(-)-Ephedrine as an auxiliary for the asymmetric synthesis of atropisomeric amides by dynamic resolution under thermodynamic control

N,N-Dialkyl-2-formylbenzamides and N,N-dialkyl-2-formyl-1-naphthamides cond ense with (-)-ephedrine in refluxing toluene to give oxazolidines both as s ingle diastereoisomers with respect to the new stereogenic centre and as si ngle conformers with respect to the slowly-rotating Ar-CONR2 bond. In the n aphthamide series, removal of the ephedrine auxiliary by hydrolysis returns the starting aldehyde (isolated by reduction to the more stable alcohol) i n enantiomerically enriched form (up to 94% ee). Overall, the two-step sequ ence amounts to a dynamic resolution under thermodynamic control. (C) 2001 Elsevier Science Ltd. All rights reserved.