NMR Studies on Imidines. III.1H and 13C Nuclear Magnetic Resonance Study on the Tautomerism and Geometrical Isomerism of 3‐Iminoisoindolinone and Some Alkylated Derivatives. Observation of E and Z Isomers About a Free Imino Grouping

Abstract

Abstract3‐Iminoisoindolinone (1) and some N‐alkyl derivatives (8, 9, 10, 11, 12, 16 and 17) have been fully examined by 1H and 13C NMR spectroscopy. 3‐(Methylimino) isoindolinone (12) cannot be obtained by reaction of 1 with methylamine, because it rearranges to 3‐imino‐2‐methylisoindolinone (11), which reacts further to 2‐methyl‐3‐(methylimino) isoindolinone (10). Both compounds have been shown to adopt the E configuration predominantly (88% E for 11 at‐55°C (CDCl3); 100% for 10). 3‐(Methylimino) isoindolinone (12) favours the Z configuration (96%).Analogous results are found for the butyl derivatives (16, 17). 3‐Imino isoindolinone (1) is present as the imino tautomer for 70% in DMSO‐d6 solution as established by comparison of 13C NMR chemical shift values of 1 with those of model compounds, 3‐imino‐2‐methyl isoindolinone (11) and 3‐(dimethylamino) isoindoleninone (8). The tautomeric equilibrium is more extreme towards the imino form for the N‐methyl and N‐butyl derivatives 12 and 16. 2, 3, 4, 5‐tetrahydroisoindolino [2,1‐a] pyrimidin‐6‐one served as the imino model compound together with 10. 1H and 13C NMR data are given for several phthalic acid derivatives.