1968 Volume 41 Issue 12 Pages 2927-2931
In the presence of cyanide ions, an α-ketoaldehyde dimerizes to give an acylformoin. The tautomerism of this compound was studied. It was found that the tautomerism between I and II is affected by the solvents and by the substituents. In proton-accepting solvents (EtOH, THF), I predominates. In ethanol-free chloroform, II is dominant for almost all substituents. In ethanol-containing chloroform, some acylformoins exist as I, while the others exist as II. The former case is observed when R=t-Bu and p-X–C6H4 (X=H, t-Bu, Cl, and Br); the latter case, when R=Me, i-Pr, and p–Me-C6H4. In the former case, ethanol reacts slowly with I to give an O-ethyl derivative (III). When R=2,4,6-Me3–C6H2, II predominates in all states. When R=p-Cl–C6H4 and p-Br–C6H4, I and II were isolated as crylstals. The solvent effects are interpreted in terms of the hydrogen-bonding interactions of I with basic and hydroxylic solvents.
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