A novel stereocontrolled synthesis of cis-fused bicyclic lactams via [3 + 2]-cycloaddition of alkynyltungsten complexes with tethered aziridines.

Treatment of alkynyltungsten complexes with tethered aziridines in the presence of BF(3).Et(2)O led to [3 + 2]-cycloaddition reactions, affording bicyclic tungsten-enamine species stereoselectively. The stereochemistry of the resulting product reveals that ring opening of aziridine is initiated by S(N)2 attack of the tungsten fragment. Decomplexation of these organometallics with I(2) in CH(2)Cl(2), followed by hydrolysis, afforded only cis-fused bicyclic lactams efficiently. [reaction: see text]