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Synthesis of 3,4-dihydro-2H-1,4-oxazines

Recent Literature

Aziridines react with propargyl alcohols in the presence of Zn(OTf)2 as the Lewis acid catalyst, following an SN2-type ring-opening mechanism to furnish the corresponding amino ether derivatives. In the presence of Zn(OTf)2 and tetrabutylammonium triflate salt, those amino ethers further undergo intramolecular hydroamination via 6-exo-dig cyclization to provide 3,4-dihydro-2H-1,4-oxazine products.
B. Singh, M. Kumar, G. Goswami, I. Verma, M. K. Ghorai, J. Org. Chem., 2023, 88, 4504-4518.

A Rh(II)-catalyzed reaction between 1-tosyl-1,2,3-triazoles and halohydrins provides 2,6-substituted 3,4-dihydro-2H-1,4-oxazines under basic conditions. The reaction is proposed to undergo a rhodium carbenoid 1,3-insertion into O-H followed by an annulation.
K. D. Jones, M. J. Nutt, E. Comninos, A. N. Sobolev, S. A. Moggach, T. Miura, M. Murakami, S. G. Stewart, Org. Lett., 2020, 22, 3490-3494.

A solvent- and metal-free regioselective cyclization affords 1,4-oxazine and 1,4-oxazepine derivatives as exo-dig products. Substrates for the cyclization step can be produced in a highly diastereomeric fashion by Grignard reaction as key synthetic step following Cram’s rule.
J. K. Vandavasi, W.-P. Hu, H.-Y. Chen, G. C. Senadi, C.-Y. Chen, J.-J. Wang, Org. Lett., 2012, 14, 3134-3137.