Influence of the bridgehead substituent on the stereoselective leuckart reaction of 2-norbornanones - Skeletal rearrangement versus structural retention

The synthesis of chiral amine norbornane derivatives has been achieved by m eans of the Leuckart reaction of various 2-norbornanones, We propose an ion ic mechanism for this process in which the formation of a 2-formylamino-2-n orbornyl cation is the common initial step. The reaction pathway and the is olated products are strongly dependent on the nature of the bridgehead subs tituents; hydrogen and alkyl groups yield only enantiopure 2-norbornyl form amides with structural retention, whereas O-acyl or N-acyl groups favour a pinacol-type skeleton rearrangement through a cascade of Wagner-Meerwein re arrangements and intramolecular transamidations.