Preparation of 2-trimethylsilylmethyl-1-alkene; cross-coupling and protodesilylation sequence from 1,1-dibromo-1-alkene
摘要:
A new method for the preparation of exomethylene type allylsilane is described. Selective mono-protodesilylation of 1-trimethylsityl-2-trimethylsilylmethyl-2-alkenes 2 with PPTS afforded 2-trimethylsilylmethyl-l-alkeiles 4 in excellent yields. Since the resulting allylsilanes 4 possess an exomethylene unit, the reactions of 4 with carbonyl compounds in the presence of Lewis acids gave the corresponding product 7 having an exomethylene unit in excellent yields. (c) 2007 Elsevier Ltd. All rights reserved.
Synthesis and Reaction of Bromoallylsilane: A Short Access to β,γ-Disubstituted α-Methylene-γ-butyrolactone
摘要:
(Z)-beta-Bromoallylsilanes (1a-c) were prepared by a stereoselective Ni-catalyzed cross-coupling reaction of 1,1-dibromo-4-phenylbutene (4) with silylmethylmagnesium halide. Sakurai-Hosomi reaction of la with aldehyde gave syn-3-alkyl-2-bromo-4-hydroxyalkene (2a, 2c, and 2c) and that with acetal gave syn-4-alkoxy-3-alkyl-2-bromoalkene (2b and 2d) stereoselectively. The products with formyl function reacted with a Ni-carbonyl complex to give beta,gamma-disubstituted (alpha-methylene-gamma-butyrolactones (3) in good yields. Pd-catalyzed cross-coupling reaction of la-c or 4 with silylmethylmagnesium halide gave 1, 1-bis(silylmethyl)-1-alkenes (1d-i), which reacted with dimethyl acetal to generate more functionalized allylsilane (6).
Various 2-alkylidenethietanes were synthesized by intramolecular nucleophilicsubstitution reactions at an sp2 carbon of vinyl halides with thiolate moieties. The reaction pathway of the substitution reactions was confirmed as a very rare SNVπ mechanism by theoretical and experimental studies.
This article presents a full account of intramolecular vinylic substitution reactions of bromoalkenes having an acetylthio moiety, which give sulfur-containing heterocycles such as dihydrothiophene, tetrahydrothiopyran, and 2-alkylidenethietane derivatives. The reaction pathways of the substitution reactions were investigated by theoretical and experimental studies.