Pd-Catalyzed Allylation of Imines to Access α-CF3-Substituted α-Amino Acid Derivatives

Recent advances in the synthesis of fluorinated amino acids and peptides

The site-selective modification of amino acids, peptides, and proteins has always been an intensive topic in organic synthesis, medicinal chemistry, and chemical biology due to the vital role of amino acids in life. Among the developed methods, the site-selective introduction of fluorine functionalities into amino acids and peptides has emerged as a useful approach to change their physicochemical and biological properties. With the increasing demand for life science, the direct fluorination/fluoroalkylation of proteins has also received increasing attention because of the unique properties of fluorine atom(s) that can change the protein structure, increase their lipophilicity, and enable fluorine functionality as a biological tracer or probe for chemical biology studies. In this feature article, we summarized the recent advances in the synthesis of fluorinated amino acids and peptides, wherein two strategies have been discussed. One is based on the fluorinated building blocks to prepare fluorinated amino acids and peptides with diversified structures, including the transformations of fluorinated imines and nickel-catalyzed dicarbofunctionalization of alkenes with bromodifluoroacetate and its derivatives; the other is direct fluorination/fluoroakylation of amino acids, peptides, and proteins, in which the selective transformations of the functional groups on serine, threonine, tyrosine, tryptophan, and cysteine lead to a wide range of fluorinated α-amino acids, peptides, and proteins, featuring synthetic convenience and late-stage modification of biomacromolecules. These two strategies complement each other, wherein transition-metal catalysis and new fluoroalkylating reagents provide powerful tools to selectively access fluorinated amino acids, peptides, and proteins, showing the prospect of medicinal chemistry and chemical biology.

Sustainable radical approaches for cross electrophile coupling to synthesize trifluoromethyl- and allyl-substituted tert-alcohols

Trifluoromethylated molecules have gained privileged recognition among the medicinal and pharmaceutical chemists. Sustainable photoredox- and electrochemical processes were employed to facilitate the relatively less explored radical cross-electrophile coupling to access trifluoromethyl- and allyl-substituted tert-alcohols. Reactions proceed through trifluoromethyl ketyl radical and allyl radical intermediates, which undergo challenging radical-radical cross-coupling. The developed transformations are mild and chemo-selective to give cross-coupled products and deliver a wide range of valuable trifluoromethyl- and allyl-containing tertiary alcohols. Both processes can also be applied for the synthesis of amine variant containing trifluoromethyl and allyl moiety, which is considered as amide bioisostere.

Enantioselective Bifunctional Ammonium Salt-Catalyzed Syntheses of 3-CF3S-, 3-RS-, and 3-F-Substituted Isoindolinones

We herein report the ammonium salt-catalyzed synthesis of chiral 3,3-disubstituted isoindolinones bearing a heteroatom functionality in the 3-position. A broad variety of differently substituted CF3S- and RS-derivatives were obtained with often high enantioselectivities when using Maruoka's bifunctional chiral ammonium salt catalyst. In addition, a first proof-of-concept for the racemic synthesis of the analogous F-containing products was obtained as well, giving access to one of the rare examples of a fairly stable α-F-α-amino acid derivative.

Catalytic asymmetric synthesis of quaternary trifluoromethyl α- to ε-amino acid derivatives via umpolung allylation/2-aza-Cope rearrangement

In this study, we developed an efficient Ir-catalyzed cascade umpolung allylation/2-aza-Cope rearrangement of tertiary α-trifluoromethyl α-amino acid derivatives for the preparation of a variety of quaternary α-trifluoromethyl α-amino acids in high yields with excellent enantioselectivities. The umpolung reactivity empowered by the activation of the key isatin-ketoimine moiety obviates the intractable enantioselectivity control in Pd-catalyzed asymmetric linear α-allylation. In combination with quasi parallel kinetic resolution or kinetic resolution, the generality of this method is further demonstrated by the first preparation of enantioenriched quaternary trifluoromethyl β-, γ-, δ- and ε-amino acid derivatives.

A Broad Substrate Scope of Aza-Friedel-Crafts Alkylation for the Synthesis of Quaternary α-Amino Esters

A versatile synthetic protocol of aza-Friedel-Crafts alkylation has been developed for the synthesis of quaternary α-amino esters. This operationally simple alkylation proceeds under ambient conditions with high efficiency, regioselectivity, and an exceptionally broad scope of arene nucleophiles. A key feature of this alkylation is the role associated with the silver(I) salt counteranions liberated during the reaction. Taking advantage of a phase-transfer counteranion/Brønsted acid pair mechanism, we also report a catalytic enantioselective example of the reaction.

Asymmetric synthesis of quaternary α-trifluoromethyl α-amino acids by Ir-catalyzed allylation followed by kinetic resolution

Facile access to quaternary α-trifluoromethyl α-amino acids has been developed. This sequential reaction involves an Ir-catalyzed asymmetric allylation of α-trifluoromethyl aldimine esters followed by an unprecedented kinetic resolution.