Resolution of 4-aminoflavan into its optical isomers; nuclear magnetic resonance spectra of 4-aminoflavan and 3-aminoflavanone derivatives

(�)-2,4-cis-4-Aminoflavan obtained by reduction of 4-oximinoflavan has been resolved into enantiomeric forms by fractional crystallization of its amine salts with (+)-camphor-10-sulphonic acid and with (-)-di-O-benzoyltartaric acid. The pairs of diastereoisomeric salts thus separated were converted into (+)- and (-)-2,4-cis-4-aminoflavan hydrochlorides, from which the free bases and the optically active N-acetyl and N-benzoyl derivatives were prepared. N.m.r. data unequivocally establish the 2,4-cis configuration of all these 4-substituted flavan derivatives. 3-Aminoflavanone prepared by the Neber rearrangement of 4-oximinoflavan, and also by controlled catalytic hydrogenation of 3-oximinoflavanone, is shown from N.M.R. data on suitable derivatives to have the 2,3-trans configuration.