title: Addition of lithiated 5-hydroxymethyl-1,3-dithiane to benzaldehyde: HMPA-controlled trans stereoselectivity.
abstract: Addition of 5-substituted dithianyl anions to carbonyl compounds normally produces trans adducts. The presence of a nucleophilic hydroxymethyl group in position 5 dramatically decreases the trans stereoselectivity of the reaction in THF. The trans/cis ratio shows a bell curve dependence on HMPA, fitted to a quantitative model involving a series of equilibrated ion pairs, of which an intermediate contact ion pair possessing three (effective) HMPA molecules yields the trans adduct with much higher stereoselectivity. [structure: see text]
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208-2436, USA.
authors.forename: Zaiguo
authors.initials: Z
authors.lastname: Li
authors.forename: Alexei N
authors.initials: AN
authors.lastname: Kurchan
authors.forename: Andrei G
authors.initials: AG
authors.lastname: Kutateladze