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[10.4.0.01,15]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).