An asymmetric synthesis of 4-aryl-1,4-dihydropyridines

Article abstract of DOI:10.3987/COM-96-7565

Phenyllithium was found to attack preferentially 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 bulky 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%.