Intramolecular Cyclizations via Carbenoid Intermediates in Complexation of Alkynyltungsten Compounds with Co2(CO)8: A New Route to the Pauson−Khand Reaction

[[abstract]]The reactions of Co2(CO)8 with alkynes RCCR′ form (RCCR′)-Co2(CO)6 complexes. 1 Organic reactions 2-6associated with this functionality can be grouped into three major categories: (1) [2 + 2 + 1] cyclization with alkenes to form cyclopentenones (Pauson-Khand reaction), 2-4 (2) formation of a propargylic cation equivalent (the Nicholas reaction), 2,5 and (3) protection of an alkyne group. 6 The versatility of these reactions is well recognized, and they are frequently employed as a key step in synthesis of complex molecules. 7 Organic carbenoids are useful intermediates in organic synthesis. 8,9 Development of new synthetic method involving carbenoid intermediates has received considerable attention. 9 Although there are numerous investigations on (RCCR′)- Co2(CO)6 complexes, 2-6 generation of a carbenoid intermediate from this functionality remains entirely unknown. Here we reportseveral intramolecular cyclizations via carbenoid intermediates generated from Co2(CO)6 complexation of functionalized alkynyltungsten compounds. The synthetic utility of these cyclizations is manifested by the synthesis of cyclopentenone derivatives.[[fileno]]2010327010090[[department]]化學