Deracemization of alkyl diarylmethanes using (-)-sparteine or a chiral proton source

In a first stage, deracemization of 2-(1-phenylethyl)pyridine 1 and chlorph eniramine 2 was investigated in the presence of (-)-sparteine as a chilal l igand. Whereas (R)-2-(1-phenylethyl)pyridine 1 was obtained in 65% ee with 2,6-di-tert-bulyl-4-methylphenol as a proton donor, the opposite stereosele ction was observed with EtOH leading to (S)-2-(1-phenylethyl)pyridine 1 in 53% ee, A second methodology making use of (+)-(R)-1-[5-chloro-2-(methylarn ino)-phenyl]-1,2,3,4-tetrahydroisoquinoline 4 as a chiral proton source gav e higher enantioselectivities, affording (R)-1 and (R)-2 in up to 84 and 75 % ee, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.