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Paper | Regular issue | Vol 34, No. 5, 1992, pp.943-953
Published online, 1st January, 1970
DOI: 10.3987/COM-91-5959
Diastereoselective Reduction of Derivatives of 3,4-Dihydro-1-methylidene-2-tartaroylisoquinoline

Zbigniew Czarnocki, David B. MacLean, and Walter A. Szarek

*Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1

Abstract

Various enamides were prepared from 3,4-dihydro-6,7-dimethoxy-1-methylisoquinoline by reaction with (R,R)-tartaric acid derivatives. The enamides were reduced with hydrogen over a platinum catalyst to afford diastereomeric mixtures enriched in the (1R)-isomer. The diastereoselectivity of the reduction step was assessed by conversion of the mixtures into N-acetylsalsolidine and measurement of its specific rotation. The enamide (5c), in which the hydroxyl groups of the 2-tartaroyl group are unprotected, cyclizes to an aminal (9) in the presence of acids. The reduction of 5c with sodium borohydride in acidic media afforded a diastereomeric mixture enriched in the (1S)-isomer.