SYNTHESIS OF 2-METHOXYMETHYL-l,4-DIOXASPIRO[4.5]-DECANE

• In a 50-ml three-necked round-bottomed flask fitted with a reflux condenser, a dropping funnel and a stirrer unit, place 4.0 g (0.025 mol) of 2-hydroxy-methyl-l,4-dioxaspiro[4.5]decane, 85 mg (1 mol %) of tetrabutyl-ammonium hydrogen sulphate, 10 ml of dichloromethane, 50 per cent w/w aqueous sodium hydroxide (from 2.6 g of sodium hydroxide and 2.6 g of water), and stir vigorously for 30 minutes. 

• Cool the flask in an ice-water bath and from the funnel add dropwise over a period of 1 hour 3.8 g (0.03 mol) of dimethyl sulphate. 

• Stir the mixture vigorously at room temperature until t.l.c. analysis (1) reveals that the reaction is complete (usually about 3 hours). 

• Add 1 ml of concentrated aqueous ammonia and stir for a further 30 minutes at room temperature to decompose excess dimethyl sulphate. 

• Pour the reaction mixture into water, add 20 ml of dichloromethane, separate the organic layer and wash with water until the washings are neutral. 

• Dry over magnesium sulphate and evaporate the solvent on a rotary evaporator. 

• Distil the residue under reduced pressure to obtain the product, 3.4 g (78%), b.p. 76-77 °C/1.5mmHg.

Notes to keep in mind:

1. The t.l.c. analysis may be performed on Silica gel G plates using toluene: methanol, 9:1; the starting material has R F 0.26, the product has R F 0J0.

Cognate preparations: Allylation, benzylation and but-2-enylation of 1,2-0-cyclohexylidene glycerol

• Use 4.0 g (0.025 mol) of starting material, 425 mg (5mol %) of tetrabutylammonium hydrogen sulphate, 20 ml of t rans- 1,2-dichloroethylene, 0.03 mol of either allyl chloride, benzyl chloride or crotyl chloride (l-chlorobut-2-ene), and 6.0 g of sodium hydroxide dissolved in 6g of water. 

• Stir the mixture vigorously and heat under reflux until t.l.c. analysis shows the reaction to be complete (0.75-2 hours). 

• Work-up the reaction mixture as above to isolate the products, which have the following characteristics: O-allyl ether 77 per cent yield, b.p. 103-105 °C/2.5mmHg, R F 0.76; O- benzyl ether 74 per cent yield, b.p. 156-160 °C/2 mmHg, R F 0.66; O-but-2-enyl ether 84 per cent, b.p. 111-113 °C/2mmHg, R F 0.86.