“…However, one efficient, versatile, and robust method to construct this polyheterocyclic core is through a one-pot cascade sequence Ugi–3CR/ aza Diels–Alder cycloaddition/ N –acylation/decarboxylation/dehydration, reported first by Zhu and co-workers [27], and further optimized by us many times [22,23,28,29,30,31,32,33,34]. Thus, for the in vitro assays against SiHa, HeLa, and CaSki cell lines, we synthesized some of our previously reported pyrrolo[3,4- b ]pyridin-5-ones 1a – j [22,32], and the new ones 1k – l , specifically prepared for the present study (Figure 1). Thus, 4-chlorobenzaldehyde ( 2a ) or benzaldehyde ( 2b ) were combined sequentially with the 3-morpholinopropan-1-amine ( 3 ), the corresponding isocyanides 4a – b , and maleic anhydride ( 5 ) via the strategy mentioned before, using benzene as solvent, scandium (III) triflate as Lewis-acid catalyst, and microwaves (MW) as heat source to afford the polyheterocycles 1k – l in 46% ( 1k ) and 45% ( 1l ) yields, respectively, which are excellent considering the molecular complexity of the products, and that only one experimental procedure was needed in their synthesis (Scheme 1).…”