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