Silylation and (Hetero)aryl/alkenylation of Unactivated Alkenes via Radical-Mediated Distal 1,4-Migration with Hydrosilanes under Organophotocatalysis

We report a novel organic photoredox catalysis to achieve unprecedented γ-(hetero)aryl/alkenyl-δ-silyl aliphatic amines via silyl-mediated distal (hetero)aryl/alkenyl migration of aromatic/alkenyl amines bearing unactivated alkenes with hydrosilanes. This protocol features mild and metal-free reaction conditions, high atom economy, excellent selectivity, and functional group compatibility. Mechanistic studies suggest that silylation and (hetero)aryl/alkenylation involve photoredox hydrogen atom transfer catalysis and subsequent 1,4-migration of a remote (hetero)aryl/alkenyl group from nitrogen to carbon.

Selective C(sp2)-H bond functionalization of olefins via visible-light-induced photoredox-quinuclidine dual catalysis

The site selective C(sp²)-H bond functionalization of olefins has been achieved through a visible-light-induced photoredox-quinuclidine dual catalysis upon merging the quinuclidinium radical cation addition to alkene strategy and the distal heteroaryl ipso-migration strategy. This synthetic protocol features a simple operation with readily available starting materials in good step-economy to access alkenylheteroaromatic products in moderate to good yields under mild conditions. A plausible cascade catalytic reaction mechanism is also proposed.

Electrochemical alkene azidocyanation via 1,4-nitrile migration

An electrochemical method for the azidocyanation of alkenes via 1,4-nitrile migration has been developed. This organic oxidant free method is applicable across various alkene containing cyanohydrins, and provides access to a broad range of synthetically useful 1,2-azidonitriles (28 examples). This methodology was extended to an electrochemical alkene sulfonylcyanation procedure, as well as to access a trifunctionalized hexanenitrile from a malononitrile starting material. The orthogonal derivatization of the products was also demonstrated through chemoselective transformations.

Intermolecular Carbosilylation of α-Olefins with C(sp3 )-C(sp) Bond Formation Involving Silylium-Ion Regeneration

A regioselective addition of alkynylsilanes across unactivated, terminal alkenes is reported. The reaction is initiated by the capture of a sterically unhindered silylium ion by a silylated phenylacetylene derivative to form a bis(silylated) ketene‐like carbocation. This in situ‐generated key intermediate is the actual catalyst that maintains the catalytic cycle by a series of electrophilic addition reactions of silylium ions and β‐silicon‐stabilized carbocations. The computed reaction mechanism is fully consistent with the experimental findings. This unprecedented two‐component carbosilylation establishes a C(sp³)−C(sp) bond and a C(sp³)−Si bond in atom‐economic fashion.

Radical Heteroarylation of Alkenes and Alkanes via Heteroaryl Migration

Heteroarenes are important units in organic chemistry and are ubiquitous in natural products, pharmaceuticals, and numerous artificial molecules. Despite great efforts devoted to accessing heteroarenes, the development of new methods to efficiently produce heteroarenes remains a long-term interest. Recently, the strategy of radical-mediated heteroaryl migration has supplied a robust toolkit for the synthesis of a diversity of heteroaryl-containing compounds. This Account summarizes our recent achievements in this field and provides insight into the incorporation of heteroarenes into organic skeletons.

Copper-promoted difunctionalization of unactivated alkenes with silanes

An efficient copper-catalyzed cascade difunctionalization of N-allyl anilines toward the synthesis of silylated indolines using commercially available silanes has been reported. This strategy provides a new avenue for the synthesis of a diverse array of indolines in reasonable yields. Preliminary mechanistic investigations indicate that the reaction probably proceeds via a radical pathway with unactivated alkenes as radical acceptors and simple silanes as radical precursors. This protocol is distinguished by its atom economy, broad substrate scope and readily available starting materials.

Generation of Heteroaryl-Substituted Sulfonyl Compounds from Sulfur Dioxide via Remote Heteroaryl ipso-Migration

The generation of heteroaryl-substituted sulfonyl compounds via a catalyst-, base-, and additive-free three-component reaction of heteroaryl-substituted tertiary alcohols, aryldiazonium tetrafluoroborates, and DABCO·(SO₂)₂ under mild conditions is developed. Various functional groups are tolerated well in this transformation, and a broad substrate scope is demonstrated. A preliminary mechanistic investigation shows that this reaction undergoes a radical process, including the insertion of sulfur dioxide, sulfonyl radical addition to unactivated alkene, and remote heteroaryl ipso-migration.

Radical-mediated rearrangements: past, present, and future

Rearrangement reactions, one of the most significant transformations in organic chemistry, play an irreplaceable role in improving synthetic efficiency and molecular complexity. Concomitant cleavage and reconstruction of chemical bonds can display the great artistry and the glamour of synthetic chemistry. Over the past century, ionic rearrangement reactions, in particular those involving cationic pathways, have represented most of the research. Alongside the renaissance of radical chemistry, radical-mediated rearrangements have recently seen a rapid increase of attention from the chemical community. Many new radical rearrangements that extensively reveal the migratory behaviour of functional groups have been unveiled in the last decade. This Review provides a comprehensive perspective on the area from the past to present achievements, and brings up the prospects that may inspire colleagues to develop more useful synthetic tools based on radical rearrangements.

Direct Access to α-Aminosilanes Enabled by Visible-Light-Mediated Multicomponent Radical Cross-Coupling

α-Aminosilanes are an important class of organic compounds that show biological activity. In this communication, a new approach to α-aminosilanes that utilizes photoredox catalysis to enable three-component coupling of organo(tristrimethylsilyl)silanes with feedstock alkylamines and aldehydes is presented. A wide range of highly functionalized α-aminosilanes can be obtained in good yields under mild conditions. Both primary amines and secondary amines are compatible with this transformation. Moreover, optically pure α-aminosilanes are accessible by using chiral amines. Mechanistic studies indicate that reactions proceed through radical/radical cross-coupling of silyl radicals with α-amino alkyl radicals.

Catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides via selective C-F bond activation

A regioselective carbosilylation of alkenes has emerged as a powerful strategy to access molecules with functionalized silylated alkanes, by incorporating silyl and carbon groups across an alkene double bond. However, to the best of our knowledge, organic fluorides have never been used in this protocol. Here we disclose the catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides mediated by tBuOK. The main feature of this transformation is the selective activation of the C-F bond of an organic fluoride by the silyl boronate without undergoing potential side-reactions involving C-O, C-Cl, heteroaryl-CH, and even CF3 groups. Various silylated alkanes with tertiary or quaternary carbon centers that have aromatic, hetero-aromatic, and/or aliphatic groups at the β-position are synthesized in a single step from substituted or non-substituted aryl alkenes. An intramolecular variant of this carbosilylation is also achieved via the reaction of a fluoroarene with a ω-alkenyl side chain and a silyl boronate.

Synergistic Ni/Cu catalyzed migratory arylsilylation of terminal olefins

Synthesis of organosilanes from alkenes is a very important topic owing to their wide applications. A Ni/Cu dual metal-catalyzed arylsilylation of terminal alkenes, featuring migratory selectivity, has been developed. A wide diversity of aliphatic silanes have been prepared from terminal alkenes, aryl halides and Suginome's reagent. This protocol is highlighted by excellent regioselectivity, mild reaction conditions and good functional group tolerance. In addition to benzylic positions, carbon-carbon bonds can also be constructed at allylic positions. Preliminary mechanistic studies suggest that the copper cocatalyst promotes the transmetalation of Suginome's reagent, and the addition of a PyrOx ligand inhibits the formation of side-products from the carbon-Heck pathway. Moreover, studies toward the nature of the PyrOx ligand revealed that the steric hindrance of the oxazoline moiety greatly affects the chain-walking process, but not the arylation step.

Radical heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration

Described herein is the radical-mediated heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration.

Radical-Mediated Remote Functional Group Migration

Alkenes are ubiquitous in natural products and are extensively used as synthetic feedstocks in multiple fields including organic synthesis, medicinal chemistry, and materials science. Radical-mediated difunctionalization of alkenes provides a powerful tactic for alkene utilization. Despite the considerable progress made in the past several decades, state-of-the-art methods are highly dependent upon activated alkenes in which a proximal group with a π-electron system (e.g., aryl, carbonyl, and heteroatom) is requisite to stabilize the nascent alkyl radical intermediate via p-π conjugation or p orbitals of the heteroatom. In contrast, the transformation of unactivated alkenes, such as aliphatic alkenes, remains challenging.To overcome this obstacle, we have recently disclosed the strategy of intramolecular distal functional group migration (FGM), which has been efficiently applied in radical difunctionalization of unactivated alkenes. A portfolio of functional groups, such as cyano, heteroaryl, oximino, formyl, and alkynyl groups, showcase the excellent migratory aptitude. Mechanistically, after the addition of an extrinsic radical to the alkene, the newly formed active alkyl radical is rapidly captured by the intramolecular migratory group to generate a cyclic intermediate. Subsequent cleavage of the cyclic C-C bond of the intermediate leads to the functionalized product through the FGM process. Based on the strategy of FGM, a set of elusive difunctionalizations of unactivated alkenes have been accomplished (Part A).Alongside this research, an upgraded highly efficient synthetic strategy, "dock-migration," is created for intermolecular difunctionalization of alkenes. A diversity of sulfone-based dual-function reagents are developed. The intermolecular transformation is initiated by docking the dual-function reagent to the alkene, followed by intramolecular migration of the functional group. Compared to the original FGM protocol, the scope of alkenes is significantly extended from the strategically placed tertiary alcohol-substituted alkenes to general alkenes. Both activated and unactivated alkenes are well tolerated. By this approach, radical-mediated fluoroalkylheteroarylation, fluoroalkylalkynylation, and alkylation of alkenes have been achieved (Part B).Direct elaboration of C-H bonds into the targeted functional groups represents one of the most ideal and straightforward methods for molecular functionalization. The FGM strategy proves to be an ingenious tool for radical-mediated functionalization of remote unactivated C(sp³)-H bonds. Based on the FGM process, we have accomplished: (a) remote C(sp³)-H heteroarylation and cyanation of unprotected alcohols via the cascade of alkoxy radical-enabled hydrogen atom transfer (HAT) and intramolecular functional group (e.g., heteroaryl, cyano) migration, and (b) distal C(sp³)-H vinylation of propargylic alcohols through consecutive alkenyl radical-promoted HAT process and subsequent alkenyl migration (Part C).

Iron-catalyzed acylation-functionalization of unactivated alkenes with aldehydes

Herein, an iron-catalyzed acylation-functionalization of unactivated alkenes with aldehydes via distal group ipso-migration is reported.

Aromatization-driven deconstruction/refunctionalization of unstrained rings

Aromatization-driven ring-opening/functionalization of common unstrained rings has been developed with the in situ generation of pre-aromatic fused spiro heterocycles as the key step.

Atom Transfer Oxidative Radical Cascade of Aryl Alkynoates towards 1,1-Dichalcogenide Olefins

An oxidative trifunctionalization of aryl alkynoates has been devised via the chalcogenide radical triggered intramolecular 1,4-aryl migration/decarboxylation cascade to prepare 1,1-dichalcogenide tetrasubstituted alkenes in high yields (up to 98 %). This operationally simple reaction proceeds under metal-free conditions, can be executed on gram scale, and highlights formal 1,1-difunctionalization of alkynes. Synthetic potential of this protocol was demonstrated through a twofold cascade rearrangement to access highly conjugated tetra-selenylated alkenes along with a cross-dehydrogenative annulation to prepare fluorene derivative.

Cleavage of carbon–carbon bonds by radical reactions

This review provides insights into the in situ generated radicals triggered carbon–carbon bond cleavage reactions.

Intramolecular nitration–aminocarbonylation of unactivated olefins: metal-free synthesis of γ-lactams

A novel, metal-free synthesis of valuable γ-lactams through the radical-mediated nitration–aminocarbonylation of unactivated olefins is reported.

Cyanotrifluoromethylthiolation of unactivated dialkyl-substituted alkynes via cyano migration: synthesis of trifluoromethylthiolated acrylonitriles

Herein a novel, elusive cyanotrifluoromethylthiolation of unactivated dialkyl-substituted alkynes by means of intramolecular distal cyano migration is reported.

Phosphinoyl-functionalization of unactivated alkenes through phosphinoyl radical-triggered distal functional group migration

Reported herein is a novel, mild, and practical protocol for the radical-mediated phosphinoyl-functionalization of unactivated alkenes through distal functional group migration.

Azidoheteroarylation of unactivated olefins through distal heteroaryl migration

A novel azidoheteroarylation of unactivated olefins by means of intramolecular distal heteroaryl migration is herein reported.