The cobalt-mediated [2 + 2 + 2] cycloaddition of a,w-diynes to the 2,3-double bond of indole.
The reaction of 1-acetyl- or 1-(phenylsulfonyl)indole with a,w-diynes and CpCo(C2H4)2 yields CpCo-complexed dihydrocarbazoles. 1-(Trimethylsilyl)-1,6-heptadiyne gives an adduct in which the silyl moiety is distal to the phenylsulfonamide. 1-(Trimethylsilyl)-1,7-octadiyne results in an unusual diene complex resulting from C-H activation at C-2 of the indole. The behavior of a no. of terminally substituted 4-aza-1,7-octadiynes to the reaction is investigated. The oxidn. of one dihydrocarbazole complex with triphenylcarbenium hexafluorophosphate or with Fe(NO3)3 furnishes an h5-cyclohexadienyl cobalt complex and its subsequent conversion into substituted diene complexes or to the demetalated carbazole is discussed.
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