
TY  - JOUR
A1  - Brown, DJ 
A1  - Nagamatsu, T 
T1  - Isomerizations akin to the Dimroth rearrangement. III. The conversion of simple s-Triazolo[4,3-a]pyrimidines into their [1,5-a] Isomers
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1977
VL  - 30
IS  - 11
SP  - 2515
EP  - 2525
KW  - 
UR  - https://doi.org/10.1071/CH9772515 
N2  - The treatment of 2-hydrazinopyrimidines (1) with acylating agents under appropriate conditions is used to prepare s-triazolo[4,3-a]pyrimidine (6a) and its derivatives bearing alkyl or aryl groups at the 3-, 5-, 6- , or 7-position. These compounds rearrange in acid or alkali to give the corresponding s-triazolo[1,5-a]pyrimidines (7). Rates for such isomerizations in alkali increase steeply in the range pH 10-12.5; in acid, they reach maxima at pH values corresponding approximately to the pKa of each substance (in the range pH 1.5-2.5) and fall off on both sides. Rearrangement of the parent heterocycle (6a) is slowed significantly by each added 3-, 6-, and 7-alkyl group and slowed profoundly by a 5-alkyl group: for example, 3,5,7-trimethyltriazolo[4,3-a]pyrimidine rearranges 2500 times more slowly than the unsubstituted heterocycle at pH 11.3. The isomeric systems (6) and (7) are distinguished easily by their tabulated u.v. and N.M.R. spectra. 
ER  -

