A facile and diastereoselective access to substituted cyclopentanones from Fischer alkenyl carbene complexes and 1-amino-1-azadienes

Fischer alkenyl carbene complexes 1 undergo cyclopentannulation to alkenyl N,N-dimethylhydrazones (1-amino-1-azadienes) 2 to furnish substituted cyclopentenes 3 (45–55%) in a regio and diastereoselective way, along with minor amounts of pyrroles 4 (25–28%). Enantiopure carbene complexes derived from (−)-8-phenylmenthol 7a and (−)-8-(2-naphthyl)menthol 7b afforded, in addition to pyrrole 4a (12–15%), trans,trans-cyclopentenes 8/9 (35–43%) and cis,cis-cyclopentenes 10/11 (23–25%) with fairly to excellent face selectivity (78% for 7a and 92% for 7b).