Highly selective synthesis of tricyclic compounds from semithioglycoluril, formaldehyde and amines

A highly selective one-pot synthesis of new 6-substituted 4-thioxohexahydro-5H-2,3,4a,6,7a-pentaazacyclopenta[cd]inden-1(2H)-ones by cycloaminomethylation of semithioglycolurile with formaldehyde and amines is proposed. A mechanism for the process is suggested.