Synthesis of functionalized thiazoloindole-3-thiones and their spirocongeners from 2-acylethynyl-4,5,6,7-tetrahydroindoles and carbon disulfide

Abstract

Accessible 2-acylethynyl-4,5,6,7-tetrahydroindoles underwent stereoselective base-catalyzed (NaOH/DMSO, room temperature) [3+2]-cyclization with carbon disulfide to deliver 5,6,7,8-tetrahydro-1H,3H-thiazolo[3,4-a]indole-3-thiones incorporating Z-α,β-ethylenic ketones in yields of up to 76%. The synthesized compounds were quantitatively aromatized to the indole derivatives under the action of the recyclable oxidant DDQ. The 5,6,7,8-tetrahydro- and thiazolo[3,4-a]indole-3-thiones can cyclize with another molecule of 2-acylethynylpyrroles under the above conditions to afford the corresponding 1H,1′H-spiro[pyrrolo[1,2-c]thiazole-3,3′-thiazolo[3,4-a]indoles] in 54–86% yields.