Enantioselective direct Mannich reaction of functionalized acetonitrile to N -Boc imines catalyzed by quaternary phosphonium catalysis

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.

Asymmetric Synthesis of 3-Phenyl-2,3-dihydro-1H-pyrrolo[3,2-b]pyridine-3-carbonitriles Catalyzed by Phase-Transfer Catalyst Derived from tert-Leucine

Chiral phase-transfer catalysts derived from tert-leucine were synthesized and used in the asymmetric synthesis of 4-azaindoline derivatives. By this method, both enantiomers of the corresponding products were obtained in excellent yield (up to 99%) with high enantio­selectivities (up to 91% ee) and diastereoselectivities (up to >99: 1 dr).

Enantioselective Construction of Single and Vicinal All-Carbon Quaternary Stereocenters through Ion-Pair-Catalyzed 1,6-Conjugate Addition

An asymmetric 1,6-conjugate addition to presynthesized δ-aryl-δ-cyano-disubstituted para-quinone methides through bifunctional phosphonium-amide-promoted ion-pair catalysis for acyclic all-carbon quaternary stereocenter construction has been described. Both acyclic and cyclic 1,3-dicarbonyls participate in the asymmetric alkylation reaction, furnishing a wide array of diarylmethanes bearing a single acyclic quaternary carbon stereocenter or vicinal cyclic and acyclic quaternary carbon stereocenters with high efficiency and excellent stereoselectivity. Computational studies elucidate the origin of the enantioselectivity.

Enantioselectivity switch in asymmetric Michael addition reactions using phosphonium salts

Efficient access to two enantiomers of one chiral compound is critical for the discovery of drugs. However, it is still a challenging problem owing to the difficulty in obtaining two enantiomers of one chiral catalyst. Here, we report a general method to obtain both enantiomeric products via fine tuning the hydrogen-bonding interactions of phosphonium salts. Amino acid derived phosphonium salts and dipeptide derived phosphonium salts exhibited different properties for controlling the transition state, which could efficiently promote the Michael addition reaction to give opposite configurations of products with high yields and enantioselectivities. Preliminary investigations on the mechanism of the reaction and applications of the products were also performed.

Synthesis of 4-Azaindolines Using Phase-Transfer Catalysis via an Intramolecular Mannich Reaction

A series of bifunctional asymmetric phase-transfer catalysts containing novel fluorine-containing urea groups derived from cinchona alkaloids have been synthesized and successfully applied in the asymmetric intramolecular Mannich reaction. The 4-azaindoline products bearing multiple substrates were obtained in excellent yield (90-99%), with high enantioselectivity (up to 95%) and diastereoselectivity (up to >99:1).

N-Protecting group tuning of the enantioselectivity in Strecker reactions of trifluoromethyl ketimines to synthesize quaternary α-trifluoromethyl amino nitriles by ion pair catalysis

An enantioselective Strecker reaction to construct trifluoromethylated quaternary stereocenters with N-PMP and unexplored N-Boc trifluoromethyl ketimines catalyzed using an organophosphine dual-reagent catalyst has been developed. The enantioselectivities of the corresponding products with the same catalyst could be switched by using different N-protecting groups (N-PMP or N-Boc). The trifluoromethyl amino nitriles were obtained in high yield and high enantioselectivity in a short time and could be easily converted to a variety of useful trifluoromethyl-containing compounds.

Chiral Phase-Transfer Catalysts with Hydrogen Bond: A Powerful Tool in the Asymmetric Synthesis

Asymmetric phase-transfer catalysis has been widely applied into organic synthesis for efficiently creating chiral functional molecules. In the past decades, chiral phase-transfer catalysts with proton donating groups are emerging as an extremely significant strategy in the design of novel catalysts, and a large number of enantioselective reactions have been developed. In particular, the proton donating groups including phenol, amide, and (thio)-urea exhibited unique properties for cooperating with the phase-transfer catalysts, and great advances on this field have been made in the past few years. This review summarizes the seminal works on the design, synthesis, and applications of chiral phase-transfer catalysts with strong hydrogen bonding interactions.

An organocatalytic asymmetric Mannich reaction for the synthesis of 3,3-disubstituted-3,4-dihydro-2-quinolones

The first organocatalytic asymmetric Mannich reaction employing 3,4-dihydro-2-quinolones has been developed for the synthesis of biologically important 3,3-disubstituted-dihydro-2-quinolones. N-Boc imine precursor amidosulfones as well as pre-formed N-Boc imine were used for this purpose. Cyclohexyldiamine derived bifunctional amino-thiourea catalysts were employed to provide the products in high enantio- and good diastereoselectivities.