Vanadyl Species Catalyzed 1,2-Oxidative Trifluoromethylation of Unactivated Olefins

Expedient Azide-Alkyne Huisgen Cycloaddition Catalyzed by a Combination of VOSO4 with Cu(0) in Aqueous Media

A series of vanadium(III), vanadyl(IV/V) species, inorganic metal oxides, and transition-metal oxides was examined as cocatalysts with Cu(0) powder for copper(I)-catalyzed azide-alkyne cycloaddition. Among them, vanadyl(IV) species bearing acetylacetonate, acetate, and sulfate, vanadyl(V) isopropoxide, and vanadate were suitable for the click reactions of per-acetyl and per-benzyl β-azido glycosides with three different terminal alkynes in CH3CN. Water-soluble vanadyl(IV) sulfate was further selected for efficient click reactions for unprotected β-glycosyl azides and even compatible with a thiol-containing substrate in aqueous media at ambient temperature.

Pyridinium-Masked Enol as a Precursor for Constructing Alpha-Fluoromethyl Ketones

We present herein a pyridinium-masked enol as a versatile platform to produce ketones bearing tri-, di-, and monofluoromethyl in the presence of [Ir(dF(Me)ppy)]2(dtbbpy)]PF6 under blue light (455 nm) irradiation. By simply changing the F-source, α-trifluoromethyl ketones, α-difluoromethyl ketones, and α-monofluoromethyl ketones could be easily prepared in moderate to excellent yields in one step, making it a practical tool for the synthesis of fluorine-containing ketones. In addition, the pyridinium-masked enol could also be extended to the synthesis of sulfonyl ketones. The findings of the present protocol contribute to the arsenal of fluorine chemistry and might have potential applications in the pharmaceutical and agrochemical industries.

Enantioselective Radical-Type 1,2-Alkoxy-Phosphinoylation to Styrenes Catalyzed by Chiral Vanadyl Complexes

A series of vanadyl complexes bearing 3-t-butyl-5-bromo, 3-aryl-5-bromo, 3,5-dihalo-, and benzo-fused N-salicylidene-tert-leucinates was examined as catalysts for 1,2-alkoxy-phosphinoylation of 4-, 3-, 3,4-, and 3,5-substituted styrene derivatives (including Me/t-Bu, Ph, OR, Cl/Br, OAc, NO₂ , C(O)Me, CO₂ Me, CN, and benzo-fused) with HP(O)Ph₂ in the presence of t-BuOOH (TBHP) in a given alcohol or cosolvent with MeOH. The best scenario involved the use of 5 mol % 3-(2,5-dimethylphenyl)-5-Br (i.e., 3-DMP-5-Br) catalyst at 0 °C in MeOH. The desired catalytic cross coupling reactions proceeded smoothly with enantioselectivities of up to 95 % ee of (R)-configuration as confirmed by X-ray crystallographic analysis of several recrystallized products. The origin of enantiocontrol and homolytic substitution of the benzylic intermediates by vanadyl-bound methoxide and radical type catalytic mechanism were proposed.

Asymmetric Synthesis of Trifluoroethyl-Based, Chiral 3-Benzyloxy-1- and -2-Phenyl-quinazolinones of Biomedicinal Interest by Radical Type Cross-Coupling to Olefins

Several 2-substituted (H, Ph, and S-Me) and 1-substituted (H, Ph, and Bn), 3-hydroxy-1,3-quinazolin(di)ones were utilized for the first time as radical trapping agents in asymmetric 1,2-oxytrifluoromethylation of styrenes catalyzed by chiral vanadyl methoxide complexes bearing 3,5-disubstituted-N-salicylidene-t-leucinate templates. The effects of catalysts and solvents on the asymmetric induction were systematically examined. The best and complementary scenarios involved the use of vanadyl complexes V(O)-1 and V(O)-2, which bear 3-(2,5-dimethyl)phenyl-5-bromophenyl and 3-t-butyl-5-bromophenyl groups in an i-propanol solvent at ambient temperature. The corresponding (R)-cross-coupling products by V(O)-1 were obtained in 45-71% (for 2-substituted series) and 59-93% yields (for 1-substituted series) for p-/m-methylstyrenes and m-halo/CF₃/CO₂Me-styrenes in 38-63% ees (the best in 2-H case) and 60-84% ees (the best in 1-benzyl cases), respectively. The corresponding (S)-cross-coupling products by V(O)-2 were obtained in 28-55% (for 2-substituted series) and 45-72% yields (for 1-substituted series) for the same substrate class in 50-91% ees (85-91% ees in 2-phenyl cases) and 64-75% ees (up to 74-75% ees for each 1-H, Ph, and Bn cases), respectively. Theoretical calculations were carried out to explain the origin and extent of enantiocontrols. They both may serve as potential inhibitors of acetohydroxyacid synthase and epidermal growth factor receptor (EGFR) kinases.

Theoretical study for evaluating and discovering organic hydride compounds as novel trifluoromethylation reagents

Trifluoromethylation reaction is one of the significant and practical organic chemical reactions, and the design and discovery of novel trifluoromethylation reagents have been attracting more and more attention. Trifluoromethyl-substituted organic hydride compounds (XH) have the potential to be novel trifluoromethylation reagents in organic synthesis due to the favorable tendency of XH˙⁺ releasing ˙CF₃ to form stable aromatic structures in terms of thermodynamics. The key elementary step of the trifluoromethylation is the radical cation (XH˙⁺) generation by catalysis or single-electron activation releasing ˙CF₃ to form a stable aromatic structure, which also provides the thermodynamic driving force of the chemical process. In this work, 47 new trifluoromethylation reagent candidates of XHs were designed and calculated for the Gibbs free energy and activation free energy [ΔG^‡_RD(XH˙⁺)] of XH˙⁺ releasing ˙CF₃ using the density functional theory (DFT) method, in order to quantitatively measure the reactivity of XHs as trifluoromethylation reagents, and to establish the molecular library as well as reactivity database of novel trifluoromethylation reagents for synthetic chemists. According to the and ΔG^‡_RD(XH˙⁺) values, all the XHs can be reasonably divided into 3 classes, including class 1 (excellent trifluoromethylation reagents), class 2 (potential trifluoromethylation reagents) and class 3 (not trifluoromethylation reagents). To our delight, 15 XHs with a 1,4-dihydropyridine structure and 3 XHs with a 3,4-dihydropyrimidin-2-one structure are identified to be novel excellent and potential trifluoromethylation reagents, respectively, according to their reactivity data. The relationship between the structural features, including methylation, heteroatom, substituents, conjugated structure and so on, and the reactivity of XHs as trifluoromethylation reagents are also discussed in this work. The computation results indicate that trifluoromethyl-substituted 1,4-dihydropyridine compounds and 3,4-dihydropyrimidin-2-one analogues could be possible trifluoromethylation reagents in organic synthesis. This work may provide the theoretical basis and references for discovering organic hydride compounds as novel reagents for trifluoromethylation or other alkylation reactions.

Metal-Ion Specific Recognition with Amplified Transcription from Subnanometer to Submillimeter or Real-Time Domain by Self-Assembled Vanadyl Quartets

Vanadyl(V) complexes 1 and 2 bearing a nematic liquid crystal (LC) like a p-heptoxyphenyl group or a fluorous-tag p-nonafluoroheptoxyphenyl (NFH) group at the C5 position of the N-salicylidene template were designed and synthesized. Each complex was subjected to MVO₃-induced self-assembly to form metal-ion, encapsulated quartet clusters 3-M and 3'-M. The Na⁺ in cluster complex 3-Na or 3'-Na can be readily replaced by Rb⁺, Ag⁺, or Hg²⁺ in an aqueous layer to form cluster complexes by ion swapping at the H₂O/CDCl₃ bilayer interface. Selectivity profiles were examined with alkali-metal ions, Ag⁺, and Hg²⁺ through metal-ion competition experiments. The 3'-Na has an exclusive selectivity for Hg²⁺ in the presence of Zn²⁺ and Cd²⁺. Cluster complexes 3-M were utilized as chiral dopants to nematic LC materials. The effects of the encapsulated metal ions within the alkali family and Ag⁺ on Cano's line widths and helical pitch changes were viewed in wedge cells under a polarized microscope. Their correlations with the ionic radius were identified. The subnano information of the metal ions can thus be asymmetrically amplified to Cano's line spacings of the submilimeter domain. Conversely, the effects of the encapsulated alkali metal ions and Hg²⁺ in 3'-M on the interactions of their NFH tails toward fluorous silica gel (FSG) were performed via HPLC analyses. Their retention times became longer as the sizes of encapsulated, alkali metal ions increased. The increasing ion size from Na⁺ to Cs⁺ caused the four lower rim NFH tags of the cluster to be closer due to reduced cone angles. Their interactions among NFH tail groups on FSG became larger, thus leading to distinctive separations with t_R from 7.36 to 10.27 min. The retention time difference between 3'-Na and 3'-Hg on HPLC was ∼3.6 min, resulting in discernible separation. The individual ion size differences on the subnano scale can thus be amplified and unambiguously established in the real time domain.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Graphene oxide-catalyzed trifluoromethylation of alkynes with quinoxalinones and Langlois' reagent

The direct C–H trifluoromethylation of alkynes and quinoxalinones has been achieved using a graphene oxide/Langlois' reagent system. This multi-component tandem reaction using graphene oxide as the catalyst and Langlois' reagent as the robust CF₃ radical source results in the formation of olefinic C–CF₃ to access a series of 3-trifluoroalkylated quinoxalin-2(1H)-ones.

The direct C–H trifluoromethylation of alkynes and quinoxalinones using a graphene oxide/Langlois' reagent system.

A benzene-bridged divanadium complex-early transition metal catalyst for alkene alkylarylation with PhI(O2CR)2via decarboxylation

The synthesis, structure and catalytic activity of a benzene-bridged divanadium complex were comprehensively studied. The reduction of (Nacnac)VCl2 (1) (Nacnac = (2,6-iPr2C6H3NCMe)2HC) supported by β-diketiminate with potassium graphite (KC8) by employing benzene as the solvent allows access to the benzene-bridged inverted-sandwich divanadium complex (μ-η6:η6-C6H6)[V(Nacnac)]2 (2a), which can catalyze alkene alkylarylation with hypervalent iodine(iii) reagents (HIRs) via decarboxylation to generate regioselectively diverse indolinones. Furthermore, the mild nature of this reaction was amenable to a wide range of functionalities on alkenes and HIRs. Mechanistic studies revealed a relay sequence of decarboxylative radical alkylation/radical arylation/oxidative re-aromatization.

One-pot synthesis of 2-chloro-2-thio/selenocyanato ketones from β-keto acids

The chlorothiocyanato difunctionalization reaction has been achieved, and a variety of α-chlorothio/selenocyanato difunctional ketones are synthesized through one-pot strategy from β-keto acids.