Indolines functionalized elimination

Similar to Thesing (Scheme 1, equation 1), Chou and Ko prepared a thieno[3,4-(i]indole via NBS benzylic bromina-tion of the corresponding indoline followed by elimination of HBr [6], Mukaiyama s group [7] and Tilstam [8] discovered that the indoline-to-indole transformation was possible by A -functionalization of indoline using A -tcrt-butylphe-nylsulfinimidoyl chloride and trichloroisocyanuric acid, respectively, followed by DBU-induced elimination. In the latter case, indole yields were 72% to 89%, which included... 

Heating 2-amidofuran 253 at 165 °C was reported to give the phenolic indoline 252 in 87% yield, and this occurs by elimination of thiophenol from the initially formed cycloadduct. The cycloaddition behavior of the thermally more robust iV-ethyl carbamate derivative 255 proceeded quite smoothly to furnish phenol 254 in 80% yield when heated at 160 °C for 7h. It should be noted that the phenolic functionality present in the aromatic ring of indolines 252 and 254 has the potential to be transformed into an aryl triflate and used for palladium-catalyzed cross-coupling chemistry to afford more highly functionalized products (Scheme 13.58) [102]. 

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