Unusual “replacement” of carbonyl containing functions at position 3 of coumarin by a cyano group

Abstract

The reaction of coumarins containing electron acceptor groups at position 3 (CN, CO2Et, COMe, COPh, etc.) with compounds containing active methylene groups, in particular cyanoacetamide and ethyl cyanoacetate, under Michael reaction conditions leads to the formation to 4-substituted derivatives of 3,4-dihydroxycoumarin [1]. Further reactions of these compounds gave tricyclic compounds containing an ~-pyrone ring [2] or substituted 3-(o-hydroxyphenyl)propionic acids [3].We have observed that the reaction of 3-acetyl(3-ethoxycarbonyl)coumarins Ia-b with cyanoacetylhydrazine and its Nacetyl-and N-propionyl-derivatives IIa-c under Michael conditions gave an unexpected result. The reaction product was 3cyanocoumarin (III), in yields of 32-63 % depending on the structure of the starting material.

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

“…IR spectrum, ν, cm −1 : 2720 (N-H); 1710, 1680-1650 (С=О, С=N). 1H NMR spectrum (DMSO-d 6 ), δ, ppm (J, Hz): 1.13 (3H, t, 3 J = 7.2, СН 3 СН 2 ); 3.56 (1 Н, d, 3 J 4,4' = 2.1, H-4'); 4.07 (2H, q, 3 J = 7.2, CH 3 CH 2 ); 4.71 (1H, d, 3 J 4,4' = 2.1, H-4); 6.60-7.00 (4H, m, CН arom. ), 10.36 (1H, s, OH enol); 11.40 (3H, bs, NH 2 + NH) (enolic form).…”

“…The respective adducts 5 (see the experimental section) and 6* 3 [1], in the 1 H NMR spectra of which the signals of the aromatic protons are represented by multiplets at 6.70-7.10 for 5 and 7.00-7.40 ppm for 6, were used as model compounds for the reaction products D and E.…”

“…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.…”