HOMOGENEOUS CATALYSIS. CONVERSION OF 4-PENTENALS TO CYCLOPENTANONES BY EFFICIENT RHODIUM-CATALYZED HYDROACYLATION.

Article abstract of DOI:10.1021/om00094a025

A variety of complexes of the type left bracket Rh(diphosphine) right bracket ** plus have been investigated as catalysts for hydroacylation, the intramolecular cyclization of 4-pentenals to cyclopentanones. All of the complexes studied effect this conversion in weakly or noncoordinating solvents at 20 degree C, but the most effective catalyst was found to be the rhodium(I) species containing diphos ((C//6H//5)//2P(CH//2)//2P(C//6H//5)//2). This complex converts 4-pentenal at a remarkably fast rate of one turnover every 6 s at 20 degree C in CH//3NO//2 and CH//2Cl//2 solutions. These catalysts are effective for 4-pentenals bearing mono substituents at the 2-, 3-, 4-, and 5-positions and disubstitution at the 3-position. Disubstitution at the 2-position slows the rate and effectiveness of catalysis considerably, and substrates having disubstitution at the terminal 5-position are not turned over by these catalysts.