Scope and mechanism of stannylalumination of 1-alkynes

Terminal acetylenes react with Bu{sub 3}SnAlEt{sub 2} in the presence of Cu{sup +} or Pd{sup 0} catalysts to give 1,2-dimetallo-1-alkenes in highly regio- and stereoselective reactions. These intermediates can be selectively functionalized at the vinyl-aluminum bond to provide vinylstannanes, which upon transmetalation and further reaction with electrophiles give stereodefined trisubstituted olefins. In sharp contrast to the normal behavior of alkylaluminum reagents, this process tolerates a number of functional groups including OH, OAc, OTHP, and Br. Mechanistic investigations suggest that the addition of Bu{sub 3}SnAlEt{sub 2} to 1-alkynes proceeds via stannylcupration followed by capture of the stannylcuprate adduct by electrophilic aluminum.