[CH3:1][CH:2](C(O)=O)C(O)=O.O1C=CCCC1.S(=O)(=O)(O)O.[OH-].[Na+].[N:22]1[O:23][C:24]([C:31]([OH:33])=O)=[C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][C:26]=12.S(Cl)(Cl)=O>C1C=CC=CC=1.O.C(O)(=O)C>[C:31]([C:24]1[O:23][N:22]=[C:26]2[CH:27]=[CH:28][CH:29]=[CH:30][C:25]=12)(=[O:33])[CH2:1][CH3:2]Added to 75 ml of dry benzene were 5.3 g (45 mmol) of methylmalonic acid and 11.4 g (0.135 mmol) of 3,4-dihydropyran, followed by the addition of 1 droplet of concentrated sulfuric acid under stirring over a water bath. After one hour, 6 g of sodium hydroxide were added. After the resultant mixture was stirred for 5 minutes, an insoluble material was filtered off. Then, 1.8 g of 60% sodium hydride was added in small portions to the filtrate. After evolution of hydrogen gas subsided, a solution of the acid chloride, which had been prepared from 6.5 g (0.04 mol) of 2,1-benzisoxazole-3-carboxylic acid prepared above in the procedure (1) and 30 ml of thionyl chloride in benzene, was added dropwise under ice cooling. After the resultant solution was stirred for 2 hours at room temperature, 6 ml of acetic acid were added, followed by heating under reflux for 8 hours. After ice cooling, water was added and the reaction product was extracted with ethyl acetate. The extract was purified by silica gel chromatography (eluent: 30:1 n-hexane/ethyl acetate), so that 3-propionyl-2,1-benzisoxazole was obtained as colorless crystals. Analytical results of the crystals obtained: Yield: 5.6 g (80%). Melting point: 51°-53° C.
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