Reactivity of vinyl sulphonic esters. Part X. Effect of the substituents on the cyclisation of arylthiovinyl sulphonates to benzo[b]thiophens

Abstract

Cyclisation of either meta- and para-phenylsulphonyl-substituted 2-arylthio-1,2-diphenylvinyl 2,4,6-trinitro-benzenesulphonate in dichloromethane with boron trifluoride as catalyst affords 2,3-diphenyl-5-phenylsulphonyl-benzo[b]thiophen. The position of the substituent in the product indicates that a rearrangement occurs in the cyclisation of the meta-substituted derivative, whereas with the para-derivative the position of the substituent in respect to the sulphur atom is retained. The results are discussed in terms of the meta-directing effect of the phenylsulphonyl-group. A close connection is found with the cyclisation of vinyl sulphonates having ortho,para-directing substituents in the arylthio-residue.