Carbonyliron-induced coupling of olefins via ferracyclopentane complexes: the photochemical and thermal reactions of dimethyl cyclobut-3-ene-cis-1,2-dicarboxylate with carbonyliron reagents

Abstract

Dimethyl cyclobut-3-ene-cis-1,2-dicarboxylate (7) reacts with [Fe₂(CO)₉](20 °C) and [Fe(CO)₅](h_ν,20 °C) to form ferratricyclononane complexes (8) and (11), respectively. Subsequent insertion of carbon monoxide leads to displacement of the metal from the central five-membered ferracycle, with formation of the corresponding cyclic ketones, (9) and (12) respectively. Hydrogenolysis of the iron–carbon σ bonds is achieved by treatment of the complexes with hydrogen and Raney nickel, yielding the respective biscyclobutyl derivatives (10) and (13). Thermolysis of the complexes results in cleavage of the four-membered rings with formation of methyl acrylate and/or dimethyl fumarate. Tetracarbonyliron complexes of (7) and of cyclobut-3-ene-cis-1,2-dicarboxylic anhydride (6) are also reported.