合成路线1

The reaction of diketene (I) with 2-bromoethanol (II) by means of dimethylaminopyridine (DMAP) in dichloromethane gives acetoacetic acid 2-bromoethyl ester (III), which is condensed with 3-nitrobenzaldehyde (IV) by means of piperidine acetate in isopropanol yielding the corresponding 3-nitrobenzylidene derivative (V). The cyclization of (V) with methyl 3-aminocrotonate (VI) by heating at 80 C affords 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-(2-bromoethyl) 5-methyl diester (VII), which is condensed with chloromethyl ethyl ether (VIII) by means of NaH in THF to afford the corresponding 1-ethoxymethyl derivative (IX). The reaction of diester (IX) with NaCN and tetrabutylammonium cyanide or sodium p-toluenesulfonate and benzyltriethylammonium chloride (BTEACl) in DMF gives 1-(ethoxymethyl)-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid monomethyl ester (X). The optical resolution of (X) through the cinchonidine salt yields, after crystallization, the cinchonidine salt of the (R)-enantiomer (XI), which is treated with HCl to eliminate the cinchonidine, and esterified with 1,3-dibromopropane and K2CO3 in acetone to afford (R)-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-(3-bromopropyl) 5-methyl diester (XII). Finally, this compound is condensed with 4,4-diphenylpiperidine (XIII) by means of K2CO3 in DMF at 100 C.