A convenient domino access to substituted alkyl 1,2-dihydropyridine- 3carboxylates from propargyl enol ethers and primary amines

A convenient domino access to substituted alkyl 1,2-dihydropyridine-3- carboxylates from propargyl enol ethers and primary amines was reported. A solution of propargyl sinyl ether 1a and p-anisidine in toluene was placed in a microwave-special closed vial and the solution was irradiated for 30 minutes in a single-mode microwave oven. The reaction mixture was dried over anhydrous sodium sulfate and filtrated using dichloromethane as solvent. After removing the solvent at reduced pressure the products were purified by flash column chromatography. Accordingly, the microwave irradiation of an ethanolic mixture of propargyl enol ether 1 a and MeONH2.HCl in the presence of NaOAc yielded the methyl 2-phenyl-4-pyridinecarboxylate in a convenient 54% yield. These results seem to point out to a new reaction pathway involving different thermally-driven rearrangements of the 2,4-dienal 3 intermediate.This research was supported by the Spanish Ministerio de Ciencia e Innovación, the European Regional Development Fund (CTQ2005-09074-C02-02 and CTQ2008-06806-C02-02) and the Spanish MSC ISCIII (RETICS, RD06/0020/1046, and RD06/0020/0041), CSIC (Proyecto Intramural Especial 200719), FUNCIS (REDESFAC PI01/06 and 35/06) and the Fundación Instituto Canario de Investigación del Cancer (FICI-G.I.N808/2007). G.M.-A. thanks Spanish MEC for a FPU grant.Peer Reviewe