[OH-].[K+].[C:3]([O:9][CH2:10][CH3:11])(=[O:8])[CH2:4][C:5]([CH3:7])=[O:6].[CH2:12](Cl)/[CH:13]=[CH:14]/[CH2:15]Cl>[Cl-].C(C([NH3+])(C(=O)CCCCCCC)C(=O)CCCCCCC)(=O)CCCCCCC.S1(CCCC1)(=O)=O>[C:3]([C:4]1[CH2:15][CH:14]([CH:13]=[CH2:12])[O:6][C:5]=1[CH3:7])([O:9][CH2:10][CH3:11])=[O:8]4-Carbethoxy-5-methyl-2-vinyl-2,3-dihydrofuran was prepared using a phase transfer procedure similar to that of Example I. For the reaction, three grams tricaprylylmethylammonium chloride, 62 grams potassium hydroxide, and 100 mls sulfolane were charged to a reactor and a mixture of 65 grams ethyl acetoacetate and 95 grams 1,4-dichlorobutene-2 slowly added over a period of one hour while maintaining the temperature below 30° C. The mixture was then stirred for two hours at ambient temperature and then heated to 150° C. until the reaction was essentially complete. The reaction mixture was poured into ice-water, extracted with ether, and the ether evaporated using a rotary evaporator. The resulting product, which consisted of essentially a 1:1 mixture of 4-carbethoxy-5-methyl-2-vinyl-2,3-dihydrofuran and ethyl-1-acetyl-2-vinylcyclopropane-1-carboxylate, was distilled. Sixty grams of the 4-carbethoxy-5-methyl-2-vinyl-2,3-dihydrofuran obtained from the distillation was combined with 100 mls ethyl acetate and 0.4 grams supported hydrogenation catalyst (5% Pd on carbon) and hydrogenated in the usual manner. The catalyst was removed at the conclusion of the hydrogenation by filtration and ethyl acetate stripped under reduced pressure to obtain crude 4-carbethoxy-2-ethyl-5-methyl-2,3-dihydrofuran. Distillation of the crude product yielded essentially pure 4-carbethoxy-2-ethyl-5-methyl-2,3-dihydrofuran with chemical and physical properties and fragrance characteristics the same as described for the product of Example IX.
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