Highly Enantioselective Synthesis of Phosphorus-Containing ϵ-Benzosultams by Bifunctional Phosphonium Salt-Promoted Hydrophosphonylation

Enantioselective Synthesis of Biphenyl-Bridged ϵ-Sultams by Organocatalytic Mannich Reactions of Cyclic N-Sulfonylimines with Unactivated Ketones

A highly enantioselective Mannich reaction of biphenyl-bridged seven-membered cyclic N-sulfonylimines with methyl alkyl ketones is disclosed in this study. The reaction was performed under organocatalysis by using a quinine-derived primary amine as the catalyst in combination with a Brønsted acid as the co-catalyst. High yields (up to 89 %) and excellent enantioselectivities (up to 97 % ee) were observed. For methyl alkyl ketones containing a larger alkyl substituent, specific regioselective addition to the C=N bond is favored at the methyl group. On the contrary, ketones containing a smaller alkyl substituent or hydroxyacetone substrates gave major syn selective Mannich products at the methylene group.

Catalytic Asymmetric Synthesis of Atropisomers Bearing Multiple Chiral Elements: An Emerging Field

With the rapid development of asymmetric catalysis, the demand for the enantioselective synthesis of complex and diverse molecules with different chiral elements is increasing. Owing to the unique features of atropisomerism, the catalytic asymmetric synthesis of atropisomers has attracted a considerable interest from the chemical science community. In particular, introducing additional chiral elements, such as carbon centered chirality, heteroatomic chirality, planar chirality, and helical chirality, into atropisomers provides an opportunity to incorporate new properties into axially chiral compounds, thus expanding the potential applications of atropisomers. Thus, it is important to perform catalytic asymmetric transformations to synthesize atropisomers bearing multiple chiral elements. In spite of challenges in such transformations, in recent years, chemists have devised powerful strategies under asymmetric organocatalysis or metal catalysis, synthesizing a wide range of enantioenriched atropisomers bearing multiple chiral elements. Therefore, the catalytic asymmetric synthesis of atropisomers bearing multiple chiral elements has become an emerging field. This review summarizes the rapid progress in this field and indicates challenges, thereby promoting this field to a new horizon.

Design and Application of Peptide-Mimic Phosphonium Salt Catalysts in Asymmetric Synthesis

Chiral phosphonium salt catalysis, traditionally classified as a type of phase transfer catalysis, has proven to be a powerful strategy for the stereoselective preparation of diverse optically active molecules. However, there still remain numerous forbidding issues of reactivity and selectivity in such well-known organocatalysis system. Accordingly, the development of new and high-performance phosphonium salt catalysts with unique chiral backbones is highly desirable, yet challenging. This Minireview describes the prominent endeavours in the development of a new family of chiral peptide-mimic phosphonium salt catalysts with multiple hydrogen-bonding donors and their applications in a plethora of enantioselective synthesis during the past few years. Hopefully, this minireview will pave a way for further developing much more efficient and privileged chiral ligands/catalysts featuring exclusively catalytic ability in asymmetric synthesis.

Stereodivergent Access to [6.7]-Fused N-Heterocycles Bearing 1,3-Nonadjacent Stereogenic Centers by Pd-Catalyzed [4 + 2] Annulations

We describe a highly efficient stereodivergent [4 + 2] annulation reaction of vinyl benzoxazinaones and seven-membered cyclic N-sulfonyl aldimines for the synthesis of a wide array of N-heterocycles with 1,3-nonadjacent stereogenic centers via palladium catalysis. The polarity of solvents was found to play a key role in the switch of diastereoselectivity. Furthermore, good enantioselectivities of these reactions were achieved by the employment of commercially available Wingphos as the chiral ligand.

Catalytic asymmetric synthesis of medium-sized bridged biaryls

Despite the persistent presence of medium-sized (seven- to nine-membered) scaffolds in natural products and biologically active molecules, their asymmetric syntheses have always been considered a formidable task; therefore, they have remained underdeveloped when compared to the enantioselective synthesis of five- and six-membered ring scaffolds. One important class of such medium-sized ring frameworks includes seven- to nine-membered biaryl bridged carbo- and heterocycles. These medium-ring-sized biaryl frameworks possess more configurational stability than the related smaller ring structures and are common features of valuable natural products, bioactive compounds, chiral catalysts, and molecular motors. Due to these exciting properties and broad applications, over the last few years, the catalytic enantioselective synthesis of medium-sized bridged biaryls has seen an upsurge. This highlight article describes the development of organocatalysed and transition-metal catalysed transformations for procuring seven-, eight-, and nine-membered bridged biaryls bearing a chiral axis/one or more asymmetric carbon centres.