A Route to Indoles via Modified Fischer Indole Intermediates from Sulfonanilides and Ketene Dithioacetal Monoxides

An S−N variant of the N−N‐based Fischer indole synthesis has been developed. Treatment of sulfonanilides and ketene dithioacetal monoxides with a powerful acid anhydride provides N‐sulfonyl‐2‐methylsulfanylindoles. The initial interrupted Pummerer reaction would yield the key S−N‐tethered precursor in situ that then undergoes [3, 3] sigmatropic rearrangement, after which the endgame to the indole ring follows the Fischer manner