2008

Ring closure reactionsO 0130 Site-Specific Preparation of 4-Substituted-6-fluoro(carboalkoxyl)benzo[b]furans

and Benzo[b]thiophenes via Base-Catalyzed Cyclization of Enyne Derivatives. — The site-specific synthesis of benzofurans and benzothiophenes (V) follows a reaction course in which the base catalyzes the isomerization of the enyne to an allene interme-diate which undergoes 6π cycloaddition to form the two-ring system. Subsequent isomerization affords the final product. The base-catalyzed cyclization is not restricted to fluorinated enynes, but also extended to alkoxycarbonyl-substituted enynes [cf. (VIII)]. In addition, this cyclization procedure is further utilized for the preparation of more complex heterocyclic aromatic compounds as is illustrated by the synthesis of naphthothiophene (XII). — (WANG, Y.; BURTON*, D. J.; J. Fluorine Chem. 128 (2007) 9, 1052-1057; Dep. Chem., Univ. Iowa, Iowa City, IA 52242, USA; Eng.) — H. Hoennerscheid

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