Intramolecular Cycloaddition of O-tert-Butyldimethylsilyloximes in the Presence of BF3·OEt2
摘要:
Intramolecular cycloaddition of novel 1,3-dipoles, N-boranonitrones, was examined. Treatment of O-tert-butyldimethylsilyloximes 9-12 having olefin moieties with 2 equiv of BF3 center dot OEt2 generated N-boranonitrones, which underwent intramolecular cycloaddition to afford N-nonsubstituted cycloadducts 16 (and/or 18) after extractive workup. Despite the Lewis-acidic conditions, the olefin geometry of the substrates was retained in the cycloadducts in the present cycloaddition. The electronic nature of the N-boranonitrones appeared to be electrophilic. In the case of substrate 11c, having an electron-donating methyl group at an internal position of the olefin moiety, the cycloaddition gave the bridged cycloadduct 18b. The cycloaddition proceeded at relatively low temperature, and the diastereoselectivity was high.
[EN] STEROIDAL COMPOSITIONS AND METHODS OF TREATING LIPOGENIC CANCERS [FR] COMPOSITIONS STÉROÏDIENNES ET MÉTHODES DE TRAITEMENT DE CANCERS LIPOGÉNIQUES
[3,3]-Sigmatropic rearrangement of silyl ketene acetals of methyl α-(allyloxy) acetates.
作者:Stanley Raucher、Linda M Gustavson
DOI:10.1016/s0040-4039(00)84311-7
日期:1986.1
Although the lithium enolate undergoes [2,3]-sigmatropic rearrangement to give , the silylketeneacetals undergo [3,3]-sigmatropic rearrangement to give . This is the first reported [3,3]-sigmatropic rearrangement of a 1,1-dioxy-3-oxa-1,5-diene.
Synthesis and Lewis acid catalyzed Claisen rearrangement of 2-(1,3-oxazolin-2-yl)-substituted allyl vinyl ethers
作者:Hannes Helmboldt、Martin Hiersemann
DOI:10.1016/s0040-4020(03)00590-8
日期:2003.6
Allylvinylethers containing an acceptor function in the 2-position are useful substrates for the Lewis acid-catalyzed Claisenrearrangement. The first synthesis of acyclic 2-(1,3-oxazolin-2-yl)-substituted allylvinylethers is reported. The Lewis acid catalyzed Claisenrearrangement of these allylvinylethers afforded the rearrangement products with low to moderate diastereo- and enantioselectivity