1-Phenoxycarbonyl- 1,2-dihydropyridine

Substituted 3-pyridinecarboxaldehydes can be prepared by Vilsmeier for-mylation of dihydropyridine intermediates. Various 3-substituted pyridines (161) can be transformed into 3-substituted l-(phenoxycarbonyl)-1,2-dihydro-pyridines (162) using NaBH4 and phenyl chloroformate in methanol. Treatment of these 1,2-dihydropyridines with Vilsmeier reagent (POCIj/DMF) gives 3-substituted 5-formyI-1 -(phenoxycarbonyl)-1,2-dihydropyridines (163), which are aromatized with sulfur to provide 5-substituted 3-pyridinecarboxaldehydes (164). The formylation of 4-substituted 1-(phenoxycarbonyl)-1,4-dihydropyridines 165 and subsequent aromatization give 3-pyridinecarboxaldehydes 166(87H2159). 

Stereoselective Diels-Alder reactions have been reported in several cases. Enantioselective Diels-Alder reactions of l-phenoxycarbonyl-l,2-dihydropyridine with 1-alkylated acryloyl-pyrazolidin-3-ones using a chiral cationic palla-dium-phophinooxazolidine catalyst afforded chiral isoquinuclidines with excellent enantioselectivity <2005TL5677>. Bismuth(lll) chloride-mediated diasteroselective intramolecular [4-f2] cycloaddition reactions of A-allyl derivatives of pyrazole aldehydes led to fused sulfur-containing pyrazole heterocycles <2003SC3063>. A highly diastereoselective intramolecular hetero-Diels-Alder approach toward tetracyclic pyrazoles from 5-(3-methyl-2-butenylthio)-3-methyl-l-phenyl-4-pyrazolecarboxaldehyde has been reported <1997SL1155>. 

The enantioselective Diels-Alder cyclization of N-phenoxycarbonyl-1,2-dihydropyridine 129 with 1-alkylated acryloyl-pyrazolidin-3-ones (130) using chiral... 

One can indirectly substitute the pyridine ring with electrophiles by using an electron-rich dihydropyridine intermediate. Dihydropyridines 150 can be prepared by a one-pot synthesis utilizing a copper-catalyzed Grignard addition to l-(phenoxycarbonyl)pyridinium chloride (149). Dihydropyridines 150 undergo regiospecific Friedel-Crafts acylation in good yield with many... 

Tetrahydropyridines and Dihydropyridines. A review article covering dihydropyridine chemistry has appeared. l-Benzyl-l,2,5,6-tetrahydrop)U idines (366) may be obtained by sodium borohydride reduction of 1-benzylpyri-dinium salts (367). They react with phenoxycarbonyl chloride to give l-phenoxycarbonyl-l,2,5,6-tetrahydropyridines (368) and with phosgene to give 1-chlorocarbonyl derivatives (369). 1,2,5,6-Tetrahydropyridines (370) can be recovered from (368) and (369) by alkaline and acid hydrolysis, respectively. ... 

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