2-Methylene-1,3-dicarbonylcompounds reacted with alky vinylethers in benzene to give hetero-Diels–Alderreaction products, 3,4-dihydro-2H-pyrans, regioselectively and/or chemoselectively.
Various alkyl 6-ethoxy-2-phenyl-5,6-dihydro-4H-pyran-3-carboxylate 2A are easily converted to the corresponding nicotinates 3 by reaction with hydroxylamine hydrochloride in refluxing absolute ethanol.