Organocatalytic Asymmetric Direct Vinylogous Michael Initiated Ring Closure Reaction of 4-Nitroisoxazole Derivatives to 3-Isopropylidene Oxindoles

Diversity-Oriented Synthesis of Spirooxindoles via Asymmetric Organocatalytic Regiodivergent Cascade Reactions

A regiodivergent strategy for the asymmetric diversity-oriented synthesis of spirooxindoles via organocatalytic cascade reactions is developed. Two regioselective pathways can be precisely controlled with different aminocatalysts in the reaction of 2-hydroxycinnamaldehydes and β,β-disubstituted 3-alkylidene oxindoles. The cascade vinylogous Michael/oxa-Michael/aldol reactions gave spiro-bridged oxindoles bearing two adjacent quaternary stereocenters, while the cascade oxa-Michael/Michael reactions gave spirooxindoles. Moreover, during the synthetic application studies, an acid-catalyzed rearrangement of spiro-bridged oxindoles was found to yield biologically important 3-alkylidene oxindoles.

Ag(I)-catalyzed asymmetric (2+4) annulation reaction of 5-alkenyl thiazolones: synthesis of enantioenriched spiro[cyclohexenamines-thiazolones]

The first metal-catalyzed (2+4) annulation of 5-alkenyl thiazolones and α,α-dicyanoalkylidenes has been developed via vinylogous Michael/cyclization/isomerization reaction. This (2+4) annulation reaction is catalyzed by a chiral Ag-(R)-DTBM-SEGPHOS catalyst, delivering enantioenriched spiro[cyclohexenamines-thiazolone] having contiguous quaternary and tertiary stereocenters in good to excellent yield (up to 80%) and excellent stereoselectivities (up to 97% ee and >20 : 1 dr). This methodology has high functional group tolerance and produces a broad range of enantioenriched products under mild reaction conditions.

Silver-Catalyzed Asymmetric Double Desymmetrization via Vinylogous Michael Addition of Prochiral α,α-Dicyanoalkenes to Cyclopentendiones

An asymmetric double desymmetrization methodology has been developed for synthesizing densely functionalized chiral cyclopentylcyclohexane scaffolds. We have constructed four chiral centers, including an all-carbon quaternary stereocenter in a single C-C bond formation event. The methodology has high functional-group tolerance and delivers a broad range of enantioenriched products. This vinylogous Michael addition reaction of prochiral α,α-dicyanocyclohexane to 2,2-disubstituted cyclopentene-1,3-dione is catalyzed by a chiral Ag-(R)-DTBM-SEGPHOS catalyst.

Enantioselective Synthesis of Thiazolopyran Derivatives via a Direct Vinylogous Michael-oxa-Michael Sequence

An efficient diastereo- and enantioselective direct vinylogous Michael-oxa-Michael sequence between 5-alkenyl thiazolones and isopropylidene oxindoles has been developed. The reaction is catalyzed by a bifunctional squaramide catalyst that allows to access a wide range of densely substituted thiazolopyran derivatives containing a quaternary stereocenter. This protocol is flexible toward different sterically and electronically tuned substrates and is amenable to gram-scale synthesis and several synthetic transformations.