[C:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:11][C:10]([CH3:13])([CH3:12])[S:9][C:8]=2[CH:14]=1)([OH:3])=O.C(Cl)(=O)[C:16]([Cl:18])=O.Cl>CCOCC>[Cl:18][CH2:16][C:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:11][C:10]([CH3:13])([CH3:12])[S:9][C:8]=2[CH:14]=1)=[O:3]A mixture consisting of 10 g of 5-carboxy-2,2-dimethyl-1,3-benzoxathiole (IV), 10 g of oxalyl chloride and 20 ml of ether was boiled gently for 2 hours. The solution was cooled and evaporated and the residue (V) was added to an ether solution of diazomethane prepared from 25 g of N-nitroso-N-methyl urea. After stirring the mixture for 18 hours at room temperature the solution (VI) was acidified with methanolic hydrogen chloride and then evaporated to leave a solid residue which was recrystallized from ether/hexane to yield 6 g of 5-chloroacetyl-2,2-dimethyl-1,3-benzoxathiole (VII), m.p. 84°-86° C.
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