Pteridine studies. Part XLII. Addition reactions between alcohols and pteridine

Abstract

Pteridine in methanol at 20–25° gave an equilibrium mixture of pteridine, 3,4-dihydro-4-methoxypteridine (the 1:1-adduct)(1a), and 5,6,7,8-tetrahydro-6,7-dimethoxypteridine (the 2:1-adduct)(2a). Similar results were obtained with ethanol and isopropyl alcohol. The 2:1-adduct of methanol (2a) and of ethanol (2b) were isolated and analysed. The cation of pteridine in methanol afforded an equilibrium mixture of the cation of the 1:1-adduct (3a) and of the 2:1-adduct (4a). Isopropyl alcohol gave similar results.

In the presence of sodium methoxide, methanol and pteridine produced the 2:1-adduct (2a) immediately. However, pteridine readily decomposed in isopropyl alcohol containing sodium isopropoxide. Pteridine did not react with t-butyl alcohol under any conditions.

Evidence for the above was obtained from u.v. and n.m.r. spectral studies which are discussed. Electronic and steric effects on the reactions, and the kinetic and thermodynamic modes of reaction, are distinguished and discussed.