Preparation of benzo[b]thiophenes

Abstract

A process for the preparation of benzo[b]thiophenes of the general formula I ##STR1## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4 independently denote hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 haloalkyl, nitro, cyano, halo, C.sub.1 -C.sub.4 alkylcarbonyl, benzoyl, C.sub.1 -C.sub.4 alkylcarbonylamino, benzoylamino,N-(C.sub.1 -C.sub.4 alkyl)phenylamino, C.sub.1 -C.sub.4 alkoxycarbonyl, C.sub.1 -C.sub.4 alkylsulfonyl, phenylsulfonyl, aminosulfonyl, aminocarbonyl, C.sub.1 -C.sub.4 phenylalkyl and nitrobenzyl or R.sup.1 +R.sup.2 or R.sup.2 +R.sup.3 or R.sup.3 +R.sup.4 denote a butadienediyl chain optionally substituted by R.sup.1 to R.sup.4, in which a) thiophenols of the general formula II ##STR2## in which the substituents R.sup.1 to R.sup.4 have the aforementioned meanings, are reacted with chloroacetaldehyde at a temperature ranging from 0.degree. to 150.degree. C. and b) the resulting (arylthio)acetaldehydes of the general formula III ##STR3## in which the substituents R.sup.1 to R.sup.4 have the aforementioned meanings, are cyclized by passing them into polyphosphoric acid or a mixture of phosphoric acid and phosphorus pentoxide at a temperature ranging from 100.degree. to 300.degree. C. and a pressure ranging from 0.001 to 1 bar.

Dependencies are inferred from the claim text.