Regioselectivity in [3 + 4] and [3 + 5] Annulation Reactions of Bis(trimethylsilyl) Enol Ethers with Acylsilane Dicarbonyl Dielectrophiles
摘要:
A number of 1,4- and 1,5-acylsilane dicarbonyl compounds were synthesized using Corey-Brook dithiane methods. These dicarbonyl substrates were annulated with the bis(trimethylsilyl) enol ether of methyl acetoacetate in the presence of TMSOTf, affording bicyclic ethers bearing silicon substituted at the bridgehead position: The annulation reactions proceeded with excellent regiochemical and good to excellent stereochemical control via a neighboring group participation mechanism. The silicon substituent was subsequently removed by treatment with fluoride ion. The overall transformation of annulation and desilylation represents a formal inversion of the regioselectivity normally exhibited with keto aldehyde dielectrophilic substrates in this process.
Preparation and Reactivity of Acyclic Chiral Allylzinc Species by a Zinc‐Brook Rearrangement
作者:Markus Leibeling、Khriesto A. Shurrush、Veronika Werner、Lionel Perrin、Ilan Marek
DOI:10.1002/anie.201602393
日期:2016.5.10
The zinc‐Brook rearrangement of enantiomerically enriched α‐hydroxy allylsilane produces a chiral allylzinc intermediate, which reacts with retention of configuration in the presence of an electrophile. Two remarkable features of this transformation are the stereochemical outcome during the formation of the allylzinc species and the complete stereocontrol in the organized six‐membered transition state
Treatment of chlorobis(methyldiphenylsilyl)methyllithium with various alkyl and aryl Grignard reagents and CuCN center dot 2LiCl afforded 1,1-disilylalkylcopper species. The aerobic oxidation of the resulting copper reagents provided a variety of acylsilanes in good yields. Meanwhile, treatment of dichloro(methyldiphenylsilyl)methyllithum with Bu2CuLi center dot LiCN provided 1-cyano-1-silylalkylcopper species via consecutive double 1,2-migration of alkyl and cyano groups. (c) 2005 Elsevier Ltd. All rights reserved.
α-Sulfenylation of acylsilanes and aldehydes with N-(phenylthio)succinimide
作者:Chih-Hao Huang、Kang-Shyang Liao、Surya Kanta De、Yeun-Min Tsai
DOI:10.1016/s0040-4039(00)00515-3
日期:2000.5
The reactions of acylsilanes with N-(phenylthio)succinimide in the presence of p-toluenesulfonic acid in acetonitrile give alpha-sulfenylated acylsilanes in good yields. Aldehydes with alpha-alkyl substituent afford moderate yields of alpha-sulfenylated products under the same conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.
The Scope and Limitations of Intramolecular Radical Cyclizations of Acylsilanes with Alkyl, Aryl, and Vinyl Radicals
5-Exo cyclizations of primary and secondary radicals with acylsilanes successfully give cyclopentyl silyl ethers. The corresponding 6-exo cyclizations are sensitive to changes of the size of silyl groups. Secondary radicals undergo 6-exo cyclizations with acylsilanes more slowly. Reaction of aryl radical with acylsilane proceeds well for 5-exo cyclization but not for 6-exo cyclization. Vinyl radicals give best results in 5-exo cyclizations with acylsilanes but give low yields (similar to 30%) in 6-exo cyclizations. Intramolecular cyclizations of vinyl radicals with acylsilanes give enol silyl ethers regiospecifically.