1,3-Allylic Strain as a Control Element in the Paternò−Büchi Reaction of Chiral Silyl Enol Ethers: Synthesis of Diastereomerically Pure Oxetanes Containing Four Contiguous Stereogenic Centers
摘要:
The facial diastereoselectivity in the Patemo-Buchi reaction of chiral silyl enol ethers and benzaldehyde was studied. The substituents (R(S), R(L)) at the stereogenic carbon atom (-C*HR(S)R(L)) attached to the beta-position of the silyl enol ether were varied in order to evaluate the influence of steric bulk and electronic effects. The combined yields for the two diastereomeric 3-(silyloxy)oxetanes a and b. range between 44% and 76%. In accordance with the 1,3-allylic strain model the facial diastereoselectivity (diastereomeric ratio (dr) = alb) was best with large(R(L) = t-Bu, SiMe(2)Ph) and polar (R(L) = OMe) substituents at the gamma-position of the silyl enol ether (dr up to >95/5). Two regioselective ring opening reactions were applied to the product oxetanes 29a, 50, and 51. They furnished diastereomerically pure diols (52, 53) and triols (31) in excellent yields.
Nickel-catalyzed Conjugate Addition of Arylboron Reagents to α,β-Unsaturated Carbonyl Compounds with the Aid of a Catalytic Amount of an Alkyne
作者:Eiji Shirakawa、Yuichi Yasuhara、Tamio Hayashi
DOI:10.1246/cl.2006.768
日期:2006.7
Alkynes in combination with a catalytic amount of a nickel complex were found to catalyze the conjugate addition of arylboron reagents to α,β-unsaturated carbonyl compounds, where use of an optical...
The reaction of benzenesulfonylchlorides with enones was investigated. β-Ionone and benzalacetone in the presence of a palladium catalyst were found to afford the conjugate addition products instead of the expected Heck type products. The reaction tolerates a wide variety of substituents on the benzenesulfonylchloride. It should be noted that no cleavage of the C–Br and C–I bonds was observed in
Indium-catalyzed coupling reaction between silyl enolates and alkyl chlorides or alkyl ethers
作者:Yoshihiro Nishimoto、Takahiro Saito、Makoto Yasuda、Akio Baba
DOI:10.1016/j.tet.2009.03.106
日期:2009.7
The coupling reactions of alkyl chlorides with silyl enolates catalyzed by InBr3, and the coupling reactions of alkylethers with silyl enolates catalyzed by the combined Lewis acid of InBr3/Me3SiBr are described. In both reaction systems, various types of silyl enolates were used to give corresponding α-alkylated esters, ketones, carboxylic acids, amides, thioesters, and aldehydes.
描述了烷基氯化物与InBr 3催化的烯醇硅酸酯的偶联反应,以及烷基醚与InBr 3 / Me 3 SiBr的路易斯酸催化的烯醇硅酸酯的偶联反应。在两个反应系统中,都使用了各种类型的甲硅烷基烯酸酯,以生成相应的α-烷基化的酯,酮,羧酸,酰胺,硫代酯和醛。