Access to polyfunctionalized carbazoles through π-extension of 2-methyl-3-oxoacetate indoles

Abstract

A structurally diverse set of polyfunctionalized carbazoles was efficiently synthesized in acceptable to excellent yields.

Synthesis of Spiro Polycyclic N-Heterocycles and Indolecarbazoles via Merging Oxidative Coupling and Cascade Palladium-Catalyzed Intramolecular Oxidative Cyclization

“…1 H NMR spectra were recorded at 400 MHz and 13 C NMR spectra were recorded at 101 MHz by using an Agilent 400 MHz NMR spectrometer. Chemical shifts were calibrated using residual undeuterated solvent as an internal reference (1H NMR: CDCl 3 7.26 ppm, DMSO-d 6 2.50 ppm, 13 C NMR: CDCl 3 77.16 ppm, DMSO-d 6 39.52 ppm). Data are reported as follows: chemical shift, multiplicity (s = singlet, br s = broad singlet, d = doublet, t = triplet, q = quartet, m = multiplet), and coupling constants (J) were reported in Hertz (Hz).…”

“…A purplish-black solid (108 mg, 76% yield); mp 152−154 °C; purified over a column of silica gel (petroleum ether/EtOAc = 7:1); 1 H NMR (400 MHz, CDCl 3 ) δ 8.02 (dd, J = 7.2, 1.2 Hz, 1H), 7.94−7.90 (m, 1H), 7.70−7.62 (m, 3H), 7.48 (d, J = 8.1 Hz, 1H), 7.41 (t, J = 7.9 Hz, 2H), 7.36−7.30 (m, 1H), 7.29−7.21 (m, 3H), 7.10−7.05 (m, 1H), 6.93 (s, 1H), 4.15 (t, J = 6.8 Hz, 4H), 1.87 (dd, J = 14.3, 7.1 Hz, 2H), 1.79−1.72 (m, 2H), 0.88 (t, J = 7.4 Hz, 3H), 0.78 (t, J = 7.4 Hz, 3H). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) δ 185.1, 184.5, 145.8, 137.1, 136.1, 136.0, 134.4, 133.2, 133.1, 133.1, 132.2, 129.1, 128.1, 127.6, 126.6, 125.6, 122.3, 122.2, 120.8, 120.4, 120.1, Table 4. Scope for C(sp2)−C(sp2) Cyclization a a Reaction conditions: 3a (0.1 mmol), Pd(OAc) 2 (0.005 mmol), FeCl 3 (0.1 mmol), (NH 4 ) 2 S 2 O 8 (0.3 mmol), CH 3 CN (1 mL), 100 °C, sealed tube for 2 h. Isolated yields are indicated.…”

“…A purplish-black solid (143 mg, 78% yield); mp 138−140 °C; purified over a column of silica gel (petroleum ether/EtOAc = 7:1); 1 H NMR (400 MHz, DMSO-d 6 ) δ 7.84 (d, J = 7.3 Hz, 1H), 7.78 (d, J = 6.9 Hz, 1H), 7.75−7.66 (m, 2H), 7.59−7.45 (m, 4H), 7.20 (t, J = 6.7 Hz, 2H), 7.08 (dd, J = 13.0, 7.2 Hz, 2H), 6.90 (t, J = 7.5 Hz, 1H), 6.68 (s, 1H), 4.27−4.06 (m, 4H), 1.65 (s, 2H), 1.49 (s, 2H), 1.09 (dd, J = 29.8, 11.5 Hz, 12H), 0.90 (s, 8H), 0.72 (dt, J = 14.5, 6.8 Hz, 6H). 13 C{ 1 H}NMR (101 MHz, DMSO-d6) δ 184. 4, 184.3, 145.6, 137.0, 136.2, 134.2, 134.0, 132.9, 131.8, 130.5, 127.6, 127.5, 126.6, 125.6, 122.3, 122.1, 120.8, 120.4, 120.3, 119.5, 111.0, 110.8, 109.1, 104.6, 46.0, 43.9, 31.7, 31.5, 30.0, 29.6, 29.0, 29.0, 28.9, 28.7, 26.4, 22.5, 22.4, 14.3, 14.3.…”

“…12 In 2019, Fu's group developed formal [4 + 2] annulation of 2-methyl-3-oxoacetate indoles with naphthalene-1,4-dione (Scheme 1d). 13 In 2020 14 and 2021, 15 we developed cobalt/ copper-catalyzed [4 + 1] cycloamination of indolylquinones and various (hetero)aromatic amines for the synthesis of polycyclic N-heterocycles (Scheme 1e,f). In 2022, Wang's group reported the B(C 6 F 5 ) 3 -catalyzed [4 + 2] cyclization/ oxidative reaction to construct diverse carbazolequinones (Scheme 1g).…”

Cobalt-Catalyzed Cycloamination: Synthesis and Photophysical Properties of Polycyclic N-Heterocycles

“…Therefore, much effort has been devoted to developing synthetic methods for the construction of annellated polycyclic complex bearing a quinone skeleton. The representative approaches have usually involved the classical Friedel–Crafts reactions, introduction of the 9,10-carbonyl functions by oxidation of the corresponding hydrocarbon, Lewis acid catalyzed intramolecular cyclization by Lewis acid as catalyst, thermal or Lewis acid catalyzed Diels–Alder reaction followed by aromatization, and transition-metal-catalyzed oxidative cyclization . Despite their merits, many existing synthetic approaches have several shortcomings, such as the preparation of the prerequisite functional groups, multiple reaction steps, harsh reaction conditions, expensive catalysts, and low product yields.…”