Post-condensational modifications of the Groebke‐Blackburn‐Bienaymé reaction products for scaffold-oriented synthesis

Synthesis of Triazolo[4',5':4,5]furo[2,3-c]pyridine via Post Modification of an Unusual Groebke-Blackburn-Bienaymé Multicomponent Reaction

The Groebke-Blackburn-Bienaymé (GBB) reaction is a well-established three-component reaction for synthesizing imidazofused scaffolds from heterocyclic amidines, aldehydes, and isonitriles. However, the replacement of pyridoxal as an aldehyde component in this reaction results in the formation of the furo[2,3-c]pyridine skeleton as an "unusual GBB product". Despite the interesting nature of this unusual reaction, not much work was further reported. The present research investigates the optimization strategy for the synthesis of novel tricyclic triazolo[4',5':4,5]furo[2,3-c]pyridines via diazotization of 2,3-diamino-furo[2,3-c]pyridines specifically synthesized utilizing the chemistry of tert-alkyl isocyanide.

Transition-metal-free intramolecular double hydrofunctionalization of alkyne to access 6/7/5-fused heterocyclic skeletons

We describe a novel intramolecular double hydrofunctionalization cyclization of alkyne with nitrogen and oxygen nucleophilic groups to construct valuable 6/7/5-fused heterocyclic products. This post-Groebke-Blackburn-Bienaymé (GBB) reaction introduces a new class of functionalized isocyanides. Transition-metal-free cyclization, broad substrate scope, and high atom economy were some features of the present protocol.

Synthesis of Imidazo[1,2-a]pyridine-Fused 1,3-Benzodiazepine Derivatives with Anticancer Activity via a One-Pot Cascade GBB-3CR/Pd(II)-Catalyzed Azide-Isocyanide Coupling/Cyclization Process

A new one-pot synthesis of imidazo[1,2-a]pyridine-fused 1,3-benzodiazepine derivatives via a sequential GBB-3CR/Pd(II)-catalyzed azide-isocyanide coupling/cyclization process was developed. The Groebke-Blackburn-Bienaymé three-component reactions (GBB-3CR) of 2-aminopyridine, 2-azidobenzaldehydes, and isocyanides in the presence of a catalytic amount of p-toluenesulfonic acid gave azide intermediates without separation. The reaction was followed by using another molecule of isocyanides to produce imidazo[1,2-a]pyridine-fused 1,3-benzodiazepine derivatives in good yields by the Pd(II)-catalyzed azide-isocyanide coupling/cyclization reaction. The synthetic approach produces novel nitrogen-fused polycyclic heterocycles under mild reaction conditions. The preliminary biological evaluation demonstrated that compound 6a inhibited glioma cells efficiently, suggesting potentially broad applications of the approach for synthesis and medicinal chemistry.