Compound 19a

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InChIKey MVCQGKKTRKEJMW-SRCWFGGASA-N

Compound data: CIF

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

CH₂Cl₂ (1.1 mL) was added to a vial containing 19 (6.0 mg, 0.011 mmol). The vessel was cooled to -78 °C before addition of 2,6-lutidine (25 μL, 0.21 mmol) followed by Tf₂O (7.2 μL, 0.043 mmol), each in one portion. After 10 min, the reaction was complete as determined by TLC analysis. The reaction was quenched with saturated NaHCO₃, allowed to warm to r.t., and diluted with Et₂O. The layers were separated, and the aqueous phase was extracted 4 x Et₂O. The combined organics were dried over Na₂SO₄, filtered, and concentrated. The crude residue was left under vacuum 1.5 h prior to addition of CH₃CN (1.1 mL). TBAI (39.8 mg, 0.11 mmol) was added in one portion. The vial was sealed with a Teflon® coated cap, covered in foil, and heated to 65 °C (ext. T, oil bath). After 17.5 h, the reaction was complete as determined by TLC analysis. The reaction was cooled to r.t., concentrated, and the crude residue was purified by silica gel column chromatography (20% EtOAc/petroleum ether) to provide the bis-iodide 19a (7.8 mg, 93%) as a white solid. For X-ray crystallography, the product was recrystallized from CH₂Cl₂ by slowly diffusing pentane vapor into the solution at r.t. m.p.: 210-212 °C (decomposition). TLC: R_f = 0.21 (20% EtOAc/petroleum ether). ¹H-NMR (CD₃OD, 500 MHz) δ 5.29 (d, 1H, J = 1.5 Hz, C16-H), 4.87 (s, 1H, C16-H), 4.75 (d, 1H, J = 6.5 Hz, C14-H), 4.17 (dd, 1H, J₁ = 8.0 Hz, J₂ = 4.0 Hz, C12-H), 3.97 (d, 1H, J = 9.5 Hz, C3-H), 3.68 (dd, 1H, J₁ = 9.5 Hz, J₂ = 1.1 Hz, C5-H), 3.64 (d, 1H, J = 11.0 Hz, C20-H), 3.57 (dd, 1H, J₁ = 11.0 Hz, J₂ = 6.0 Hz, C18-H), 3.40 (d, 1H, J = 11.0 Hz, C20-H), 3.33 (dd, 1H, J₁ = 11.0 Hz, J₂ = 5.5 Hz, C18-H), 3.21 (ddd, 1H, 9.5 Hz, 6.5 Hz, 4.6 Hz, C7-H), 3.20 (s, 1H, C4-OH), 2.95 (dd, 1H, J₁ = 13.3 Hz, J₂ = 9.5 Hz, C7-H), 2.45 (ddd, 1H, J₁ = 8.0 Hz, J₂ = J₃ = 5.5 Hz, C11-H), 2.16-2.26 (m, 1H, C2-H), 2.08-2.12 (m, 2H, C5-OH & C12-OH), 1.99-2.05 (m, 2H, C1-H & C7-H), 1.98 (s, 3H, 3 x C17-H), 1.84 (dd, 1H, J₁ = 14.0 Hz, J₂ = 5.5 Hz, C10-H), 1.36 (ddd, 1H, J₁ = 14.0 Hz, J₂ = 11.5 Hz, J₃ = 8.5 Hz, C1-H), 0.93 (s, 9H, Si(CH₃)₂(C(CH₃)₃)), 0.93 (d, 3H, J = 7.0 Hz, C2-CH₃), 0.17 (s, 3H, Si(CH₃)₂(C(CH₃)₃)), 0.12 (s, 3H, Si(CH₃)₂(C(CH₃)₃)). ¹³C-NMR (CD₃OD, 125 MHz) δ 152.2, 141.7, 115.7, 87.9, 83.7, 81.6, 81.3, 78.6, 78.0, 74.0, 70.6, 50.3, 44.9, 40.1, 33.8, 33.2, 32.0, 25.7, 20.9, 18.1, 16.9, 12.0, -1.0, -4.5, -5.3. IR (NaCl Thin Film) ν = 3502, 2927, 1762, 1379, 1226, 1051, 839 cm^-1. MS (TOF MS ES+) m/z Calculated for C₂₇H₄₂I₂O₈Si + Na (M+Na): 799.0636; Found: 799.0637. [α]_D = 2.56 ° (c 0.78, CH₂Cl₂).