Iridium-Catalyzed Aerobic α,β-Dehydrogenation of γ,δ-Unsaturated Amides and Acids: Activation of Both α- and β-C-H bonds through an Allyl-Iridium Intermediate

Cu/TEMPO catalyzed dehydrogenative 1,3-dipolar cycloaddition in the synthesis of spirooxindoles as potential antidiabetic agents

A series of spiro-[indoline-3,3'-pyrrolizin/pyrrolidin]-2-ones, 4, 5 and 6 were synthesized in a sequential manner from Cu-TEMPO catalyzed dehydrogenation of alkylated ketones, 1 followed by 1,3-dipolar cycloaddition of azomethine ylides via decarboxylative condensation of isatin, 2 and l-proline/sarcosine, 3 in high regioselectivities and yields. The detailed mechanistic studies were performed to identify the reaction intermediates, which revealed that the reaction proceeds via dehydrogenative cycloaddition. Additionally, the regio and stereochemistry of the synthesized derivatives were affirmed by 2D NMR spectroscopic studies. The synthesized derivatives were explored further with molecular docking, in vitro antioxidant, and anti-diabetic activities.

γ-C (sp3)-H bond functionalisation of α,β-unsaturated amides through an umpolung strategy

The nucleophilic γ-phenylation and γ-alkylation of α,β-unsaturated amides have been developed. This umpolung reaction allows the regioselective introduction of phenyl and alkyl groups to a vinylketene N,O-acetal, which is generated in situ from an α,β-unsaturated N-alkoxyamide, followed by N-O bond cleavage in a two-step, one-pot process.

Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals

A new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic γ,δ-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including non-substituted α-, β-, and γ- and/or δ-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

Iridium-Catalyzed Cross-Coupling Reactions of Alkenes by Hydrogen Transfer

A range of Ru-, Rh-, or Pd-catalyzed vinylic C-H/C-H cross-coupling reactions of olefins have been demonstrated to provide 1,3-dienes, using a quantitative amount of metal oxidants. Although transfer hydrogenation and C-H alkenylation are two important areas that evolved independently, we herein report the first iridium-catalyzed cross-coupling reactions of alkenes by integration of directed C(alkenyl)-H alkenylation and transfer hydrogenation to obviate the usage of a metal oxidant, employing a hydrogen acceptor such as inexpensive chloranil.

Copper-catalyzed dehydrogenative γ-C(sp3)-H amination of saturated ketones for synthesis of polysubstituted anilines

Metal-catalyzed β-C-H functionalization of saturated carbonyls via dehydrogenative desaturation proved to be a powerful tool for simplifying synthesis of valuable β-substituted carbonyls. Here, we report a copper-catalyzed dehydrogenative γ-C(sp3)-H amination of saturated ketones that initiates the three-component coupling of saturated ketones, amines and N-substituted maleimides to construct polysubstituted anilines. The protocol presented herein enables both linear and α-branched butanones to couple a wide spectrum of amines and various N-substituted maleimides to produce diverse tetra- or penta-substituted anilines in fair-to-excellent yields with good functional group tolerance. The mechanism studies support that this ketone dehydrogenative γ-C(sp3)-H amination was triggered by the ketone α,β-dehydrogenation desaturation that activates the adjacent γ-C(sp3)-H bond towards functionalization. This α,β-dehydrogenation desaturation-triggered cascade sequence opens up a new avenue to the remote C(sp3)-H functionalization of saturated ketones and has the potential to enable the rapid syntheses of complex compounds from simple starting materials.

Radical α,β-Dehydrogenation of Saturated Amides via α-Oxidation with TEMPO under Transition Metal-Free Conditions

A transition metal-free radical process for the selective α,β-dehydrogenation of saturated amides under mild conditions is developed. Utilizing radical activation strategy, the challenging issue associated with the low α-acidity of amides is resolved. For the first time, α,β-unsaturated Weinreb amides and acrylamides could be efficiently prepared directly from corresponding saturated amides. Mechanistic studies confirm the radical nature of this transformation. Two gram scale α,β-dehydrogenation have also been performed to demonstrate the utility of this method.

Intermolecular, Branch-Selective, and Redox-Neutral Cp*IrIII -Catalyzed Allylic C-H Amidation

Herein, we report the redox-neutral, intermolecular, and highly branch-selective amidation of allylic C-H bonds enabled by Cp*Ir^III catalysis. A variety of readily available carboxylic acids were converted into the corresponding dioxazolones and efficiently coupled with terminal and internal olefins in high yields and selectivities. Mechanistic investigations support the formation of a nucleophilic Ir^III -allyl intermediate rather than the direct insertion of an Ir-nitrenoid species into the allylic C-H bond.

Benchmark study of popular density functionals for calculating binding energies of three-center two-electron bonds

Density functional theory (DFT) can be used to study the three-center two-electron (3c2e) bonding mode, which is universal in catalysts containing alkaline-earth (Ae) and boron-group (Bg) elements. However, because of the delocalization pattern of the 3c2e bond, the wavefunction cannot be accurately described by DFT methods. The calculated energies of Ae and Bg catalysts therefore fluctuate greatly when different functionals are used, largely because of inconsistent DFT-calculated binding energies of 3c2e bonds. Nevertheless, with the development of supercomputers and theoretical calculation software, the DFT method is becoming increasingly popular for studying Ae and Bg catalysts. In this study, we compared the performances of 21 functionals with the high-level composite G3B3 method in calculations for the binding energies of 3c2e bonds. Several frequently used post-Hartree-Fock methods were also tested. The calculation results indicate that the M06-2X, MN12-L, and MN15 functionals give consistent and reliable binding energies for common 3c2e bonds. © 2018 Wiley Periodicals, Inc.

Ir-Catalyzed Intermolecular Branch-Selective Allylic C-H Amidation of Unactivated Terminal Olefins

An efficient method for intermolecular branch-selective allylic C-H amidation has been accomplished via Ir(III) catalysis. The reaction proceeds through initial allylic C-H activation, supported by the isolation and crystallographic characterization of an allyl-Ir(III) intermediate, followed by a subsequent oxidative amidation with readily available dioxazolones as nitrenoid precursors. A diverse range of amides are successfully installed at the branched position of terminal alkenes in good yields and regioselectivities. Importantly, the reaction allows the use of amide-derived nitrenoid precursors avoiding problematic Curtius-type rearrangements.

Chemoselective α,β-Dehydrogenation of Saturated Amides

We report a method for the selective α,β-dehydrogenation of amides in the presence of other carbonyl moieties under mild conditions. Our strategy relies on electrophilic activation coupled to in situ selective selenium-mediated dehydrogenation. The α,β-unsaturated products were obtained in moderate to excellent yields, and their synthetic versatility was demonstrated by a range of transformations. Mechanistic experiments suggest formation of an electrophilic SeIV species.

Aerobic conversion of benzylic sp3 C–H in diphenylmethanes and benzyl ethers to CO bonds under catalyst-, additive- and light-free conditions

Catalyst-, additive- and light-free aerobic conversion of benzylic C–H to CO bonds is, for the first time, reported.

Platinum-Catalyzed Desaturation of Lactams, Ketones, and Lactones

The development of a general platinum-catalyzed desaturation of N-protected lactams, ketones, and lactones to their conjugated α,β-unsaturated counterparts is reported. The reaction operates under mildly acidic conditions at room temperature or 50 °C. It is scalable and tolerates a wide range of functional groups. The complementary reactivity to the palladium-catalyzed desaturation is demonstrated in the efficient conversion of iodide, bromide, and sulfur-containing substrates.

Iridium-Catalyzed α-Selective Arylation of Styrenes by Dual C-H Functionalization

An IrI -system modified with a ferrocene derived bisphosphine ligand promotes α-selective arylation of styrenes by dual C-H functionalization. These studies offer a regioisomeric alternative to the Pd-catalyzed Fujiwara-Moritani reaction.

Copper-Catalyzed Dehydrogenative Diels-Alder Reaction

A practical and effective copper-catalyzed dehydrogenative Diels-Alder reaction of gem-diesters and ketone with dienes has been established. The active dienophiles were generated in situ via a radical-based dehydrogenation process, which reacted with a wide variety of dienes to afford various polysubstituted cyclohexene derivatives in good to excellent yields.

General, Mild, and Selective Method for Desaturation of Aliphatic Amines

A novel method for desaturation of aliphatic amines into enamines as well as allylic and homoallylic amines has been developed. This general protocol operates via putative aryl hybrid Pd-radical intermediates, which combine the signature features of radical chemistry, a hydrogen atom transfer (HAT) process, and transition metal chemistry, a selective β-hydride elimination step, to achieve efficient and selective desaturation of amines. These hybrid Pd-radical intermediates are efficiently generated under mild photoinduced conditions and are capable of a 1,n-HAT (n = 5-7) event at C(sp3)-H sites. The selectivity of HAT is tunable by varying different auxiliaries, which highlight the generality of this method. Remarkably, this desaturation method, which operates under mild conditions and does not require employment of exogenous photosensitizers or oxidants, can be performed in a practical scalable fashion from simple amines.