Stable Axially Chiral Cyclohexylidenes from Catalytic Asymmetric Knoevenagel Condensation.

Axially chiral cycloalkylidenes are interesting but less developed axially chiral molecules. Here, a bispidine-based chiral amine catalytic system was developed to promote efficiently the asymmetric Knoevenagel condensation of N-protected oxindoles and benzofuranones with 4-substituted cyclohexanones. A variety of alkylidenecycloalkanes with stable axial chirality were obtained in good yields and fairly good er (enantiomeric ratio). Based on the absolute configuration determination of product and DFT calculations, a possible mechanism of stereoselective induction was proposed.

Chiral cobalt(ii) complex-promoted asymmetric para-Claisen rearrangement of allyl α-naphthol ethers.

Due to experiencing a challenging dearomatization process, the aromatic sigmatropic rearrangement of allyl naphthyl ethers is a difficult yet efficient method to build useful naphthalenone skeletons. Here, we report a para-Claisen rearrangement-based asymmetric dearomatization of allyl α-naphthol ethers enabled by a N,N'-dioxide/CoII complex. A variety of naphthalenones were obtained in moderate to good yields with good to excellent ee values. Interestingly, by exchanging the allyl group on the ether and that at the para-position of the benzene ring, enantiodivergent synthesis can be achieved. Experimental studies and DFT calculations revealed that aryl allyl ethers tend to transform via a stepwise allyl π-complex migration pathway, while, alkyl allyl ethers transformed through a concerted ortho-Claisen rearrangement/Cope rearrangement sequence.

Catalytic Enantioselective Nucleophilic Addition to Arynes by a New Quaternary Guanidinium Salt-Based Phase-Transfer Catalyst.

Owing to the mild generation methods, arynes have been widely used in synthetic chemistry. However, achieving asymmetric organocatalytic reactions with arynes remains a formidable and infrequent challenge, primarily because these neutral and transient species tend to spontaneously quench. To address this issue, a solid-liquid phase-transfer strategy is devised in which the generation speed of arynes could be controlled by the in situ generated fluoride-based chiral phase-transfer catalyst. In this study, we present a catalytic enantioselective nucleophilic addition reaction involving arynes, utilizing an amino amide-based guanidinium salt QG•X. Furthermore, we demonstrate the broad compatibility of this reaction with various arynes and cyclic/acyclic ß-keto amides, leading to the creation of diverse α-aryl quaternary stereocenters with good stereoselectivity. Mechanistic investigations have uncovered the potential involvement of a chiral intramolecular cationic-anionic pair and HF during the ion exchange between QG•X and CsF for nucleophile activation and aryne generation. Additionally, DFT calculations suggested that the observed high levels of enantioselectivity can be attributed to steric repulsion and the cumulative noncovalent interactions between the catalysts and substrates.