Synthesis of 4-oxo-6-styryl-4H-pyran-2-carbonitriles and their application for the construction of new 4-pyrone derivatives

Synthesis of 2-cyano-6-styryl-4-pyrones has been developed on the basis of 6-metylcomanic acid via modifications of the methyl and carboxyl groups. Reactions of these pyrones with nucleophiles proceeded as an attack at the cyano group, whereas 1,3-dipolar cycloaddition of stabilized azomethine ylides occurred at the styryl moiety stereo- and regioselectively. The effective approach based on the side chain manipulation of the 2-cyano-6-styryl-4-pyrones led to 2-azolyl-6-styryl-4-pyrones and 4-pyrone conjugates with the pyrrolidine moiety. Reactivity of the prepared 2-cyano-6-styryl-4-pyrones was estimated with the use of quantum chemical calculations, and the observed chemoselectivity was explained by charge and orbital controls. The photophysical properties of the cyanopyrones were determined in view of further application as simple molecular fluorophores with large Stokes shifts. Graphical abstract