Defluorinative Ring‐Opening Indolylation of Siloxydifluorocyclopropanes: Controlled Synthesis of α‐Fluoro‐β‐Indolyl‐Propanones for Carbazole Construction

Abstract

A catalytic defluorinative ring-opening indolylation of siloxydifluorocyclopropanes was reported. It was found that AgBF 4-catalyzed reaction of siloxydifluorocyclopropanes with indoles could be controlled to deliver α-fluoro-β-indolylpropanones within 1.5 hours at room temperature. Cyclization of these α-fluoroketone derivatives were then carried out in the presence of trifluoroacetic anhydride in toluene at room temperature. Carbazoles were formed efficiently via an intramolecularly nucleophilic addition of the in situ formed enamine intermediate to the keto carbonyl, followed by a sequential hydrolysis and eliminations of trifluoroacetic acid and hydrogen fluoride.

Synthesis of benzo[a]carbazole derivatives via intramolecular cyclization using Brønsted acidic carbonaceous material as the catalyst

“… 28 Liu et al proposed a metal-free, sequential triple C–C coupling-radical-cyclization procedure to regioselectively generate substituted carbazole compounds using DMAP as the only reagent. 29 Through the transition-metal and exogenous-oxidant-free C–H bond amination approach, P. Zhang et al also produced the carbazole-derived alkaloids clausine and glycozoline. 30 They also developed a technique for an environmentally secure electrochemical C–H bond dehydrogenative amination.…”