Brønsted base-catalyzed assembly of sulfochromeno [4,3-b] pyrrolidines via tandem [3+2] cycloaddition-SuFEx click reaction of ethenesulfonyl fluorides and azomethine ylides

The synthesis of sulfochromeno [4,3-b] pyrrolidines is described. Under the catalysis of 20 mol% Brønsted base and using 4Å molecular sieves as HF scavenger, imines derived from salicylaldehydes and diethyl aminomalonate react with ethenesulfonyl fluorides through a tandem [3+2] cyclization-SuFEx click reaction to produce sulfochromeno [4,3-b] pyrrolidines in high yields.