Synthesis of 4H-thieno[3,2-c]chromenes by intramolecular arylation of 4-aryloxy-methyl-5-iodothiophene-2-carbaldehydes

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

“…The cyclization was performed under the same conditions as those used for compound 6a, and the reaction progress was monitored by TLC. Complete cyclization of compounds 6b-o required irradiation for 4-30 hours and the yields of thienochromenes 7bp were in the range 33-90% (Table 1, entries [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

“…Only in the case of 6e were the isomeric 4H-thieno [3,2-c]chromene-2-carbaldehydes 7e (entry 6) and 7p (entry 17) obtained in a 2:5 ratio according to NMR data. However, compound 7e was the main product in the case of Pd-catalyzed cyclization 6e using method D. 12 The UV spectra of 4H-thieno [3,2-c]chromene-2-carbaldehydes have been reported only for compounds 7a-f. 19 The main emission band in the luminescence spectra of Figure 3 In situ experimental (black curves) and simulated (red curves) EPR spectra of glass solutions of compounds 6a (Spectrum 1) and 5a (Spectrum 2) in acetonitrile after UV irradiation at 77 K…”

“…These are based on annulation reactions of benzopyrans with a thiophene core 10 or on the formation of a pyran ring. [11][12][13] In the latter case, cross-cou-pling reactions catalyzed by transition metals are most often used to form the C-C bond between the benzene and thiophene rings. Despite its effectiveness, this approach has disadvantages associated with the toxicity and high cost of the catalyst, the use of ligands, and the laborious purification of the reaction products.…”

“…Previously, we have developed two methods for the synthesis of 4H-thieno [3,2-c]chromenes based on palladiumcatalyzed intramolecular arylation of compounds 5a (Method B) 11 or compounds 6a-o (Method D), 12 differing in the position of iodine in the molecule (Table 1); the yields of compounds 7a-i obtained by these methods were in the ranges 20-69% and 44-85%, respectively.…”

“…15 Compounds 6a-o were synthesized by the reaction of the appropriate phenol 4a-o with 5-iodo-4-(chloromethyl)thiophene-2-carbaldehyde (2), obtained by iodination of aldehyde 1. 12 Note that the latter approach is preferable because of the ready availability of phenols 4a-o.…”