Rhenabenzenes and Unexpected Coupling Products from the Reactions of Rhenacyclobutadienes with Ethoxyethyne

Treatment of Na[Re(CO)5] with methyl 3-(naphthalen-1-yl)propiolate (NpC≡CCO2Me) followed by acetyl chloride and alcohols ROH (R = Me, nPr) afforded the rhenacyclobutadiene complexes Re{-C(Np)═C(CO2Me)C(OR)═}(CO)4. Reactions of these rhenacyclobutadiene complexes with HC≡COEt produced the rhenabenzene complexes Re{-C(Np)═C(CO2Me)C(OR)═CHC(OEt)═}(CO)4 and new rhenacyclobutadienes with a pendant vinyl substituent Re{-C(Np)═C(C(OR)═CH(CO2Et))C(OMe)═}(CO)4. In the vinyl-substituted rhenacyclobutadiene products, the ethyl of the ester group is from the alkyne HC≡COEt, the alkyl of the ReC(OR) group is from the ester group of the starting rhenacyclobutadienes, and the alkyl group of the OR of the vinyl substituent is from the ReC(OR) group of the starting rhenacyclobutadienes. A plausible mechanism for the formation of the vinyl-substituted rhenacyclobutadienes is discussed.