title: Highly Stereoselective Cationic Cyclization Assisted by a Sulfenyl Group. Scope, Limitation, and Mechanism.
abstract: When 8-acetoxy-2-methyl-9-(phenylthio)-2-nonene (1a) was treated with an acid, followed by a base, alkylative cyclization proceeded to give a mixture of 1,2-disubstituted cyclohexanes: 2a, 3a, and 4a. The stereochemistry of the reaction was only slightly affected by the leaving group and the reaction conditions, such as the temperature, solvent, and acid. However, the bulkiness of the sulfenyl group had a great effect on the stereochemical course of the reaction. High trans selectivity was attained when 1c (a derivative of 1a with a bulkier sulfenyl group) was used as a substrate. On the other hand, the length and rigidity of the carbon chain of the substrate also had a major effect on the stereochemistry of the reaction; a high cis selectivity was observed when 10a (a one-carbon-fewer analog of 1a) or 15a (a derivative with one more double bond in the carbon chain than in 1a) was used as the substrate. The reaction proceeded via a 6,5- or 5,5-fused-ring intermediate. The sulfenyl-group-assisted reaction could be a useful method for the stereoselective cyclization of acetates of alpha-sulfenylated secondary alcohols.
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan.
authors.forename: Changqing
authors.initials: C
authors.lastname: Liu
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Kudo
authors.forename: Yukihiko
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saigo