Rearrangements, oxazole reactions pyrimidines

Nucleophilic substitution in the azine ring is a normal reaction. The fused oxazole ring, however, is susceptible to nucleophilic ring opening reactions, especially in oxazolium salts and dihydro derivatives. When fused to pyrimidine, substituents in the pyrimidine ring may promote a Dimroth rearrangement of the latter. 

This type of rearrangement can also occur as a consequence of in situ formation of a suitable intermediate, such as in the case of tandem or cascade reactions. Examples of the isoxazole-to-oxazole rearrangement have been studied both computationally and experimentally, providing evidence of the involvement of a 1,2,4-oxadiazole intermediate (2009JOC351). Synthetically useful cascade rearrangements have also been reported for the one-pot synthesis of indazoles (2011SL3018) and a series of isoxazolo-pyrimidines (2011OL4749). 

Sandmeyer synthesis (isatin) 145 Schmidt-Druey synthesis (pyridazine) 461 Schollkopf synthesis (oxazole) 173 Sharpless-Katsuki epoxidation 24 Shaw synthesis (pyrimidine) 468 Skraup-Doebner-Miller synthesis (quinoline) 400 Smiles rearrangement 446 Sommelet-Hauser rearrangement 136 Staudinger reaction 53 Steglich reagent (DMAP) 348 Stork isoxazole annelation 191... 

---