Organocatalytic stereoselective construction of polycyclic benzo[b]thiophenes from 2-aminobenzo[b]thiophenes and alkynyl-substituted enones

A highly efficient protocol for stereoselective synthesis of novel polycyclic benzo[b]thiophene derivatives was developed. Using quinine-derived bifunctional thiourea (5 mol%) as a catalyst, asymmetric [3+3] annulation of N-(benzo[b]thiophen-2-yl)-sulfonamide with 2-alkynyl cycloenone could provide dihydrobenzo[4,5]thieno[2,3-b]pyridine derivatives in moderate to good yields (up to 93%) with mostly excellent enantioselectivities (up to 97% ee) under mild conditions. In addition, large-scale experiments and derivatizations were explored. In particular, the target product in large-scale experiments could be easily purified by filtration and the filtrated product showed >99% ee.