Structural diversity in compound collections that are exposed to biological screenings determine the potential of any library to provide hit and lead structures in drug discovery process. While organic synthesis has focused only on a small percentage of chemical space as far as structural diversity in synthetic small molecules is concerned, a vast unknown chemical space remains untapped for its potential to deliver biologically interesting small molecules. To identify chemical probes and drug candidates therefore requires compound libraries rich in structural diversity which in turn is determined by the number of different chemotypes or scaffolds that a compound library represents. Consequently, synthetic designs aiming at divergent access1-3 to structurally distinct scaffolds and libraries are highly desired.

Branching cascades strategy1 transforms a common precursor into diverse scaffolds that are used for library synthesis. The substrates follow different cascade or domino reactions and each cascade sequence lead to a distinct scaffold decorated with functions that can be explored for library synthesis. Aminoxazoline scaffold represent an interesting class of molecules, known to exhibit biological activity. Here we present our endeavors to build two aminoxazoline compound libraries for the European lead factory (ELF) consortium by exploiting branching cascades approach. Thus, chromonylidene b-ketoesters A can be transformed into two distinct scaffolds i.e. pyridine and benzopyran B and C resp. Olefination of the ketones followed by iodine mediated aminoxazoline synthesis would yield two distinct scaffolds D and E ready for library synthesis by using the functional group decoration in them.