Base-Mediated Nitrophenyl Reductive Cyclization for the Synthesis of Hexahydro-2,6-methano-1-benzazocines.

A Diels-Alder reaction leading to 4-nitrophenylcyclohexanones followed by a newly developed base-mediated reductive cyclization of the resulting ketone tethered to the nitrobenzene moiety gives access to the hexahydro-2,6-methano-1-benzazocine ring system present in several biologically interesting natural products such as aspernomine. The scope of the reaction was explored with eight substituted nitrobenzenes, obtaining yields of up to 87%. The highest cytotoxicity was observed in benzazocine 4h, bearing an enone moiety, which was active against eight cancer cell lines.