Unsaturated amidals 1, derived from allylic alcohols and containing a stereogenic amidal center, undergo amidomercuration with high 1,3-stereoinduction from the amidal center. In substrates derived from secondary allylic alcohols, the influence of the stereogenic amidal center overrides the competing 1,2stereoinduction from the allylic substituent. Consequently, starting from a single secondary allylic alcohol, the amidal auxiliary enables the selective preparation of either a syn or an anti vicina! aminoalcohol.
Diastereoselective electrophilic heterocyclization reactions are commonly employed to control the relative stereochemistry in cyclic and, via cleavage of the heterocycle, in acyclic c0mpounds.Z4
Several practical limitations can be encountered in using this strategy. For example, the level of stereoinduction from the resident stereogenic center may not be acceptable, and only one of the two possible diastereomeric relationships between the resident and the newly created stereocenters can usually be obtained with acceptable selectivity. Also, the strategy is generally best applied to substrates in which the resident stereogenic center resides endocyclic with respect to the newly forming ring. In this letter we describe our preliminary results on the use of a removable phthalimidederived auxiliary to direct the stereochemical course of the amidomercuration of allylic alcohols.4
Harding and co-workers3 have reported the stereoselective amidomercuration cyclizations of N-acyl amidals derived from N-acetoxymethyl carbamates and chiral secondary allylic and homoallylic alcohols. We were curious as to the relative influence of a resident stereogenic center positioned at the amidal center, adjacent to the nucleophilic amide functionality. Along these lines we investigated the cyclizations of N-acyl amid& 1. Mercuric acetate promoted cyclization of la followed by borohydride reduction ( 1. 1.5 eq Hg(OAc)z / 1.5 eq NaHC03 / 0 0 l.HgX, N . ..1.