Intramolecular cyclization of amido-(thio) ureidoacetals in acidic and basic conditions

Abstract

The reactivity and selectivity of amide and (thio) urea groups toward the acetal groups in amido-(thio) ureidoacetals were competitively examined in acidic and basic conditions. The acid-catalyzed cyclization of amido-ureidoacetals afforded only imidazolinone derivatives. The corresponding cyclization of amido-thioureidoacetals afforded mostly 5-methoxyiminothiazolidine and small amount of pyrazinone and thiohydantoin derivatives. These product ratios were varied with acidity, which might be expected through the different reaction mechanism. Amido-(thio)ureidoacetals gave (thio)hydantoin derivatives in good yield in the presence of base by intramolecular amide-exchange reaction. The details of the proposed reaction mechanisms are discussed.