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.
diastereoselective method was developed for the [2,3]-sigmatropic rearrangement of N-allyl ammonium ylides, affording products in up to 95% isolated yields and up to 97:3 dr; most of the desired products were formed within 1 minute. For the asymmetric reaction, a chiral auxiliary was introduced to the starting compound, affording the rearrangement product with high diastereoselectivities. A rapid and diastereoselective
N-Alkylation and [2,3]-sigmatropic rearrangement of N-allyl α-amino esters
作者:Iain Coldham、Mark L. Middleton、Philip L. Taylor
DOI:10.1039/a705550a
日期:——
N-Alkylation of N-allyl α-amino esters and [2,3]-Stevens rearrangement occur in one pot on warming in the solvent DMF, with the bases K2CO3 and DBU; this in situ formation of the quaternary ammonium salts and rearrangement of the subsequent ylides gives N,N-dialkylated allyl glycine derivatives.