1,1 -dichloro-2,6-dimethyl-3,5-dioxo-4-

Wen found that A-sulfamoyloxamic acid (12), a by-product formed during the permanganate oxidation of 2,1,3-benzothiadiazole (Section II,A,1), can be converted into 3,4-dichloro-l,2,5-thiadiazole-1,1-dioxide (53) by reaction with phosphorus pentachloride. Other thiadiazole-1,1-dioxides that were derived from 12 by methylation of its disilver salt include 2-methyl-3-oxo-4-methoxy-l,2,5-thiadia-zoline-1,1-dioxide (54) and 2,5-dimethyl-3,4-dioxo-l,2,5-thiadia-zolidine-1,1-dioxide (55). 

Dichloro-2,6-dimethyl-3,5-dioxo-4-ethyl- E12b, 536 (R-CH2-CO-A-CO-CH2-R + TeCl4)... 

The following alkoxypyrazines have been prepared from the corresponding dichloropyrazines and alkoxide ions 2,3-dimethoxy-5,6-dimethyl(and diphenyl) (797) 2,3-dibenzyloxy (sodium benzyl oxide in benzyl alcohol at reflux for 24 hours (883)] [but 23-dichloropyrazine with sodium hydride and benzyl alcohol in xylene gave l,4-dibenzyl-2,3-dioxo-l,2,3,4-tetrahydropyrazine)(988)] 2-chloro-5-methoxy (838) 2,5-diethoxy-3,6-dimethyl (872) 2methanolic sodium methoxide refluxed for 2 h) 2,5-dimethoxy-3-phenyl (817) 2-chloro-5-methoxy(and ethoxy)-3,6-diphenyl (817) 2,5-dimethoxy-3,6-dimethyl (and diisopropyl) (844) 2,5-dimethoxy-3-isopropyl-6-methyl (methanolic potassium methoxide at reflux for 6 days) (844) 2(5)-s-butyl-3-chloro-6-ethoxy-5(2)-isobutyl (93) 2-chloro-6-methoxy (838, 883) 2,6-dimethoxy (reflux for 8h) (832) 2,6-diethoxy (reflux for 14 h) (883) 2-benzyloxy-6-chloro (1 equiv. of sodium hydride and benzyl alcohol in benzene at reflux) (832) 2,6-dibenzyloxy (5 equiv. of sodium benzyloxide in benzene at reflux gave 70%) (832) and 3,5-dimethoxy-2-methyl (535). 

King Jr reported a facile synthesis of chlorinated dioxo-lanones by a simple, one-pot, direct addition of phosgene to 1,2-diones (Ref. 225). Thus, the reaction of 2,3-butane dione with phosgene in the presence of pyridine affords trans-4,5-dichloro-4,5-dimethyl-1,3-dioxolane-2-one in 82% yield as shown in scheme 172. 

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