HELVETICA CHIMICA ACTA- Vo1.66, Fasc.2 (1983)-Nr.61 ... 61. Synthesis of 2-0x0-2H-[ 1,2,4]oxadiazolo-[2,3-c~pyrimidine-5- carbamates ... Dedicated to Prof. Albert Hiirlimann on the occasion of his 60th birthday ... Summary Thermal cyclization of the pyrimidine-N-oxide dicarbamate 2 gives a 95 : 5 mixture of the 2-0x0-2 H-[ 1,2,4]oxadiazoIo [2,3-a]- and [2,3-~]pyrimidinecarba - mates 3 and 4. An efficient procedure for the conversion of 3 to 4, and vice versa, is ...