Tin-Free Radical Acylation Reactions with Methanesulfonyl Oxime Ether

Visible-Light-Driven Photocatalyst-Free Deoxygenative Radical Transformation of Alcohols to Oxime Ethers

A visible-light-driven deoxygenative cross-coupling of alcohols with sulfonyl oxime ethers has been developed by using xanthate salts as alcohol-activating groups. Upon convenient generation and direct photoexcitation of xanthate anions, a broad range of alcohols including primary ones can efficiently undergo this transformation to afford diverse oxime ethers and derivatives. This one-pot protocol features mild conditions, broad substrate scope, and late-stage applicability, without the need for any external photocatalysts or electron donor-acceptor complex formation.

Metal-free synthesis of N-sulfonylformamidines via skeletal reconstruction of sulfonyl oximonitriles

We firstly develop an unprecedented domino reaction of sulfonyl oximonitriles with secondary amines to streamline synthesis of N-sulfonylformamidines in decent to high yields under mild reaction conditions.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Visible Light-Induced Pd-Catalyzed Alkyl-Heck Reaction of Oximes

A visible light-induced palladium-catalyzed oxidative C-H alkylation of oximes has been developed. This mild protocol allows for an efficient atom economical C-C bond construction of alkyl-substituted oximes. A broad range of primary, secondary, and tertiary alkyl bromides and iodides, as well as a range of different formaldoximes, can efficiently undergo this transformation. The method features visible light-induced generation of nucleophilic hybrid alkyl Pd radical intermediates, which upon radical addition at the imine moiety and a subsequent β-hydrogen elimination deliver substituted imines.

A silver-catalyzed radical ring-opening reaction of cyclopropanols with sulfonyl oxime ethers

A silver-catalyzed ring-opening reaction of cyclopropanols with sulfonyl oxime ethers has been developed. The protocol was conducted under mild reaction conditions to provide a series of γ-keto oxime ethers with moderate to good yields. The reaction proceeded in a stereoselective manner for CF3-containing oxime ethers to provide a single stereoisomer, while an inseparable E and Z mixture was obtained for CN-containing oxime ethers. Mechanistic studies indicate that the reaction proceeded via a radical mechanism.

Silver-catalyzed remote Csp3-H functionalization of aliphatic alcohols

Aliphatic alcohols are common and bulk chemicals in organic synthesis. The site-selective functionalization of non-activated aliphatic alcohols is attractive but challenging. Herein, we report a silver-catalyzed δ-selective Csp3-H bond functionalization of abundant and inexpensive aliphatic alcohols. Valuable oximonitrile substituted alcohols are easily obtained by using well-designed sulphonyl reagents under simple and mild conditions. This protocol realizes the challenging δ-selective C-C bond formation of simple alkanols.

C-H Xanthylation: A Synthetic Platform for Alkane Functionalization

Intermolecular functionalizations of aliphatic C-H bonds offer unique strategies for the synthesis and late-stage derivatization of complex molecules, but the chemical space accessible remains limited. Herein, we report a transformation significantly expanding the chemotypes accessible via C-H functionalization. The C-H xanthylation proceeds in useful chemical yields with the substrate as the limiting reagent using blue LEDs and an easily prepared N-xanthylamide. The late-stage functionalizations of complex molecules occur with high levels of site selectivity, and a variety of common functionality is tolerated in the reaction. This approach capitalizes on the versatility of the xanthate functional group via both polar and radical manifolds to unlock a wide array of C-H transformations previously inaccessible in synthesis.

Control of asymmetry in the radical addition approach to chiral amine synthesis

The state-of-the-science in asymmetric free radical additions to imino compounds is presented, beginning with an overview of methods involving stereocontrol by various chiral auxiliary approaches. Chiral N-acylhydrazones are discussed with respect to their use as radical acceptors for Mn-mediated intermolecular additions, from design to scope surveys to applications to biologically active targets. A variety of aldehydes and ketones serve as viable precursors for the chiral hydrazones, and a variety of alkyl iodides may be employed as radical precursors, as discussed in a critical review of the functional group compatibility of the reaction. Applications to amino acid and alkaloid synthesis are presented to illustrate the synthetic potential of these versatile stereocontrolled carbon-carbon bond construction reactions. Asymmetric catalysis is discussed, from seminal work on the stereocontrol of radical addition to imino compounds by non-covalent interactions with stoichiometric amounts of catalysts, to more recent examples demonstrating catalyst turnover.

Trifluoromethyl ketones: properties, preparation, and application

Trifluoromethyl ketones (TFMKs) are exceedingly valuable synthetic targets in their own right and as synthons in the construction of fluorinated pharmacons. This Feature Article provides an overview of the properties of TFMKs, an in-depth discussion of the methods available for their synthesis, and two illustrative examples of their application as key intermediates in medicinal chemistry.

Facile nucleophilic substitution of sulfonyl oxime ethers: an easy access to oxime ethers, carbonyl compounds and amines

Sulfonyl oxime ethers undergo facile nucleophilic substitutions with various nucleophiles to yield the corresponding oxime ethers which provide an easy access to amines and carbonyl compounds.

Cobalt catalyzed functionalization of unactivated alkenes: regioselective reductive C-C bond forming reactions

The cobalt catalyzed hydroaldoximation and hydrocyanooximation of unactivated alkenes is reported. Secondary and tertiary aldoximes and oximonitriles are synthesized with excellent regioselectivity under mild conditions, and conversion of the products to valuable intermediates is documented. The reactions expand the arsenal of reductive carbon-carbon bond forming reactions as well as regioselective functionalizations of unactivated double bonds.

Dimethylzinc-initiated radical reactions

Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions. This Account describes our investigations of radical reactions initiated by dimethylzinc. In 2001, we unexpectedly observed this reaction while investigating the amidophosphane-copper-catalyzed asymmetric addition of dimethylzinc to N-sulfonyl imines with tetrahydrofuran (THF) as reaction solvent. However, instead of adding the desired methyl group to the N-sulfonyl imine, we produced the THF adduct in excellent yield. This result laid the foundation for our discovery of novel modes of reactivity. Further investigations of the unexpected addition reaction revealed that a trace amount of air was needed for reaction progress, indicating that radical intermediates were involved. Indeed, controlled injection of air into the reaction flask by a syringe pump through a sodium hydroxide tube afforded the products in good to excellent yield. In addition, the reaction proved to be chemoselective for a C=N bond over a C=O bond, as well as for 1,4-addition over 1,2-addition. We developed asymmetric variants of the radical addition reaction of ethers to imines using chiral N-sulfinyl imines to produce the adducts in reasonably high stereoselectivity (up to 11:1). A 93:7 diastereomeric ratio of the adduct was obtained when bis(8-phenylmenthyl) benzylidenemalonate was used in the radical addition of ethers to C=C bonds. Interestingly, in the presence of dimethylzinc and air, arylamines, alkoxyamines, and dialkylhydrazines react with THF to give amino alcohols, oximes, and hydrazones, respectively, in moderate to high yields. We performed a tin-free intermolecular addition of functionalized primary alkyl groups, generated from their corresponding iodides, to N-sulfonyl imines using dimethylzinc, air, boron trifluoride diethyl etherate, and a catalytic amount of copper(II) triflate. Direct C-H bond cleavage from cycloalkanes was also feasible in the presence of dimethylzinc, air, and boron trifluoride diethyl etherate to give the corresponding cycloalkyl radicals, which were suitable nucleophiles for N-sulfonyl imines. In all of the above reactions, dimethylzinc was a superior radical initiator than other conventional initiators such as dibenzoyl peroxide, diethylzinc, and triethylborane. We hope the coming decades will witness the report of other novel radical initiators that would complement the reactivity modes of existing ones.

Tin-free radical carbonylation of alkylsulfonyl derivatives into alkylcarbonyl derivatives

A simple radical approach based on tin-free radical carbonylation is devised for the direct conversion of alkylthiosulfonates, alkylsulfonyl cyanides, and alkylsulfonyl oxime ethers into the corresponding alkyl thiol esters, acyl cyanides, and acylated oxime ethers in a single step. The present approach is very simple, highly efficient, and minimizes the formation of byproducts.

Powerful CarbonCarbon Bond Forming Reactions Based on a Novel Radical Exchange Process

Xanthates and related derivatives have proved to be extremely useful for both inter- and intramolecular radical additions. The broad applicability of the intermolecular addition to un-activated olefins opens tremendous opportunities for synthesis, since various functional groups can be brought together under mild conditions and complex structures can be rapidly assembled. The presence of the xanthate in the product is also a powerful asset for further modifications, by both radical and non-radical pathways. Of special importance is the access to highly substituted aromatic and heteroaromatic derivatives and the synthesis of block polymers through a controlled radical polymerisation mediated by various thiocarbonylthio group containing agents (RAFT and MADIX processes).

Reactive Ketimino Radical Acceptors: Intermolecular Alkyl Radical Addition to Imines with a Phenolic Hydroxyl Group

Intermolecular carbon radical addition to the carbon-nitrogen double bond of ketimines was studied. In the study on the reactivity of various aldimines, we found that the aldimine 7 having a phenolic hydroxyl group shows an excellent reactivity toward nucleophilic carbon radicals. A remarkable effect of phenolic hydroxyl group is assumed to be the stabilization of intermediate aminyl radical provided by a hydroxyl group. The screening of reactive ketimino acceptors showed that ketimines 15, 17, and 19 having a phenolic hydroxyl group exhibit excellent reactivities. The radical addition to ketimines 15, 17, and 19 took place regioselectively at the imino carbon to give the C-alkylated products without the formation of N-alkylated products. Enantioselective ethyl radical addition to ketimine 15 using chiral box ligand and Zn(OTf)2 gave the diethylated product 30 in 80% ee.

Triethylborane-Induced Intermolecular Radical Addition to Ketimines

The intermolecular carbon radical addition to ketimines was investigated by using triethylborane as a radical initiator. The screening of reactive radical acceptors showed that pyruvic hydrazone 3 and isatin hydrazone 7 exhibit good reactivities toward nucleophilic alkyl radicals. The reaction of 3 and 7 proceeded effectively even under aqueous-medium reaction conditions. In the presence of BF(3).OEt(2), the radical addition to chiral ketimine 11 proceeded with good diastereoselectivities.

Photoinduced Atom-Transfer Cyclization of α-Iodocycloalkanones Bearing an Allenyl Side Chain

[reaction: see text] Irradiation of alpha-iodocycloalkanones bearing an allenyl side chain with a sunlamp effected atom-transfer cyclization to give cyclized products in good yield. A mechanism, involving radical atom-transfer cyclization accompanied by 1,5- and 1,4-hydrogen transfers, is proposed.

Novel radical alkylation of carboxylic imides

Although alkylation is one of the most important and fundamental organic reactions, radical-mediated alkylations of carboxylic acid derivatives have not been well studied. The first successful radical alkylation of carboxylic imides is achieved by the addition of an alkyl radical to a ketene O,N-acetal and the subsequent cleavage of N-O bond. It is noteworthy that alkyl halides activated with an electron-withdrawing group undergo alkylations under tin-free conditions due to 1,2-phenyl transfer from silyl to oxygen.

A new synthesis of pyrroles

The radical reaction between an N-ethylsulfonylenamide and an alpha-xanthyl ketone gives an intermediate gamma-keto imine which spontaneously ring-closes to the pyrrole.