SET pathway in tributylstannyllithium addition to alkynyl Fischer carbene complexes

The reaction of tributyltin lithium with Fischer type alkynyl carbene complexes has been studied. The reaction proceeds via a nucleophilic pathway to produce the conjugate addition product, and a single electron transfer pathway to afford cyclopentannulated derivatives derived from two units of the alkyne complex. Structure of the latter was confirmed by crystal structure determination of a representative complex.