Methyl Ketones as Alkyl Halide Surrogates: A Deacylative Halogenation Approach for Strategic Functional Group Conversions

Dual-nickel/photoredox-catalyzed acylation of spiro-dihydroquinazolinones with carboxylic acids via an aromatization-driven deconstructive strategy

Dual-nickel/photoredox-catalyzed aromatization-mediated deconstruction and acylation of spiro-dihydroquinazolinones with carboxylic acids serving as acyl electrophiles is described. A series of synthetical ketone scaffolds with functional group tolerance could be obtained under mild conditions. A radical pathway involving an N-centered radical inducing β-scission to form a C-centered radical is proposed for these transformations.

Co(III)-Catalyzed, N-Amino-Directed C-H Coupling with 4-Hydroxy-2-alkynoates for Indole Synthesis

Conventional synthetic organic chemistry typically relies on site-centered reactivity for the reaction discovery. Herein, skeleton-chaperoned reactivity is exploited for reaction development, with the skeleton utilized as a structural scaffold for assisting functional group activation into a proper reactivity sequence. A Co(III) catalytic method has been developed for N-amino-directed C-H coupling with 4-hydroxy-2-alkynoates, allowing convenient access to 2-alkene-3-carboxylic acid type indole derivatives. This reaction features phenyl/pyrrole/lactone skeleton-chaperone reactivity and simultaneous conversion of five functional groups.

Deacylative Homolysis of Ketone C(sp3)-C(sp2) Bonds: Streamlining Natural Product Transformations

The homolytic cleavage of C-C bonds adjacent to specific functional groups has lately emerged as a versatile approach for molecular diversification. Despite the ubiquity and synthetic utility of ketones, radical fragmentation of their α-C-C bonds has proven to be a formidable challenge. Here, we present a broadly applicable deacylative strategy designed to homolytically cleave aliphatic ketones of various complexities, including transformations of cycloalkanones into carboxylic acids tethered to C-centered free radicals that can be engaged in diverse radical-based processes. The method involves ketone activation through treatment with hydrogen peroxide, yielding gem-dihydroperoxides. Subsequent single-electron-transfer reduction mediated by a low-valent metal complex generates alkyl radicals that can be captured selectively with a radicophile of choice, including through catalytic cross-coupling. The logic of our deacylative functionalization is exemplified by the total synthesis of 14 natural products, one analogue, and two drugs starting from readily available natural products, showcasing its transformative power in complex settings. This approach obviates the need for complex reagents and allows the controlled conversion of ketones to reconstructed products, making the process highly applicable across a spectrum of domains.

Halodealkenylation: Ozonolysis and Catalytic FeII with Vitamin C Convert C(sp3)-C(sp2) Bonds to C(sp3)-Halide Bonds

As part of our investigations into C-C bond scission and functionalization, we report a halodealkenylation in which the C(sp3)-C(sp2) bonds of alkenes are cleaved and C(sp3)-halide bonds are formed, via a radical intermediate. These transformations occur through Criegee ozonolysis and FeII-catalyzed reductive coupling assisted by vitamin C as a stoichiometric reductant. We applied this strategy to the formal synthesis of (R,R,R)-γ-tocopherol.

Ketone Skeletal Modification via a Metallaphotoredox-Catalyzed Deacylation and Acylation Strategy

Herein, we describe a dual catalytic strategy that employs dihydroquinazolinones, derived from ketone analogs, as versatile intermediates for acylation via α C-C cleavage with 2-pyridyl esters, facilitating the efficient synthesis of a variety of ketones. The reaction accommodates a wide range of ketones and carboxylic acids, showing tolerance to various functional groups. The versatility of this synthetic technique is further highlighted through its application in the late-stage modification of pharmaceuticals and biologically active natural products.

Shuttle HAT for mild alkene transfer hydrofunctionalization

Hydrogen atom transfer (HAT) from a metal-hydride is a reliable and powerful method for functionalizing unsaturated C-C bonds in organic synthesis. Cobalt hydrides (Co-H) have garnered significant attention in this field, where the weak Co-H bonds are most commonly generated in a catalytic fashion through a mixture of stoichiometric amounts of peroxide oxidant and silane reductant. Here we show that the reverse process of HAT to an alkene, i.e. hydrogen atom abstraction of a C-H adjacent to a radical, can be leveraged to generate catalytically active Co-H species in an application of shuttle catalysis coined shuttle HAT. This method obviates the need for stoichiometric reductant/oxidant mixtures thereby greatly simplifying the generation of Co-H. To demonstrate the generality of this shuttle HAT platform, five different reaction manifolds are shown, and the reaction can easily be scaled up to 100 mmol.

Direct Excitation Strategy for Deacylative Couplings of Ketones

The homolysis of chemical bonds represents one of the most fundamental reactivities of excited molecules. Historically, it has been exploited to generate radicals under ultraviolet (UV) light irradiation. However, unlike most contemporary radical-generating mechanisms, the direct excitation to homolyze chemical bonds and produce aliphatic carbon-centered radicals under visible light remains rare, especially in metallaphotoredox cross couplings. Herein, we present our design of the dihydropyrimidoquinolinone (DHPQ) reagents derived from ketones, which can undergo formal deacylation and homolytic C-C bond cleavage to release alkyl radicals without external photocatalysts. Spectroscopic and computational analysis reveal unique optical and structural features of DHPQs, rationalizing their faster kinetics in alkyl radical generation than a structurally similar but visible-light transparent radical precursor. Such a capability allows DHPQ to facilitate a wide range of Ni-metallaphotoredox cross couplings with aryl, alkynyl and acyl halides. Other catalytic and non-catalyzed alkylative transformations of DHPQs are also feasible with various radical acceptors. We believe this work would be of broad interest, aiding the synthetic planning with simplified operation and expanding the synthetic reach of photocatalyst-free approaches in cutting-edge research.

Homologation of Ketones: Direct Transformation of Alkyl Ketones to Aryl Ketones via Photoredox Catalyzed Deacylation-Aroylation Sequence

Ketones, as essential functional group skeletons, have garnered significant interest due to their diverse transformations. Herein, we describe a versatile photoredox catalyzed deacylation-aroylation strategy that enables the direct transformation of alkyl ketones to aryl ketones. This process involves photoredox deacylation of dihydroquinazolinones derived from alkyl ketones to generate alkyl radicals, followed by subsequent NHC-catalyzed or NHC-mediated radical aroylation.

Molecular Editing of Ketones through N-Heterocyclic Carbene and Photo Dual Catalysis

The molecular editing of ketones represents an appealing strategy due to its ability to maximize the structural diversity of ketone compounds in a straightforward manner. However, developing efficient methods for the arbitrary modification of ketonic molecules, particularly those integrated within complex skeletons, remains a significant challenge. Herein, we present a unique strategy for ketone recasting that involves radical acylation of pre-functionalized ketones facilitated by N-heterocyclic carbene and photo dual catalysis. This protocol features excellent substrate tolerance and can be applied to the convergent synthesis and late-stage functionalization of structurally complex bioactive ketones. Mechanistic investigations, including experimental studies and density functional theory (DFT) calculations, shed light on the reaction mechanism and elucidate the basis of the regioselectivity.

Visible Light-Induced, Nickel-Catalyzed Late-Stage 4-Alkylation of Hantzsch Esters with Alkyl Bromide

Herein, visible light-induced, nickel-catalyzed direct functionalization of the Hantzsch esters (HEs) with readily accessible alkyl bromides has been successfully achieved by taking advantage of HE as the reductant and substrate through an aromatization-dearomatization process. In this strategy, the single electron reduction of alkyl bromides by reactive Ni(I) species is essential for the success of this late-stage transformation. A wide range of 4-alkyl-1,4-dihydropyridines were rapidly assembled in moderate to good yields under mild conditions, rendering this photoinduced approach attractive for synthetic and medicinal chemistry.

Deacylative arylation and alkynylation of unstrained ketones

Ketones are ubiquitous in bioactive natural products, pharmaceuticals, chemical feedstocks, and synthetic intermediates. Hence, deacylative coupling reactions enable the versatile elaboration of a plethora of chemicals to access complex drug candidates and natural products. Here, we present deacylative arylation and alkynylation strategies for the synthesis of a wide range of alkyl-tethered arenes and alkynes from cyclic ketones and methyl ketones under dual nickel/photoredox catalysis. This reaction begins by generating a pre-aromatic intermediate (PAI) through the condensation of the ketone and N'-methylpicolino-hydrazonamide (MPHA), followed by the oxidative cleavage of the PAI α-C─C bond to form an alkyl radical, which is subsequently intercepted by a Ni complex, facilitating the formation of diverse C(sp3)-C(sp2)/C(sp) bonds with remarkable generality. This protocol features a one-pot reaction capability, high regioselectivity and ring-opening efficiency, mild reaction conditions, and a broad substrate scope with excellent functional group compatibility.