Preparation of R-(+)-3,4-dimethoxybenzyl, 2-methoxy-1-naphthyl sulfoxide and diastereoselective addition of lithiated anion of this reagent to cyclic nitrone. Asymmetric synthesis of optical pure isoquinoline alkaloids

摘要

The addition of the lithium carbanion of (R)-(+)-3,4-dimethoxybenzyl 2-methoxy-1-naphthyl sulfoxide 3 to cyclic nitrone 4, under kinetically controlled conditions gave isoquinoline sulfoxide derivatives 5 and 6 in high diastereoselectivities, Under equilibrium controlled conditions poor diastereoselectivity results. The chiral (R)-(+)-3,4-dimethoxybenzyl 2-methoxy-1-naphthyl sulfoxide 3 was easily prepared by the reaction of 3,4-dimethoxybenzylmagnesium chloride 2 with (-)-(S) menthyl 2-methoxy-naphthalene sulfinate 1 in dry benzene. This methodology allows for the synthesis of the isoquinoline alkaloid (R)-(-)-norlaudanosine 8 in three efficient synthetic steps. [References: 19]