PtCl₄-catalyzed Cycloreorganization of 1,6- and 1,7-Enynes

Transition metal catalyzed reaction of enynes has been the subject of extensive study, because enynes can form the metallacyclopentenes via simultaneous complexation with two unsaturated bonds.1 The metallacyclopentenes can undergo β-elimination followed by reductive elimination to lead to the cycloisomerized products. When the rate of the β-elimination slows down, the reductive elimination of the metallacyclopentenes becomes competitive to lead to the bicyclic compounds or reorganized products. The latter is formally a metathesis of enynes. Since Katz reported skeletal reorganization of enynes catalyzed by a Fisher-type tungsten carbene complex,2 Trost,3 Mori,4 and Murai5 have reported similar enyne metatheses by various metal complexes containing Pd, Ru, Pt, Ir, etc. Among these, PtCl2 turned out to be the most efficient and