Asymmetric phenol oxidation. Stereospecific and stereoselective oxidative coupling of a chiral tetrahydronaphthol

Abstract

The study of the factors which determine the intermolecular asymmetric phenol oxidation shows the importance of the stereochemical control exerted by asymmetry in the substrate. The oxidative coupling of (S)-(+)-2-hydroxy-3,4,8-trimethyl-5,6,7,8-tetrahydronaphthalene ((S)-(+)-1) resulted in the completely stereoselective formation of the optically active dinaphthol (S,S)-(+)-trans-2a. The results argue against the necessity of an asymmetric oxidant in intermolecular phenol coupling reactions. The synthesis of enantiomerically pure (S)-(+)-1 was completed by a six-step route from racemic 7-methoxy-5,6-dimethyl-1,2,3,4-tetrahydro-1-naphthoic acid ((R,S)-16), which was resolved via its (+)-dehydroabietylamine salts. The chiroptical data of the tetrahydronaphthols 1, 10, 16, and 23-26 and of dinaphthol 2a are presented. Diastereomeric charge-transfer interactions, which resulted in long-range asymmetric influences, were observed in amides 27 and 29.