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■ An Asymmetric Synthesis of 4-Aryl-1,4-dihydropyridines

Chen-Yu Cheng, Jy-Yih Chen, and Mei-Jing Lee

*Institute of Pharmaceutical Sciences, National Taiwan University, 1, Sec. 1, Jen-Ai Road, Taipei 10018, Taiwan, R.O.C.

Abstract

Phenyllithium was found to attack preferenitally the ester group of 5-(4,4-dimethyl-4,5-dihydro-oxazol-2-yl)-2,6-dimethylnicotinic acid ethyl ester (6) to give phenyl ketone (7) and diphenylcarbinol (8), despite the directing effect of the oxazoline group. By replacing the ethyl ester in 6 with a butyl tert-butyl ester, the desired 1,4-addition with PhLi to give 4-phenyldihydropyridine derivative (12) in 67% was observed. As a chiral version of the above reaction, 2-[5-(tert-butoxycarbonyl-2,6-dimethyl-3-pyridyl]-4-(S)-methoxymethyl-5-(S)-phenyl-δ²-oxazoline (13) reacted with PhLi to give 3-(tert-butoxycarbonyl)-2,6-dimethyl-N-ethoxycarbonyl-5-[(4S,5S)-4-methoxymethyl-5-phenyl-4,5-dihydro-oxazol-2-yl]-4-(S)-phenyl-1,4-dihydropyridine (1) and its C-4 epimer (2) in a ratio of 5:1 and a total yield of 54%.