Studies on the origin of cis-diastereoselectivity of the titanium-mediated cyclopropanation of carboxylic esters with Grignard reagents. Stereochemistry of the intramolecular cyclization of β-metalloketones

Datа on the stereochemistry of the intramolecular cyclization of β-metaloketones into 1,2-disubstituted cyclopropanols are in agreement with the cyclopropanation of carboxylic esters with alkoxytitanacyclopropane reagents proceeding via the β-titanoketone intermediates with the metal atom bound to a secondary carbon. Hypothesis for the origin of cis-diastereoselectivity of the cyclization of the β-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.