Highly Enantioselective Dimerization of α,β-Enones Catalyzed by a Rigid Quaternary Ammonium Salt

Photocatalytic Three-Component Acylcarboxylation of Alkenes with CO2

γ-Keto acid is a valuable chemical motif in a wide range of fields including organic, biological, and medicinal chemistry. However, its single-step synthesis is challenging because of the mismatch of the carbonyl polarity and low tolerance of carboxylic acids. Herein, we report the single-step syntheses of γ-keto acids using alkenes and CO2. Our photocatalytic system enabled the transformation of alkenes under mild conditions in high yields (up to 95%) with broad substrate generality (35 examples).

Ten undescribed diterpenoid quinones derived from the Salvia miltiorrhiza

This study aimed to report the structure elucidation of the compounds isolated from Salvia miltiorrhiza, and their biological evaluations. Ten undescribed diterpenoid quinones and 10 known analogues were isolated from the dried roots of S. miltiorrhiza. Their structures were elucidated by extensive analysis, including nuclear magnetic resonance, high-resolution mass spectra, and ultraviolet and infrared spectra. Their absolute configurations were determined by comparing the experimental and calculated electronic circular dichroism spectra. In the evaluation of bioactivities, Salvianolactone acid I, epi-danshenspiroketallactone F, danshinspiroketallactone, grandifolia G, and 2H-Naphtho [1,8-bc]furan (10 μM) significantly increased cell viability and decreased the nuclear transport of p-P65 in lipopolysaccharide-induced bronchial epithelial cells. It was concluded that the diterpenoid quinones might belong to potent targeted lung-protective agents.

Magnesium-Promoted Reductive Carboxylation of Aryl Vinyl Ketones: Synthesis of γ-Keto Carboxylic Acids

Direct reductive carboxylation of easily prepared aryl vinyl ketones under the atmosphere of carbon dioxide led to the selective formation of γ-keto carboxylic acids in 38-86% yields. The reaction is characterized by the carbon-carbon bond formation of carbon dioxide at the β-position of enone, with the use of magnesium turnings that can be easily handled as the reducing agent and the eco-friendly reaction conditions such as no pressuring, no lower or higher reaction temperature, and short reaction time. This protocol showed a wide substrate scope and provided a useful and convenient alternative to access biologically important γ-keto carboxylic acids.

Bi(OTf)3-Catalyzed Alkyl-Intercepted Meyer-Schuster Rearrangement of Propargylic Alcohols for the Synthesis of 1,2,3,5-Tetrasubstituted Pentane-1,5-diones

An alkyl intercepted Meyer-Schuster rearrangement reaction with α,β-unsaturated ketones as the electrophiles was first investigated, which provided a facile method to construct 2-methylene-pentane-1,5-diones. Then the in situ generated 2-methylene-pentane-1,5-diones underwent a Michael addition to give diverse 2-malononitrile methyl substituted pentane-1,5-diones in a one-pot fashion. This transformation was reliable on a gram scale. The high yield, convenient experimental operation, and 100% atom economy made it a valuable method for the construction of 1,2,3,5-tetrasubstituted pentane-1,5-dione derivatives.

Enantioselective Total Synthesis of (-)-Spiroxins A, C, and D

Spiroxins A, C, and D are metabolites that have been identified in the marine fungal strain LL-37H248. Their unique polycyclic structures and intriguing biological activities make them attractive targets for the synthetic community. Based on a scalable enantioselective epoxidation of 5-substituted naphthoquinone, an oxidation/spiroketalization cascade, ortho-selective chlorination of the phenol unit, and oxime-ester-directed acetoxylation, an enantioselective total synthesis of (-)-spiroxins A and C and the first total synthesis of (-)-spiroxin D have been achieved.

A Method for the Catalytic Enantioselective Synthesis of Chiral α-Azido and α-Amino Ketones from Racemic α-Bromo Ketones, and Its Generalization to the Formation of Bonds to C, O, and S

A new and practical method has been developed for the transformation of racemic α-bromo ketones to chiral α-azido and α-amino ketones with high enantioselectivity using phase transfer, ion-pair mediated reactions with a recoverable chiral quaternary salt (10 mol %) as catalyst in fluorobenzene-water. The process has been generalized to a variety of other attachments including of C, O, S, and NHR.

Directed C–C bond cleavage of a cyclopropane intermediate generated fromN-tosylhydrazones and stable enaminones: expedient synthesis of functionalized 1,4-ketoaldehydes

An efficient method to construct functionalized 1,4-ketoaldehydes bearing all-carbon α-quaternary centersviaregioselective C–C bond activation has been described.

Recent advances in asymmetric phase-transfer catalysis

The use of chiral nonracemic onium salts and crown ethers as effective phase-transfer catalysts have been studied intensively primarily for enantioselective carbon-carbon or carbon-heteroatom bond-forming reactions under mild biphasic conditions. An essential issue for optimal asymmetric catalysis is the rational design of catalysts for targeted reaction, which allows generation of a well-defined chiral ion pair that reacts with electrophiles in a highly efficient and stereoselective manner. This concept, together with the synthetic versatility of phase-transfer catalysis, provides a reliable and general strategy for the practical asymmetric synthesis of highly valuable organic compounds.

Organocatalytic regioselective Michael additions of cyclic enones via asymmetric phase transfer catalysis

Cyclohexanone and cycloheptanone can be enantioselectively functionalized in the 3-position with up to 92% ee and 87% ee, respectively, by the base-promoted dimerization of the corresponding enones using 3,4,5-tribenzyloxybenzyl cinchoninium bromide, as a new effective catalyst.