4b
Typical Procedure for the Synthesis of Vinylcycloalkanols: Drying of cerium chloride: CeCl3 heptahydrate (100 g, 0.268 mol) was heated under reduced pressure (HV pump) in a Büchi Kugelrohr oven with continuous rotation of the bulb, at first with an air bath temperature of 70-80 °C for 5-6 h, then for 3-4 h at 110-120 °C, and finally for about 12 h (overnight) at 150-160 °C. The vaporized water was collected in cooling traps (liquid N2) and the thawed condensates were collected (about 34 mL). The dried (strongly hygroscopic) ivory-colored CeCl3 was stored under an argon atmosphere at r.t. in the dark. No loss in activity could be observed during storage over several months. Precomplexation of the ketone: Cyclododecanone (36.4 g, 0.2 mol) was, with stirring, added to a suspension of 5.0 g anhyd CeCl3 (0.02 mol, 0.1 mol equiv.) in anhyd THF (100 mL) at r.t. under an inert atmosphere. After 0.5-2 h, the yellowish colored suspension became homogenous and uniformly gel- (or yogurt-)like. To this mixture, of a 1 M solution of vinyl magnesium bromide (320 mL) in anhyd THF (0.32 mol, ca 1.6 mol equiv.) was added with stirring via a cannula within 10 min, whereby the temperature of the reaction mixture increased to 35-40 °C. After the exothermic phase of the reaction, stirring was continued for 20-30 min and the conversion of the starting ketone was monitored by TLC and GC analyses (normally more than 80% had been consumed after 15 min). Work-up: The now greyish-brown reaction mixture was poured into cold water (1 L ) and t-BuOMe (500 mL) were added. With stirring, a 10% aqueous HCl solution was added until the slimy or gel-like consistency of the mixture disappeared, and the mixture became clear and two-phased (pH < 3). The organic phase was washed several times with water, then with sat. NaHCO3 solution, and brine. After drying (MgSO4) and evaporation of the solvent under reduced pressure, the crude 1-vinylcyclododecanol 6 (GC purity about 90%) was purified either by bulb-to-bulb distillation (HV) and subsequent crystallization from hexane-t-BuOMe (95:5, v/v) or by chromatography on a short column (silica gel, eluent, hexane-t-BuOMe 97:3-95:5). Allylic alcohol 6 was obtained in yields of 75-85% as a colorless waxy solid (mp 53 °C). 1H NMR (300 MHz, CDCl3): 5.98 (dd, J = 10.8, 17.4 Hz, 1 H), 5.20 (dd, J = 1.4, 17.4 Hz, 1 H), 5.01 (dd, J = 1.4, 10.8 Hz, 1 H), 1.9-1.2 (m, 23 H). 13C NMR (75 MHz, CDCl3): 145.3 (d); 111.0 (t); 75.3 (s); 34.6(2), 26.3(2), 25.9, 22.5(2), 22.1(2), 19.5(2)(6 t). EI-MS (GC/MS): 210.2 (2, M
+
), 192.2 (50, M - 18), 77.7(98), 67(100), 55(97). Also see:
