Doubly diastereoselective conjugate addition of homochiral lithium amides to homochiral alpha,beta-unsaturated esters containing cis- and trans-dioxolane units.

As part of a long-term goal directed towards the ab initio asymmetric synthesis of unnatural amino sugars, the doubly diastereoselective conjugate addition reactions of the antipodes of lithium N-benzyl-N-(alpha-methylbenzyl)amide to a range of homochiral alpha,beta-unsaturated esters containing cis- and trans-dioxolane units was investigated. These reactions resulted in "matching" and "mismatching" effects. In the "matched" cases a single diastereoisomer of the corresponding beta-amino ester (containing three contiguous stereocentres) is produced.

Asymmetric synthesis of 3,4-anti- and 3,4-syn-substituted aminopyrrolidines via lithium amide conjugate addition.

The diastereoselective conjugate addition of homochiral lithium amides to methyl 4-(N-allyl-N-benzylamino)but-2-enoate has been used as the key step in a simple and efficient protocol for the preparation of 3,4-substituted aminopyrrolidines. This protocol provides a complementary and stereoselective route to both anti- and syn-3-amino-4-alkylpyrrolidines as well as anti- and syn-3-hydroxy-4-aminopyrrolidines, in high de and ee viabeta-amino enolate functionalisation. This methodology has been applied to the synthesis of anti-(3S,4S)- and syn-(3R,4S)-3-methoxy-4-(N-methylamino)pyrrolidine.

Lithium amide conjugate addition for the asymmetric synthesis of 3-aminopyrrolidines.

Conjugate addition of homochiral lithium amides to methyl 4-(N-benzyl-N-allylamino)but-2-enoate, chemoselective N-deprotection and concomitant cyclisation, followed by enolate functionalisation and deprotection allows access to syn- and anti-3,4-disubstituted aminopyrrolidines in > 98% d.e. and > 98% e.