Palladium-Catalyzed Four-Membered Ring Annelation Reactions at Dibenzobarrelene

Abstract

A palladium-catalyzed coupling process of dibenzobarrelene with annelated aryl halides leads to special benzocyclobutenes, resembling Diels-Alder adducts of antiaromatic benzocyclobutadienes with anthracene. Moderate steric pressure in intermediary five-membered palladacycles seems to be decisive for this type of transformation.

Key words

benzocyclobutenes - C-H activation - domino processes - palladium catalysis - steric pressure

References and Notes

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19

CCDC 697535 (for 10), CCDC 697536 (for 12), CCDC 697537 (for 14), and CCDC 697538 (for 19) contain the supplementary crystallographic data. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

20

General Procedure for Palladium-Catalyzed Coupling Reactions of Aryl Halides with Dibenzobarrelene (4): A mixture of aryl halide (3.00 mmol), dibenzobarrelene (4; 202 mg, 1.00 mmol; or in the ratio outlined in Table  [¹] ), K₂CO₃ (1.1 g, 8.0 mmol), n-Bu₄NBr (645 mg, 2.00 mmol), Pd(OAc)₂ (12 mg, 0.05 mmol) and DMF (10 mL) in a sealed tube (for convenience) was stirred under argon at 100 ˚C for 3 d. After diluting with H₂O (50 mL), the reaction mixture was extracted three times with diethyl ether or methyl tert-butyl ether (50 mL). The Et₂O extract was filtered through silica and concentrated. The crude product was purified by flash chromatography (hexanes or hexanes-dichloro-methane on silica gel).
Selected Analytical Data: Compound 6: colorless solid; mp 42 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 1.44-1.55 (m, 9 H), 4.44-4.58 (m, 6 H), 7.61 (d, J = 6.6 Hz, 2 H), 7.81 (d, J = 9.2 Hz, 1 H), 7.88 (d, J = 9.2 Hz, 1 H), 8.19-8.29 (m, 3 H), 8.36 (dd, J = 1.7, 8.7 Hz, 1 H), 8.64 (d, J = 1.6 Hz, 1 H), 8.90 (d, J = 8.8 Hz, 1 H), 9.51 (s, 1 H). ^¹³C NMR (101 MHz, CDCl₃): δ = 14.53 (2 × q), 14.58 (q), 61.27 (t), 61.41 (t), 61.61 (t), 123.54 (d), 124.72 (d), 125.51 (d), 127.39 (d), 128.11 (s), 128.50 (d), 129.27 (s), 129.86 (d, phenylene), 129.98 (d), 130.09 (s), 130.28 (d, phenylene), 130.90 (d), 131.33 (s), 133.40 (s), 133.65 (s), 140.44 (s), 144.75 (s), 166.49 (2 × s), 166.57 (s), one singlet was superimposed.
Compound 8: colorless solid; mp 126 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 2.18 (s, 6 H), 3.66 (dd, J = 1.4, 2.6 Hz, 2 H), 4.58 (dd, 2 H), 6.67 (s, 2 H), 6.92 (dd, J = 3.2, 5.4 Hz, 2 H), 7.09 (dd, J = 3.2, 5.3 Hz, 2 H), 7.21 (dd, J = 3.2, 5.4 Hz, 2 H), 7.40 (dd, J = 3.2, 5.3 Hz, 2 H). ^¹³C NMR (101 MHz, CDCl₃): δ = 16.63 (q), 46.02 (d), 47.67 (d), 124.05 (d), 124.54 (d), 125.81 (d), 126.00 (d), 128.22 (d), 129.37 (s), 140.54 (s), 143.14 (s), 143.44 (s). MS (EI, 70 eV): m/z (%) = 308.7 (5) [M⁺], 307.7 (19) [M⁺ - 1], 178.8 (15), 177.8 (100), 130.9 (7), 129.9 (58).
Compound 10: colorless solid; mp 156 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 3.81 (t, J = 4.3 Hz, 1 H), 3.94 (t, J = 4.3 Hz, 1 H), 4.63 (d, J = 3.8 Hz, 1 H), 4.76 (d, J = 4.0 Hz, 1 H), 6.65 (t, J = 8.0 Hz, 1 H), 6.67 (t, J = 8.0 Hz, 1 H), 6.88 (d,
J = 7.3 Hz, 1 H), 7.02 (d, J = 7.3 Hz, 1 H), 7.08 (d, J = 8.1 Hz, 1 H), 7.16-7.21 (m, 2 H), 7.34 (t, J = 8.2 Hz, 1 H), 7.41-7.50 (m, 4 H), 7.68 (d, J = 8.1 Hz, 1 H), 7.77 (d, J = 8.1 Hz, 1 H). MS (EI, 70 eV): m/z (%) = 331 (3), 330 (13), 203 (2), 178 (13), 163 (2), 153 (13), 152 (100), 151 (6).
Compound 12: colorless solid; mp 265 ˚C. ^¹H NMR (200 MHz, CDCl₃): δ = 3.97 (d, J = 4.0 Hz, 2 H), 4.80 (d, J = 4.0 Hz, 2 H), 6.56-6.64 (m, 2 H), 6.87-6.95 (m, 2 H), 7.19-7.24 (m, 2 H), 7.45-7.64 (m, 6 H), 7.83 (d, J = 7.1 Hz, 2 H), 8.54 (d, J = 7.8 Hz, 2 H). MS (EI, 70 eV): m/z (%) = 380 (15), 202 (100), 187 (2), 178 (4), 152 (1).
Compound 14: yellow solid; mp 287 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 4.10 (t, J = 4.8 Hz, 1 H), 4.23 (t, J = 4.8 Hz, 1 H), 4.77 (d, J = 4.0 Hz, 1 H), 4.89 (d, J = 4.0 Hz, 1 H), 6.50 (t, J = 7.3 Hz, 1 H), 6.61 (t, J = 7.3 Hz, 1 H), 6.88 (d,
J = 7.3 Hz, 1 H), 6.98 (d, J = 7.3 Hz, 1 H), 7.19-7.24 (m, 2 H), 7.45-7.51 (m, 2 H), 7.72 (s, 1 H), 7.89-7.94 (m, 3 H), 8.02-8.14 (m, 4 H). MS (FAB): m/z (%) = 405 (35), 404 (71), 226 (21).
Compound 18: yellow solid; mp 265 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 4.31 (dd, J = 3.5, 7.3 Hz, 1 H), 4.63 (dd, J = 2.8, 7.3 Hz, 1 H), 4.76 (d, J = 3.5 Hz, 1 H), 5.16 (d, J = 3.0 Hz, 1 H), 6.44 (‘t’, J = 7.3 Hz, 1 H), 6.50 (dd, J = 1.3, 7.3 Hz, 1 H), 6.61 (‘t’, J = 7.3 Hz, 1 H), 6.86 (d, J = 7.3 Hz, 1 H), 7.21-7.26 (m, 2 H), 7.30 (d, J = 6.6 Hz, 1 H), 7.37 (‘t’,
J = 8.3 Hz, 1 H), 7.45-7.57 (m, 4 H), 7.60 (‘t’, J = 6.6 Hz, 1 H), 7.99 (d, J = 8.3 Hz, 1 H), 8.01 (s, 1 H), 8.42 (dd, J = 0.8, 8.6 Hz, 1 H). ^¹³C NMR (101 MHz, CDCl₃): δ = 49.13 (d), 50.17 (d), 51.35 (d), 51.45 (d), 117.37 (d), 122.44 (d), 122.75 (d), 124.15 (d), 124.23 (d), 124.27 (d), 124.37 (d), 124.92 (d), 124.94 (d), 125.01 (d), 125.31 (d), 125.38 (d), 126.25 (d), 126.33 (d), 127.07 (s), 127.49 (d), 129.31 (s), 130.06 (d), 133.78 (s), 139.04 (s), 139.91 (s), 140.17 (s), 141.19 (s), 143.78 (s), 144.20 (s), 146.72 (s). MS (EI): m/z (%) = 380 (5.7) [M⁺], 202 (87.1), 178 (100), 108 (6.4), 59 (19.3), 43 (16.4), 29 (6.4).
Compound 19: slightly yellow fluorescent solid; decomposition started at 160 ˚C. MS (EI): m/z (%) = 406 (15) [M⁺ - M_anthracene], 228 (29), 202 (6), 178 (100) [M⁺ _anthracene], 152 (10), 89 (7), 76 (6), 45 (8).
Compound 20: Diastereoisomeric mixture; yellow solid; mp 168 ˚C; six times fractionated crystallization with i-PrOH gave one pure diastereoisomer. ^¹H NMR (400 MHz, CDCl₃): δ = 0.91-1.01 (m, 2 H), 1.29-1.35 (m, 2 H), 1.47-1.59 (m, 3 H), 1.63-1.89 (m, 6 H), 1.94-2.02 (m, 1 H), 2.32-2.38 (m, 1 H), 2.45-2.60 (m, 4 H), 2.67 (s, 1 H), 3.20 (d, J = 3.5 Hz, 1 H), 3.73 (d, J = 3.5 Hz, 1 H), 4.43 (t, J = 8.3, 8.6 Hz, 1 H), 7.17 (d, J = 8.3 Hz, 1 H), 7.35-7.44 (m, 2 H), 7.89 (d, J = 8.3 Hz, 1 H), 7.94-7.99 (m, 1 H), 8.32 (s, 1 H), 8.62-8.69 (m, 1 H). ^¹³C NMR (101 MHz, CDCl₃): δ = 28.12 (t), 28.24 (t), 29.18 (t), 31.53 (t), 32.78 (t), 36.30 (d), 37.10 (d), 37.57 (d), 39.63 (t), 39.72 (t), 44.30 (d), 44.42 (d), 49.21 (d), 54.14 (d), 120.43 (d), 124.01 (d), 124.31 (d), 126.67 (d), 128.78 (d), 129.64 (s), 130.01 (d), 130.26 (s), 130.51 (d), 131.79 (s), 132.34 (s), 137.31 (s), 140.46 (s), 144.15 (s). MS (EI): m/z (%) = 364 (100) [M⁺], 323 (8), 283 (9), 270 (16), 253 (36), 239 (25), 229 (17), 202 (11), 67 (9), 49 (11), 41 (8).
Compound 21: orange-red solid; mp 222 ˚C. ^¹H NMR (200 MHz, CDCl₃): δ = 7.17 (d, J = 6.8 Hz, 1 H), 7.24 (s, 1 H), 7.28-7.55 (m, 5 H), 7.67 (dd, J = 6.8, 8.1 Hz, 1 H), 7.79-7.97 (m, 3 H), 8.09 (d, J = 9.9 Hz, 4 H), 8.55 (s, 1 H). ^¹³C NMR (50 MHz, CDCl₃): δ = 124.30 (d), 124.45 (d), 125.38 (d), 125.42 (d), 127.07 (d), 127.31 (d), 127.36 (d), 127.72 (d), 127.93 (d), 128.14 (d), 128.47 (s), 128.52 (d), 128.73 (s), 130.72 (s), 130.95 (d), 131.03 (s), 131.62 (s), 139.63 (s), 140.68 (s), 141.69 (s). MS (EI): m/z (%) = 328 (100) [M⁺], 163 (20), 149 (5.4), 43 (5.7), 27 (8.6).