Cobalt-mediated [2+2+2]-cycloaddition of alkynes to imidazole to form 3a,7a-dihydrobenzimidazoles and a novel synthesis of quinolines.
The Co complexes I (R = SiMe3, Et, OMe, CO2Me, X = O) were obtained as pure antiisomers by reaction of the alkylnylimidazole II with RC.tplbond.CSiMe3 and cyclopertadienylcobalt dicarbonyl. I (R = SiMe3, X = H2) was similarly obtained as a syn-anti mixt. I (R = SiMe3, X = O) was demetalated or desilylated to I (R = H, X = O). Demetalation, aromatization, and imine hydrolysis of I (R = OMe, X = O) gave the quinolinone III.
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