The first example of the Fischer-Hepp type rearrangement in pyrimidines
A N-nitroso moiety can be used for the activation of chloropyrimidines toward a nucleophilic substitution reaction with amines. The subsequent treatment of the obtained products with aq H2SO4 can lead to either N-denitrosation to obtain 4,6-pyrimidinediamines or to a Fischer-Hepp type rearrangement to obtain 5-nitroso-4,6-pyrimidinediamines. It was found that the outcome of the reaction strongly depends on the structure of the pyrimidines. Activation of the pyrimidine ring by three groups with a positive mesomeric effect is crucial for the intramolecular nitroso group migration.
The scope and mechanism of phosphonium-mediated SNAr reactions in heterocyclic amides and ureas
(Chemical Equation Presented) An efficient "one-step" synthesis of cyclic amidines and guanidines has been developed. Treatment of cyclic amides and ureas with benzotriazol-l-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP), base, and nitrogen nucleophiles leads to the formation of the corresponding cyclic amidines and guanidines, typically in good to excellent yields. This method has also been used to prepare heteroaryl ethers and thioethers using phenol and thiophenol nucleophiles. Time course NMR and HPLC-MS studies have facilitated explicit characterization of the proposed intermediates (the phosphonium salt and HOBt adduct); the data reveal a stepwise reaction pathway.
Wan, Zhao-Kui,Wacharasindhu, Sumrit,Levins, Christopher G.,Lin, Melissa,Tabei, Keiko,Mansour, Tarek S.
p. 10194 - 10210
(2008/04/12)
An efficient direct amination of cyclic amides and cyclic ureas
An efficient one-step amination of cyclic amides and ureas has been developed. Treatment of cyclic amides and cyclic ureas with BOP in the presence of DBU in various solvents led to the formation of cyclic amidines and cyclic guanidines in good to excellent yields. Concise syntheses of biologically intriguing kinetin and potent kinase inhibitor olomoucin were thus achieved in just one and two steps, respectively.