Tandem cyclization of alkynylmetals bearing a remote leaving group via cycloalkylidene carbenes

Treatment of terminal alkynes bearing a remote leaving group with MNR2 (M = Li, Na, K) gives bicyclo[n.3.0]-1-alkenes (n = 3, 4). The tandem cyclization proceeds through a mechanism involving exo-cyclization of an alkynylmetal intermediate and intramolecular C-H insertion of the resulting carbenoid.