Deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls
作者:Shengfei Jin、Hang T. Dang、Graham C. Haug、Viet D. Nguyen、Hadi D. Arman、Oleg V. Larionov
DOI:10.1039/d0sc03118f
日期:——
challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation
Intermolecular and Intramolecular Ketone–Nitrile Reductive Coupling Reactions Promoted by TiCl4–Sm System
作者:Longhu Zhou、Yongmin Zhang
DOI:10.1016/s0040-4020(00)00077-6
日期:2000.5
The intermolecular and intramolecular reductive coupling reactions of ketones with nitriles have been successfully promoted by low-valent titanium prepared by the TiCl4-Sm system. Substituted ketones, monocyclic alpha-amino alcohols and monocyclic amines composed of a number of substitution patterns have been prepared in good yields at room or THF reflux temperature under neutral conditions. The procedure can avoid over reduction of the resulting of ketones, alpha-amino alcohols or amines. The crystal structures of two monocyclic alpha-amino alcohols are reported. (C) 2000 Elsevier Science Ltd. All rights reserved.
Ipso substitution of triarylvinyl cations by alkoxide anions
Photolysis and solvolysis of triarylbromoethanes 1 in the presence of alkoxide anions in alcohols resulted in significant formation of products derived from ipso substitution by alkoxide anions. Photolysis of 1-aryl-1-bromo-2,2-diphenylethenes 1Aa and 1Ab with 10 mol equiv of alkoxide anions gave 1-alkoxy-1-aryl-2,2-diphenylethenes 2A and 3,3-dialkoxy-6-(2,2-diphenylvinylidene)-1,4-cyclohexadienes 3A (ipso adducts). However, the photolysis with weak bases such as TEA, pyridine, NaHCO3, and K2CO3 did not give ipso adducts 3A but only enol ethers 2A. Interestingly, photolysis of 2,2-bis(p-alkoxyphenyl)-1-bromo-1-phenylethenes 4a and 4b with NaOEt in ethanol afforded ipso adducts 6a and 6b, respectively, which had a 1,2-aryl-rearranged structure. Furthermore, solvolysis of 1-bromo-1-(p-methoxyphenyl)ethenes 1Aa, 1Ba, and 1Ca in ethanol containing 10 mol equiv of NaOEt at 120-130-degrees-C for 1-3 days provided p-ethoxyphenyl-substituted enol ethers 2bb, p-ethoxyphenyl-substituted bromoethenes 1b, and p-methoxyphenyl-substituted enol ethers 2ab, respectively. The major formation of p-ethoxyphenyl-substituted compounds (ipso-substituted products) suggests that there is no large difference in ipso substitution between vinyl cations generated by photolysis and solvolysis. On the basis of the results obtained above the factors affecting ipso attack on arylvinyl cations are discussed.
Papillon-Jegou,D. et al., Bulletin de la Societe Chimique de France, 1978, vol. <II>, p. 234 - 240