The stereoselective synthesis of tetrahydrothiopyrano[2,3-b]indole skeletons via tandem reaction of indoline-2-thiones to Baylis–Hillman adduct acetates

Indoline-2-thiones (5) were applied as 1,3-dinucleophiles in a tandem reaction with Baylis–Hillman adduct acetates (4) to give novel tetrahydrothiopyrano[2,3-b]indole skeletons (6). The effect of different solvents, bases, and catalysts on the yields and stereochemical outcome was studied in detail. The results indicated that acetonitrile as solvent and K2CO3 as base, under reflux conditions, were the optimum conditions. Products 6a–6l were obtained in high diastereoselectivity and yield (up to 94%).