Chemoselective Annulation of 2‐Benzothiazolimines Enabled by Bifunctional Phosphonium Salt: Highly Enantioselective Synthesis of Indole‐fused Cyclic Thiourea Scaffolds

Abstract

A highly efficient chemoselective and stereoselective annulation utilizing 2-benzothiazolimines as unusual C2synthons by thiourea-based bifunctional phosphonium salt catalysis has been developed. This asymmetric protocol provides a rapid access to highly functionalized and indole-fused cyclic thiourea scaffolds that bear benzothiazole cores in high yields with excellent both diastereo-and enatioselectivities. This transformation proceeds under mild reaction conditions and expands the catalytic potential of phosphonium salt catalysts.

Asymmetric Mannich/Cyclization Reaction of 2-Benzothiazolimines and 2-Isothiocyano-1-indanones to Construct Chiral Spirocyclic Compounds

“…Wang's group utilized 2-benzothiazoleimines as unusual C2-synthons and obtained highly functionalized and indole-fused cyclic thiourea scaffolds bearing benzothiazole cores through thiourea-based bifunctional phosphonium salt catalysis. The corresponding products were obtained in high yields with excellent diastereo-and enantioselectivities [25] (Scheme 1c). Inspired by their work, we will continue our project to obtain bioactive heterocycles using 2-benzothiazolimines as C2-synthons.…”

“…Previous reports and our work. (a) [2 + 3] cyclization reaction [23]; (b) [2 + 4] cyclization reaction [24]; (c) [2 + 3] cyclization reaction [25]; (d) our research plan.…”