Categories: Synthesis of N-Heterocycles >
Synthesis of 2H-azirines
Various substituted enamine derivatives can be conveniently converted to the corresponding 2H-azirines mediated by phenyliodine (III) diacetate (PIDA). The formed 2-aryl-2H-azirines allow the synthesis of indole-3-carbonitriles or isoxazoles via thermal rearrangements.
X. Li, Y. Du, Z. Liang, X. Li, Y. Pan, K. Zhao, Org. Lett., 2009, 11, 2643-2646.
Rh2(Piv)4 catalyzes a convenient gram-scale method for the preparation of 2-halo-2H-azirine-2-carboxylic acid esters and amides from 5-heteroatom-substituted 4-haloisoxazoles. In addition, rhodium catalysis is successfully applied in the synthesis of azirine-2-carboxylates from non-halogenated 5-alkoxyisoxazoles.
N. V. Rostovskii, A. V. Agafonova, I. A. Smetanin, M. S. Novikov, A. F. Khlebnikov, J. O. Ruvinskaya, G. L. Starova, Synthesis, 2017, 49, 4478-4488.
An efficient rhodium-catalyzed rearrangement of α-oximino ketenes derived from α-diazo oxime ethers provides 2H-azirines bearing quaternary centers and allows for subsequent rearrangement to highly substituted pyrroles in excellent yields.
Y. Jiang, W. C. Chan, C.-M. Park, J. Am. Chem. Soc., 2012, 134, 4104-4107.
The ketone, enol, and enolate forms of 3-sulfonyloxyimino-2-methyl-1-phenyl-1-butanones can afford different intramolecular cyclization products, depending on the conditions. Reactions under basic conditions afford 2H-azirines via a neutral enol (DABCO) or isoxazoles and oxazoles via an anionic enolate (t-BuOK), while acidic conditions afford oxazoles (AcOH) and isoxales (TFA) via neutral ketones.
Y. Ning, Y. Otani, T. Ohwada, J. Org. Chem., 2018, 84, 203-219.