Oxidation and Reduction

Maity S., Hoz S.

Chung W., Choi J., Jeong I., Im J.K., Yang B., Moon H.

AbstractAn unprecedented N-chlorinative ring contraction of 1,2-diazines was discovered and investigated with an electrophilic chlorinating reagent, trichloroisocyanuric acid (TCICA). Through optimization and mechanistic analysis, the assisting role of n-Bu4NCl as an exogenous nucleophile was identified, and the optimized reaction conditions were applied to a range of 1,4-dimethoxyphthalazine derivatives. Also, an improvement of overall efficiency was demonstrated by the use of a labile O-silyl group. A bicyclization/ring-opening mechanism, inspired by the Favorskii rearrangement, was proposed and supported by the DFT calculations. Furthermore, the efforts on scope expansion as well as the evaluation of other electrophilic promoters revealed that the newly developed ring contraction reactivity is a unique characteristic of 1,4-dimethoxyphthalazine scaffold and TCICA.

Zhang C., Qiu Y., Zhang J., Chen L., Xu S., Guo H., Luo J., Tan Y.

Leitch M.A., O’Neil G.W.

A series of experiments were performed to determine if SmI2(H2O)n reductions of allylic benzoates was stereospecific to alkene geometry. The results indicate that for alkyl-substituted alkenes, the reaction is stereospecific (i.e. the cis- and trans-isomers select for the opposite major diastereomer). However, the introduction of a phenyl substituent causes the reaction to become non-stereospecific, both cis- and trans-isomers converging to the same major diastereomer. A potential rationale is presented based on stabilization of a proposed organosamarium intermediate by the phenyl group that allows for isomerization of alkene geometry to a sterically preferred trans-configuration at the transition state. The data provide further insights into the mechanism of this reaction, the nature of allylic organosamarium complexes, and the unique reactivity of benzene rings in samarium-mediated transformations.

Sharma K., Surineni N., Gholap S.L.

The first stereoselective total synthesis of (−)-Inohanalactone is reported. The salient features of this synthesis are highly Z-selective Wittig olefination and chemoselective oxidation of 1,4 diol to the γ-butyrolactone. The synthesis was accomplished from readily available 2,3-O-isopropylidene- l -erythrose derived from d -ribose in eight steps with 32% overall yield.

Gale-Day Z.J.

AbstractTraditionally, metal-catalyzed cross-coupling reactions rely on stable but expensive metals, such as palladium. However, the recent development of synthetic organic electrochemistry allows for in situ redox manipulations, expanding the use of cheaper, abundant and sustainable metals, such as nickel and copper as efficient cross-coupling catalysts. This short review covers the recent advances in metal-catalyzed electrochemical coupling reactions, with a focus on reactions of sp2 electrophiles and nucleophiles with sp3 coupling partners to form both C–C and C–heteroatom bonds.1 Introduction2 Nickel-Catalyzed C–C sp2–sp3 Coupling Reactions3 Coupling of Aryl Groups with Heteroatomic Nuclei4 Conclusion

Li C., Ung S.P., Mechrouk V.A.

AbstractOrganophosphorus compounds have numerous useful applications, from versatile ligands and nucleophiles in the case of trivalent organophosphorus species to therapeutics, agrochemicals and material additives for pentavalent species. Although phosphorus chemistry is a fairly mature field, the construction of C–P(V) bonds relies heavily on either prefunctionalized substrates such as alkyl or aryl halides, or requires previously oxidized bonds such as C=N or C=O, leading to potential sustainability issues when looking at the overall synthetic route. In light of the recent advances in photochemistry, using photons as a reagent can provide better alternatives for phosphorylations by unlocking radical mechanisms and providing interesting redox pathways. This review will showcase the different photomediated phosphorylation procedures available for converting C–H bonds into C–P(V) bonds.1 Introduction1.1 Organophosphorus Compounds1.2 Phosphorylation: Construction of C–P(V) Bonds1.3 Photochemistry as an Alternative to Classical Phosphorylations2 Ionic Mechanisms Involving Nucleophilic Additions3 Mechanisms Involving Radical Intermediates3.1 Mechanisms Involving Reactive Carbon Radicals3.2 Mechanisms Involving Phosphorus Radicals3.2.1 Photoredox: Direct Creation of Phosphorus Radicals3.2.2 Photoredox: Indirect Creation of Phosphorus Radicals3.2.3 Dual Catalysis3.3 Photolytic Cleavage4 Conclusion and Outlook

Kubicskó K., Farkas Ö.

Oxidation mechanism pathways of psychedelic N,N-dimethyltryptamine, or the so-called “spirit molecule”, with monoamine oxidase A enzyme were determined.

Ura Y.

AbstractCatalytic anti-Markovnikov (AM) oxidation of terminal alkenes can provide terminally oxyfunctionalized organic compounds. This short review mainly summarizes our recent progress on the Pd-catalyzed AM oxidations of aromatic and aliphatic terminal alkenes to give terminal acetals (oxidative acetalization) and aldehydes (Wacker-type oxidation), along with related reports. These reactions demonstrate the efficacy of the PdCl2(MeCN)2/CuCl/electron-deficient cyclic alkenes/O2 catalytic system. Notably, electron-deficient cyclic alkenes such as p-benzoquinones (BQs) and maleimides are key additives that facilitate nucleophilic attack of oxygen nucleophiles on coordinated terminal alkenes and enhance the AM selectivity. BQs also function to oxidize Pd(0) depending on the reaction conditions. Several other factors that improve the AM selectivity, such as the steric demand of the nucleo­philes, slow substrate addition, and halogen-directing groups, are also discussed.1 Introduction2 Anti-Markovnikov Oxidation of Aromatic Alkenes to Terminal Acetals­3 Anti-Markovnikov Oxidation of Aromatic Alkenes to Aldehydes4 Anti-Markovnikov Oxidation of Aliphatic Alkenes to Terminal Acetals­5 Anti-Markovnikov Oxidation of Aliphatic Alkenes to Aldehydes6 Conclusion

Luo H., Sun K., Xie Q., Li X., Zhang X., Luo X.

Sloane S.E., Reyes A., Vang Z.P., Li L., Behlow K.T., Clark J.R.

A copper-catalyzed reduction of alkynes to alkanes and deuterated alkanes is described under transfer hydrogenation and transfer deuteration conditions. Commercially available alcohols and silanes are used interchangeably with their deuterated analogues as the hydrogen or deuterium sources. Transfer deuteration of terminal and internal aryl alkynes occurs with high levels of deuterium incorporation. Alkyne-containing complex natural product analogues undergo transfer hydrogenation and transfer deuteration selectively, in high yield. Mechanistic experiments support the reaction occurring through a cis-alkene intermediate and demonstrate the possibility for a regioselective alkyne transfer hydrodeuteration reaction.

Fu J., Shi L., Gao S., Chang L., Wang B.

AbstractThe Mizoroki–Heck reaction is considered as one of the most ingenious and widely used methods for constructing C–C bonds. This reaction mainly focuses on activated olefins (styrenes, acrylates, or vinyl ethers) and aryl/vinyl (pseudo) halides. In comparison, the studies on unactivated alkenes and alkyl electrophiles are far less due to the low reactivity, poor selectivity, as well as competitive β-H elimination. In the past years, a growing interest has thus been devoted and significant breakthroughs have been achieved in the employment of unactivated alkenes and alkyl electrophiles as the reaction components, and this type of coupling is called as Heck-type or Heck-like reaction, which distinguishes from the traditional Heck reaction. Herein, we give a brief summary on Heck-type reaction between unactivated alkenes and alkyl electrophlies, covering its initial work, recent advancements, and mechanistic discussions.1 Introduction2 Intramolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles2.1 Cobalt-Catalyzed Intramolecular Heck-Type Reaction2.2 Palladium-Catalyzed Intramolecular Heck-Type Reaction2.3 Nickel-Catalyzed Intramolecular Heck-Type Reaction2.4 Photocatalysis and Multimetallic Protocol for Intramolecular Heck-Type Reaction3 Intermolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles3.1 Electrophilic Trifluoromethylating Reagent as Reaction Partners3.2 Alkyl Electrophiles as Reaction Partners4 Oxidative Heck-Type Reaction of Unactivated Alkenes and Alkyl Radicals5 Conclusions and Outlook

Leitch D.C., Becica J.

AbstractThe activation of strong C–O bonds in cross-coupling catalysis can open up new oxygenate-based feedstocks and building blocks for complex-molecule synthesis. Although Ni catalysis has been the major focus for cross-coupling of carboxylate-based electrophiles, we recently demonstrated that palladium catalyzes not only difficult C–O oxidative additions but also Suzuki-type cross-couplings of alkenyl carboxylates under mild conditions. We propose that, depending on the reaction conditions, either a typical Pd(0)/(II) mechanism or a redox-neutral Pd(II)-only mechanism can operate. In the latter pathway, C–C bond formation occurs through carbopalladation of the alkene, and C–O cleavage by β-carboxyl elimination.1 Introduction2 A Mechanistic Challenge: Activating Strong C–O Bonds3 Exploiting Vinylogy for C–Cl and C–O Oxidative Additions4 An Alternative Mechanism for Efficient Cross-Coupling Catalysis5 Conclusions and Outlook

Gopalaiah K., Tiwari A.

Zheng L., Jiang Q., Bao H., Zhou B., Luo S., Jin H., Wu H., Liu Y.

An unprecedented exploration of tertiary amines as alkyl radical equivalents for cross-coupling with aromatic alkynes to access allylarenes has been achieved by a P/N heteroleptic Cu(I)-based photo...