Transition-metal Catalyzed Oraganic Reactions involving Vinylidene-metal Complexes

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Transition-metal can act as a trigger for cycloaromatization of an enediyne. In the presence of Et_3N and 5 mol% [RhCl (i-Pr_3P) _2] catalyzes the reaction of the acyclic enediyne to produce aromatic hydrocarbon. The cyclization similar to Saito-Myers reaction proceeds via vinylidene-rhodiumn and 1,4-organorhodium diradical to afford the product.Cycloaromatization of acyclic enediynes triggered by rhodium (I) catalyst followed by radical cascade reaction with alkenes providing a new C-C bond has been also examined. In the presence of Et_3N and [RhCl (i-Pr_3P) _2], (Z) -3-dodecene-1,5-diyne slowly added by a syringe pump reacted with ethyl acrylate in benzene at 80 ﾟC to give ethyl 3- [2- (1- (E) -propenyl) phenyl] propanoate in 53% isolated yield. The similar reactions with other alkenes, such as ethyl methacrylate, methyl vinyl ketone, and dimethyl maleate took place to give the corresponding adducts in moderate to good yields. Exclusive formation of E-olefinic product was observed in all cases. The example of rhodium-catalyzed tandem C-C bond forming reaction with ethyl acrylate was also observed for the reaction of (Z) -1-cyclohexylhex-3-ene-1,5-diyne and (Z) -1-tert-butyldimethylsilyloxyoct-5-ene-3,7-diyne leading to the formation of ethyl 3- [2- (1-cyclohexenyl) phenyl] propanoate and ethyl 3- [2- (2- (E) -tert-butyldimethylsilyloxy-ethenyl) phenyl] propanoate, respectively. The catalytic reaction of (E) -Methyl 4-oxa-6- ((Z) -2-propynylidene) undec-2-en-7-ynoate proceeds at 50 ﾟC to give benzoisodehydrofurane (E-form) as a sole product in 65% yield even without slow addition technique. The intervention of a vinylidene-rhodium and a 1,4-organorhodium diradical is proposed for intermediates of this catalytic reaction.