New nitrogen-containing rhodium catalysts
The reaction of (Ph3P)3RhCl with MeNHNHMe.2HCl, in an inert atm., produced the N-contg. Rh complex Ph3PRhCl4NHMeNHMe (I). The use of I in the homogeneous hydrogenation of the exocyclic methylene group of methacycline-HCl allowed virtually asym. synthesis of the required clin. active enantiomer of doxocycline. Further, the amt. of Rh necessary for the complete hydrogenation was considerably less than the amts. indicated in the literature.