Compound 15
(1R,2R,4S,5S,6R,7R,10S)-4,7,10-Tribromotricyclo[4.4.1.12,5]dodec-8-ene-3,11-dione
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.
The [6 + 4] cycloadduct 4aA (13.2 mg, 0.07 mmol) was suspended in CCl4 (0.5 mL) and added a freshly prepared solution of Br2 in CCl4 (105 µL, 2.0 M, 3.0 equiv). After stirring for 2 h at rt the suspension was diluted with CDCl3 (0.5 mL) and stirred for another 30 min. at rt. All volatiles were removed under reduced pressure and the crude product purified by FC on silica gel (gradient pentane/EtOAc 9:1 to 7:3). The desired product 15 was obtained in 55% yield, >20:1 dr as brown crystals. 1H NMR (400 MHz, CDCl3) δ 6.07 – 5.97 (m, 2H), 4.90 – 4.84 (m, 2H), 4.02 (d, J = 2.9 Hz, 1H), 3.54 (br s, 1H), 3.40 (br s, J = 1.4 Hz, 1H), 2.96 (q, J = 3.7 Hz, 1H), 2.91 – 2.85 (m, 2H), 2.26 (dt, J = 13.8, 4.2 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 206.3, 200.9, 130.5, 130.2, 62.2, 59.7, 53.3, 49.3, 46.5, 43.7, 43.7, 23.3. HRMS calc. for C12H1179Br281BrO2 448.8181 [M+Na]+, found 448.8183. Crystal data for 15: C12H11Br3O2, M = 426.94, monoclinic, space group P 21 (no. 6), a = 13.187(2) Å, b = 6.5102(11) Å, c = 14.954(3) Å, β = 90.144(4)°, Flack parameter = -0.005, V = 1283.8(4) Å3, T = 296 K, Z = 4, dc = 2.209 g cm-3, μ(Mo Kα, λ = 0.56086 Å) = 5.042 mm-1, 45331 reflections collected, 7817 unique [Rint = 0.0362], which were used in all calculations. Refinement on F2, final R(F) = 0.028, Rw(F2) = 0.0671. CCDC number 1457777. The crystals were obtained after recrystallization from CDCl3.
