Iodoethane → ethyl 3,4-dihydro-2H-pyran-2-carboxylate

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Reaction Steps

The synthesis of 2,5-dioxabicyclo[2.2.2]octan-3 one was achieved through a three step reaction sequence as illustrated below: ##STR3## Sodium 3,4-dihydro-2H-Pyran-2-carboxylate was esterified with ethyl iodide in dimethylformamide to afford ethyl 3,4-dihydro-2H-pyran-2-carboxylate. Subsequent hydroboration with a borane solution in tetrahydropyran at 0° C., followed by oxidation with a sodium dichromate-sulfuric acid aqueous solution and subsequent treatment with sodium hydrogen sulfite gave ethyl 5-hydroxytetrahydropyran-2-carboxylate as a stereoisomer mixture. The hydroxytetrahydropyran ester was heated in a dilute solution in the presence of a catalytic amount of p-toluenesulfonic acid, any ethyl alcohol being liberated was removed through a Soxhlet extractor containing type 5A molecular sieves. Column chromatographic separation of the reaction products and subsequent repeated recrystallization gave the bicyclic lactone as colorless crystals; the overall yield was approximately 20%.

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