Condensed thiophen ring systems. Part XVIII. Thienoazepines and thienobenzoxazoles from 6-azidobenzo[b]thiophens

Abstract

Photolysis of 6-azido-2,3-dibromobenzo[b]thiophen (11) in an excess of diethylamine for 18 h gave mainly 7-amino-2,3-dibromo-6-diethylaminobenzo[b]thiophen (13). After 9 h the major product was 2,3-dibromo-6-diethylamino-8H-thieno[2,3-c]azepine (15). In the presence of pyrene and with a reaction time of 18 h, 6-azidobenzo[b]thiophen (9), its 2,3-dibromo-derivative (11), and methyl 6-azidobenzo[b]thiophen-2-carboxylate (10) gave 7-amino-6-diethylaminobenzo[b]thiophen (14) and 6-aminobenzo[b]thiophen (no thienoazepine in this case), the thienoazepine (15), and methyl 6-diethylamino-8H-thieno[2,3-c]azepine-2-carboxylate (16), respectively. Thermolysis of the azides (10) and (11) in a mixture of polyphosphoric and acetic acids gave the corresponding 2-methylthieno[3,2-g]benzoazoles, (19) and (20)(angular products), respectively; 6-azidobenzo[b]thiophen 1,1-dioxide (12) gave the linear product, 2-methylthieno [2,3-f]benzoxazole 5,5-dioxide (21), under these conditions.