Gm. Coppola et Re. Damon, ACETYLENIC AMIDES .3. THE SYNTHESIS OF 5-METHYLENE-2,4-IMIDAZOLIDINEDIONES FROM 2-PROPYNAMIDES AND ISOCYANATES, Journal of heterocyclic chemistry, 32(4), 1995, pp. 1141-1144
2-Propynamides react with aryl isocyanates in the presence of triethyl
amine to give 5-methylene-2,4-imidazolidinediones 5 in good yields. If
the propynamide contains a terminal trimethylsilyl group, Z-trimethyl
silylidenehydantoin (7) is produced.