SELECTIVE HYDROGENATION OF 4H-1-BENZOPYRAN-4-ONE DERIVATIVES WITH GROUP 8-10 METAL-CATALYSTS

The chemo-, regio-, and stereo-selectivities on the hydrogenation of 2 -methyl- (1 a) and/or 3-methyl-4 H-1-benzyopyran-4-one (1 b) have been examined with group 8 approximately 10 metal catalysts at ambient tem perature under ordinary atmospheric pressure of hydrogen. The hydrogen ation of 1 a with Raney-Ni gave selectively a saturated ketone (2 a). A saturated alcohol (3 a) was produced f rom 2 a with Raney-Co. The hy drogenolysis product (4 a) was formed with other noble metal catlysts (Ru, Rh, Pd, Os, Ir, and Pt). The selectivity to the saturated alcohol (3 b) from 1 b was generally low, in comparison with that from 1 a to 3 a, at 50% conversion. In the hydrogenation of 1 a and 1 b, cis satu rated alcohols (3 a and 3 b) were predominantly obtained, but a trans- 3 b was preferentially formed only at the hydrogenation of 1 b with Pd catalyst. These results are discussed on the basis of a proposed hydr ogenation mechanism of 1 a and 1 b.