Breaking of the C-C bond of cyclobutanones by rhodium(I) and its extension to catalytic synthetic reactions

A study of rhodium(I)-catalyzed synthetic transformations involving selective breaking of the C-C bond or to the carbonyl group of cyclobutanones is described. Decarbonylation took place on treatment of a cyclobutanone with an equimolar amount of (Ph(3)P)(3)RhCl at reflux in toluene to afford the corresponding cyclopropane. The formation of the cyclopropane suggests that Rh(I) undergoes an insertion into the bond between the carbonyl carbon and the a-carbon in the initial step. Catalytic decarbonylation of cyclobutanone was also achieved. The mode and rate of the reaction depended greatly on the ligands of the rhodium(I) complex. When a cyclobutanone bearing a hydrogen atom at the 3-position was used, appropriate choice of the catalyst system led to the selective formation of either a cyclopropane or an alkene. Breaking of the carbon-carbon bond was next combined with hydrogenolysis. When cyclobutanone was treated under hydrogen pressure with a catalytic amount of a rhodium(I) complex having a bidentate diphosphine ligand like 1,2-bis(diphenylphosphino)ethane, a ring-opened alcohol was produced in good yield. Selective breaking of C-C bonds by a soluble transition metal complex is achieved in these practical synthetic processes.