Regio- and Diastereoselective Dimerization of Diazo Carbonyls: A Cooperative Catalytic Approach to Complex Scaffolds with Four Contiguous Stereocenters

Starting from readily available o-diazoacyl-substituted arene carboxylates, scaffolds with the 5,9-epoxycyclohepta[b]pyran-2(3H)-one core were obtained by cooperative Rh^II, Lewis and Brønsted acid catalysis. Four new bonds, three functional groups (lactone, ketal, and alcohol) and four contiguous stereocenters are formed during this regio- and diastereoselective process in a single synthetic step. Intensive optimization and mechanistic studies, including the trapping, isolation, and elucidation of reaction intermediates, led to a plausible mechanistic scenario. The reaction is proposed to involve carbonyl ylides but also transient species of the ketocarbene equilibrium that undergo a cascade of cycloaddition and skeletal rearrangements.     

Organocatalytic Conjugate Addition of Azide Ion to α,β‐Unsaturated Aldehydes

An efficient and simple amine‐catatalyzed azide conjugate addition to α,β‐unsaturated aldehydes has been developed. In the presence of a catalytic amount of tertiary amine with a 1:1 mixture of NaN₃ and 37% HCl in CH₂Cl₂, α,β‐unsaturated aldehydes provided β‐azido aldehydes, which could be transformed into 1,3‐amino alcohols.     

Catalytic Asymmetric Conjugate Addition of Indolizines to α,β-Unsaturated Ketones

A catalytic enantioselective conjugate addition of indolizines to enones is described. The chiral phosphoric acid (S)-TRIP activates α,β-unsaturated ketones, thereby promoting an enantioface-differentiating attack by indolizines. Using this reaction, several alkylated indolizines were synthesized in good yields and with enantiomeric ratios of up to 98:2.     

Conjugate Addition of a Silyl Ketene Acetal to α,β‐Unsaturated Lactones

Abstract

Conjugate addition of a silyl ketene acetal [Me₂C?C (OMe)OSiMe₃] to α,β‐unsaturated lactones (namely, 5,6‐dihydro‐2H‐pyran‐2‐one, 2(5H)‐furanone as Michael acceptor) occurs efficiently at room temperature in the presence of a nucleophilic catalyst, tetra‐n‐butyl ammonium bibenzoate (TBABB), in THF as well as Lewis acid catalysts such as Yb(OTf)₃ and I₂ in CH₂Cl₂, giving the corresponding 1,4‐adducts in excellent yields.     

Conjugate Addition Reactions of Functionalized Organozinc-copper Reagents to α,β-Unsaturated Esters

Theconjugateadditionoforganometal1icstoMichaelacceptorsisanimportantsyntheticmethodforcarbon-carbonbondformation'.FunctionalizedorganozincreagentsaremoreusefulinthatfleldbecausetheytolerateabroadrangeoffunctionalitiesandreactinthepresenceofCuCN'2LiClwithvariouselectrophilesinexcellentyields"'.Thus,apolyfunctionalizedorganicmoleculecanbeformedinonestep.However,CuCNhasbeentheonlycoppersaltsinceitwasfirstusedinl988,',andunsaturatedestersdonotreactwithfunctionalizedorganozincreagentsundergener…     

Copper Hydride-Catalyzed Conjugate Reduction-Aldol Addition Domino Reaction of α,β-Unsaturated Carboxylates with Ketones

Copper hydride‐catalyzed conjugate reduction‐intermolecular aldol addition domino reactions were realized using α,β‐unsaturated carboxylates as hydride acceptors and a silane as the reducing reagent. High diastereoselectivities were achieved with 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene as the ligand and tert‐butyl acrylate as the hydride acceptor.     

Conjugate Addition of Alkyllithium Reagents to α,β-Unsaturated N,N',N'-Trimethylhydrazides

The site of nucleophilic attack by an alkyllithium reagent upon an α,β-unsaturated carbonyl compound is governed by, among other factors, the nature of the group attached to the carbonyl.¹ Thus the amount of carbonyl addition decreases in favor of conjugate addition for the α,β-unsaturated series: aldehyde, ketone, ester, amide. We wish to report that α,β-unsaturated carboxylic acid trimethylhydrazides, which have an exceptionally unreactive carbonyl group², undergo exclusive conjugate addition with simple alkyllithium reagents.³ Furthermore, the derived hydrazide lithium enolates can be transformed in convenient and useful ways.     

A Facile Convergent Approach to Octopus Polyestrone

IntroductionDendrimersarehighlybranchedlnonodispersepolymers'.ThroughjudiciouschoiceofbranchedbuiIdingblocksandftnctionalgroup,onecanpreciseIycontroltheirshape,dimension,density,polarity,flexibilityandsolubility,givingrisetouniquephysicalandchemicalproperties'.Inthelastdecadedendrimershaveattractedeverincreasingattentioninorganic.super-molecular'polymerchemistryandcoordinationchemistry.andhavebeenwide]yusedascatalyst'-micellemimicry',immuno-diagnostics',andgene-deliveringvectors'etc.Theconnec…     

A New Approach to α—Bromochalcones

α-Bromo benzolymethylene triphenylphosphorane 3 has been synthesized by the reaction of benzoylmethylene triphenylphosphorane 1 with N-bromosuccinimide in the yield of 87% and can react with aromatic aldehydes 4 to give α-bromochalcones 5 in good yields.     

Indium Mediated Conjugate Addition of Allyl Bromide to Nitroalkenes in DMF—H2O Media

Allylindium bromide prepared by metallic indium and allyl bromide was added to nitroalkenes to give conjugate addition compounds in moderate to good yields in an aqueous media.     

Catalytic Asymmetric Conjugate Addition of Thiols to α,β-Unsaturated Thioamides: Expeditious Access to Enantioenriched 1,5-Benzothiazepines

Softly does it: The title reaction proceeded under proton transfer conditions with a catalyst prepared from commercially available reagents to afford the desired product in high enantioselectivity. The reaction was compatible with a free amino group, thus allowing for expeditious access to enantiomerically enriched 1,5-benzothiazepines, which are important chemical entities in medicinal chemistry.     

Copper(II) Bromide–Catalyzed Conjugate Addition of Indoles to α,β‐Enones

Copper(II) bromide was found to be an efficient catalyst for the conjugate addition of indoles to α,β‐enones in acetonitrile at room temperature.     

Generation of α-Boryl Radicals and Their Conjugate Addition to Enones: Transition-Metal-Free Alkylation of gem-Diborylalkanes

A transition-metal-free method for the alkylation of gem-diborylalkanes with α,β-unsaturated ketones has been developed. It is demonstrated that the α-boryl radicals can be generated efficiently from gem-diborylalkanes with the aid of catechol and oxidants. The α-boryl radicals formed through such process can be engaged in conjugate addition reaction with α,β-unsaturated ketones. This transformation is a straightforward method for the synthesis of γ-borylketones.     

High Diastereoselectivity in the Conjugate Addition of Functionalized Alcohols to a Chiral(E)-Nitroalkene

Nitr0alkenesareversatilesyntheticintermediatesaspowerfulelectron-deficientreactantsincycloadditionandconjugatadditionreacti0ntoproducealargevarietyfunctionalizedcarbocyclicrings'.Purthermore,thenitrogrouPcanbeconvertedintoawiderangeoffiinctionalities2-Al0ughDiels-Alderreaction3andcyclopropanationoffunctionalizedcarbonnucleophiles4toY-chiralnitr0alkenehavebeenreportedrecently.Sofarthedetailedresearch0ftheconjugateadditionsoffimctionalizedalcoholst0chira1nitf0keneshasn0tbeenreported.Herewewish…     

Highly Efficient Syntheses of β-Cyanoketones via Conjugate Addition of Me3SiCN to Aromatic Enones

An efficient 1,4‐addition of Me₃SiCN to aromatic enones has been achieved with excellent yields (91% –99%) using CsF (1 mol%) as the catalyst and H₂O (4 equiv.) as the additive in refluxing dioxane within 7 h. The perfect regioselectivity is proposed accounting from H₂O‐facilitated reversion of the 1,2‐adduct in the presence of CsF and subsequent irreversible 1,4‐addition reaction.     

B(C6F5)3-Catalyzed Conjugate Addition Reactions: Addition of C–H Aromatics as Nucleophiles to Nitroalkenes

Russian Journal of Organic Chemistry - A mild and efficient B(C6F5)3-catalyzed conjugate addition of N, N-dialkylanilines to aromatic nitroalkenes is reported. The catalyst shows excellent...     

The Reaction of Phosphoryl Chlorides with Enamines - A New Approach to β-Ketophosphonates

Abstract

Several approaches are available for the preparation of β-ketophosphonate esters. A Michaelis-Arbuzov approach using the reaction of an α-halo ketone with a trialkyl phosphite may in certain instances be controlled to favor the preparation of the target materials. However, an alternative pathway leading to the formation of vinyl phosphate esters often predominates. (This reaction system has recently been reviewed by Borowitz and Borowitz.¹) An alternative approach is that developed in recent years by Wiemer, et al.² involving the rearrangement of vinyl phosphate esters to the β-ketophosphonates.     

Conjugate Addition of Indoles with Electron‐Deficient Olefins Catalyzed by Fe‐Exchanged Montmorillonite K10

Conjugate addition of indoles with a variety of electron‐deficient olefins in the presence of Fe‐exchanged montmorillonite K10 affords the corresponding Michael adduct in excellent yields with high selectivity. The catalyst was also found to be recyclable.