The Identification of a Novel Highly Condensed Pentacyclic Heteroaromatic Ring System 1,3,5,5b,6,8,10,10b‐Octaazacyclopenta[h,i]Aceanthrylene and its Application in the Synthesis of 5,7‐Substituted Pyrazolo[4,3‐d]Pyrimidines

Pyrazolo[4,3-d]pyrimidines are of interest as potential kinase inhibitors. This article describes the formation of a novel highly conjugated, condensed, centrosymmetric heteroaromatic compound, 4,9-dichloro-2,7-diisopropyl-1,3,5,5b,6,8,10,10b-octaazacyclopenta[h,i]aceanthrylene (3), during the chlorination of 5,7-dihydroxypyrazolo[4,3-d]pyrimidine (1) with phenylphosphonic dichloride. The nucleophilic attack of benzylamine on 3 afforded N-benzyl-5-chloro-3-isopropyl-1H-pyrazolo[4,3-d]pyrimidin-7-amine (6), which was further substituted to yield a pyrazolo[4,3-d]pyrimidine analogue of roscovitine, a well-known cyclin-dependent kinase inhibitor.