Synthesis of 1,4-dihydropyridines in cyclocondensation reactions (review)

Reduction of 2-amino-1-(4-nitrophenyl)-1 H-pyrido[3,2-b]indole-3-carbonitrile by sodium borohydride and sodium cyanoborohydride

“…On heating with excess acetal in methanol, base 4 and hydrochloride 5 are readily converted to N {[2 imino 1 (4 nitrophenyl) 2,3,4,5 tetrahydro 1H pyrido[3,2 b] indol 3 yl]methylimino)methyl} N methylmethanamine (6), which was also isolated as chloride 7. The structure of compounds 6 and 7 was confirmed by 1 H NMR data.…”

“…The product was obtained from dihydropyrido indole 2 (0.33 g, 1 mmol), NaBH 3 (CN) (0.12 g, (2 mmol), and methanol (10 mL) as described for the synthesis of 4 by method A (except that the reaction was carried out under argon). The hydrochloride was isolated as in method A to give 0.3 g of hydro chloride 5 identical to the compound obtained by method A. N {[2 Imino 1 (4 nitrophenyl) 2,3,4,5 tetrahydro 1H pyrido[3,2 b]indol 3 yl]methyliminomethyl} N methyl methanamine (6). A solution of tetrahydropyridoindole 4 (0.05 g, 0.15 mmol) and DMF dimethyl acetal (0.045 mL, 0.3 mmol) in methanol (1 mL) was stirred at reflux for 0.5 h. The solvent was evaporated to dryness.…”

“…1,2 Many indole derivatives are pharma ceutical agents used in medical practice, 3,4 and 1,4 di hydropyridine derivatives exhibit biological activities. 5, 6 Therefore, combination of these fragments in one molecule may prove to be of interest as regards the search of com pounds with new biological properties in the 4,5 dihydro Our work deals with the reduction of 1 aryl δ carboline derivatives exemplified by the reduction of 2 amino 1 (4 nitrophenyl) 1H pyrido [3,2 b]indole 3 carbonitrile (1a), which is a 2 imino 2,5 dihydropyrido[3,2 b]indole 1b derivative in a tautomeric form (see Refs 1,2,7), with sodium borohydride and sodium cyanoborohydride. These reducing agents do not tend 8, 9 to reduce nitro and cyano groups in the absence of catalysts, although some excep tions still have been reported.…”

Synthesis of pyridines by cyclocondensation of acetyl and benzoyl pyruvates with enamines

“…The most valuable method for the synthesis pyridines with acceptor substituents in positions 3 and 5 of the nucleus is the Hantzsch synthesis [1,2]. In one variant of the Hantzsch synthesis for the preparation of pyridines condensation of ethyl ethoxymethyleneacetoacetate (or other products of the reaction of β-dicarbonyl compounds with ethyl orthoformate) with enamines of β-dicarbonyl compounds is used [3].…”

p-(Dimethylamino)benzaldehyde modification of the Hantzsch reaction: Synthesis of 3-(1H-benzimidazol-2-yl)-5,7-dimethoxyquinolines

“…In our opinion this variation of the Hantzsch reaction can be efficiently used as a novel and convenient method for preparation of compounds with a γ-unsubstituted pyridine ring which we have also demonstrated in our work on the synthesis of novel quinoline compounds. We began with the fact that one of the methods of preparing 1,4-dihydropyridines is based on a three component [1+3+2] cyclocondensation of aldehydes with β-aminocrotonic ester and acetoacetic ester [4]. This method can be extended by varying the nature of the reaction components, in particular was use of 5-aminopyrazoles and dimedone for synthesis of pyrazoloquinolines [5].…”