Access to thiopyrano[2,3-b]indole via tertiary amine-catalyzed formal (3+3) annulations of β′-acetoxy allenoates with indoline-2-thionesElectronic supplementary information (ESI) available: Experimental procedures, characterization data, copies of 1H and 13C NMR spectra and X-ray structural data (cif). CCDC 1511720. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6cc09788j

DABCO-catalyzed formal (3+3) annulations of β′-acetoxy allenoates with indoline-2-thiones are described, which provide facile access to thiopyrano[2,3- b ]indole under mild reaction conditions. The reaction might proceed via the S N 2′-S N 2′-type process between β′-acetoxy allenoate and indole-2-thiolate with the assistance of the DABCO catalyst and K 2 CO 3 additive, followed by intramolecular Friedel-Crafts reaction at the 3-position of indole and central carbon of allene. Amine-catalyzed formal (3+3) annulations of β′-acetoxy allenoates with indoline-2-thiones are described, which provide facile access to thiopyrano[2,3- b ]indole.