Facile Methods for the Synthesis of 8-Ylidene-1,2,3,8-tetrahydrobenzazecines

We have elaborated a general and simple microwave-assisted method for the synthesis of original 8-ylidene decorated benzazecines. We have shown that under the action of electron-deficient alkynes in acetic acid the starting benzoannulated azacyclic allenes or 1-alkyl(benzyl)-1-phenylethynyl-substituted isoquinolines underwent transformations leading to benzazecines in high yields. In acetic acid all reactions proceeded smoothly to give target products, some of which were isolated as a mixture of E/Z-isomers. Reactions with methyl propiolate in hexaflouroisopropanol (HFIP) featured regioselectivity and provided only E-isomer of 8-ylidene substituted benzazecines, whereas in case of acetylacetylene the sole products were azacyclic allenes. The key structure was unambiguously assigned by the means of X-ray crystallography. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim