A Route to Regioselectively Functionalized Carbazoles, Dibenzofurans, and Dibenzothiophenes through Anionic Cyclization of Benzyne-Tethered Aryllithiums

Abstract

The treatment of 2-fluorophenyl 2-iodophenylamines, ether, and thioether, easily prepared from commercially available products, with 3.3 equiv of t-BuLi and further reaction with selected electrophiles gives rise to functionalized carbazole, dibenzofuran, and dibenzothiophene derivatives in a direct and regioselective manner. The process involves an anionic cyclization on a benzyne-tethered aryllithium intermediate.

Reduction of Sulfoxides to Sulfides in the Presence of Copper Catalysts

“…The solvent was removed and the residue was purified by column chromatography. The analytical properties of the corresponding sulfides are in agreement with literature[63][64][65][66][67][68][69][70][71].Diphenylsulfide (1a): R f = 0.75 (n-hexane:ethyl acetate 1:5); 1 H NMR (CDCl 3 , 200 MHz): d = 7.26-7.47 ppm (m, 10H); 13 C NMR (CDCl 3 , 50 MHz): d = 135.8, 131.0, 129.2, 127.0 ppm; MS (ESI) m/z = 186 (100, M ? ), 152 (11), 92 (19), 77 (27), 65 (20), 51 (43).…”

Apparent Alkyl Transfer and Phenazine Formation via an Aryne Intermediate

“…Scheme 2 describes the preparation of the requisite n-butyl derivative 3d wherein X = Cl. Adapted from our earlier report 5 , intermediate 9a was alkylated with n-butyl bromide to afford N-methyl-N'-butyl derivative 10d, which was reduced according to the general method of Sanz 21 to afford 3d. Ultimately, we also wanted to speed up the formation of the aryne intermediate by utilizing the fluoride substrates (3b and 3e), which commenced via a Buchwald-Hartwig reaction on 2-fluoro-iodobenzene (X = F, Y = I) to give the diarylamine 6b after purification by column chromatography.…”

“…This was followed by reduction of the nitro group to give aniline 8b employing the general method of Sanz 21 using CuCl and KBH 4 in dry MeOH. Pd-catalyzed N-arylation of 8b with o-iodonitrobenzene produced the triaryl derivative 9b in 55% isolated yield after purification.…”

4.09 Nucleophilic Coupling with Arynes

“…270,271 In addition, a variety of dibenzoheterocyclic structures can be constructed efficiently by intramolecular aryl-aryl bondforming processes through the aryne cyclization (equation 28), 272,273 and the synthetic utility of this methodology has been demonstrated by total synthesis of trisphaeridine (115,Scheme 94) and N-methylcrinasiadine (116, Scheme 95). 274 Extensive studies have been conducted on the cyclization using stabilized carbanions containing imine, 275,276 sulfonyl, 277 or phosphinyl moiety, 278,279 that give indole, benzocyclobutene, or isoindolinone derivatives, respectively (Scheme 96).…”