. Recylization of the salts with ammonia leads to 4-cyano-β-carbolines. Transformation of the pyran ring with hydrazine hydrate proceeds with the participation of the cyano group as a tandem reaction with formation of pyrazolo[3’,4’:5,6]pyrido[3,4-b]indoles. Received: 22.06.2020 Revised: 03.10.2020 Accepted: 23.10.2020

Alkylation at the carbon atom of the active methylene group of 3-halomethyl derivatives of phosphonocarboxylic acid esters of the furan series with acetylacetone, acetoacetic, malonic and cyanoacetic esters in an absolute ethanol–dioxane medium (1 : 10) in the presence of sodium ethylate leads to the formation of the corresponding monoalkyl derivatives. The obtained phosphonomethylated derivatives of 3-(furylmethyl)acetylacetone and ethyl 2-(furylmethyl)acetoacetate react with hydrazine hydrate to form phosphorus-containing derivatives of (furyl)(pyrazolyl)methanes and (furyl)(pyrazolonyl)methanes, respectively. The latter in chloroform exist exclusively in enol form.

The photocatalytic construction of C(sp3)-rich α-tertiary dialkyl ethers through the reductive α-functionalization of alkyl enol ether substrates with conjugated alkenes in the presence of a Hantzsch ester terminal reductant under blue LED irradiation, is described. Pivoting on oxocarbenium ion generation via an initial TMSCl-facilitated protic activation of the enol ether substrate, subsequent single electron transfer delivers the key nucleophilic α-oxy tertiary radical capable of productively combining with a variety of alkene substrates. The new reductive functionalization strategy was simple to perform, efficient, broad in scope with respect to both alkene acceptor and enol ether donor fragments and delivered a wide range of complex α-tertiary dialkyl ether architectures.

The key nucleophile was found to be neither an enamine nor an enol, but an enolate in the direct Michael reaction of α,β-unsaturated aldehydes and non-activated ketones catalyzed by two amine catalysts namely diphenylprolinol silyl ether and pyrrolidine. This is a rare example of an enolate from a ketone serving as a key intermediate in the asymmetric organocatalytic reaction involving secondary amine catalysts because the ketone enolates are generally generated using a strong base, and the enamine is a common nucleophile in this type of reaction., The key nucleophile was found to be neither an enamine nor an enol, but an enolate in the direct Michael reaction of α,β-unsaturated aldehydes and non-activated ketones catalyzed by two amine catalysts namely diphenylprolinol silyl ether and pyrrolidine.

Three {[(isoxazol-3-yl)imino]­meth­yl}phenols were synthesized and structurally characterized. All three structures contain an intra­molecular O—H⋯N hydrogen bond and none were found to be strongly thermochromic., The synthesis and structures of three isoxazole-containing Schiff bases are reported, namely, (E)-2-{[(isoxazol-3-yl)imino]­meth­yl}phenol, C10H8N2O2, (E)-2-{[(5-methyl­isoxazol-3-yl)imino]­meth­yl}phenol, C11H10N2O2, and (E)-2,4-di-tert-butyl-6-{[(isoxazol-3-yl)imino]­meth­yl}phenol, C18H24N2O2. All three structures contain an intra­molecular O—H⋯N hydrogen bond, alongside weaker inter­molecular C—H⋯N and C—H⋯O contacts. The C—O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles

We report an Umpolung strategy of enol ethers to generate oxy-allyl cation equivalents based on the use of hypervalent iodine reagents. Under mild basic conditions, the addition of nucleophiles to aryloxy-substituted vinylbenziodoxolone (VBX) reagents, easily available in two steps from silyl alkynes, resulted in the stereoselective formation of substituted aryl enol ethers. The reaction was most efficient with phenols as nucleophiles, but preliminary results were also achieved for C- and N- nucleophiles. In absence of external nucleophiles, the 2-iodobenzoate group of the reagent was transferred. The obtained aryl enol ethers could then be transformed into alpha-difunctionalized ketones by oxidation. The described "allyl cation"-like reactivity contrast with the well-established "vinyl-cation" behavior of alkenyl iodonium salts.

A new di­thiol­ene derivative has been synthesized from [TBA]2[Zn(dmit)2] and 3-chloro-2,4-penta­nedione. Crystals were obtained by slow evaporation of an aceto­nitrile solution of the title compound, which crystallizes in the triclinic space group P . The structure of the S—C heterocycle includes two penta­dione moieties that are outside of the plane of the mol­ecule. Intra- and inter­molecular hydrogen bonds are observed, as well as C—H⋯S, S⋯S and O⋯H short contacts from other inter­molecular inter­actions., The reaction between [TBA]2[Zn(dmit)2] and 3-chloro-2,4-penta­nedione yielded single crystals of the title compound, (3E,3′E)-3,3′-[(2-sulfanylidene-1,3-dithiole-4,5-diyl)bis(sulfanediyl)]bis(4-hydroxypent-3-en-2-one), C13H14O4S5, after solvent evaporation. The title compound crystallizes in the triclinic space group P with two mol­ecules related by an inversion center present in the unit cell. The central thione ring moiety contains a carbon–carbon double bond covalently linked to two sulfoxide substituents located outside of the plane of the ring. The S—C—C—S torsion angles are −176.18 (8) and −0.54 (18)°. Intra­molecular hydrogen bonds occur within the two dione substituents (1.67–1.69 Å). Adjacent asymmetric units are linked by C—H⋯S (2.89–2.90 Å), S⋯S [3.569 (1) Å] and O⋯H [2.56–2.66 Å between non-stacked thione rings] short contacts.

C-glycosylation reactions of glycosyl picolinates with allyltrimethylsilane or silyl enol ethers were developed. Picolinate as a chelation-assisted leaving group could be activated by Cu(OTf)(2) and avoided the use of harsh Lewis acids. The glycosylations were operated under mild neutral conditions and gave the corresponding C-glycosides in up to 95% yield with moderate to excellent stereoselectivities.

We describe an efficient synthetic route to differentially protected diester, 1-(tert-butyl) 4-methyl (1R,2S,4R)-2-methylcyclohexane-1,4-dicarboxylate (+)-1, via palladium-catalyzed methoxycarbonylation of an enol triflate derived from a Hagemann's ester derivative followed by a stereoselective Crabtree hydrogenation. Diester 1 is a novel chiral synthon useful in drug discovery and was instrumental in the generation of useful SAR during a RORγt inverse agonist program. In addition, we describe a second-generation synthesis of the clinical candidate BMS-986251, using diester 1 as a critical component.

We report a new facile synthesis procedure for the C-alkylation reaction of indole and indole derivative at 3-position with cyclic enol ethers in the presence of 2.5 mol% of I2 under mild conditions. The optimum composition of the reaction mixture and catalyst were determined for maximum yield of C-alkylated indole derivative with molar ratio of indole derivative: cyclic enol ether was fixed at 1.0 equivalence: 1.5 equivalence with the presence of 2.5 mol% of I2 in acetonitrile solvent and room temperature conditions. The results showed that under optimum conditions indole derivatives can be obtained good to excellent yields (80–92%) by the C-alkylation of indoles with cyclic enol ethers.

An enantioselective catalytic synthesis of α‐acetoxylated ketones through I(I)/I(III) catalysis using a resorcinol/lactamide‐based chiral iodoarene is reported. Catalyst turnover by in situ generation of the active iodine(III) derivative is achieved by oxidation with mCPBA in the presence of acetic acid. The prior transformation of ketones to easily accessible acetyl enol ethers is beneficial and yields up to 97 % with enantioselectivities up to 88 % ee are obtained using only low catalyst loadings of only 5 mol % under mild reaction conditions., An efficient and easy acetoxylation of ketones via their enolethers is described. With low catalyst loadings of a chiral aryliodine high stereoselectivities can be obtained under mild reaction conditions.

Chemoselective domino ring opening and selective O/S-alkylation of ethers/thioethers over enol C/O alkylation has been observed. Various 2-aryl chromanones/thiochromanones with alkyl/allyl bromides were smoothly converted into the corresponding highly functionalized ethers and thioethers in excellent yields with high selectivity. An unusual, chemoselective domino ring opening and selective ether/thioether O/S-alkylation over. An unusual, chemoselective domino ring opening and selective ether/thioether O/S alkylation over enol C/O alkylation has been observed.

The palladium-catalyzed cross-coupling reaction of enol carbamates to construct highly sterically congested alkenyl compounds is presented for the first time. This protocol demonstrates the potential of using thermally stable and highly atom-economic enol electrophiles as building blocks in bulky alkene synthesis. This reaction accommodates a broad substrate scope with excellent Z/E isomer ratios, which also provides a new synthetic pathway for accessing Tamoxifen.

Copper catalysis allows the direct oxygen alkenylation of dialkyl phosphonates with alkenyl(aryl)iodonium salts with selective transfer of the alkenyl group. This novel methodology proceeds with a wide range of phosphonates under mild conditions and gives straightforward access to valuable enol phosphonates in very good yields. Financial support from the AEI (CTQ2017-88451-R), Xunta de Galicia (ED431F 2016/006; ED431C 2018/04; Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09) and the European Union (ERDF) is gratefully acknowledged. N. V.-G. thanks AEI for a predoctoral FPI fellowship SI

A highly regioselective approach to access amide enol carbamates and carbonates 5a-5c', 7a-7h, and 9 was developed through Cu(OTf)2-catalyzed reactions of ynamides 4 with t-butyl carbamates 2 and 8 and t-butyl carbonates 6. Moreover, this strategy was successfully applied to generate amide enol carbamates 11a-11s and 14a-14f from imides 10 and 13 with ynamides through an N-Boc cleavage-addition ring-opening process. A range of substituents was amenable to this transformation, and the desired amide enol carbamates and carbonates were obtained in moderate to good yields.

A combination of ruthenium catalyst with silver salt and copper salt was proved to be a highly efficient protocol for the direct addition reaction of benzoic acids with unsymmetrical trifluoromethylated internal alkynes. Diverse trifluoromethyl group-substituted (E)-enol esters were readily obtained for a broad substrate scope in moderate to good yields with excellent regio- and stereoselectivities under mild reaction conditions.