Stereochemical courses and mechanisms of ring-opening cyclization of donor-acceptor cyclopropylcarbinols and cyclization of 7-benzyloxy dibenzyl lignan lactones

Abstract

Lewis acid-mediated ring-opening cyclization of trans- and cis-cyclopropanes 1a and 1b afforded the same trans-dihydronaphthalene 2a. Moreover, Lewis acid-mediated cyclization of 7R- and 7S-benzyloxy dibenzyl lignan lactones 5a and 5b furnished trans-tetralin 6a with high diastereomeric and enantiomeric excess. Based on these results, we rationalized the mechanisms of the cyclizations via trans-selective intramolecular Friedel-Crafts alkylation/cyclization, via the SN1 pathway.