[2+2] Cycloadditions of Electron‐Poor Acetylenes to (5 Z )‐5‐[(Dimethylamino)methylene]imidazolidine‐2,4‐diones

Microwave‐assisted [2+2] cycloadditions of acetylene mono‐ and acetylenedicarboxylates 2 to (5 Z )‐5‐[(dimethylamino)methylene]imidazolidine‐2,4‐dione 4a or to the corresponding thioxo derivative 4b in MeCN furnished the highly functionalized imidazolidine‐2,4‐dione derivatives 5 and 6 or the corresponding thioxo derivatives 5 – 7 as single isomers or mixtures of two isomers ( Schemes 2 and 3, Table 1 ). When the reaction of (5 Z )‐5‐[(dimethylamino)methylene]imidazolidine‐2,4‐dione ( 4c ) with acetylenedicarboxylate 2a was performed in DMF, hydrolysis of the (dimethylamino)methylene group took place to give (2 E )‐2‐(2,5‐dioxoimidazolidin‐4‐ylidene)butanedioate 11 ( Scheme 5 ).