Cyclopentenone Annulation of 2‐Oxocycloalkane‐1‐carbonitriles

Phase‐transfer alkylation of the 2‐oxocycloalkane‐l‐carbonitriles 1a and 1b with ethyl 4‐bromo‐3‐methoxy‐2‐butenoate ( 2 ), followed by deprotection and base‐catalyzed cyclization gave the annulated cyclopentenones 5a and 5b , respectively, in high overall yields ( Scheme 1 ). Stereoselective catalytic hydrogenation of 5b followed by de‐ethoxycarbonylation afforded 14‐oxo‐cis‐bicyclo[10.3.0]pentadecane‐l‐carbonitrile ( 7 ). Treatment of 7 with LiN(i‐Pr) 2 in THF gave the known synthetic muscone precursor 8 ( Scheme 2 ). The tricyclo[10.4.0.0 1,15 ]hexadecan‐14‐one ( 14 ) was prepared from 7 in 5 steps by a reaction sequence proceeding without affecting the chiral centres ( Scheme 2 ). The structure of 14 was established by X‐ray structure analysis ( Figure ).