Deracemization of Diarylmethanes via Lateral Lithiation-Protonation Sequences by Means of Sparteine.

Abstract Deracemization of diarylmethane derivatives was investigated by lateral lithiation–protonation mediated by (−)-sparteine. Treatment of racemic 4-phenyltetrahydroisoquinoline 1 with s-butyllithium–(−)-sparteine followed by protonation of the resulting anion afforded (R)-phenyltetrahydroisoquinoline 1 in up to 88% e.e. Following the same procedure, racemic 2-(1-phenylethyl)pyridine 2 was subjected to the lithiation–protonation sequence. The stereochemical outcome of the sequence proved to be highly dependent on the proton sources giving either (S)- or (R)-2-(1-phenylethyl)pyridine 2 with EtOH or t-BuOH respectively in up to 50% e.e.