Synlett 2007(5): 0800-0802  
DOI: 10.1055/s-2007-970761
LETTER
© Georg Thieme Verlag Stuttgart · New York

New Access to a Tricyclo[3.2.1.02,7]oct-3-ene Structure

Julien Dubarle-Offnera, Jérôme Marrotb, Marie-Noëlle Ragerc, Franck Le Bideau*a, Gérard Jaouena
a Laboratoire de Chimie et Biochimie des Complexes Moléculaires, UMR CNRS 7576, Ecole Nationale Supérieure de Chimie de Paris, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
Fax: +33(1)43260061; e-Mail: franck-lebideau@enscp.fr;
b Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles Saint-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France
c Service de RMN, Ecole Nationale Supérieure de Chimie de Paris, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
Further Information

Publication History

Received 12 September 2006
Publication Date:
08 March 2007 (online)

Abstract

A thermally induced reaction cascade including an electrocyclic rearrangement, two Diels-Alder reactions and a 1,4-elimination from a simple cyclobutene carbonate can explain the synthesis of a complex tricyclo[3.2.1.02,7]oct-3-ene core structure.

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Methyl 3-Phenylcyclobut-2-enyl Carbonate ( 5). To a solution of 3-phenylcyclobutenone (3, 2.1 g, 14.5 mmol) and CeCl3·7H2O (5.6 g, 22.7 mmol) in MeOH (50 mL) at r.t. was slowly added NaBH4 (580 mg, 15 mmol) over 15 min. The reaction mixture was stirred at that temperature for 5 min, hydrolyzed with brine (50 mL) and extracted with Et2O (3 × 50 mL). The organic layer was dried over MgSO4 and evaporated to give a residue (2.1 g) which was dissolved in CH2Cl2 (150 mL) in the presence of Et3N (8 mL, 57 mmol) and 4-dimethylamino pyridine (1 g, 8 mmol). Then, ClCO2Me (4.7 mL, 60 mmol) was slowly added and the reaction mixture was stirred for 75 min at r.t. After dilution in CH2Cl2 (50 mL), it was hydrolyzed with brine (100 mL) and extracted with Et2O (3 × 100 mL). The organic layer was dried over MgSO4, evaporated and the residue was purified by flash chromatography (pentane-CH2Cl2 = 70:30) to give the carbonate 5 as a yellow oil (1.83 g, 62%). 1H NMR (400 MHz, CDCl3): δ = 7.50-7.30 (m, 5 H), 6.34 (br s, 1 H), 5.40 (dt, J = 3.9, 1.0 Hz, 1 H), 3.81 (s, 3 H), 3.23 (ddd, J = 13.1, 3.9, 1.0 Hz, 1 H), 2.83 (dt, J = 13.1, 1.0 Hz, 1H) ppm. 13C NMR (75 MHz, CDCl3): δ = 155.4, 148.6, 133.0, 129.1, 128.4, 125.6, 125.0, 71.1, 54.6, 36.9 ppm. IR (CHCl3): ν = 3062-2850, 1743, 1444, 1259 cm-1. MS (EI): m/z = 146 [MNH4 + - MeOCO2H].

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Compounds 6:
The carbonate 5 (300 mg, 1.5 mmol) in DMSO (1 mL) was heated at DMSO reflux for 1.5 h under argon. The crude reaction mixture was diluted with brine (15 mL) and extracted with EtOAc (3 × 10 mL). The organic layer was dried over MgSO4, evaporated and the residue was purified by flash chromatography (CH2Cl2-pentane = 1:2) to give the compound 6 as a white solid (84 mg, 33%). 1H NMR (300 MHz, CDCl3): δ = 7.50-7.20 (m, 10 H, arom.), 6.59 (dd, J = 6.2, 2.3 Hz, H3), 5.26 (dd, J = 4.7, 2.3 Hz, 1 H, H6), 3.71 (t, J = 3.9 Hz, 1 H, H5), 3.69 (s, 3 H, H10), 2.35 (dd, J = 6.8, 2.4 Hz, 1 H, H7), 2.23 (dd, J = 8.0, 6.2 Hz, 1 H, H2), 2.18 (dd, J = 11.7, 5.1 Hz, 1 H, H8 ), 1.57 (d, J = 11.7 Hz, 1 H, H8) ppm. 13C NMR (75 MHz, CDCl3): δ = 155.5 (C=O), 141.2 (Ph), 139.2 (C4), 135.9, 127.5, 126.7, 126.2, 126.0, 124.9 (Ph), 120.4 (C3), 75.5 (C6), 54.5 (methoxy), 38.3 (C5), 31.9 (C1), 31.2 (C8), 28.2 (C2), 27.2 (C7) ppm. Mp 117 °C. IR (KBr): 3031, 2922, 2856, 1742, 1440, 1292, 1265, 968, 755, 697 cm-1. Anal. Calcd for C22H20O3: C, 79.50; H, 6.06. Found: C, 79.50; H, 6.31.

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The carbonate 5 (368 mg, 1.8 mmol) was heated at 140 °C (neat) for 30 min. The residue was purified by flash chromatography (pentane-Et2O = 95:5, followed by pentane-Et2O = 80:20) to afford successively the tricyclic compound 6 as a white solid (62 mg, 21%), a mixture of the diastereomers 8 (69 mg, 19%) and diene 7 (10 mg, 5%).
Diastereomers 8: 1H NMR (300 MHz, CDCl3): δ = 7.50-7.20 (m, 20 H, Ph), 6.95 (d, J = 12.6 Hz, 1 H, CHtrans), 6.91 (d, J = 12.7 Hz, 1 H, CHtrans), 6.32 (br d, J = 5.1 Hz, 1 H, CH), 6.29 (dt, J = 4.3, 1.6 Hz, 1 H, CH), 5.73 (d, J = 12.6 Hz, 1 H, CHtrans), 5.65 (d, J = 4.3 Hz, 1 H, CHO), 5.63 (d, J = 12.7 Hz, 1 H, CHtrans), 5.51 (d, J = 5.1 Hz, 1 H, CHO), 3.82 (s, 3 H, OMe), 3.81 (s, 3 H, OMe), 3.77 (s, 3 H, OMe), 3.55 (s, 3 H, OMe), 2.70-2.40 (m, 4 H, CH2), 2.40-2.10 (m, 4 H, CH2) ppm. 13C NMR (75 MHz, CDCl3): δ = 155.4, 155.0, 153.4, 153.3 (CO), 142.9, 142.2, 142.1, 142.0 (Cipso), 140.1, 140.0 (CQ), 138.9, 138.4 (CH), 128.4, 128.3, 128.2, 128.1, 127.9, 127.3, 126.9, 126.8, 126.7, 125.6, 125.5, 120.6, 119.5, 118.9, 118.7 (CH), 77.2, 75.7 (CH), 55.2, 55.1, 54.8, 54.6 (CH3), 44.4, 44.1 (CQ), 29.7, 27.7, 25.5, 25.1 (CH2) ppm. HRMS: m/z calcd for C24H28O6N [M + NH4]: 426.1917; found: 426.1915.
Diene 7: 1H NMR (300 MHz, CDCl3): δ = 7.09 (d, J = 12.4 Hz, 1 H), 6.32 (dd, J = 12.4, 0.8 Hz, 1 H), 5.27 (dd, J = 1.5, 0.6 Hz, 1 H), 5.15 (d, J = 1.5 Hz, 1 H), 3.84 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 153.3, 143.6, 140.3, 139.5, 128.4, 127.8, 117.2, 116.5, 55.3 ppm. MS (EI): m/z = 178 [MNH4 + - CO2].