Catalytic hydrogenation of 6-methylenetetracyclines - using rhodium-tert phosphine complex catalyst giving a stereospecific prod. in high yield

摘要

6-Methylenetetracyclines are hydrogenated by treating a tetracycline with an exocyclic methylene group with H2 in the presence of a catalyst consisting of a complex of rhodium with a tertiary phosphine of formula PR1R2R3, (where R1 and R2 are phenyl opt. substd. by e.g. alkyl, alkoxy, halogen or dialkylamino gps; and R3 and R gamma are alkyl or benzyl gp), in a solvent which dissolves both the tetracycline and the catalyst. The process produces little or no undesired anhydrotetracyclines, the reduction is practically quantitative and the catalyst is stereoselective to the production of the 6 alpha-epimer.