Compound 16
2-((1S,4aS,5R,9R,9aS)-1-Bromo-2-oxo-1,2,3,4,4a,5,9,9a-octahydro-6H-5,9-ethenobenzo[7]annulen-6-ylidene)malononitrile
From: Organocatalytic stereoselective [8+2] and [6+4] cycloadditions
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Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.
6bB (36.5 mg, 0.146 mmol) was dissolved in CDCl3 (3 mL) and cooled to -55 ˚C. A freshly prepared solution of Br2 in CDCl3 (149 µL, 0.98 M, 1.0 equiv.) was added dropwise to the cooled solution. The brown solution was allowed to warm to rt over 3 h after which 1H NMR indicated 55% conversion of 6bB. The reaction mixture was cooled to -55 ˚C, added Br2 in CDCl3 (98.3 µL, 0.98 M, 0.66 equiv.), and allowed to warm to rt over 3 h. All solvents were removed under reduced pressure and the crude product was purified by FC (CH2Cl2) on silica gel. The monobrominated product 16 was isolated in 54% yield, >20:1 dr alongside with the dibrominated product (37% yield, 7:3 dr). 1H NMR (400 MHz, CDCl3) δ 6.94 (dd, J = 10.7, 9.0 Hz, 1H), 6.66 – 6.55 (m, 2H), 6.31 (t, J = 7.8 Hz, 1H), 4.59 (d, J = 12.2 Hz, 1H), 3.95 (t, J = 8.1 Hz, 1H), 3.86 (d, J = 7.3 Hz, 1H), 2.73 – 2.60 (m, 2H), 2.57 – 2.43 (m, 2H), 2.16 (dtd, J = 13.6, 5.2, 3.0 Hz, 1H), 1.86 (ddd, J = 26.8, 13.7, 4.5 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 201.0, 169.6, 150.1, 136.9, 128.3, 126.3, 112.8, 111.7, 81.6, 60.5, 48.3, 46.0, 41.0, 39.2, 36.9, 27.1. HRMS calc. for C16H13BrN2O 351.0103 [M+Na]+, found 351.0097. Crystal data for 16: C16H13BrN2O, M = 329.19, orthorhombic, space group P 212121 (no. 115), a = 7.7326(15) Å, b = 9.1116(18) Å, c = 19.866(4) Å, Flack parameter = 0.089, V = 1399.7(5) Å3, T = 100 K, Z = 4, dc = 1.562 g cm‑3, μ(Mo Kα, λ = 0.56086 Å) = 1.577 mm-1, 20311 reflections collected, 4244 unique [Rint = 0.0584], which were used in all calculations. Refinement on F2, final R(F) = 0.0343, Rw(F2) = 0.1057. CCDC number 1470038. The crystals were obtained after recrystallization from MeOH.
