Facile diastereoselective reactions of chiral 1,3-oxazolidines with Grignard reagents; Asymmetric syntheses of 2-substituted and 2,6-disubstituted piperidines

(S)- and (R)-2-Phenylpiperidines, (S)- and (R)-2-methylpiperidines, meso- and (2R, 6R)-2,6-diphenylpiperidines, and meso- and (2S, 6S)-2,6-dimethylpiperidines were synthesized asymmetrically starting from the diastereoselective addition of Grignard reagents to chiral 1,3-oxazolidines, converting of 1-aza-4-oxabicyclo[4.3.0]nonane derivatives as pivotal intermediates.