Catalytic Asymmetric Construction of the Tryptanthrin Skeleton via an Enantioselective Decarboxylative [4 + 2] Cyclization

The first catalytic
asymmetric construction of the tryptanthrin
skeleton has been established, taking advantage of a palladium(0)/chiral
ligand-catalyzed enantioselective decarboxylative [4 + 2] cyclization
of vinyl benzoxazinanones with isatins. This reaction has not only
provided a direct and efficient method for constructing chiral tryptanthrin
skeleta in high yields and excellent enantioselectivities (up to 97%
yield, >99% ee) but also represents the first catalytic asymmetric
decarboxylative cyclization of vinyl benzoxazinanones with isatins.