Synthesis of pyrrolo[1,2-a][1,6]benzodiazonines from pyrrolo[1,2-a][1,4]benzodiazepines and alkynes containing electron-acceptor substituents

An Update on the Synthesis of Pyrrolo[1,4]benzodiazepines

“…The parent PBD 6a required heating the amine with ethyl formate to give formamide 234c and then cyclisation with phosphoryl chloride at 40 °C while PBD 6c was prepared by coupling the amine with protected glycine 235 in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC.HCl) to produce amide 234c and then cyclisation using similar reaction conditions. In two recent publications Voskressensky et al [85,86] used the same methodology to synthesise novel PBDs 6b , d – g from amine 218a via cyclisation of amides 234b , d – g . The yields of the Bischler–Napieralski cyclisation step are noted to be from 74% with up to quantitative yield.…”

Bischler‐Napieralski Cyclization: A Versatile Reaction towards Functional Aza‐PAHs and Their Conjugated Polymers†

“…[ 8‐9 ] For example, various benzodiazepines derivatives were obtained, such as pyrrolobenzo[ b ]thieno[1,4]diazepines, [ 10 ] tricyclic pyrimido[4,5‐ b ][1,4]benzothiazepines, [ 11 ] 5 H ‐[1]benzofuro[2,3‐ d ][1,2]diazepines, [ 12 ] 11 H ‐pyrimido[4,5‐ b ][1,4]benzodiazepines [ 13 ] and pyrrolo[1,2‐ a ][1,6]benzodiazonines. [ 14 ] Despite the high efficiency in C=N bond formation within aromatic rings via Bischler‐Napieralski cyclization, its utility in synthesizing aza‐PAHs was not recognized until 2010. Since then, researchers including our group have successfully expanded the scope of Bischler‐ Napieralski cyclization into PAHs chemistry.…”