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A simple and effective method has been elaborated for the synthesis of thieno[2,3-b]indole ring system. It is based on the electrophilic recyclization of 2-alkyl-5-(2-isothiocyanoaryl)furans in the presence of anhydrous AlCl 3 .The thieno[2,3-b]indole ring system has been little studied to date and few methods of its synthesis have been reported. 1-7 Nevertheless, thieno[2,3-b]indoles are promising as physiologically active compounds. In particular, thienodolin {6-chlorothieno[2,3-b]indole-2-carboxamide} isolated from the culture broth of Streptomyces albogriseolus 8 and characterized by Japanese researches was proved to have plant-growth-regulation activity. The parent thieno[2,3-b]indole also demonstrates antifungal activity. 9

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A general method for the synthesis of isocoumarine derivatives has been developed. Bis(5‐R‐2‐furyl)methylbenzoic acids (R = methyl, ethyl) underwent recyclization and subsequent cyclization into tetracyclic isochromene‐1‐one derivatives under treatment with hydrogen chloride in methanol. It has been shown that intermediate 4‐(5‐R‐furan‐2‐yl)‐3‐(3‐oxo‐3‐R‐propyl)‐isochromene‐1‐ones can be obtained selectively by varying a concentration of the hydrogen chloride and reaction times. In the case of R = tert‐butyl only corresponding 4‐[5‐(tert‐butyl)‐2‐furyl]‐3‐(4,4‐dimethyl‐3‐oxopentyl)‐1‐isochromenones were isolated regardless of the reaction conditions.

A straightforward, efficient indole synthesis based on thermolysis of 2-(2-azidobenzyl)furans with attack of the formed nitrene moiety onto the ipso position of furan ring has been developed. The cyclization is accompanied by furan ring opening and affords indoles with a 2-acylvinyl substituent suitable for further modifications.