Stereoselective hetero-Diels–Alder reaction of 3-(trifluoroacetyl)chromones with cyclic enol ethers: synthesis of 3-aroyl-2-(trifluoromethyl)pyridines with ω-hydroxyalkyl groups

3-(Trifluoroacetyl)chromones undergo heterodiene cycloaddition to 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild conditions, producing novel fused pyrans with high stereoselectivity and in good yields. These pyrans were transformed into functionalized pyridines on treatment with ammonium acetate in ethanol. The structures of the endo-cycloadducts were established by 1H NMR spectroscopy and X-ray diffraction analysis.