Studies on the origin of cis-diastereo selectivity of the titanium-mediated cyclopropanation of carboxylic esters with Grignard reagents. Stereochernistry of the intramolecular cyclization of beta-metalloketones

摘要

Data on the stereochemistry of the intramolecular cyclization of beta-metaloketones into 1,2-disubstituted cyclopropanols are in agreement with the cyclopropanation of carboxylic esters with alkoxytitanacyclopropane reagents proceeding via the beta-titanoketone inter-mediates with the metal atom bound to a secondary carbon. Hypothesis for the origin of cis-diastereoselectivity of the cyclization of the beta-titanoketones is suggested. It explains the tendency for the preferable formation of cis-1,2-disubstituted cyclopropanols by relief of repulsion strain between the ligands at the octahedral titanium atom. (c) 2007 Published by Elsevier Ltd.