Researches on antiviral agents. 3. synthesis and transformations of racemic and chiral 6-oxiranyl pyrimidinones.

4,5‐Dihydro‐1,2,3‐oxadiazole: A Very Elusive Key Intermediate in Various Important Chemical Transformations

“… 1 H NMR35b,e and MS data35d of alleged 4,5‐dihydro‐1,2,3‐oxadiazoles, which do not support the structure assignment of these heterocycles. …”

“…In some cases, 1 H NMR data are evidently not compatible with the suggested structures as shown in Scheme . For example, the carbon‐bonded methyl group of 16 a should lead to a 1 H NMR signal with a significantly lower chemical shift value than δ =3.10 ppm,35e, 36 and the CH 2 NN unit in the five‐membered ring of 16 b should give 1 H NMR signals at clearly lower field than δ =2.45–2.96 ppm 35b. When appropriate 4,5‐dihydro‐1,2,3‐triazoles 11 are utilized as model compounds,26 the 1 H NMR signals of the CH 2 NN group in 16 b should resonate in the range of δ =4.0–4.3 ppm.…”

Regioselective Aryl Radical Cyclization: Access to Pyrimidine-Annelated Spiro Heterocycles Through 5-exo Ring Closure

“…Functionalization of uracils at C-5 and C-6 leads to biologically interesting molecules but it is not a simple task, requiring rather sophisticated and tedious reaction conditions. 20,21 We have recently reported the synthesis of a number of pyrimidine-annelated heterocycles fused at the C-5 and C-6 positions of uracil. 15,22 Herein we report the regioselective formation of spiro pyrimidine heterocycles.…”

C-C Bond Formationby Radical Cyclization: Synthesis of Pyrimidine-Annulated Heterocycles

“…15 Functionalization of uracil at the C-5 11,[16][17][18][19] and C-6 [20][21][22] leads to biologically interesting molecules, but it is not a simple task, requiring rather sophisticated and tedious reaction conditions. [23][24][25] We have recently reported the synthesis of a number of pyrimidine-annulated heterocycles by [3,3] sigmatropic rearrangements. 26 Continuation of our endevor to synthesize new heterocycles 27 prompted us to study the aryl radical cyclization for the synthesis of pyrimidine-annulated heterocyclic compounds.…”