PHOTOCHEMISTRY OF 4-AMINOPYRIMIDINES 2,6-DIMETHYL-4-AMINOPYRIMIDINE

Abstract— Ultraviolet irradiation (2537 Å) of 2,6-dimethyl-4-aminopyrimidine (I) results in an intramolecular rearrangement with the formation, either in aqueous or anyhdrous medium, of only one photoproduct, 2-amino-3-cyanopent-2-enemine (II), in quantitative yield. The quantum yield for this reaction is 0.043 einsteins/mole.
Deamination of II gives, quantitatively, 2-amino-3-cyanopent-2-en-4-one (III) and this, in turn, may be deaminated to give, quantitatively, 3-cyanopent-2-en-2-01-4-0ne (cyanoacetyl-acetone, IV). Identification of II was achieved initially through isolation of III and IV. Some of the chemical and physico-chemical properties of these compounds are reported, as well as methods for obtaining all of them on a preparative scale.
The mono-protonated form of I also gives II on irradiation, but in lower quantum yield, 7.3times10⁸ einsteins/mole. Irradiation of the doubly protonated form of I in strongly acid medium leads directly to the formation of a mixture of II, III and IV, with approxi mately the same quantum yield.
The possible mechanisms for the foregoing photochemical reactions are discussed and their significance related to the photochemistry of 4-aminopyrimidines in general and to those of nucleic acid derivatives in particular.