Microwave-Accelerated Coupling-Isomerization-Enamine Addition-Aldol Condensation Sequences to 1-Acetyl-2-amino-cyclohexa-1,3-dienes

Abstract

The microwave-accelerated consecutive reaction of electron deficient (hetero)aryl bromides 1, (hetero)aryl propargyl alcohols 2, and enamino carbonyl compounds 6 or 8 furnishes 1-acetyl-2-amino-cyclohexa-1,3-dienes 7 or 6-N,N-dimethyl carbamoyl-cyclohexenones 9, respectively, in good yields in the sense of a one-pot coupling-isomerization-enamine addition-aldol condensation sequence.

alkynes - condensations - cross-couplings - cyclizations - microwave reactions

References and Notes

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14

Typical Procedure (7a, Entry 1).
A magnetically stirred solution of 182 mg (1.00 mmol) of 1a, 139 mg (1.05 mmol) of 2a, 20 mg (0.02 mmol) of Pd(PPh₃)Cl₂, and 2 mg (0.01 mmol) of CuI in a degassed mixture of 0.5 mL of Et₃N and 1.5 mL of THF in a sealed microwave vial under nitrogen was heated by microwave irradiation to 150 °C for 15 min. After cooling to r.t. 726 mg (3.00 mmol) of enaminone 6a and 0.75 mL of AcOH were added and the reaction mixture was heated by microwave irradiation to 150 °C for another 10 min. After aqueous work-up and chromatography on silica gel (hexane-acetone, 2:1) and recrystallization from acetone 311 mg (68%) of 7a were obtained as yellow crystals. Mp. 227 °C. IR (KBr): 2219, 1632 cm^-1.¹H NMR (300 MHz, DMSO-d ₆): δ = 1.80 (s, 3 H), 2.75-2.81 (m, 1 H), 2.94-3.12 (m, 3 H), 3.68-3.89 (m, 2 H), 4.17 (d, J = 7.0 Hz, 1 H), 6.49 (d, J = 1.9 Hz, 1 H), 7.00-7.05 (m, 3 H), 7.14 (t, J = 7.4 Hz, 1 H), 7.21-7.29 (m, 4 H), 7.32 (d, J = 8.12 Hz, 2 H), 7.36 (d, J = 8.12 Hz, 1 H), 7.62 (d, J = 8.12 Hz, 1 H), 7.69 (d, J = 8.12 Hz, 2 H), 10.92 (s, 1 H), 11.72 (t, J = 6.0 Hz, 1 H). ¹³C NMR (CDCl₃, 75.5 MHz): δ = 26.6 (CH₂), 26.9 (CH₂), 38.6 (CH₃), 34.8 (CH₂), 38.2 (CH), 42.4 (CH₂), 97.7 (CH) 108.9 (C_quat.), 110.9 (C_quat.), 111.5 (C_quat.), 115.7 (CH), 118.2 (C_quat.), 118.5 (CH), 118.9 (CH), 121.0 (CH), 123.7 (CH), 125.5 (CH), 127.0 (C_quat.), 128.3 (CH), 128.5 (CH), 128.8 (CH), 132.0 (CH), 136.4 (C_quat.), 138.6 (C_quat.), 145.2 (C_quat.), 146.9 (C_quat.), 151.1 (C_quat.), 156.1 (C_quat.), 192.8 (C_quat.). MS (EI, 70 eV): m/z (%) = 457 (14) [M⁺], 414 (12) [M⁺ - CH₃CO], 327 (44) [M⁺ - C₉H₈N⁺], 144 (4) [C₁₀H₁₀N⁺], 130 (100) [C₉H₈N⁺]. Anal. Calcd for C₃₁H₂₇N₃O (457.6): C, 81.40; H, 5.91; N, 9.19. Found: C, 81.02; H, 6.05; N, 9.09.

15

All compounds have been fully characterized spectroscopically and by correct elemental analysis or HRMS, respectively.

16

Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-605608 (7a), and CCDC-605609 (9d). Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: [phone]; email: [e-mail]. ac.uk].

17

Typical Procedure (9a, Entry 1).
A magnetically stirred solution of 182 mg (1.00 mmol) of 1a, 139 mg (1.05 mmol) of 2a, 20 mg (0.02 mmol) of Pd(PPh₃)Cl₂, and 2 mg (0.01 mmol) of CuI in a degassed mixture of 0.5 mL of Et₃N and 1.5 mL of THF in a sealed microwave vial under nitrogen was heated by microwave irradiation to 150 °C for 15 min. After cooling to r.t. 576 mg (3.00 mmol) of enaminone 8a and 0.75 mL of AcOH were added and the reaction mixture was heated by microwave irradiation to 150 °C for another 10 min. After work-up and chromatography on silica gel (toluene-acetone, 3:1) and recrystallization from acetone 227 mg (66%) of 9a were obtained as light yellow crystals. Mp. 164 °C. IR (KBr): 2227, 1644, 1608 cm^-1.¹H NMR (300 MHz, DMSO-d ₆): δ = 2.79 (s, 3 H), 2.96 (s, 3 H), 2.99-3.01 (m, 2 H), 3.97 (ddd, J = 6.0, 12.0, 12.0 Hz, 1 H), 4.08 (d, J = 12.0 Hz, 1 H), 6.45 (s, 1 H), 7.31-7.50 (m, 7 H), 7.53 (d, J = 8.16 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 35.3 (CH₂), 35.5 (CH₃), 37.4 (CH₃), 43.6 (CH), 54.7 (CH), 110.6 (C_quat.), 118.5 (C_quat.), 124.2 (CH), 125.5 (CH), 128.1 (CH), 128.7 (CH), 130.4 (CH), 132.7 (CH), 137.3 (C_quat.), 147.6 (C_quat.), 158.1 (C_quat.), 168.3 (C_quat.), 194.8 (C_quat.). MS (EI, 70 eV): m/z (%) = 344 (30) [M⁺], 300(7) [M⁺ - C₂H₆N⁺], 272 (100) [M⁺ - C₂H₆NCO], 244 (6) [M⁺ - C₂H₆NCO - CO], 72 (23) [C₂H₆NCO⁺]. Anal. Calcd for C₂₂H₂₀N₂O₂ (344.4): C, 76.72; H, 5.85; N, 8.13. Found: C, 76.96; H, 5.89; N, 8.15.