Pd(II)-Catalyzed Csp2–H Carbonylative Amidation of Groebke–Blackburn–Bienaymé Reaction Products: Access to Imidazo[1,2-a]pyridine-Fused δ-Lactams

The Groebke–Blackburn–Bienaymé (GBB) reaction provides efficient access to imidazole-fused heterocycles, yet it is inevitably endowed with an isocyanide-derived secondary amino group in products. Herein, we report a Pd(II)-catalyzed sp2 C–H carbonylative amidation strategy using Co2(CO)8 as a safe CO surrogate. Leveraging the native aryl amino group as a directing motif, this protocol enables direct conversion of GBB adducts into pharmaceutically relevant imidazo[1,2-a]pyridine-fused δ-lactams with up to 86% yield. The method demonstrates exceptional functional group tolerance and eliminates prefunctionalization requirements, offering a streamlined approach to access complex nitrogen-rich architectures.