C[O-].[Na+].[CH3:4][C:5](=[CH2:9])[C:6](=[O:8])[CH3:7].[CH3:10][O:11][CH:12]([C:17]([O:19]C)=O)[C:13]([O:15][CH3:16])=[O:14].Cl>CS(C)=O>[OH:19][C:17]1[C:12]([O:11][CH3:10])([C:13]([O:15][CH3:16])=[O:14])[CH2:4][CH:5]([CH3:9])[C:6](=[O:8])[CH:7]=1A 30% solution of 35.8 g of sodium methoxide is introduced into 65 ml of dimethyl sulfoxide and, within 20 minutes, treated with a mixture of 16.7 g of 3-methyl-3-butene-2-one and 32.4 g of dimethyl methoxymalonate at a temperature of 30-35° C. The mixture is stirred for 1 hour at a temperature of 35° C., and is then acidified with hydrochloric acid and extracted repeatedly with dichloromethane. The organic phases are washed with water, dried and concentrated. Crystallization from hot ethyl acetate and hexane gives pure methyl 2-hydroxy-1-methoxy-5-methyl-4-oxocyclohex-2-enecarboxylate of melting point 117-117.5° C.
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