Mechanistic Studies on the<i>O</i>-Directed Free-Radical Hydrostannation of Disubstituted Acetylenes with Ph₃SnH and Et₃B and on the Iodination of Allylically Oxygenated α-Triphenylstannylalkenes

Abstract

[reaction: see text] The free-radical hydrostannation of 1 with Ph(3)SnH and catalytic Et(3)B in PhMe has been mechanistically probed. At high Ph(3)SnH concentrations, the O-directed hydrostannation pathway dominates, and 2 is formed with good selectivity (ca. 11.1:1). Substantially lower stannane/substrate concentrations increase the amount of tandem 5-exo-trig cyclization product 3 that is observed.