Synthesis of Diastereomeric Pyrrolidine Sulfamides via Anchimerically Assisted Nucleophilic Substitution Reactions

Abstract

The Mitsunobu reaction was employed in a key step during the development of a convenient synthetic route for the enantioselective preparation of pyrrolidine-sulfamide ligands from (R)- or (S)- [(S)-1-benzylpyrrolidin-2-yl](phenyl)methanol, and employing tert-butyl pyrrolidin-1-yl-sulfonylcarbamate as a non-conventional nucleophilic source. Although it is well documented that the exposure of this type of diastereomeric amino alcohols to the above-mentioned nucleophile usually leads to the formation of piperidines via ring expansion, either through classical nucleophilic substitution or the Mitsunobu version, only the pyrrolidine derivatives were generated with retention of configuration on the exocyclic stereocenter, owing to the neighboring group participation (internal backside nucleophilic substitution, SNib). Final removal of the N-Boc protecting group from the sulfamide fragment afforded chiral compounds with significant potential as chiral ligands in asymmetric catalysis. Keywords: Chiral pyrrolidine sulfamides, internal backside nucleophilic substitution, Mitsunobu reaction, neighboring group participation, prolinol derivatives, alcohol.