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DOI: 10.1055/s-0030-1258835
Synthesis of Trifluoromethylbenzofurans by Extended Pummerer Reaction
T. Kobatake, D. Fujino, S. Yoshida, H. Yorimitsu*, K. Oshima*
Kyoto University, Japan
Publikationsverlauf
Publikationsdatum:
21. Oktober 2010 (online)

Significance
Reported is the synthesis of 3-trifluoromethylbenzofurans 3 from phenols 1 via sequential Pummerer-[3,3]-sigmatropic rearrangement reactions mediated by Tf2O. Weakly nucleo-philic phenols require elevated reaction temperatures, while phenols bearing strong EDGs (R¹ = OMe) are not suitable substrates due to triflation of the phenol occurring in competition with the desired reaction. The meta-substituted phenols give products 9 with excellent regiocontrol (except for R³ = Me). Further useful transformations of the 2-methylthio group by Negishi cross-coupling (72% to quantitative yield, 3 examples) and by conversion to a formyl group via the sulfoxide (73% yield over two steps) were reported.