Asymmetric cyclization of 3,4-dihydro-2-vinyl-2H-1,4-benzoxazine catalyzed by palladium-BHMP catalyst

The reaction of 1,4-diacetoxy-cis-2-butene 20 with 2-(benzylamino)phenol 3 in THF in the presence of Et(3)N and a catalytic amount of Pd(0)-BHMP-beta-Ala Ic gave optically active 4-benzyl-2-vinylbenzoxazine of up to 56.2%ee. The reaction of (Z)-2-butene-1,4-diylbis(methylcarbonate) 2b instead of 20 with 2-(benzylamino)phenol 3, 4 was obtained with e.e. up to 71.4%. We could improve the enantioselectivity of (R)-4 by introducing a carboxyl group at the terminal position of the pendant side chain on the bisphosphine ligand and by using a methyl carbonate ester 2b instead of diacetate 2a.