Access to Azepino-Annulated Benzo[c]carbazoles Enabled by Gold-Catalyzed Hydroarylation of Alkynylindoles and Subsequent Oxidative Cyclization

Abstract

Herein, we report a facile and efficient synthetic method to construct azepino[1,2-a]indoles through a novel gold(I)-catalyzed intramolecular hydroarylation of alkynylindoles. A wide range of functional groups can be well tolerated in this transformation, and the corresponding highly functionalized azepino[1,2-a]indole skeletons were obtained in moderate to excellent yields. Subsequent oxidation of the products gave the interesting and valuable polycyclic carbazoles, which were widely used as the key building blocks in materials science. Letter pubs.acs.org/OrgLett

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

“… 55 Hydroarylation reactions are considered efficient owing to economically appealing, mild conditions and high-bond forming efficacy. 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.…”

Hydroarylation of alkynes via dual ortho-C–H functionalization of diaryl amines on a dicopper(i,i) platform

“…A decrease in PivOH loading to 2.5 mol% led to a reduction in the yield (58%) of the corresponding hydroarylated product (entry 9). The reaction is effective in polar protic solvent TFE, and poor yields (35-39% yield of 4.2) were obtained with other solvents like MeOH, EtOH and i PrOH (entries [12][13][14]. Aprotic solvents were found to be ineffective for this reaction (entries 15-20).…”

“…Such a shift of n CRC vibration (B200 cm À1 ) is attributed to Z 2 coordination of the alkyne to the Cu(I) centre. 23 In the 13 C NMR study, the alkyne carbon signals at d = 83.64 and 80.88 ppm for phenylacetylene were shifted to 82.45 and 79.67 ppm, respectively, on treatment with 1 (Fig. S11, ESI †), suggesting alkyne binding to Cu(I).…”

“…Intramolecular hydroarylation of aryl propiolates was efficiently accomplished to afford coumarin derivatives with Pd 8 and Au 9 catalysts. Other heterocyclic skeletons, such as 2H-chromene, 10 dihydroquinoline, 11 2-quinolinone, 12 azepino[1,2- a ]indole, 13 etc. , were derived using the same protocol under transition-metal catalysis.…”

Palladium(II)-Catalyzed Intramolecular [2 + 2 + 2] Annulation of Indolyl 1,3-Diynes: Construction of Azepino-Fused Carbazoles

“…As a part of our ongoing interest in efficient syntheses of polycyclic compounds from indole derivatives, we have developed a two-step strategy to construct azepino-annulated benzo­[ c ]­carbazoles via gold­(I)-catalyzed intramolecular hydroarylation of alkynylindoles and subsequent oxidative cyclization . In comparison to five- or six-membered rings, the construction of seven- and eight-membered rings has proven to be a long-standing and difficult endeavor as a result of their unfavorable transannular interactions and entropy effect .…”