Although the cyclohexadienone annulation is successful for indole carbene complexes (Scheme V), cyclohexadienones can’t be obtained from the reaction of 2,6-disubstituted phenyl complexes.  The reaction of these complexes occur without the incorporation of a carbon monoxide ligand of the carbene complex to give indene products of the type 65 which result from a 1,5-sigmatropic shift of the one of the ortho-substituents in 63 [1].[ A specific example is the formation of the indene 67 from the reaction of diisopropyl acetylene and the 2,6-dimethylphenyl carbene complex 66.  It was thought that the driving force for the 1,5-sigmatropic shift of the methyl group arose from the aromaticity that is regained in the benzene ring. 

It was thus proposed that the 1,5-sigmatropic shift of methyl might be prevented if a tautomerization of an enol of the type 69 to give the ketone 70 were to occur. This in fact proved to be possible [2].[The reaction of the hydroxy-substituted carbene complex 72 with 3-hexyne gave the hydroindenone 73 in 75 % yield revealing that the tautomerization of the enol is faster than the 1,5-sigmatropic shift of methyl. The reaction is also regioselective as illustrated by the reaction of complex 74 with 3-hexyne, which gave the product resulting from cyclizations to the methyl position rather than to the methylene position. The simplicity of this reaction for the construction of highly functionalized perhydroindenones makes it an attractive candidate for applications in total synthesis. 

[1] Quinn, J. F.; Bos, M. E.; Wulff, W. D., Org. Lett., 1999, 1, 161.

[2] Bos, M. E.; Wulff, W. D.; Wilson, K. J., J. Chem. Soc., Chem. Commun., 1996, 1863