Previously unknown 3-nitro-5-hydroxybenzofuran derivatives were obtained by condensation of pbenzoquinones with nitro enamines.
Information regarding the synthesis and biological activity of 2-nitro-5-hydroxybenzofurans has been presented extensively in the literature (for example, see [2][3][4][5]). At the same time, the information on 3-nitro-5-hydroxybenzofurans is limited to a small number of publications [6--8]. The direct nitration of 5-hydroxybenzofuran derivatives in the 3 position is possible under the condition of protection of the hydroxy group and the presence of a substituent (At) in the 2 position [6,7]. 3-Nitro-5-hydroxybenzofurans that have electron-donor substituents (SR and NHR groups) in the 2 position were obtained by the method in [8].
We have developed a new method for the synthesis of previously unknown 3-nitro-5-hydroxybenzofurans IIIa-f, which do not have substituents in the 2 position or have a 2-methyl group.
The method is based on the condensation of p-benzoquinone derivatives II with nitro enamines Ia,b under the conditions of the Nenitzescu reaction and generally ensures stable and satisfactory yields of the desired 3-nitrobenzofurans IIIa-f (Table 1).