Direction of hydrolysis of esters of some pyrimidine-5-carboxylic acids

Abstract

Acids 2 or ketones 3 are formed under similar conditions, while the melting points and spectral characteristics of acid 2a and ketone 3a as well as of acid 2b and ketone 3b are extremely similar. Schenone et al. [2] demonstrated the structure of acids 2a,b by their decarboxylation to the corresponding disubstituted pyrimidines. On the other hand, the evidence for the structure of ketones 3a,b given by various workers [4-6] is not entirely convincing. We carried out the hydrolysis of ester 1 under the conditions described by both groups of authors. When the hydrolysis was carried out in water as described by Schenone et al. [2], we obtained a compound with mp 150-152°C (154-155°C [2]). When the hydrolysis was carried out in ethanol as described by Danagulyan et al. [5], we obtained a compound with mp 148-150°C (146-148°C [5]). These two compounds proved identical with identical NMR spectra. The NMR spectra of a mixture of the two preparations contained one set of signals. The NMR spectra of our samples were similar to the spectra described in previous work [2, 5]. According to the C NMR spectral data (δ, ppm: 24.7, 26.5, 122.1, 159.3, 167.1, 168.5, 169.9), this compound is acid 2a rather than ketone 3a. A signal for the carbonyl carbon atom in ketone 3a would have been expected at 195-210 ppm. For example, the signal for the carbonyl carbon atom is found at 201.7 ppm in the C NMR spectrum of 5-acetyl-4,6-dichloropyrimidine synthesized in our laboratory according to the procedure of Clark et al. [7]. _______ * Deceased.