3-Substituted-quinazolin-4(3H)-ones are prominent structures in the fields of medicinal and natural product chemistry.
2)Their related analogues are, therefore, attractive for potential pharmaceutical applications.In our previous paper, 1,3) we described that fused 3-(2-bromoethyl)pyrimidin-4(3H)-ones (1) can react with primary alkylamines to afford abnormal rearranged products (fused 3-alkyl-4-alkyliminopyrimidines (2)) in addition to substituted 3-(2-alkylaminoethyl) derivatives (Fig. 1). The abnormal rearranged products seemed to be as a result of a new type of Dimroth rearrangement. We also showed that one of the rearranged products had considerable antidepressant activity, comparable to that of imipramine.In 2000, W. Szczepankiewicz and J. Suwinski reported the one-pot reaction of 2-aminobenzonitrile and formic acid to form 3-(2-cyanophenyl)quinazolin-4(3H)-one (3), instead of quinazolin-4(3H)-one, which was the anticipated product.
4)We, therefore, wondered if a Dimroth-type rearrangement with primary alkylamines could be applied to substrate 3 to afford 3-alkyl-4-alkyliminoquinazolines. Another possibility was that an addition of the nucleophile, ring opening, and ring closure (ANRORC) reaction could occur to give 3-alkylquinazolin-4(3H)-ones (4). There have already been shown that N 1 -(2,4-dinitrophenyl (or 4-nitrophenyl))inosines with primary alkylamines afford N 1 -alkyl inosines via an ANRORC mechanism.5-9) Here we have described the reaction of 3 with primary alkylamines in detail.First, we tested the reaction of 3 with methylamine in N,N-dimethylformamide (DMF) at room temperature. The product 4a in 56% yield was obtained with 2-aminobenzonitrile as a side product, as confirmed by TLC (Chart 1). In the 1 H-NMR spectrum of 4a, one methyl group appeared at 3.61 ppm, one proton singlet of the pyrimidine ring appeared at 8.06 ppm, and four aromatic region signals of the 2-cyanophenyl moiety of 3 disappeared. In the IR spectrum of 4a, the appearance of a lactam carbonyl band at 1670 cm Ϫ1 and disappearance of the nitrile band were observed. These results suggested that an ANRORC reaction had occurred in the reaction of 3 with methylamine. Similar results were seen when ethylamine was used to give the product 4b in 52% yield.In addition, a reaction between 3 and n-propylamine did not proceed at room temperature, as shown by TLC analysis. Contrary to the reactions with methylamine or ethylamine, which were added as methanol or aqueous solutions, respectively, n-propylamine was used as a neat in DMF solution; we therefore assumed that a protic solvent was necessary to allow this ANRORC reaction. Addition of methanol as a cosolvent with DMF was tested to give the desired product 4c in 51% yield. We also tested combining 3 with tert-butylamine in the presence of methanol in DMF; however, no reaction occurred. Perhaps, steric hindrance of the tert-butyl group prohibited nucleophilic attack of amino functionality to 3. Furthermore, the reaction of 3 with dimethylamine did not proceed at all. We theorized that ...