N-2,2,2-Trifluoroethylisatin ketimine as a 1,2-dipolarophile for [3+2]-addition to access optically pure spirothiazolidine oxindoles

The first report on using N-2,2,2-trifluoroethylisatin ketimine as a 1,2-dipolarophile for [3 + 2]-addition and the first asymmetric synthesis of N-2,2,2-trifluoroethylspirothiazolidine oxindoles is described. The organocatalyzed asymmetric [3 + 2]-addition reaction of N-2,2,2-trifluoroethylisatin ketimine with 1,4-dithiane-2,5-diol provided an array of N-2,2,2-trifluoroethylspirothiazolidine oxindoles (up to 25 examples) in excellent yield, enantioselectivity, and diastereoselectivity (up to 96% yield, 99% ee, and 99 : 1 dr). In addition, the synthetic utility of the developed methodology has been demonstrated by transforming optically pure spirothiazolidine into medicinally important spirothiazolidinone and spirothiazolidinone-S-oxide.