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

In a first stage, deracemization of 2-(1-phenylethyl)pyridine 1 and chlorpheniramine 2 was investigated in the presence of (−)-sparteine as a chiral ligand. Whereas (R)-2-(1-phenylethyl)pyridine 1 was obtained in 65% ee with 2,6-di-tert-butyl-4-methylphenol as a proton donor, the opposite stereoselection 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-(methylamino)-phenyl]-1,2,3,4-tetrahydroisoquinoline 4 as a chiral proton source gave higher enantioselectivities, affording (R)-1 and (R)-2 in up to 84 and 75% ee, respectively.