Photochemical Synthesis of 4H-Thieno[3,2-c]chromene and Their Optical Properties

Abstract

4 - [(2-Iodalyloxy) methyl] thiophene-2-carbaldehyde and 5-iodo-4- (aryloxymethyl)thiophene-2-carbaldehydes were obtained by interaction of phenols with 4-chloromethylthiophene-2-carbaldehyde and its 5-iodosubstituted derivative. These compounds underwent ring closure upon irradiation with UV light (254 nm) to form 4H-thieno[3,2-c]chromene-2-carbaldehyde in high yield. The formation of intermediate radical species was detected by EPR method. Comparative analysis of the ring closure methods showed that the photochemical cyclization of 5-iodo-4-(aryloxymethyl) thiophene-2-carbaldehyde is more rational than the Pd-catalyzed intramolecular arylation. A series of substituted 4H-thieno[3,2-c]chromene-2-carbaldehydes was synthesized by the photochemical cyclization of the corresponding precursors. The photophysical properties of the synthesized compounds were studied. The obtained 4H-thieno[3,2-c]chromene-2-carbaldehydes can be used as covert marking pigments.

New one-pot synthesis of 4-arylpyrazolo[3,4-b]pyridin-6-ones based on 5-aminopyrazoles and azlactones

“…Pyrazolo[3,4- b ]pyridinones 4a – i , 9a , and 10a are characterized by an abnormally high Stokes shift (107–152 nm, 1.07–1.49 eV, Table 2 ). Such luminophores, which are colorless in daylight but become colored when irradiated with UV light, are used in forensics, in protection against forgery of banknotes, securities, and other important documents [ 34 ].…”