Tunable reactivity of triphosgene-triethylamine: A study on the synthesis of pyrrole-based tricyclics

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.

Synthetic strategies and diversification of dibenzo[1,5]diazocines

Dibenzo[1,5]diazocine scaffolds are present in a wide range of organic building blocks, for example in pharmaceuticals, materials and structural chemistry. However, the development of these structural frameworks has not received significant attention owing to limited synthetic protocols and strategies. Herein, a summary of the attractive synthetic approaches for the construction of dibenzo[1,5]diazocines, epiminodibenzo[1,5]diazocines and epoxydibenzo[1,5]diazocines developed over the past two decades is presented. The spectroscopic, synthetic mechanisms for the formation of the heterocyclic rings and remarkable structural features, including in the solid-state, are discussed.

1-[2-(1H-Pyrrole-2-carbonyl)phenyl]-3-(4-methoxyphenyl)urea

For the synthesis of 1-(2-(1H-pyrrole-2-carbonyl)phenyl)-3-(4-methoxyphenyl)urea, the final product, two different methods were used, in one or two steps, from (2-aminophenyl)(1H-pyrrol-2-yl)methanone. The one-step synthesis entailed a carbonylation reaction with 1/3 equivalent of triphosgene in the presence of two equivalents of trimethylamine, followed by the addition of 4-methoxyaniline to the in situ generated aryl isocyanate. The two-step synthesis required first the preparation of phenyl(2-(1H-pyrrole-2-carbonyl)phenyl)carbamate and then a substitution reaction by 4-methoxyaniline. The first method produced the final product in 72% yield, which was the best yield. The structure of the final product was confirmed by FTIR, UV-VIS, 1H and 13C NMR spectroscopy and high resolution mass spectrometry.