[New stereoselective catalysts in doxycycline synthesis]. / Novye stereoselektivnye katalizatory v sinteze doksitsiklina.

Formation of the doxycycline diastereoisomer along with doxycycline during hydrogenation of the methacycline exocyclic double bond lowered the yield of the main product. The use of tris-(triphenylphosphine)-rhodium chloride (Wilkinson catalyst) as a catalyst provided higher stereoselectivity of the hydrogenation and resulted in predominant production of doxycycline. Inclusion of some ligands such as hydrazine or others into the composition of the compound rhodium catalyst increased its activity. The stereoselectivity during hydrogenation of the methacycline exocyclic double bond can be explained by different rates of hydrogen attachment to the two enantiomeric products of the compound rhodium catalyst addition to the exocyclic double bond.