1.4- Dioxan-2-yl ethers

The l,3-dioxane-2-ethanol (2 ml) was added dropwise to sodium hydride (396 mg of 60% dispersion, 10 mmol) at RT under argon. When the effervescence had ceased, l l,N,N, N -tetramethylenediamine (TMEDA) (1 ml) was added, the mixture stirred for a further 4 h and then a solution of the epoxide (396 mg, 1.0 mmol) in TMEDA (1.0 ml) was added dropwise. The mixture was stirred at 100-110°C for 3 days and then allowed to cool to RT. Water was added and, after 5 min the mixture extracted with ether. The extract was washed with water and the aqueous phase reextracted with ether. The combined organic extracts were dried (MgS04) and evaporated in vacuum column chromatography (4% MeOH-10% ether-86% petrol) of the residue afforded [2(R)]-L-3-0-Benzyl-4,5-0-isopropylidene-6-0-[2-(5,5-dimethyl-l,3-dioxan-2-yl)ethyl]-2-0-(l-phenylethyl)-muco-inositol (176 mg, 31%), [a]D20 +63.4° (c 1.4, CHCI3) and [S(R)]-D-4-0-Benzyl-2,3-0-isopropylidene-6-0-[2-(5,5-dimethyl-l,3-dioxan-2-yl)ethyl]-5-0-(phenylethyl)-myo-inositol (273 mg, 48%), mp 108°-110°C, [a]D20+ 29.3° (c 0.76, CHCI3) as a thick oil and a white solid respectively, and starting epoxide (65 mg, 16%). 

To a solution of 100 mL diphenyl ether was added 1.09 g l,3-dioxane-4,6-dione (1.57 mmol). A stream of nitrogen was passed through the solution for 20 min and the flask was then lowered into a large silicone oil bath preheated to 240°C. The temperature of the bath dropped to 225°C and rose again to 240°C in 5-7 min. The solution was stirred in the bath for a total of 18 min, then removed and allowed to cool. The solvent was removed under vacuum (0.1 mmHg, 110°C). Hash chromatography (1 2 to 6 1 hexanes/EtOAc) gave 0.326 g O-benzyl A-2-(rert-butyldimethylsilyloxy)-2-[8-benzyloxy-7-methoxy-4(l//)-quinolinon-5-yl]ethyl carbamate as a tan solid, in a yield of 35%. An analytical sample, m.p. 63-65°C, was obtained by recrystallization from EtOAc/ hexanes. 

Typical procedure. 5- 3 -tert-Butyldimethykilyloxy-3 -[furan-2"(5"H)-on-4"-yl]propyl -5-(2" -methoxycarbonyloxYbut-3" -en-l""-yl)-2,2-dimethyl-l,3-dioxane 829 [613] To a cooled (0 °C) solution of alcohol 828 (758.5 mg, 1.70 mmol) and pyridine (0.70 mL, 8.65 mmol) in dichloromethane (10 mL), methyl chloroformate (0.52 mL, 6.73 mmol) was carefully added over a period of 16 min. The mixture was stirred at 0 °C for 70 min, and then allowed to warm to room temperature over a period of 40 min. The reaction was subsequently quenched with saturated aq. NH4CI solution (10 mL), and the mixture was extracted with diethyl ether (3 x 30 mL). The combined extracts were washed with brine (10 mL), dried (MgS04), filtered, and concentrated in vacuo. Purification of the residue by column chromatography on silica gel (230-400 mesh, 23 g, hexane/EtOAc, 4 1 1 1) afforded carbonate 829 as a 1 1 mixture of diastereomers (604.0 mg, 1.20 mmol, 70%) as a pale-yellow oil, followed by recovered 828 (233.0 mg, 0.53 mmol, 30%). IR (neat) v ax = 1780, 1754 cm-i. 

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