Hydrochloric Acid → (3'aR,6'aS)-hexahydro-1'H-spiro(1,3-dioxolane-2,2'-pentalen)-5'-one

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Reaction Conditions

Reaction Steps

A solution of 294 mg of (1S,5R,6R,7S)-3,3-ethylenedioxy-7-hydroxy-6-ethoxycarbonylbicyclo [3.3.0]octane (III)' in methylene chloride (2 ml) as prepared in Example 1 was added to a solution of a chromic anhydride-pyridine complex in methylene chloride [prepared from chromic anhydride (688 mg), pyridine (1088 mg) and methylene chloride (18 ml)], and the mixture was stirred at room temperature for 10 minutes. The supernatant was separated, the residue was washed with ether, and the combined organic layer was extracted with 5% aqueous sodium hydroxide solution. The aqueous layer was neutralized with dilute hydrochloric acid and extracted with ether. The organic layer was successively washed with saturated aqueous copper sulfate solution, saturated aqueous sodium hydrogencarbonate solution and saturated brine, dried over sodium sulfate, and concentrated to obtain 92 mg of (1R,5S)-7,7-ethylenedioxy-2-ethoxycarbonylbicyclo[3.3.0]octan-3-one. To the thus obtained (1R,5S)-7,7-ethylenedioxy-2-ethoxycarbonylbicyclo [3,3,0]octan-3-one were added 20 mg of sodium hydroxide and 0.9 ml of water-ethanol mixed solution (4:1), and the mixture was stirred at 90° C. for 4 hours. After cooling, the reaction mixture was neutralized with dilute hydrochloric acid and extracted with ether. The organic layer was then washed with saturated brine, dried over sodium sulfate, and concentrated to give 42 mg of the title compound.

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