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Stepwise reduction of the diiminopyridine (dimpyr) complex, dimpyrZnCl2, by KC8 leads to molecular zinc compounds dimpyrZnCl (2) and dimpyrZnCl(DMAP) (3, DMAP = 4-dimethylaminopyridine), which were characterized by X-ray diffraction and EPR spectroscopy. Compound 2 shows an unusual nearly square planar geometry of the zinc atom equally ligated by two imine groups. X-ray crystallographic and EPR data suggest significant delocalization of the zinc 4p electron onto the non-innocent dimpyr ligand. The chloride in 2 can also be substituted by a methyl group upon addition of methyl lithium to generate compound 4, dimpyrZnMe. The novel alkylzinc compound displayed approximate square planar geometry around the zinc centre and significant delocalization of electron density onto the dimpyr ligand, as revealed by X-ray crystallographic studies and EPR spectroscopy, akin to 2. Further reduction of 3 leads to compound 5, dimpyrZn(DMAP)2. X-ray diffraction study of 5 revealed an unprecedented see-saw geometry around the four-coordinate zinc center with significant electron density transfer to the dimpyr ligand, supported by DFT calculations. [ABSTRACT FROM AUTHOR]

Stepwise reduction of the diiminopyridine (dimpyr) complex, dimpyrZnCl2, by KC8 leads to molecular zinc compounds dimpyrZnCl (2) and dimpyrZnCl(DMAP) (3, DMAP = 4-dimethylaminopyridine), which were characterized by X-ray diffraction and EPR spectroscopy. Compound 2 shows an unusual nearly square planar geometry of the zinc atom equally ligated by two imine groups. X-ray crystallographic and EPR data suggest significant delocalization of the zinc 4p electron onto the non-innocent dimpyr ligand. The chloride in 2 can also be substituted by a methyl group upon addition of methyl lithium to generate compound 4, dimpyrZnMe. The novel alkylzinc compound displayed approximate square planar geometry around the zinc centre and significant delocalization of electron density onto the dimpyr ligand, as revealed by X-ray crystallographic studies and EPR spectroscopy, akin to 2. Further reduction of 3 leads to compound 5, dimpyrZn(DMAP)2. X-ray diffraction study of 5 revealed an unprecedented see-saw geometry around the four-coordinate zinc center with significant electron density transfer to the dimpyr ligand, supported by DFT calculations. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis and theoretical investigation of a nonsymmetric bis(diisopropylamino)cyclopropenimine (DAC)-functionalized proton sponge derivative, coined the "Janus" sponge. The reported sponge was isolated as a monoprotonated salt, though no intramolecular hydrogen bond was observed. Homodesmotic equations supported the absence of a N-HN intramolecular hydrogen bond and a relatively low freebase strain, while DFT calculations and X-ray crystallography revealed the presence of a hydrogen bond to the Cl- counterion. Associated with this fact was the rare in-out geometry of the basic nitrogens, which represents the first such instance in a proton sponge not having an ortho-substituent and/or being in a protonated state. Furthermore, NLP donation into the cyclopropenium cation was found to stabilize this unprecedented in-out geometry. The measured pKa was determined to be 23.8, in good agreement with the computed value of 23.9. Lastly, the Janus sponge was found to have fluorescent properties both in the solid state and in solution, which notably represents the first example of a cyclopropenimine-based fluorescent organic compound. [ABSTRACT FROM AUTHOR]

A multicomponent reaction between an aziridine aldehyde dimer, isocyanide, and L-proline to afford a chiral piperazinone was studied to gain insight into the stereodetermining and rate-limiting steps of the reaction. The stereochemistry of the reaction was found to be determined by isocyanide addition, while the rate-limiting step was found to deviate from traditional isocyanide-based multicomponent reactions. A first-order rate dependence on aziridine aldehyde dimer and a zero-order rate dependence on all other reagents have been obtained. Computations at the MPWPW91/6-31G(d) level supported the experimental kinetic results and provide insight into the overall mechanism and the factors contributing to stereochemical induction. These factors are similar to traditional isocyanide-based multicomponent reactions, such as the Ugi reaction. The computations revealed that selective formation of a Z-iminium ion plays a key role in controlling the stereoselectivity of isocyanide addition, and the carboxylate group of L-proline mediates stereofacial addition. These conclusions are expected to be applicable to a wide range of reported stereoselective Ugi reactions and provide a basis for understanding the related macrocyclization of peptides with aziridine aldehydes. [ABSTRACT FROM AUTHOR]

Reduction of the cationic GeII complex [dimpyrGeCl][GeCl3] (dimpyr=2,6-(ArN=CMe)2NC5H3, Ar=2,6- iPr2C6H3) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge0, [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero-valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(CN) orbitals of the imines. This delocalization results in a partial multiple-bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X-ray crystallography and IR spectroscopy data. [ABSTRACT FROM AUTHOR]

Reduction of the cationic GeII complex [dimpyrGeCl][GeCl3] (dimpyr=2,6-(ArN=CMe)2NC5H3, Ar=2,6- iPr2C6H3) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge0, [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero-valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(CN) orbitals of the imines. This delocalization results in a partial multiple-bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X-ray crystallography and IR spectroscopy data. [ABSTRACT FROM AUTHOR]

We report herein the synthesis and characterization of a new proton sponge derivative, 1,8-bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene 4 (DACN), as well as its bis-protonated counterpart 6. A crystal structure of 6 is presented, along with variable temperature 1H NMR data on the BF4− salt ( 6⋅BF4). DFT calculations were performed to investigate the structure of the monoprotonated species 7 and to gain insight into the structural and electronic nature of all three species. The proton affinity (PA) of 4, calculated at the B3LYP/6-311G++(d,p)//B3LYP/6-31G(d,p) level, taking into account thermal corrections from the B3LYP/6-31G(d,p) method, was 282.3 kcal mol−1, while its p Ka was estimated at 27.0. NICS calculations were performed to examine the changes in aromaticity within these systems upon each successive protonation. Lastly, homodesmotic reaction schemes were used in order to estimate the factors contributing to the strong PA predicted for 4. [ABSTRACT FROM AUTHOR]

The origin of the enantioselectivity in the [Cu(R,R)-Ph-box](OTf)2-catalyzed intramolecular aminooxygenation of N-sulfonyl-2-allylanilines and 4-pentenylsulfonamides to afford chiral indolines and pyrrolidines, respectively, was investigated using density functional theory (DFT) calculations. The pyrrolidine-forming transition-state model for the major enantiomer involves a chairlike seven-membered cyclization transition state with a distorted square-planar copper center, while the transition-state model for the minor enantiomer was found to have a boatlike cyclization geometry having a distorted tetrahedral geometry about the copper center. Similar copper-geometry trends were observed in the chiral indoline-forming reactions. These models were found to be qualitatively consistent with experimental results and allow for rationalization of how substitution on the substrate backbone and N-sulfonyl substituent affect the level of enantioselectivity in these and related copper(II)-catalyzed enantioselective reactions. [ABSTRACT FROM AUTHOR]

The DielsAlder reaction can reliably provide the expected endo-product in the presence of secondary orbital overlap. It can be considerably more difficult to access a single enantiomer of the exo-product. In this paper, a D- chiro-inositol derivative is used as a chiral tether to facilitate the regio-, diastereo-, and enatioselective cycloaddition between cinnamic acid and hexa-3,5-dienoic acid. The DielsAlder reaction between these two substrates, or their respective esters, does not occur under thermal conditions. Because of the ease of removal of the chiral tether from the resulting cyclohexene, this approach could provide a viable technique to access otherwise unavailable systems. [ABSTRACT FROM AUTHOR]

To test the hypothesis that an abiotic Earth and its inert atmosphere could form chemically reactive carbon-and nitrogen-containing compounds, we designed a plasma electrochemical setup to mimic lightning-induced electrochemistry under steady-state conditions of the early Earth. Air-gap electrochemical reactions at air-water-ground interfaces lead to remarkable yields, with up to 40 moles of carbon dioxide being reduced into carbon monoxide and formic acid, and 3 moles of gaseous nitrogen being fixed into nitrate, nitrite, and ammonium ions, per mole of transmitted electrons. Interfaces enable reactants (e.g., minerals) that may have been on land, in lakes, and in oceans to participate in radical and redox reactions, leading to higher yields compared to gas-phase-only reactions. Cloud-to-ground lightning strikes could have generated high concentrations of reactive molecules locally, establishing diverse feedstocks for early life to emerge and survive globally. [ABSTRACT FROM AUTHOR]

Bis(diisopropylamino)cyclopropenimine-substituted bis-protonated proton sponge (BDC) is a useful phase-transfer catalyst for the alkylation of compound (I) with a range of alkyl halides. [ABSTRACT FROM AUTHOR]

We have evaluated a range of functionalized isocyanides in the aziridine aldehyde-driven multicomponent synthesis of piperazinones. High diasteroselectivity for each isocyanide was observed. A theoretical evaluation of the reaction course corroborates the experimental data. Moreover, the reactivity of cis- and trans-configured aziridine aldehyde dimers has been compared. This study further probes the dimer-driven mechanism of cyclization and enables an efficient access to a wide range of chiral piperazinones bearing functionalized side chains. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of fused ring aziridines, 3-oxa-1-azabicyclo[3.1.0]hexan-2-ones, with amine nucleophiles can provide either an aminomethyl oxazolidinone or an aziridinyl urea. The amine, reaction solvent, and aziridine substitution have been examined with the aid of computational studies to identify reaction conditions that provide a single product. Polar solvents provided only the aminomethyl oxazolidinone products. Formation of aziridinyl ureas required control of aziridine substitution, solvent, and reactant stoichiometry. [Copyright &y& Elsevier]

This work demonstrates how modulating hydrogen bonding between intermolecular, bifurcated, and intramolecular interactions can be used to tune the structural, electronic, and photophysical properties of cyclopropenium ions and their respective fluorophores. The basis of this switchability was examined using X-ray diffraction analysis, 1H NMR spectroscopy, DFT calculations, and fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

Chemical equations for the article "Synthesis of Chiral Piperazinones Using Amphoteric Aziridine Aldehyde Dimers and Functionalized Isocyanides" by N. B. Heine and colleagues, published in the periodical "Journal of Organic Chemistry" is presented.

Diastereoselective induction of planar chirality in ferrocenes often employs chiral sulfur-, carbon- or phosphorus-based directing groups. The origin of stereoselectivity in these reactions may be classified as (a) cyclopentadiene (Cp) ring-controlled or (b) base-controlled. These two categories are represented by auxiliaries that typically have stereogenic centers α or γ to the ferrocene core, respectively. In this study, it is shown that (−)-2-ferrocenyl-1 S-triethylsilyloxy-7a S-hexahydropyrrolo[1,2- c]imidazol-3-one, the anti-epimer of the previously reported syn-(1 R,7a S) substrate, induces lithiation of the pro- Rp rather than the pro- Sp Cp hydrogen in >95:5 dr, leading to enantiomers of the syn-derived planar chiral imidazolones upon electrophile quench and elimination. This outcome provides a practical way to prepare planar chiral enantiomers in this series without having to synthesize a more expensive D-proline-derived starting material, since both the syn and anti starting materials are available from a common L-proline-derived intermediate. The origin of stereoselectivity in lithiation of the syn and anti epimers, which have β,γ-stereogenic centers, appears to be driven primarily by the conformational bias exerted by the β-silyloxy moiety in each chiral auxiliary, which positions the urea carbonyl within the proximity of one of the two prochiral ortho Cp hydrogens. As such, stereoselectivity is likely Cp ring-controlled for both compounds despite their lack of α-ferrocenyl stereogenic centers. This conclusion is supported by the insensitivity of lithiation selectivity to the bulkiness of the base, comparisons of enantiomers, deuteration experiments, nOe difference studies, and computational modeling of the ground states and lithiation transition states for both substrates. [ABSTRACT FROM AUTHOR]

The product ratio strongly depends on the polarity of the solvent, cf. [ABSTRACT FROM AUTHOR]

We report in full detail our studies on the catalytic, asymmetric α-fluorination of acid chlorides, a practical method that produces an array of α-fluorocarboxylic acid derivatives in which improved yield and virtually complete enantioselectivity are controlled through electrophiic fluorination of a ketene enolate intermediate. We discovered, for the first time, that a third catalyst, a Lewis acidic lithium salt, could be introduced into a dually activated system to amplify yields of aliphatic products, primarily through activation of the fluorinating agent. Through our mechanistic studies (based on kinetic data, isotopic labeling, spectroscopic measurements, and theoretical calculations) we were able to utilize our understanding of this "trifunctional" reaction to optimize the conditions and obtain new products in good yield and excellent enantioselectivity. [ABSTRACT FROM AUTHOR]

Two diastereoisomeric 2-aza-5-phosphabicyclo[2.2.1]heptanes (I) and (II) are prepared and used as catalysts for the synthesis of enantiomerically enriched pyrrolines with opposite absolute configurations. [ABSTRACT FROM AUTHOR]