Compound 5

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InChIKey PBAYEDANOIXYIE-BBBLOLIVSA-N

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

The α,β-unsaturated ketone 14 (8.28 g, 32.5 mmol) was dissolved in CH₂Cl₂ (100 mL) and cooled with stirring to 0 °C. Acetaldehyde (18.4 mL, 325 mmol) was added followed by Bi(NO₃)₃·5H₂O (3.16 g, 6.51 mmol) and the reaction allowed to warm to room temperature overnight. The resulting brown suspension was diluted with diethyl ether, filtered to remove the precipitated solids. The filtrate was partitioned between saturated aqueous NaHCO₃solution and the diethyl ether. The combined organic phases were dried (MgSO₄) filtered and concentrated in vacuo to afford the crude product. Purification by flash chromatography (silica gel, 10–40% diethyl ether in petroleum ether) furnished the syn-1,3-dioxane 5 (5.30 g, 88%) as a colorless oil: R_f = 0.15 (TLC, 1:4 ethyl acetate/hexane); [α]_D²³ −7.2 (c = 0.67, CHCl₃); ¹H-NMR (500 MHz, CDCl₃) δ 5.84 (ddd, J = 17.3, 10.7, 5.8 Hz, 1H), 5.28 (app. dt, J = 17.3, 1.4 Hz, 1H), 5.15 (app. dt, J = 10.6, 1.3 Hz, 1H), 4.78 (q, J = 5.1 Hz, 1H), 4.18–4.11 (m, 2H), 2.79 (dd, A of ABX, J_AB = 16.4 Hz, J_AX = 7.1 Hz, 1H), 2.49 (dd, B of ABX, J_AB = 16.4 Hz, J_BX =5.5 Hz, 1H), 2.19 (s, 3H), 1.66 (app. dt, A of ABX₂, J_AB = 13.1 Hz, J_AX = 2.5 Hz, 1H), 1.36 (app. dt, B of ABX₂, J_AB = 13.0 Hz, J_BX = 11.3 Hz, 1H), 1.33 (d, J = 5.1 Hz, 3H); ¹³C-NMR (125 MHz, CDCl₃) δ 206.60 (e), 137.69 (o), 115.92 (e), 98.65 (o), 76.72 (o), 72.19 (o), 49.51 (e), 36.34 (e), 31.25 (o), 21.18 (o); IR (neat) 3085 (w), 2994 (w), 2917 (w), 2870 (w), 1715 (s), 1649 (w), 1408 (m), 1361 (m), 1337 (m), 1310 (w), 1150 (s), 1125 (s), 1075 (m), 991 (m), 925 (s), 910 (m), 864 (w) cm⁻¹; HRMS (ESI, [M+H]⁺) calcd for C₁₀H₁₇O₃ 185.1172, found 185.1167.