Palladium‐Catalyzed Hydroarylation of Homopropargyl Iodoindoles with Concurrent Alkyl and Iodonium Migrations

Abstract

A selective palladium‐catalyzed C(sp) arylation/carbocyclization/iodonium migration reaction sequence has been accomplished. Novel 2‐iodo‐1‐aryl‐9H‐carbazoles are now easily available. As this result is contrary to the selectivity observed using gold catalysis, the formation of 2‐iodocarbazoles is noticeable, suggesting a metal‐controlled cyclization through chemo‐ and regioselective 1,2‐alkyl migration and 1,4‐iodonium migration.

Update on novel synthetic approaches towards the construction of carbazole nuclei: a review

“…In the final step, 2-iodocarbazoles were produced after dehydration (Scheme 2). 57 The key attributes of this reaction are the selectivity induced by Pd-catalyst and the functionalization of the aryl iodide group by employing the Suzuki reaction to furnish a variety of compounds. In the subsequent year, Jatoth et al accomplished the synthesis of N-heterocycles fused with carbazole by employing TFA-mediated, metal-free, green, one-pot hydroarylation protocol.…”

“… 56 Palladium-catalyzed hydroarylation for carbazole synthesis was proposed by Martin et al in 2021, for which Pd(PPh 3 ) 2 Cl 2 was employed as a catalyst with CuI acting as a co-catalyst and triethylamine as a solvent at 40 °C to accomplish the target compounds. 57 A chemo- and regioselective synthesis of 2- iodo-1-aryl-9 H -carbazoles was achieved by employing different substrates leading towards a diverse series of three types of products. The Pd-catalysis was performed by reaction of aryl iodides 15, 2-iodo thiophenes 18 and 3-iodo-indole carbaldehydes 21 with substituted iodo alkynols 14 to furnish respective carbazoles 16, 19 and 22 in moderate yields ( Scheme 1 ).…”

“…In the next step, palladium salt coordinated with alkyne moiety to form complex B which underwent 5- endo-dig carbopalladation to generate pallada-spirocyclopentene intermediate C. Next, iodotetrahidrocarbazolium specie D was produced via 1,2-alkyl migration which was proceeded by 1,4-iodonium migration to give 2-iodo 1-aryl-4,9-dihydro-3 H -carbazol-4-ols E. In the final step, 2-iodocarbazoles were produced after dehydration ( Scheme 2 ). 57 The key attributes of this reaction are the selectivity induced by Pd-catalyst and the functionalization of the aryl iodide group by employing the Suzuki reaction to furnish a variety of compounds. In the subsequent year, Jatoth et al accomplished the synthesis of N-heterocycles fused with carbazole by employing TFA-mediated, metal-free, green, one-pot hydroarylation protocol.…”

“…View Article OnlineScheme 2 Mechanistic details for the synthesis of iodocarbazoles 16, 19 and 22 57. Scheme 3 One-pot hydroarylation for carbazole synthesis.© 2024 The Author(s).…”