Carbon-heteroatom Double Bonds Research Articles

Organocatalytic Transfer Hydrogenation and Hydrosilylation Reactions.

The reduction of different carbon-carbon or carbon-heteroatom double bonds is a powerful tool that generates in many cases new stereogenic centers. In the last decade, the organocatalytic version of these transformations has attracted more attention, and remarkable progress has been made in this way. Organocatalysts such as chiral Brønsted acids, thioureas, chiral secondary amines or Lewis bases have been successfully used for this purpose. In this context, this chapter will cover pioneering and seminal examples using Hantzsch dihydropyridines 1 and trichlorosilane 2 as reducing agents. More recent examples will be also cited in order to cover as much as possible the complete research in this field.

Computational Insight into the Enantioselective Nucleophilic Borylation of a Polarized C═O Double Bond Catalyzed by Diphosphine/Borylcopper(I) Complexes

Density functional theory calculations were performed to validate the proposed reaction mechanism for the enantioselective nucleophilic borylation of a polarized C═O double bond in the presence of diphosphine/borylcopper(I) complexes. Consequently, we successfully elucidated the origin for the regioselectivity and the mechanism for the enantioselectivity of the reaction. We also obtained theoretical explanations for the fact that the presence of a proton source gave a higher reactivity and a better enantioselectivity in the borylation reaction of aldehydes with a copper(I)/(R)-DTBM-SEGPHOS complex catalyst. This study is particularly valuable toward the development and design of novel enantioselective borylation reactions with polarized carbon–heteroatom double bonds.

ChemInform Abstract: Organocatalytic Strategies for Enantioselective Metal‐Free Reductions

AbstractReview: 107 refs.

ChemInform Abstract: Transition Metal‐Catalyzed Direct Nucleophilic Addition of C—H Bonds to Carbon—Heteroatom Double Bonds

AbstractReview: [65 refs.

Organocatalytic strategies for enantioselective metal-free reductions

One of the most important chemical transformations is the reduction of multiple bonds, carbon–carbon as well as carbon–heteroatom double bonds, since it leads very often to the generation of new stereocenters in the molecule. The replacement of metal-based catalysts with equally efficient metal-free counterparts is very appealing in view of possible future applications of non toxic, low cost, and environmentally friendly promoters on an industrial scale. This perspective will focus specially, but not exclusively, on the enantioselective reduction of the carbon nitrogen double bond; despite the historical need for and continued interest in chiral amines, their synthesis remains challenging. Three metal-free catalytic methodologies available for the reduction of carbon–nitrogen double bond will be discussed: i) binaphthol-derived phosphoric acids catalyzed reductions, with dihydropyridine-based compound as the reducing agent; ii) trichlorosilane mediated reductions, in the presence of catalytic amounts of chiral Lewis bases; iii) metal-free hydrogenation of imines through FLP (Frustrated Lewis Pair) methodology, that involves the use of a combination of a strong Lewis acid with a variety of sterically encumbered Lewis bases, for examples phosphines or tertiary amines, to activate hydrogen at ambient conditions. Special attention will be devoted to the most recent applications of the last five years.

Transition metal-catalyzed direct nucleophilic addition of C–H bonds to carbon–heteroatom double bonds

Compared with the traditional Grignard reaction, direct insertion of polar double bonds to C–H bonds via transition-metal catalysis is ideal from the viewpoint of atom-, step- and cost-economy and the avoidance of the waste emission, as well as of the complex manipulation of sensitive reagents.

Reaction of Arynes with Carbon-Heteroatom Double Bonds

Recent achievements in the construction of heterocycles by the reaction of arynes with carbon-heteroatom double bonds are reviewed. Use of the Diels-Alder type, ionic, and radical mechanisms resulted in the formation of novel heterocycles containing oxygen, nitrogen, sulfur, and selenium atoms. Abstract This review focused on the application of nano-materials in heterocyclic chemistry. The main part of review is constituted by sections in which the reactions catalyzed by nanomaterials. In the last part of this review, emphasis is given to the heterocyclic supported nanomaterials and their importance in the catalysis. Abstract Aspergillides A, B, and C are cytotoxic macrolides produced by the marine-derived fungus Aspergillus ostianus strain TUF 01F313. The unique molecular architectures of the aspergillides featuring 14-membered marocyclic structures embedded with a tetrahydro- or dihydropyran unit have attracted significant attention from the synthetic chemistry community, and thereby various synthetic approaches to these structurally as well as pharmacologically intriguing molecules have been reported by as many as 12 research groups in the past 3 years. This review describes all of the syntheses disclosed to date, focusing mainly on the methodologies employed for the diastereoselective installation of the pyran ring systems.

Celebrating 20 Years of SYNLETT - Special Account On Palladium(II)-Catalyzed Additions of Arylboronic Acids to Electron-Deficient Alkenes, Aldehydes, Imines, and Nitriles

The enantioselective synthesis of cyclic and acyclic β-aryl ketones, esters, and amides by palladium(II)-catalyzed 1,4-addition of an arylboronic acid or a potassium aryltrifluoroborate to unsaturated carbonyl compounds is described. The protocol provides simple access to biologically and pharmaceutically active compounds such as optically active chromenes, (R)-tolterodine, (R)-CDP 840, and the endothelin receptor antagonist. The palladium(II) catalysts are also efficient for Grignard-type addition of arylboronic acids to carbon-heteroatom double bonds and triple bonds of aldehydes, ketones, aldimines, and nitriles. The catalytic cycle involves transmetalation between arylboronic acid and palladium(II) complexes as the key process, the mechanism of which is discussed on the basis of characterization of the transmetalation intermediates and electronic effects of the substituents. The enantio­selection mechanism and the efficiency of a chiraphos ligand for structurally planar unsaturated ketones are discussed on the basis of the results of DFT computational studies on the modes of coordination of the substrates to the phenylpalladium(II)/(S,S)-chiraphos intermediate. This review focuses mainly on reactions of arylboronic acids; there are very few such reports for other organoboronic acids or esters, but pinacol allylboronate undergoes 1,4-addition to unsaturated N-acylpyrroles.

Principles of asymmetric synthesis

Introduction. Why we do asymmetric synthesis. What is an asymmetric synthesis? Stereoselectivity: intraligand vs. interligand asymmetric induction. Selectivity: kinetic and thermodynamic control. Single and double asymmetric induction. Glossary of stereochemical terms. References. Analytical Methods. The importance of analysis, and which method to choose. Polarimetry, the old fashioned way. Nuclear magnetic resonance. Chromatography. Summary. References. Enolate, Azaenolate, and Organolithium Alkylations. Enolates and azaenolates. Chiral organolithiums. References. 1,2 and 1,4 Additions to Carbonyls. Cram's rule: open-chain model. Cram's rule: rigid, chelate, or cyclic model. Additions using chiral catalysts or chiral nucleophiles. Conjugate additions. References. Aldol and Michael Additions of Allyls and Enolates. 1,2-Additions of allyl metals and metalloids. Aldol additions. Michael additions. References. Rearrangements and Cycloadditions. Rearrangements. Cycloadditions. References. Reductions and Hydroborations. Reduction of carbon-heteroatom double bonds. Reduction of carbon-carbon bonds. Hydroborations. References. Oxidations. Introduction and scope. Epoxidation and related reactions. Dihydroxylations. Oxidation of enolates and enol ethers. Miscellaneous oxidations. References. Index.

Thermal, three-carbon + two-atom cycloaddition of cyclopropenone ketals with carbon-heteroatom double bonds: Butenolide, furan, and γ-keto ester preparation.

A preliminary study of the thermal reaction of cyclopropenone ketals with carbon-heteroatom double bonds is detailed. The reaction with aldehyde and keto carbonyls provide butenolide ortho esters, the product of a formal three-carbon + two-atom cycloaddition of the cyclopropenone ketal across the carbon-oxygen double bond.

Cyclic nitronic esters : Synthesis of substituted 5,6-polymethylene-5,6-dihydro-4H-1,2-oxazine 2-oxides by reaction of enamines with nitroolefins

The role of structure in the reaction between enamines and nitroolefins has been evaluated. A synthetic method is presented for preparing substituted cyclic nitronic esters incorporating a 6-membered ring. Reaction of cyclopentanone, cyclohexanone and cycloheptanone enamines derived from pyrrolidine and morpholine with 2-nitro-1-phenylpropene, 2-nitro-1-phenyl-1-butene and α-nitrostilbene in hexane solvent at 0–25° led to 3-methyl-, 3-ethyl-, or 3-phenyl-4-phenyl-5,6-polymethylene-5,6-dihydro-4H-1,2-oxazine 2-oxides 9a-j (31–94% yield). Spectral data support the assigned structures and establish stereochemistry. The reaction is limited to α-substituted nitroolefins and enamines derived from cycloalkaxones having fewer than eight ring members. Enamines derived from aldehydes and acyclic ketones failed to produce nitronic esters. Alkaline hydrolysis of nitronic esters 9a-j by treatment with aqueous ethanolic potassium hydroxide, followed by acidification with acetic arid, leads to products whose structure is determined by the nature of substituents and ring size of the 5,6-polymethylene group. Esters 9d and 9e derived from cyclohexanone gave 8a-hydroxy-3-methyl-4-phenyl-4a,5,6,7,8,8a-hexahydro-4 H-1,2-benzoxazine 2-oxide ( 4), found to be identical with the product of Michael addition of cyclohexanone to 2-nitro-1-phenylpropene. Ester 9h derived from cycloheptanone gave the Nef product, 2-(1-phenyl-acetonyl)cycloheptanone ( 19). Esters 9g, j having 3,4-diphenyl substituents produced 3,4,5-triphenylisoxazole. The results of the present investigation provide additional examples of nucleophilic addition of nitronate oxygen to carbon-hetero atom double bonds; addition occurs intramolecularly on carbon of an iminium ion in the zwitterion intermediate 6.