Formation and thermal transformations of extended dipolar imidoylazimines

Abstract

Benzocinnoline N-arylbenzimidoylimides (1; R = Ar) are readily obtained from benzocinnoline N-imide and imidoyl chlorides and on heating undergo 1,5-dipolar cyclisation and retro dipolar cycloaddition to give benzocinnoline N-arylimides. In contrast the N-alkyl analogues (1; R = Me, Et) are much less stable and undergo 1,6-H shift leading ultimately to 1-(2′-aminobiphenyl-2-yl)-3-phenyl-1,2,4-triazoles. Attempts to prepare the isopropylimide (1; R = Prⁱ) lead to 4,4-dimethyl-2,6-diphenyldihydro-s-triazine. Benzocinnoline N-benzimidoylimide (1; R = H) is obtained from benzocinnoline N-imide and the methiodide salt of thiobenzamide and is converted into the 1,7-dipolar systems (1; R = COR′, PhCNPrⁱ, or PhCNPh). On heating, the acyl derivatives give benzocinnoline and oxadiazoles, the isopropylimide gives benzocinnoline and 4-isopropylaminoquinazoline, and the N-phenylimide gives benzocinnoline and 1,3,5-triphenyl-1,2,4-triazole and, unexpectedly, diphenylquinazoline, possibly via a 1,3,5-benzotriazepine.