SYNTHESIS OF CIS-1-IODO-7-OXABICYCLO[4.3.0]NONAN-8-ONE

•  At room temperature, a solution of cyclohex-1-en-1-ylacetic acid (10g) (1) and sodium hydrogen carbonate (19g) in water (300 ml), is added to a solution of iodine (38g) and potassium iodide (75g) in water (600 ml). 

• The oily precipitate is extracted after 4 hours with ether, and the ether solution washed with sodium hydrogen sulphite until the coloration of iodine has disappeared, and then with saturated sodium hydrogen carbonate solution. 

• The dried ethereal extract is evaporated in vacuo; the oily residue gives on trituration with light petroleum 8.2g (43%) of a white solid, m.p. 56 °C (2).

Dehydrohalogenation of  𝜸-iodolactone

• A solution of the foregoing lactone in pyridine (10 ml) is kept at room temperature for 2 days. 

• Ethanol (30 ml), zinc powder (5g) and (during 1 hour) concentrated hydrochloric acid (10 ml) are added with stirring and cooling. 

• The solution is filtered and extracted with benzene and the organic layer washed successively with 10 per cent hydrochloric acid, 10 per cent sodium hydrogen carbonate, and finally water. 

• Distillation of the benzene layer gives 1.4g (54%) of the unsaturated lactone, b.p. 152-153 °C/30mmHg, m.p. 28-30°C; i.r. (thin film) 1750 (conjugated y-lactone carbonyl), 1650cm⁻¹ (C=C).

Notes to keep in mind:

1. Cyclohex-1-en-1-ylacetic acid may be prepared from ethyl 1'-hydroxy-cyclohexylacetate by dehydration to the unsaturated ester followed by acidic hydrolysis to the unsaturated acid.

2. Iodolactones are unstable and should be used in further reactions without delay; recrystallisation may be carried out using an ethanol-light petroleum solvent mixture.