Pyrimidines as Surrogates for 1,3‐Dicarbonyl Compounds in peri Annulation of Perimidines en Route to 1,3‐Diazapyrenes

Abstract

A highly efficient protocol for acid‐mediated peri annulation of perimidines with pyrimidines has been developed. Pyrimidines, used as surrogates for 1,3‐dicarbonyl compounds, furnish benzo[gh]perimidines, which includes hardly available analogues, non‐substituted, or mono‐substituted at C‐6, C‐8. Limitations of reactions that use 5‐bromopyrimidines are investigated.

Synthesis of 7‐Bromo‐1,3‐diazapyrenes

“…Heating of the mixtures in 86 % polyphosphoric acid (PPA) gave rise to pentacyclic 7 H ‐imidazo[4′,5′:4,5]benzo[1,2,3‐ gh ]perimidine ( 9 ) along with small amounts of 1,3‐diazapyrene ( 3 ) resulting from unexpected loss of the halogen atom (Scheme ) . Analogous result was obtained when 8 was subjected to acidic catalysis at very high temperature (180 °C in 70 % aqueous H 2 SO 4 ), suggesting dihydropyrimidine 8 serves as a common intermediate in these unusual ANRORC process.…”

“…Concentrated sulfuric acid produced sulfonation product 7 only (Scheme ). The S E Ar reaction at C‐4 position of bromopyrimidine 5 took place at room temperature in methanesulfonic acid, leading to alkylation product 8 ; however, no peri ‐annulation was observed under these conditions (Scheme ) …”

“…Analogous result was obtained when 8 was subjected to acidic catalysis at very high temperature (180 °C in 70 % aqueous H 2 SO 4 ), suggesting dihydropyrimidine 8 serves as a common intermediate in these unusual ANRORC process. While acquiring analytical data for 7‐(5‐bromo‐3,4‐dihydropyrimidin‐4‐yl)‐1 H ‐perimidines 8 , we noticed that all these materials were decomposing upon heating in solid state before reaching melting point. Mass‐spectral analysis of the melts revealed that all these materials experienced loss of CH 4 N 2 moiety while retaining bromine atom.…”

“…Preparation of starting materials, 7‐(5‐bromo‐3,4‐dihydropyrimidyl‐4)‐1 H ‐perimidines 8a – h was detailed in our previous report . Synthesis of compounds 8i – o was performed according to the same procedures, and their yields and properties are listed below.…”

“…Typically, 6,8‐disubstituted 1,3‐diazapyrenes are readily available via acid‐catalyzed peri ‐annulation of perimidines 1 with 1,3‐diketones 2 (Scheme ) . We have also recently disclosed a related process employing pyrimidines 4 as synthetic equivalents of 1,3‐dicarbonyl compounds . It was shown that unsubstituted pyrimidine 4 (R 2 , R 3 = H) can also be successfully employed as surrogates of 1,3‐dialdehydes, which are unstable under acidic conditions.…”