α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

α-Amino Acids: An Emerging Versatile Synthon in Visible Light-Driven Decarboxylative Transformations

α-Amino acids have been widely recognized as environmental-benign and non-fossil carbon sources both in biological and synthetic chemistry. In recent years, with the remarkable development of visible-light photocatalysis in organic synthesis, α-amino acid and its derivatives have received tremendous attention as radical precursors via photocatalyzed decarboxylation, thus realizing diverse aminoalkylated transformations or constructions of novel N-bearing heterocyclic motifs by taking advantage of N-atoms from α-amino acid. This review aims to provide a comprehensive update on the recent exploitation of α-amino acids in visible light photocatalysis, with particular emphasis on the types of α-amino acids employed and their distinct mechanisms applied wherein.

Recent Advances in the Enantioselective Radical Reactions

The review covers research published since 2017 and is focused on enantioselective synthesis using radical reactions. It describes recent approaches to the asymmetric synthesis of chiral molecules based on the application of the metal catalysis, dual metal and organocatalysis and finally, pure organocatalysis including enzyme catalysis. This review focuses on the synthetic aspects of the methodology and tries to show which compounds can be obtained in enantiomerically enriched forms.

Ion-Pairing Catalysis in Stereoselective, Light-Induced Transformations

With the rapid development of photoredox catalysis, numerous concepts for asymmetric induction were successfully and broadly adapted from polar two-electron transformations to radical chemistry. While this applies to organocatalysis or transition metal chemistry, asymmetric ion-pairing catalysis remains a niche application within light-driven reactions today. This perspective gives an overview of recent examples, strategies, and their application in stereoselective transformations at the interface of ion-pairing and photo(redox) catalysis.

Enantioselective synthesis of isoxazole-containing spirooxindole tetrahydroquinolines via squaramide-catalysed cascade reactions

A class of o-sulfonylaminostyryl isoxazole synthons were designed and demonstrated to be useful building blocks in asymmetric cascade aza-Michael/Michael reaction with 3-olefinic oxindoles. This squaramide-catalysed cascade reaction afforded structurally complex isoxazole-containing spirooxindole tetrahydroquinolines bearing three contiguous stereocenters in good to excellent yields (up to 99%) with high diastereoselectivities (up to >20 : 1 dr) and enantioselectivities (up to 88% ee). Moreover, the gram-scale synthesis and synthetic transformations were also demonstrated.

Photoredox Activation of Inert Alkyl Chlorides for the Reductive Cross-Coupling with Aromatic Alkenes

The inertness of chloroalkanes has precluded them as coupling partners for cross-coupling reactions. Herein we disclose a general strategy for the activation of inert alkyl chlorides through photoredox catalysis and their use as coupling partners with alkenes. The catalytic system is formed by [Ni(OTf)(Py₂ ^Ts tacn)](OTf) (1_Ni ), which is responsible for the Csp³ -Cl bond activation, and [Ir(^NMe2 bpy)(ppy)₂ ]PF_6, (PC_Ir ^NMe2 ), which is the photoredox catalyst. Combined experimental and theoretical studies show an in situ photogenerated Ni^I intermediate ([Ni(Py₂ ^Ts tacn)]⁺ ) which is catalytically competent for the Csp³ -Cl bond cleavage via a S_N 2 mechanism for primary alkyl chlorides, forming carbon-centered free radicals, which react with the olefin leading to the formation of the Csp³ -Csp³ bond. These results suggest inert alkyl chlorides can be electrophiles for developing new intermolecular strategies in which low-valent aminopyridine nickel complexes act as key catalytic species.

Catalytic Asymmetric Reductive Azaarylation of Olefins via Enantioselective Radical Coupling

Visible-light-driven photocatalytic reductive azaarylation has been widely used to construct the important imine-containing azaarene derivatives. In addition to the direct use of various commercially available cyanoazaarenes as feedstocks, the synthetic advantages include precise regioselectivity, high efficiency, mild reaction conditions, and good functional group tolerance. However, although many efficient reductive azaarylation methods have been established, the example of an enantioselective manner is still unmet, which most likely can be ascribed to the highly reactive radical coupling as the key step of forming stereocenters. Exploring the feasibility of enantiocontrol thus constitutes an attractive but highly challenging task. Here, we demonstrate that chiral hydrogen-bonding/photosensitizer catalysis is a viable platform as it enables the realization of the first enantioselective manifold. A variety of acyclic and cyclic enones as the reaction partners are compatible with the dual catalyst system, leading to a wide array of valuable enantioenriched azaarene variants with high yields and ees. Regulating the types of chiral catalysts represents one of the important manners to success, in which several readily accessible Cinchona alkaloid-derived bifunctional catalysts are introduced in asymmetric photochemical reactions.

Recent Progress in Organophotoredox Reaction

In the past decade, visible light photoredox catalysis has been established as a gentle and powerful strategy for the activation of organic molecules. As an important part of it, organic...

Catalyst-free visible light-induced decarboxylative amination of glycine derivatives with azo compounds

A visible light-induced, catalyst-free decarboxylative amination of glycine derivatives with azo compounds was achieved to deliver functionalized aminals under mild reaction conditions.

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.

Syntheses of new chiral chimeric photo-organocatalysts

A new family of chiral chimeric photo-organocatalysts derived from phosphoric acid were synthesized and their spectroscopic and electrochemical properties were investigated. Then, the ability of these photo-activable molecules to catalyse an asymmetric tandem electrophilic β-amination of enecarbamates was evaluated.

Enantioconvergent Substitution Reactions of Racemic Electrophiles by Organocatalysis

Over the past decades, the development of enantioselective catalysis using organocatalysts has evolved into an active research field and a number of enantioselective transformations have been established. However, despite their being a highly desirable process for the synthesis of organic molecules in an enantioenriched form, the enantioconvergent substitution reactions of racemic electrophiles using organocatalysts still present several challenges. Although intrinsic difficulties in the catalytic stereocontrol abound due to the initial chiral information of racemic electrophiles, in recent years, mechanistically diverse enantioconvergent processes have been intensively investigated in organocatalysis. This Minireview focuses on recent achievements in the development of enantioconvergent substitution reactions of racemic electrophiles using organocatalysts. The contents are classified on the basis of the mechanistic types of enantioconvergent processes.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Ring expansion and ring opening of 3-halooxindoles with N-alkoxycarbonyl-O-tosylhydroxylamines for divergent access to 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas

The reaction of N-alkoxycarbonyl-O-tosylhydroxylamines with indol-2-ones in situ generated from 3-halooxindoles has been developed for divergently accessing 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas in good to excellent yields.

Recent developments in enantioselective photocatalysis

Enantioselective photocatalysis has rapidly grown into a powerful tool for synthetic chemists. This review describes the various strategies for creating enantioenriched products through merging enantioselective catalysis and photocatalysis, with a focus on the most recent developments and a particular interest in the proposed mechanisms for each. With the aim of understanding the scope of each strategy, to help guide and inspire further innovation in this field.

Enantioselective intramolecular [2 + 2] photocycloaddition using phosphoric acid as a chiral template

The enantioselective intramolecular [2 + 2] photocycloaddition of 4-bishomoally-2-quinolone (quinolinone) using phosphoric acid as a chiral template has been developed. Mechanistic studies using several NMR measurement techniques and density functional theory (DFT) calculations indicate that π-π interactions between the phenyl ring on phosphoric acid and quinolinone play important roles in the enantioselectivity.

Cooperative photoredox and chiral hydrogen-bonding catalysis

Chiral hydrogen-bonding catalysis is a classic strategy in asymmetric organocatalysis. Recently, it has been used to cooperate with photoredox catalysis, becoming a powerful tool to access optical pure compounds via radical-based transformations.

Asymmetric aerobic decarboxylative Povarov reactions of N-aryl α-amino acids with methylenephthalimidines via cooperative photoredox and chiral Brønsted acid catalysis

This work realizes a new synthetic utility of methylenephthalimidines as a 1,2-synthon and the synthesis of valuable chiral isoindolin-1-ones featuring a 3,3-spiro-tetrahydroquinoline-based stereocenter.

Photoredox-catalysed formal [3+2] cycloaddition of N-aryl α-amino acids with isoquinoline N-oxides

This work realizes a new synthetic utility of N-aryl α-amino acids as a 1,2-synthon, a new strategy to achieve dearomatization of isoquinolines, and the synthesis of valuable diazabicyclo[3.2.1]octane-based compounds.