Study on the cycloaddition reactions of pyrrolotriazepine derivatives with nitrile oxides. Synthesis of new fused tricyclic ring systems

Abstract

Representatives of new tricyclic ring systems based upon the pyrrolotriazepine core, have been synthesized at our laboratory using cycloaddition reactions of 1-aryl-pyrrolotriazepinones or 1,4-diarylpyrrolotriazepines in a dichloromethane solution at room temperature, with nitrile oxides generated in situ from N-hydroxyarylcarboximidoyl chlorides with triethylamine. The reaction between 1-aryl-3H-pyrrolo[2,1-d][1,2,5]triazepin-4(5H)-ones and the corresponding nitrile oxides led to 3,11b-diaryl-5H,11bH-[1,2,4]oxadiazolo[4,5-b]pyrrolo[2,1-d][1,2,5]triazepin-6(7H)-one derivatives. Cycloaddition reactions of 1,4-diaryl-5H-pyrrolo[2,1-d][1,2,5]triazepines under similar conditions gave two products, depending on which double bond was involved in the cycloaddition: 3,6,11b-triaryl-7H,11bH-[1,2,4]oxadiazolo[4,5-b]pyrrolo[2,1-d][1,2,5]triazepines and 3,6,11a-triaryl-11,11a-dihydro[1,2,4]oxadiazolo[4,5-b]pyrrolo[1,2-e][1,2,5]triazepines. The structures of the new compounds were also justified by 2D NMR and single-crystal X-ray measurements.