Powerful Approach to Heterocyclic Skeletal Diversity by Sequential Three-Component Reaction of Amines, Isothiocyanates, and 1,2-Diaza-1,3-dienes

By highly efficient, one-pot, three-component reactions,
combining
one set of 1,2-diaza-1,3-dienes (DDs), primary amines, and isothiocyanates
in a different sequential order of addition, heterocyclic skeletal
diversity can be achieved. The key feature discriminating the different
heterocyclic core formation is the availability of the N or S heteronucleophile to give the first Michael
addition step affording regioselective substituted 2-thiohydantoins
or 2-iminothiazolidinones. The hydrazone or enehydrazino side chain
at the 5-position of both heterocycles represents a valuable functionality
to reach novel 5-hydroxyethylidene derivatives difficult to obtain
by other methods.