Highly enantioselective intramolecular aza-spiroannulation onto indoles using chiral rhodium catalysis: asymmetric entry to the spiro-β-lactam core of chartellines
A versatile, highly enantiocontrolled entry to the spiro-β-lactam core of chartellines has been developed by expanding the scope of oxidative nitrogen atom transfer methodology based on chiral Rh-nitrenoid species.
Highly asymmetric bromocyclization of tryptophol by using chiral anionic phase-transfer catalyst and DABCO-derived brominating reagent is described. Optimization of the reaction conditions revealed that the reaction rate was accelerated together with improvement of enantioselectivity by addition of catalytic DABCO-derived brominating reagent. From tryptophol, 3-bromofuroindoline could be directly obtained in excellent enantioselectivities by employing this novel methodology.