A double alkylation—ring closing metathesis approach to spiroimines

As part of a programme directed towards the synthesis of the marine toxins, the spirolides and gymnodimine, a convenient synthesis of the key bicyclic spiroimine ring systems has been developed. The method involves double alkylation of a simple lactam, Grubbs ring closing metathesis of the resultant dialkylated lactam then reduction of the lactam to an imine.