Solid-phase syntheses of 1,2,4-trisubstituted urazole and thiourazole derivatives

Solid-phase syntheses of 1,2,4-trisubstituted urazole and thiourazole derivatives have been accomplished. The synthesis began with the coupling of carbonylimidazole-Wang resin with a disubstituted hydrazine. The resultant carbazate was coupled with an isocyanate or isothiocyanate. Subsequent heating of the resin in the presence of triethylamine or potassium t-butoxide induced cyclization and released the desired (thio)urazole into solution. Most of the products were obtained in high yields and purities. Structural diversity can be further expanded at the R-2 substituent by performing the palladium-mediated Suzuki coupling reaction.