Alkylidenemalonic acid

Under various reaction conditions, dialkylsulfur diimides 1 react with alkylidenemalonic acid derivatives 2 to furnish the 1 /4,2,6-thiadiazines 3a-k or 5a, b.2s The cleavage of the substituent R2 from the 126,2,6-thiadiazines of type 4 required for the preparation of3a-k or 5a, b is only successful when R2 is a benzyl group. This debenzylation is catalyzed by acids. 

Melhod A The sulfur diimide 1 (5 mmol) and the alkylidenemalonic acid derivative 2 (5 mmol) were finely ground together and warmed to 60 °C for 4-48 h. The products were isolated and purified by column chromatography (silica gel, CHCl3/EtOAc 1 1) and subsequent recrystallization from MeCN/Et20. Method B Compound 4 (3 mmol) in EtOH (50 mL) was heated under reflux in the presence of /j-toluene-sulfonic acid (20 mg) for 72 h. The product was filtered under suction and dried in vacuo. 

Cyclic alkylidenemalonic acid esters from aldehydes... 

Alkylidenemalonic acid esters s. a,3-Ethylene-a-dicarboxylic acid esters... 

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