Cyclization of Vinylketene Dithioacetals: A Synthetic Strategy for Substituted Thiophenes

Abstract

A synthetic strategy for the synthesis of substituted thiophenes is described by the one‐pot reaction of indoles with ketene dithioacetals under mild reaction conditions. Promoted by triflic acid (TfOH), the reaction of indoles with the easily available α‐acetyl ketene dithioacetals resulted in the formation of vinylketene dithioacetals via condensation instead of the well known nucleophilic addition‐alkylthio elimination process. In thepresence of CuBr2, vinylketene dithioacetals can cyclize into the corresponding substituted thiophenes. This transformation may benefit from the acidic reaction conditions and the steric effects of the 2‐substituted indoles.

Visible-Light-Induced Formation of Thiavinyl 1,3-Dipoles: A Metal-Free [3+2] Oxidative Cyclization with Alkynes as Easy Access to Thiophenes

“…To the best of our knowledge, there have been few studies on the photoredox reactions of ketene dithioacetals and the studies have been limited to the coupling reactions with aryldiazonium salts or alkenes or need an other photo-redox-active reactant . There have been few reports about the visible-light-mediated synthesis of thiophenes, − ,− with some syntheses of benzothiophenes from alkynes with o -methylthio-arene diazonium salts or 2-halothioanisoles. − We are glad to see that our proposed [3+2] oxidative cylization of ketene dithioacetals and alkynes (Scheme b) could proceed smoothly under extremely simple and mild reaction conditions without using base, acid or oxidants. − Clearly, α-acyl ketene dithioacetals were activated by visible light to form a previously unknown thiavinyl 1,3-dipole intermediate that thus initiates this [3+2] cyclization.…”

Construction of pyrroles, furans and thiophenes via intramolecular cascade desulfonylative/dehydrogenative cyclization of vinylidenecyclopropanes induced by NXS (X = I or Br)

“…The synthetic methods of these heterocyclic compounds have been widely reported and are of great concern. 2 To date, the traditional synthetic methods for these heterocycles, including Paal–Knorr condensation, 3 Hantzsch reaction, 4 Feist–Benary reaction, 5 Hinsberg reaction, 6 transition metal-catalyzed cyclizations, 7 and photochemical reactions, 8 have been developed for many years. However, the above reactions frequently employ different synthetic protocols to obtain the starting substrates depending on the required heteroatoms such as N, O, and S. Thus, the development of new strategies that facilitate rapid construction of each of these heterocycles by a single method and provide functionalized pyrroles, furans, and thiophenes in a one-pot manner would be extremely useful and highly desirable.…”