Reaction of aryl biphenyl-2-yl thioketones with ditosyldiazomethane; internal cyclisation of the thioketone S-methylides to afford benzo[c]thiophene derivatives. Structure determination of the products by Raney nickel degradation and X-ray crystallographic analysis

Abstract

The reaction of arylbiphenyl-2-yl thioketones 1 with ditosyldiazomethane in the presence of copper acetylacetonate has been investigated. It involves internal cycloaddition of intermediary thioketone S-methylides 8 and 23 to afford eventually benzo[c]thiophene derivatives 16, and 24 and 25, respectively. The structure of product 16 was determined by means of spectroscopy and chemical evidence. Furthermore the structure was unambiguously established by X-ray crystallographic analysis of compound 16c(X = MeO). The results are discussed in terms of cyclisation/rearrangement of the transient thioketone S-methylides 8 and 23 as a key step in consideration of the other plausible routes leading to their structural isomers 10, 11, 14, 15 and 17.