N-Heterocyclic carbene-catalyzed β-addition of enals to 3-alkylenyloxindoles: synthesis of oxindoles with all-carbon quaternary stereocenters

Enantioselective SN 2 Alkylation of Homoenolates by N-Heterocyclic Carbene Catalysis

The functionalization of the β-carbon of enals with electrophiles is a signature umpolung reactivity of N-heterocyclic carbene (NHC) derived homoenolates. However, only a limited number of electrophiles are shown to be compatible, with most of them being π-electrophiles. In this study, the successful enantioselective β-alkylation of homoenolates is reported using Csp3 electrophiles through an SN 2 strategy. The protocol shows a broad scope regarding alkyl electrophiles, delivering good yields, and excellent enantioselectivities (up to 99% ee). It enables the installation of drug-like structural motifs in either enals or alkylating agents, demonstrating its potential as a valuable tool for late-stage modification. Furthermore, a concise synthetic route is presented to chiral pyrroloindoline-type skeletons. Preliminary mechanistic studies support a direct SN 2 mechanism.

N-Heterocyclic Carbene-Catalyzed [3 + 2] Annulation of 3,3'-Bisoxindoles with α-Bromoenals: Enantioselective Construction of Contiguous Quaternary Stereocenters

An NHC-catalyzed enantio- and diastereoselective [3 + 2] annulation of α-bromoenals with bisoxindoles is developed, affording efficient access to various spirocyclic bisoxindole alkaloids. This protocol tolerates a broad substrates scope, with various spirocyclic bisoxindoles obtained in generally excellent enantioselectivities. More importantly, two contiguous sterically congested all-carbon quaternary stereocenters are successfully created during this process.

The N-heterocyclic carbene-catalyzed [3 + 2] annulation of isoindigos with enals: the enantioselective construction of three contiguous stereogenic centers

An NHC-catalyzed enantioselective [3 + 2] annulation of enals and isoindigo is introduced as an efficient strategy for the construction of dimeric spirocyclic bisindoline alkaloid derivatives with moderate yields and good enantioselectivities.

NHC-Catalyzed Cascade Reaction between β-Methyl Enals and Dienones for Quick Construction of Complex Multicyclic Lactones

A NHC-promoted cascade reaction between β-methyl enal and dienone is developed for quick access to multicyclic lactone molecules bearing quaternary chiral carbon centers. Our study constitutes the first 1,6-addition of the acylazolium vinyl enolate γ-carbon via NHC catalysis and provides rapid access to complex lactone molecules that are otherwise difficult to prepare. The structurally sophisticated lactone products bearing up to four fused ring structures are afforded in up to quantitative yields with good to excellent enantioselectivities.

Highly enantioselective 1,6-addition of dienolates to coumarins and chromones through N-heterocyclic carbene catalysis

An efficient protocol employing NHC-organocatalysis in asymmetric γ,δ-difunctionalization of cyanocoumarins and nitrochromones via a 1,6-addition of dienolates is established.

NHC-catalyzed β-specific addition of N-based nucleophiles to allenoates

N-heterocyclic carbene (NHC) catalyzed reactions of nitrogenous heterocycles or trifluoromethylated acylhydrazone with allenoates gave regiospecific β-adducts. DFT calculations rationalized the origination of regio- and E/Z selectivities.

Axial-to-Central Chirality Transfer for Construction of Quaternary Stereocenters via Dearomatization of BINOLs

All-carbon quaternary stereocenters are versatile building blocks, and their asymmetric construction has attracted much attention. Herein, we disclose an axial-to-central chirality transfer strategy for the synthesis of chiral quaternary stereocenters via dearomatization of (S)-BINOLs. The reaction proceeded smoothly with a wide range of propargyl carbonates to afford chiral spiro-compounds in high yields with excellent enantioselectivities. In addition, the strategy was extended to kinetic resolution of rac-BINOLs albeit with moderate s value.