Diisopropyloxy(η2-cyclopentene)titanium for the diastereoselective synthesis of various 1,2-disubstituted cyclopentanes
摘要:
The reaction of 3 equiv of cyclopentylmagnesium chloride with 2 equiv of titanium(IV) isopropoxide at low temperature (-70 to -50 degrees C) leads to the formation of 1 equiv of diisopropyloxy(eta(2)-cyclopentene)titanium containing low amounts of the starting Grignard reagent. The sequential addition of two electrophiles onto this titanium complex involved as an intermediate in Kulinkovich-type reactions delivers various 1,2-disubstituted cyclopentane rings with generally high diastereoselectivity. Mechanistic considerations and possible extensions of this method are discussed. (c) 2006 Elsevier Ltd. All rights reserved.
1-Methoxy-2-alkanones are prepared from ate-complexes formed from 1,2-dimethoxyethenyllithium and trialkylboranes by the reaction with BF3:Et2O, followed by basic hydrogen peroxide oxidation.