Cu-Catalyzed Decarboxylative Annulation of N -Phenylglycines with Maleimides: Synthesis of 1 H -Pyrrolo[3,4- c ]quinoline-1,3(2 H )-diones.

A novel protocol for the construction of functionalized 1 H -pyrrolo[3,4- c ]quinoline-1,3(2 H )-diones (PQLs, 3 ) from N -phenylglycines and maleimides was developed. The cascade reaction was enabled by heating a mixture of the two substrates in the presence of di- tert -butyl peroxide (DTBP) as an oxidant and anhydrous CuBr as a catalyst in chlorobenzene. Consequently, a diverse series of PQLs 3 were synthesized in moderate-to-good yields (43-73%). The synthesis of the PQLs was enabled via a one-pot cascade reaction that proceeded through subsequent oxidative decarboxylation, 1,2-addition, intramolecular cyclization, tautomerization, and aromatization reactions. This protocol can be used for the synthesis of functionalized PQLs via a one-pot oxidative decarboxylation annulation reaction rather than through a series of multistep reactions, making it suitable for both combinatorial and parallel syntheses of PQLs.