2-amino-3-cyano-4H-pyrans

Isomerizations of 2-Amino-3-cyano-4H-pyrans to 3-Cyano-3,4-dihydro-2H-pyridones... 

G. Brahmachari, B. Banerjee, Facile and one-pot access to diverse and densely functionalized 2-amino-3-cyano-4H-p)frans and pyran-annulated heterocyclic scaffolds via an eco-friendly multicomponent reaction at room temperature using urea as a novel organo-catalyst, ACS Sustainable Chem. Eng. 2 (2014) 411-422. 

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). 

A series of 2-amino-3-cyano-6-methyl-4-aryl-4H-pyran-5-ethylcarboxylate derivatives (43) were synthesized by Ghashang et al. [124] from three-component reaction between substituted aromatic aldehydes, malononitrile, and ethyl acetoacetate employing zirconyl oxychloride as an inexpensive catalyst rmder refluxing in EtOH-water medium (Scheme 23). 

SCHEME 23 Zr0Cl2.8H20 synthesis of 2-amino-3-cyano-6-methyl-4-aryl-4H-pyran-5-ethylcarboxylate derivatives 43 [124]. 

Cyclocondensation of 3-methyl-l-(5-substituted-3-phenyl-lH-indol-2-ylcarbonyl)-5-(4fi)-pyrazolones with arylidene derivatives of malononitrile using a catalytic amount of triethylamine in refluxing ethanol affords heterocycle [ ]-fused 6-amino-4-aryl-5-cyano-4H-pyrans (14JHC303). Other fused 6-amino-4-aryl derivatives arise from the three-component reaction of benzaldehydes, active methylene compounds (malononitrile/ ethyl cyanoacetate) and 1,3-dicarbonyl compounds catalyzed by 1,8-diaz-abicyclo[5.4.0]undec-7-ene (DBU) in refluxing water (14JHC618). Similar pyrazole[f)]-fused derivatives are obtained from the reaction of benzaldehydes, malonitrile, and 3-substituted-2-pyrazolin-5-ones using sodium... 

H-Pyran-3-carboxylic acid, 6-amino-5-cyano-2,4-diphenyl-ethyl ester... 

Utilization of acetic acid (90CCC718, 95BML2783) and mixtures of acetic and sulfuric acids (81JHC309), as well as triphenylmethylborofluor-ide (86JPR35), leads to 3-cyano-3,4-dihydropyridin-2-ones, which can be oxidized into the corresponding cyanopyridones by nitrosylsulfuric acid. Authors (81JHC309) have studied the synthesis of 3-cyanopyridones 264 systematically, and have shown that the latter can be obtained by different routes from 2-amino-4H-pyrans 59, as well as from related dihydro- 265 and tetrahydropyridone 266 (Scheme 104). 

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). 

Amino-4-aryl-3-cyano-7,7-dimethyl-5,6,7,8-tetrahydro-4H-benzo[f>]pyran 281 were reacted with benzylidene malononitrile in the presence of piperidine at 160 °C to afford pyrido[3,4-frJqu inclines 341 (89JPR971) (Scheme 65). 

Dibenzylidenecyclopentanone and malononitrile in methanol heated to reflux, a little Na-methoxide added, and refluxed 0.5 hr. 2-methoxy-7-benzylidene-3-cyano-4-phenyl-6,7-dihydro-5H-l-pyrindine. Y 48%. F. e. s. H.-H. Otto, Arch. Pharm. 307, 422 (1974) 2-amino-4H-pyran ring s. a. ibid. 307, 444. 

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