An Efficient Process for the Manufacture of Carmegliptin

A short and high-yielding synthesis of carmegliptin (1) suitable for large-scale production is reported. The tricyclic core was assembled efficiently by a decarboxylative Mannich addition−Mannich cyclization sequence. Subsequent crystallization-induced dynamic resolution of enamine 7 using (S,S)-dibenzoyltartaric acid was followed by diastereoselective enamine reduction to give the fully functionalized tricyclic core with its three stereogenic centers. The C-3 nitrogen was introduced by Hofmann rearrangement of amide 28, and the resulting amine 10 was coupled with (S)-fluoromethyl lactone 31. Following cyclization to lactam 13 and amine deprotection, 1 was obtained in 27−31% overall yield with six isolated intermediates.