Synthesis of 3,4-Dihydro-2H-1,4-benzoxazines
An efficient synthesis of 3,4-dihydro-1,4-benzoxazine derivatives in excellent enantio- and diastereospecificity (ee > 99%, de > 99%) proceeds via Lewis acid-catalyzed SN2-type ring opening of activated aziridines with 2-halophenols followed by Cu(I)-catalyzed intramolecular C-N cyclization in a stepwise fashion.
A. Mal, I. A. Wani, G. Goswami, M. K. Ghorai, J. Org. Chem., 2018, 83, 7907-7918.
The use of the chiral bisphosphorus ligand WingPhos enables a versatile, regio- and enantioselective palladium-catalyzed tandem allylic substitution to provide a series of chiral vinyl-substituted heterocycles, including tetrahydroquinoxalines, piperazines, dihydro-2H-benzo[b][1,4]-oxazines, and morpholines, in exellent ees and yields. The protocol features mild reaction conditions.
C. Qian, W. Tang, Org. Lett., 2020, 22, 4467-4470.