Catalytic methods for the synthesis of spirooxindoles, pyrroloindolines, and flavanones
This thesis discloses catalytic, enantioselective dipolar cycloadditions to deliver new nitrogen-containing heterocycles and formal hydroarylations of olefins that have previously not been possible.
Catalytic, enantioselective, dearomative cycloadditions of stabilized, α-substituted azomethine ylides with 3-nitroindoles occur in the presence of a catalytic complex generated from Cu(OTf)2 and (R)-Difluorphos. These reactions set four contiguous stereocenters, two of which are fully substituted. Overcoming the barrier of breaking aromaticity, this catalyst system delivers pyrrolo[3, 4b]indoles with exoÃ Â´-selectivity in moderate-to-good yields (39-85%) with high diastereoselectivity (up to 98 : 1 : 1 dr) and enantioselectivity (up to 96% ee).
Catalytic, enantioselective, dipolar cycloadditions of highly reactive nitrile imines with methyleneindolinones occur in the presence of a catalyst generated from Mg(NTf2)2 and a chiral aminoindanol-derived bisoxazoline ligand. The catalyst system designed overcomes a rapid competing background reaction to deliver spiro[pyrazolin-3,3′-oxindoles] in up to 98% yield and 99% ee.
Conjugate additions of arylboronic acids to challenging 2-alkylchromones occur in aqueous medium in the presence of a catalyst system generated from Pd(TFA)2 and 1,10-phenanthroline. This system overcomes the problem of competing protodeboronation and biaryl-forming reactions to deliver 2-alkyl-2-aryl-chromanones in up to 90% yield, providing a new and effective means of generating a fully substituted carbon center.
In all of these projects, effective catalyst design principles were established to overcome challenges that made these types of reactions previously impossible.