Simple preparation of cobaloxime dienyl complexes and their exo selective Diels–Alder cycloadducts: Progress toward transition metal-mediated Diels–Alder reactions which are catalytic in metal dienyl complex

A new method for the synthesis of cobaloxime dienyl complexes (cobaloxime=pyridine(dimethylglyoxime)2Co) which involves a zinc-mediated hydrocobaltation of enynes is reported. Use of this dienyl complex synthesis method allows subsequent Diels–Alder reactions of these complexes to be accomplished without isolation of the dienyl complexes. A new silane-based cobaloxime-substituted cycloadduct demetallation protocol is then reported which provides Diels–Alder cycloadducts and cobalt complexes which have been recycled into the zinc-mediated dienyl complex synthesis.