Efficient one-pot access to 2,9-dihydrothiopyrano[2,3-b]indole scaffolds showing large stokes shifts

Abstract

A simple, mild and efficient one-pot approach for the construction of 2-aryl-3-nitro-2,9-dihydrothiopyrano[2,3-b]indole derivatives has been realized in CH2Cl2 medium at ambient temperature via three-component tandem reaction of N-protected-2-chloro-3-formylindoles, sodium hydrosulfide and β-substituted nitroolefins/δ-substituted nitrodienes using DABCO (10 mol%) as an organocatalyst, followed by dehydration in the presence of activated molecular sieves (4 Å). The significant advantages of this protocol are simple operation, shorter reaction time, high atom economy, good to high yields (73% -89%) and wider substrate scope. In addition, all the synthesized compounds have shown the large positive Stokes shift values (5632-6081 cm-1). A wide range of functionalized 2,9-dihydrothiopyrano[2,3-b]indoles were realized in good to high yields. Interestingly, these compounds have shown large Stokes shift values ranging from 5750-6081 cm-1. © 2015 SIOC, CAS, Shanghai & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.