Stereoselective synthesis of thiazino[4,3-a]indoles using the thia-Pictet-Spengler reaction of indoles bearing N-tethered thiols and vinylogous thiocarbonates.

An inter- as well as intra-molecular thia-Pictet–Spengler cyclization of N-tethered thiols and vinylogous thiocarbonates is described for the stereoselective synthesis of N-fused thiazinoindole derivatives. The strategy is extended to one-pot, sequential Friedel–Crafts alkylation – Pictet–Spengler cyclization and the synthesis of thiazino-oxepino-indole.