Chelate‐Controlled Asymmetric Synthesis of 2‐Substituted 2,3‐Dihydropyridin‐4(1H)‐ones: Synthesis of D ‐ and L ‐aminodeoxyaltrose derivatives

Asymmetric methylation and phenylation of the chiral pyridinium salt 7, as well as methylation of chiral pyridinium salt 18, with Grignard reagents occurred in good yield and with good‐to‐excellent diastereoselectivities (Schemes 2 and 3, resp.). These results are best explained by assuming chelate control to govern the asymmetric alkylation/arylation process. The minimum‐energy conformations of the out‐of‐plane twisted pyridinium salts 7 and 18, as determined by the ‘Molecular Simulations Cerius‐Dreiding II’ program, are in good agreement with the postulated asymmetric chelate‐control mechanism.