Extended Dötz-like cyclization reactions towards the synthesis of eight-membered ring-containing polycycles: scope and theoretical studies.

The reaction between cyclobutene-containing dienyl Fischer carbene complexes (FCCs) and alkynes has been studied from both an experimental and a theoretical point of view. We have found that the reaction follows different pathways depending on the nature of the terminal double bond of the carbene complex. Thus, eight-membered carbocycles have been obtained from an extended Dötz-like reaction of dienyl FCCs and indolyl- or benzofuryl-substituted alkenyl FCCs. On the other hand, phenyl- and naphthyl-substituted alkenyl FCCs follow a typical benzannulation pathway giving rise to cyclohexadienones. DFT calculations have allowed us to formulate detailed mechanistic proposals and to provide an explanation for the formation of either the benzannulation products or the eight-membered carbocycles.