Selective hydrogenation of α,β-unsaturated oxosteroids with homogeneous rhodium catalysts

Abstract

A comparative study of the ligand ( 5– 10) effect on the rhodium catalytic activity and selectivity in the homogeneous hydrogenation of α,β-unsaturated oxosteroids ( 1– 4) is reported. The highest activity for C C reduction was observed with phosphite ligands, being diphosphite 10 the most active. Furthermore, the presence of phosphite 6 significantly enhances the chemo and α-diastereoselectivity for the hydrogenation reaction. The β-methyl groups of the steroidal framework lead to a very high α-diastereoselectivity, even in the absence of phosphorous ligands. Substrate 4 is the paradigm presenting higher than 94% α-diastereoselectivity for any catalytic system studied. The catalytic system formed from rhodium and the new diphosphite 10 also revealed a remarkable tendency for the C O reduction and a noteworthy stability.