Partial hydrogenation of substituted pyridines and quinolines: a crucial role of the reaction conditions

Abstract Hydrogenation of pyridyl and quinolyl compounds 2-substituted with a carbonyl group ( 1a – c and 2b , c ) using PtO 2 and 1 equiv. of HCl (conditions A ) provides clean and total formation of the desired amino alcohol (hydrogenation of the heterocyclic ring and of the carbonyl) while under conditions B 1 and/or B 2 (concentrated HCl or pure CF 3 CO 2 H) the heterocyclic ring remains untouched and other aromatic parts are hydrogenated providing complex mixtures. When the heterocyclic ring is substituted by an alkyl group (quinaldine 3 ) conditions A provide mixtures while under conditions B 2 (pure CF 3 CO 2 H) the benzene ring is cleanly hydrogenated leading to a pure product.