Compound 6a

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InChIKey OUQSQVLBEYUXQH-SRFBTDKCSA-N

Compound data: CIF

Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

In a round bottom flask equipped with a stir bar, 6 (1.75 g, 2.328 mmol) was dissolved in 10:1 dichloromethane : methanol (233 mL). The reaction mixture was cooled to -78 °C. Ozone was then bubbled through the solution until a light blue color persisted. The reaction was monitored by taking small aliquots from the solution, quenching those aliquots with thiourea and analyzing them by TLC. When TLC analysis indicated completion of the reaction, the residual ozone was purged from the reaction mixture with oxygen for 10 min. The reaction was quenched with thiourea (709 mg, 9.310 mmol), after which it was stirred at -78 °C for 30 min and then at room temperature for 1 h. After residual thiourea was filtered off via gravity filtration, the reaction mixture was concentrated in vacuo. Flash chromatography (silica gel, 15-20% ethyl acetate : petroleum ether) of the crude material provided pure ketoaldehyde 6a (1.4 g, 89%) as a white solid. Recrystallization procedure for x-ray analysis: keto-aldehyde (20 mg) was transferred to a 1 dram vial. Et₂O was added dropwise to the keto-aldehyde while the vial was heated in a warm water bath (50 °C) until all the solids dissolved. The vial was covered with a rubber septum and an outlet needle placed in the septum. After 12 h, no solvent remained and keto-aldehyde 6a was obtained as colorless rectangular crystals. m.p.: 170°C (decomposition). TLC: R_f = 0.62 (1:2 ethyl acetate:pentane), one spot. ¹H-NMR (500 MHz, CDCl₃, residual solvent peak referenced to 7.24 ppm) δ 9.67 (d, J=4.0, 1H), 7.36-7.26 (m, 5H), 5.01 (d, J=11.2, 1H, AB), 4.81 (dd, J=11.2, 9.4, 1H), 4.48 (d, J=11.2, 1H, AB), 4.38 (s, 1H), 3.90 (dd, J=6.0, 1.8, 1H), 3.88 (d, J=11.2, 1H), 3.48 (d, J=11.0, 1H), 3.48 (d, J=8.2, 1H), 2.96 (ddd, J=9.3, 5.7, 4.3, 1H), 2.59 (dd, J=11.2, 4.0, 1H), 2.55 (dd, J=12.7, 9.4, 1H), 2.50 (d, 1.6, 1H), 2.28-2.17 (m, 2H), 1.94-1.84 (m, 2H), 1.67 (ddd, J=13.7, 9.8, 7.3, 1H), 1.44 (s, 3H), 1.43 (s, 3H), 1.27 (d, J=7.0, 3H), 0.82 (s, 9H), -0.03 (s, 3H), -0.04 (s, 3H) ppm. ¹³C-NMR (125 MHz, CDCl₃) δ 208.82, 201.12, 138.28, 128.34, 127.58, 127.38, 111.49, 86.83, 82.08, 75.68, 74.79, 73.81, 69.43, 65.42, 56.36, 52.21, 52.01, 44.40, 41.89, 29.16, 28.61, 27.15, 26.79, 25.79, 18.35, 17.50, -5.34, -5.47 ppm. FTIR (thin film) 3425, 3031, 2961, 2949, 2929, 2855, 1755, 1723, 1497, 1455, 1384, 1339, 1296, 1248, 1230, 1163, 1134, 1120, 1093, 1067, 1004, 987, 958, 936, 910, 875, 840, 776, 736, 700 cm^-1. HRMS: Calculated for C₃₃H₄₇BrNaO₈Si (M+Na⁺): 701.2116; Found: 701.2122. [α]_D = 31.9 ° (c 1.13, CH₂Cl₂). Elemental analysis: Calculated for C₄₁H₅₅BrO₆Si: %C = 58.31, %H = 6.97, %Br = 11.76; Found: %C = 58.26, %H = 6.71, %Br = 11.49.