Studies of heteroaromatic systems by nuclear magnetic resonance spectroscopy. 4‐pyrimidones and 4‐pyrimidthiones

Publisher Website
Google Scholar
Abstract
Proton magnetic resonance spectral parameters of 4‐pyrimidone, 1‐ and 3‐alkyl‐4‐pyrimidones as well as some of their thione analogs are presented and are compared to those of 4‐substituted pyrimidines. It was found that the ortho, meta and para coupling constants in each series were constant for 4‐substituted pyrimidines, the 1‐alkyl‐ and the 3‐alkyl‐4‐pyrimidones. A particularly large meta (J2, 6) coupling constant was an outstanding feature found in 1‐methyl‐, 1‐ethyl‐ and 1‐benzyl‐4‐pyrimidones and also in 1‐methyl‐4‐pyrimidthione but was virtually zero for the corresponding 3‐alkyl‐4‐pyrimidones. These findings are interpreted in terms of the aromatic character of these 4‐pyrimidones and thiones. During the synthetic aspects of this work, an interesting carbon‐sulfur cleavage was discovered when it was observed that 2‐benzylmercapto‐4‐pyrimidones were readily hydrolyzed by hot concentrated hydrochloric acid to the corresponding 2‐thiouracils.