2.4- Diphenyl-6,7-dihydropyridines

Methyl-8-(2-chlorophenyl)-3,4-dihydro-177,877-pyrido[2,l-f][l,4]oxazine-7,9-carboxylate was obtained by cyclization of l,4-dihydropyridine-3,5-dicarboxylate 338 in the presence of 3M HC1 <1997CAP2188071>. Mild catalytic hydrogenation of oxazinone 339 over 5% Pd/C catalyst afforded 3,4-diphenyl-9-hydroxyperhydropyrido[2,l-f][l,4]oxazin-l-one via sequential iV-carbobenzyloxy (fV-Cbz) deprotection and reductive amination <1998TL3659>. 

Chloro-4-phenylquinoline, (20.0 mg 0.083 mmol), diphenyl phosphate (1 mol %), Hantzsch dihydropyridine (50.7 mg, 0.200 mmol) and benzene (2.0 mL) were added to a screw-capped vial and the mixture was exposed to an argon atmosphere. The resulting yellow solution was allowed to stir at 60 °C for 12 h. The solvent was evaporated in vacuo, and the residue was purified by column chromatography over silica gel to afford the corresponding amine (94 %). 

Many pyrans are less stable or less accessible than pyrylium salts or pyranones but some suitably substituted 4//-pyrans can be used to prepare pyridines. Ethyl 6-amino-5-cyano-2,4-diphenyl-4H-pyran-3-carboxylate (196) on heating with ammonium acetate gives the corresponding pyridine-3-carboxylate (195), but when the ester group in (196) is replaced by a cyano group, a dihydropyridine (197) is obtained by a different and more complex reaction (81JHC309). 

Cyano-4,6-diphenyl-2-tellurono-l,2-dihydropyridine, obtained from the 2-chloropy-ridine derivative and sodium hydrogen telluride in ethanol, reacted with methyl iodide to produce 3-cyano-4,6-diphenyl-2-pyridyl methyl telluriumi. 

From this survey we found that several proton acids catalyze the reduction of ketimines using Hantzsch dihydropyridine 2 as the hydride donor. With regard to the different acids tested diphenyl phosphate... 

Average value obtained using 2,6-diphenyl-4-(2,4,6-triphenyl-l-pyridinio)phenoxide, 1-hexadecyl-4-[(oxocyclohexadienylidene)ethylidene]-l,4-dihydropyridine, l-hexadecyl-5-hydroxyquinoline and l-hexadecyl-6-hydroxyquinoline, average deviation <9 % calculated from [47d]. Abbreviations SDS = sodium dodecyl sulfate DBS = dodecyl benzenesulfonate CTAC = hexadecyltri-methylammonium chloride CTAB = hexadecyltrimethylammonium bromide DTAC = dodecyl-trimethylammonium chloride DTAB = dodecyltrimethylammonium bromide DHP = dihexadecyl phosphate DDDAB = didodecyldimethylammonium bromide DMPC = dimyristoylphosphati-dylcholine DPPC = dipalmitoylphosphatidylcholine POPC = l-palmitoyl-2-oleoylphosphati-dylcholine PCA = phosphatidic acid. 

Reaction of l,5-diphenyl-l,3,5-pentanetrione (45) with DMFDMA was carried out in propyl acetate under reflux for 12 h, followed by removal of the solvent by vacuum distillation. The oily residue was dissolved in another solvent (usually ethanol) and cyclization with various amines under reflux in the presence of catalytic amounts of concentrated hydrochloric acid was performed to form 1-substituted 3,5-dibenzoyl 4-oxo-l,4-dihydropyridines (46) (Scheme 17). 

A mixture of l-benzoyl-4-(3-indolyl)-l,4-dihydropyridine, dihenzylamine, 10%-Pd-on-carbon, and diphenyl ether stirred 5 hrs. at 205-210° under N2 -> 3-(4-pyridyl)-indole. Y 75%. D. Beck and K. Schenker, Helv. 51, 260 (1968). 

Aniline, p-Chloraniline, Benzidene Diphenylamine Dialkyl-, Dimethy l-Diethy l-aniline 1,4-Dihydropyridines 2-Pyridone Pyridine, Lutidine, Collidine, 2,2 -Di-pyridyl. Quinoline, 2,3-Diphenyl-quinoxaline... 

A mixture of 4-dicyanomethylene-2,6-diphenyl-4H-pyran, isopropylamine, and alcohol refluxed overnight -> 2-amino-3-cyano-l-isopropyl-6-phenyl-4-phenacyl-idene-l,4-dihydropyridine. Y 83%. F. e. s. J. A. Van Allan and G. A. Reynolds, J. Heterocyclic Chem. 8, 367 (1971). 

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