Transformations of coumarins accompanied by intermediate opening and recyclization of the lactone ring 3.* Study of the reactions of 3-ethoxy-carbonylcoumarins with cyanoacetyl-hydrazines by NMR spectroscopy

Abstract

The reaction of 3-ethoxycarbonylcoumarin with derivatives of cyanoacetylhydrazine directly in the sample tube of the NMR spectrometer was investigated by 1 H NMR spectroscopy. The structure of the components of the reaction mixtures was established, and their relative concentrations at the various stages of the reaction were estimated. The sequence of processes occurring in the reactions was analyzed. Both the general characteristics and the differences in the course of the reaction with cyanoacetylhydrazine or its N-isopropylidene derivative as second component were established.In a continuation of earlier researches in which the reaction of 3-ethoxycarbonylcoumarin 1 with cyanoacetylhydrazines 2 was studied by mass spectrometry [2, 3] we have investigated the reaction by 1 H NMR spectroscopy directly in the tube used to record the spectra. As second component of the reaction we used both cyanoacetylhydrazine 2a itself and its isopropylidene derivative 2b. The reaction was conducted in 1 ml of methanol-d 4 with the components 1 + 2a and 1 + 2b in an equimolar ratio.