Highly Chemoselective and Enantioselective Synthesis of 3,4-2-Pyrindin-2-ones by an NHC-Catalyzed [3 + 3] Cyclization.

A highly chemoselective and enantioselective cyclization of γ-chloroenals and ketimines has been developed to synthesize enantiopure 3,4-2-pyrindin-2-ones as major products. It is proposed that the intermediate enone reacted with an enamine to proceed with a [3 + 3] cyclization, thereby affording 3,4-2-pyrindin-2-ones as major products. Interestingly, the addition of LiCl promoted the formation of the enamine and accelerated the [3 + 3] cyclization.

NHC-Catalyzed Asymmetric Formal [4 + 2] Annulation To Construct Spirocyclohexane Pyrazolone Skeletons.

A chiral N-heterocyclic carbene (NHC)-catalyzed [4 + 2] annulation of γ-chloroenals and α-arylidene pyrazolinones was developed in the absence of expensive oxidants. The reaction proceeds smoothly via a vinyl enolate intermediate to afford spirocyclohexane pyrazolones in moderate to good yield (up to 86%) with high diastereoselectivities (up to 15:1 ) and excellent enantioselectivities (up to >99% ).

N-Heterocyclic Carbene-Catalyzed Asymmetric Benzoin Reaction in Water.

A chiral N-heterocyclic carbene-catalyzed benzoin condensation reaction in water has been developed, affording α-hydroxy ketones in good to high yields and high enantioselectivities. Water was proposed as a proton shuttle in the aqueous asymmetric condensation reaction.

NHC-catalyzed [4+2] cycloaddition reactions for the synthesis of 3'-spirocyclic oxindoles via a C-F bond cleavage protocol.

A chiral NHC-catalyzed cycloaddition of γ-fluoroenals is developed. The nucleophilic γ-carbon generated via C-F bond cleavage undergoes highly enantioselective cycloaddition (up to >99% ee) to isatins and provides 3'-spirocyclic oxindoles in good yields (up to 91%).

Synthetic Access to Oxazolidin-4-ones via Elimination/[3+2] Cycloaddition Reaction.

Elimination/[3+2] cycloaddition reactions of simple enals and unprotected isatins with haloamides have been developed. This transformation provides rapid access to highly functionalized oxazolidin-4-ones that are represented in bioactive compounds.