Synthesis, characterisation and crystal structure of 1,2-bis(6-methylpyridin-2-yl)ethene-1,2-diol

Abstract

From the benzoin condensation of pyridine-2-carbaldehyde Buehler et al. 1 reported that instead of the expected benzoin (2-hydroxy[1,2-di(pyridin-2-yl)]ethane-1-one), 1,2-di(pyridin-2-yl)ethene-1,2-diol was produced. The authors proposed that chelation (one type of hydrogen bond) is an important factor in increasing the stability of the three enediols studied, (Fig. 1). They observed a decreasing order of stability asFurthermore, the benzoin condensation of quinoline-2carbaldehyde in the presence of KCN and pyridine also does not give the expected benzoin product, 2 but instead the stable 1,2-di(quinolin-2-yl)ethane-1,2-diol (a) and its reduction product 1,2-di(quinolin-2-yl)ethene-1,2-diol (b) were obtained, (Fig. 2). Compound (a) was assigned the trans-chelated structure from its physical and chemical properties, and its stability was attributed to conjugation and steric hindrance. Additional support for the chelated structure (two intramolecular hydrogen bonds between N•••H-O) was deduced by IR spectroscopy because the absorption band for the hydroxyl group was missing.Another similar study was made by Buehler et al. 3 where they showed that 6-methylquinoline-2-carbaldehyde gave 1,2-bis (6-methylquinoline-2-yl)ethene-1,2-diol, 1,2-bis(-(6-methylquinoline-2-yl)ethane-1,2-diol and 6-methylquinoline-2-carboxylic acid. The enediol was also assigned a trans-chelated structure. In order to study the influence of chelation on the stability of enediols Buehler et al. 4 during the benzoin condensation of quinolin-2-aldehyde N-oxide found that the oxygen atom did not prevent the formation of 1,2-di(quinolin-2-yl)ethane-1,2-diol N,N'-dioxide. The probable structures proposed for the enediols are trans-configurations which may be written as shown in (Fig. 3). Buehler 5 has suggested that for the stability of hindered enediols two factors are responsible: (1) the system is highly conjugated, the two rings being in conjugation through the double bond of the enediol group and (2) the substituents in the ortho positions are of sufficient size to interfere with the normal reactivity of the hydroxyl groups.In recent studies to obtain styrylpyridines, [6][7][8] it was found that the condensation reaction of 2-methylpyridine with

Synthesis, Characterisation and Crystal Structure of a Co-crystal of Two Components: 1,2-bis(6-methylpyridin-2-yl)ethane-1,2-dione and 1-(pyridin-2-yl)-2-(6-methylpyridin-2-yl)ethane-1,2-dione

“…13 In addition, it has been reported that reaction of (6methylpyridin-2-yl)methanol and 2-pyrdinecarboxaldehyde without solvent and catalyst yielded the compound 1,2-bis(6methylpyridin-2-yl)ethene-1,2-diol, with single-crystal X-ray diffraction showing that it is a symmetrical molecule with two intramolecular hydrogen bonds. 14 As a result, it was proposed to isolate the precursor 2hydroxy-[1,2-bis(6-methylpyridin-2-yl)]ethan-1-one (1) from the reaction of (6-methylpyridin-2-yl)methanol and 2pyridincarboxaldehyde according to Scheme 1 and justify the proposal that the compounds with a -CO-COH-group could be oxidised to -CO-CO-in solution in the presence of oxygen. However, the reaction results were more interesting, as proposed in Scheme 2.…”