A visible-light-enabled,photocatalyst-free hydroacylation reaction of azodicarboxylic acid derivatives was described.This radical conjugate addition(RCA)protocol relied on the dual role of 4-acyl-1,4-dihydropyridine(acyl-DHP)reagents that besides being as radical reservoirs,they also enabled the conversion of radical adducts to anion intermediates via reduction.Under“catalyst-oxidant-additive free”conditions,a wide range of structurally different acyl hydrazide products were readily obtained in 56%—99%yields.The utility of this transformation was further demonstrated by the scale-up synthesis and downstream derivatization.
Li LiuJing WangXiaoying FengKun XuWei LiuXia PengHongguang DuJiajing Tan
Aldehydes are a kind of important synthons and reagents in organic synthesis.The efforts on transformations of aldehydes are highly rewarding and have always attracted considerable attention.Herein,a cross-coupling of aldehydes withα-haloboronates has been achieved under dual nickel/photoredox catalysis system.Considering theα-haloboronates can be easily obtained from aldehydes with our deoxygenative difunctionalization of carbonyls(DODC)strategy,this protocol provides a formal deoxygenative cross-coupling of aldehydes to one-carbon-prolonged ketone products.The mild conditions enabled good functional group tolerance and broad substrate applicability.The application of this method was presented via a tunable synthesis of two ketones with very similar skeletons from two same aldehydes.
Wereport a base-promoted catalyst-free protocol for the highly regioselective hydroacylation of styrenes with hydrazones derived from naturally abundant aldehydes.This protocolgeneratedlinearketoneswith goodfunctional grouptolerance anda broadsubstrate scope under mild conditions.Mechanistic studies showed that the addition of hydrazone anion to a styrene double bond was the key step,different from previoushydroacylationpathways(viaorganometallic complexes or radical intermediates).
Summary of main observation and conclusion Direct functionalization of alkenes and direct transformation of carboxamides are two exciting areas that have attracted considerable attention in recent years.We report herein that secondary amides,the least reactive derivatives of carbonyl compounds,upon activated with triflic anhydride,can serve as effective hydroacylating reagents in partner with alkenes to yield ketones at ambient temperature.The method was applied to the one-step synthesis of racemic dihydro-ar-turmerone.In this method,alkenes serve as surrogates of organometallic reagents,which allows the orthogonal chemoselective reactions.The ready availability of many olefins such as camphene and norbornene permits one-step ketone synthesis that would require several steps by conventional methods.
Density functional theory（DFT） method was used to explore the origin of the regioselectivity of Cocatalyzed hydroacylation of 1,3-dienes.The reaction of 2-methyl-1,3-butadiene and benzaldehyde with1,3-bis（diphenylphosphino）propane ligand was chosen as the model reaction.The energies of the intermediates and transition states in the stages of oxidative cyclization,β-H elimination and C-H reductive elimination were investigated.Computational results show that β-H elimination is the ratedetermining step for the whole catalytic cycle.C1-Selective oxidative cyclization is favored over C4-selective oxidative cyclization.Besides.C4-selective oxidative cyclization is kinetically disfavored than all the steps in C1-hydroacylation mechanisms,consistent with the experimentally obtained C1-selective hydroacylation products.Analyzing the reason for such observation,we suggest that both electronic and steric effects contribute to the C1-selectivity.On the electronic aspect,C1 is more electron rich than C4 due to the methyl group on C2,which makes the electrophilic attack of aldehyde carbon on C1 more favorable.On the steric aspect,the methyl group locates farther from the ligands in the transition state of C1-selective oxidative cyclization than in that of C4-selective oxidative cyclization.
In this paper, we used density functional theory(DFT) computations to study the mechanisms of the hydroacylation reaction of an aldehyde with an alkene catalyzed by Wilkinson's catalyst and an organic catalyst 2-amino-3-picoline in cationic and neutral systems. An aldehyde's hydroacylation includes three stages: the C–H activation to form rhodium hydride(stage I), the alkene insertion into the Rh–H bond to give the Rh-alkyl complex(stage II), and the C–C bond formation(stage III). Possible pathways for the hydroacylation originated from the trans and cis isomers of the catalytic cycle. In this paper, we discussed the neutral and cationic pathways. The rate-determining step is the C–H activation step in neutral system but the reductive elimination step in the cationic system. Meanwhile, the alkyl group migration-phosphine ligand coordination pathway is more favorable than the phosphine ligand coordination-alkyl group migration pathway in the C–C formation stage. Furthermore, the calculated results imply that an electron-withdrawing group may decrease the energy barrier of the C–H activation in the benzaldehyde hydroacylation.
