open access

https://hdl.handle.net/2115/97527

Size-selective synthesis of calix[n]furan[2n]thiazoles bearing meso-CH2 bridges

英語

Paal-Knorr reaction

2025-01

World Scientific Publishing

Journal of porphyrins and phthalocyanines

29(1-2)

184-190

Size-selective synthesis of calixpyrrole-related macrocycles remains challenging, particularly for ring-contracted and expanded analogues, although calix[4]-type macrocycles are often obtained as major products via conventional acid-catalyzed condensation reactions of aryl monomers. Here, we found that the strain-based design of thiazole-containing macrocycles enables the size-selective synthesis of calix[nn]furan[2nn]thiazoles (nn = 1 or 2) in which two thiazole units are linked by a methylene bridge. The DFT calculation through StrainViz analysis revealed that calix[1]furan[2]thiazole bearing a methylene bridge had a total strain of 11.2 kcal/mol, which was smaller than that of calix[3]pyrrole (13.4 kcal/mol). The target calix[1]furan[2]thiazole was almost exclusively formed in 45% yield by a Hantzsch reaction between the corresponding bis(alpha alpha-bromoketone) and bis(thioamide) at 0.50 mM concentration. When the substrate concentration was increased above 10 mM, the calix[6]-type product, calix[2]furan[4]thiazole, was formed as the major product. Despite the existence of the meso-CH2-bridge, the obtained macrocycles were stable to air oxidation. Acid-catalyzed hydrolysis of the furan rings in calix[1]furan[2]thiazole and subsequent Paal-Knorr reaction afforded calix[1]pyrrole[2]thiazole. We also found that the deformation angles alpha alpha determined from the single crystal X-ray structures show a good correlation with the total strain and synthetic yield of calix[3]-type compounds via direct macrocyclization.

学術雑誌論文

Accepted Manuscript

Electronic version of an article published as Journal of porphyrins and phthalocyanines, 29(1-2), 2025, pp.184-190 DOI:10.1142/S1088424625500105 ©2025 World Scientific Publishing Company https://www.worldscientific.com/worldscinet/jpp

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