Domino-Annulation-Based Approach to Synthesize Bridged Bis-thiopyrano[2,3-]indoles and Unbridged Thiopyrano[2,3-]indoles.

A novel domino strategy for the construction of intricate bridged bis-thiopyrano[2,3-]indoles was disclosed, which involved one molecule of 3-formylchromones and two molecules of indoline-2-thiones, enabling the formation of four new bonds in a single operation. The transformation occurred under mild reaction conditions, facilitated by the synergistic action of the base NaHCO and the catalytic acid ZnCl. Notably, when these bridged bis-thiopyrano[2,3-]indole skeletons were treated with alkyl halides under basic conditions, they underwent deconstruction to yield alkylthio-substituted indole-decorated thiopyrano[2,3-]indoles.