Synthesis of ethyl ortho-substituted benzoylacetates and investigation of the influence of ortho-substituents on keto-enol tautomerism and MS fragmentation behaviour

A series of seven ethyl 2-acetyl-(2-substituted benzoyl)acetates II-VIII was synthesized, together with their parent compound I, from the corresponding acid chlorides. The tautomerism of these β-tricarbonyl compounds in tetrachloromethane was studied by 1H NMR spectroscopy and former results concerning this problem were critically evaluated. A further series of seven ortho-substituted ethyl benzoylacetates X-XV and XVII was obtained from the corresponding precursors II-VIII. The keto-enol tautomerism of these β-keto esters was studied by 1H NMR in different solvents and compared with ethyl benzoylacetate IX as standard. Differences caused by the ortho-substituents are discussed. Investigation of the mass spectrometric fragmentation of the β-keto esters IX-XV and XVII showed both common fragmentation pathways due to the same substance class and typical differences in relative intensities according to the nature of the ortho-substituent.