Methyl chloroformate → N-(Methoxycarbonyl)maleimide

To a 1000 ml 3-neck round bottom flask was added 400 ml of ethyl acetate. The flask was placed in an ice bath and the temperature was allowed to drop to about 0° C. To the cooled flask was sequentially added with stirring 7.76 g of maleimide and 8.8 ml of N-methylmorpholine. Then, through an addition funnel was added to the stirring mixture 6.26 ml of methyl chloroformate at a rate so as not to raise the temperature above 3° C. Through the addition funnel was then added 5 ml of ethyl acetate as washing and the washing was added to the reaction mixture. The reaction mixture was stirred for 30 minutes at between 0°-3° C. Thereafter, the reaction mixture was filtered through a Buchner funnel. The flask was washed 2× with 10 ml of ethyl acetate and the washings were also filtered. The resulting precipitate was washed 2× with 10 ml of ethyl acetate. The combined filtrate and washings were extracted with 100 ml of ice cold water, dried (10 g Na2SO4), and evaporated to dryness under reduced pressure. The residue was redissolved in 50-100 ml of ethyl acetate:isopropyl ether (40:60 /v:v) using a water bath at 60° C. The resulting solution was filtered, cooled until crystals appeared. After 30 minutes in an ice bath, the cooled solution and crystals were filtered through a sintered glass funnel and the crystals washed 2× with 20 ml of isopropyl ether. The crystals were vacuum dried overnight, M.P. 61°-63° C.