Reactions of polyfluoro-arenols and -heteroarenols with activated dimethyl sulphoxide. Facile [2,3]-sigmatropic rearrangement reactions giving de-aromatised products

Abstract

Pentafluorophenol reacted with the reagent dimethyl sulphoxide–dicyclohexylcarbodi-imide–orthophosphoric acid below room temperature to give the ether (1), the [2,3]-rearrangement product (2), and (3) a derivative of (2). Under similar conditions, 2,3,5,6-tetrafluorophenol gave (7) and (8), and 1,3,4,5,6,7,8-heptafluoro-2-naphthol gave (12) and (13). Reaction of polyfluoroarenols with dimethyl sulphoxide–trifluoroacetic anhydride at low temperatures followed by deprotonation with triethylamine resulted in more efficient rearrangement reactions; 4-bromo-3,5,6-trifluoropyridin-2-ol gave the ether (14) and the products of rearrangement both to carbon and nitrogen, (15)(after hydrolysis) and (16) respectively; 2,4,5,6-tetrafluoropyridin-3-ol resulted in the overall replacement of the 2-fluorine by CHO (17) and by CH(SMe)₂(18); and with 2,5,6-trifluoropyrimidin-4-ol and 5-fluoro-4,6-dimethoxypyrimidine-2-ol, simple rearrangement products (21) and (22) were obtained. Hydrolysis of (21) gave the 5-fluorouracil derivative (23). Sodium borohydride reduction and Raney nickel desulphurisations of some of the rearrangement compounds gave phenolic products. Reaction of the sulphone from (13) with base (DBU) effected the overall efficient replacement of the 1-fluorine in the 2-naphthol by CHO (35) and by CH(SO₂Me)₂(36).