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 se lective breaking of the C-C bond or to the carbonyl group of cyclobuta nones is described. Decarbonylation took place on treatment of a cyclo butanone with an equimolar amount of (Ph(3)P)(3)RhCl at reflux in tolu ene to afford the corresponding cyclopropane. The formation of the cyc lopropane suggests that Rh(I) undergoes an insertion into the bond bet ween the carbonyl carbon and the a-carbon in the initial step. Catalyt ic decarbonylation of cyclobutanone was also achieved. The mode and ra te of the reaction depended greatly on the ligands of the rhodium(I) c omplex. When a cyclobutanone bearing a hydrogen atom at the 3-position was used, appropriate choice of the catalyst system led to the select ive formation of either a cyclopropane or an alkene. Breaking of the c arbon-carbon bond was next combined with hydrogenolysis. When cyclobut anone 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 c omplex is achieved in these practical synthetic processes.