Double electrooxidative C–H functionalization of (het)arenes with thiocyanate and 4-nitropyrazolate ions

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Silanol as a removable directing group for the Pd(II)-catalyzed direct olefination of arenes

Need some direction? Silanol was developed as a directing group for the Pd(II)-catalyzed oxidative Heck-type reaction of arenes. A one-pot C-H activation/desilylation process of benzyldiisopropylsilanol was also demonstrated, providing a powerful approach for the synthesis of ortho-alkenyl-substituted alkylarenes. Considering the easily attachable and readily removable properties of the silanol group, this reaction will find broad synthetic applications.     

Effective metal-free electrooxidative thiocyanation of anilines

An original anodic C–H thiocyanation of anilines with NH₄SCN has been developed, allowing to obtain the products in 88–98% yields under potentiostatic diaphragm electrolysis on glassy carbon electrodes at E_anode = 0.60 V and moderate consumption of electricity. The preliminary voltammetric analysis included the assessment of the changes in the thiocyanate ion curve after the addition of aniline, as well as the measurements of the potentials of the reagents and products, which gave insight into mechanisms of the process (formation of thiocyanate radical and thiocyanogen) and was necessary for its optimization.     

Recent advances in electrooxidative radical transformations of alkynes

During the past few years, electrochemical oxidative reactions through radical intermediates have emerged as an environmentally-benign, powerful platform for the facile formation of C–E(E = C, N, S, Se, O and Hal) bonds through singleelectron-transfer(SET) processes at the electrodes. Functionalized unsaturated molecules and unusual structural motifs can, for instance, be directly constructed under exceedingly mild reaction conditions through initial radical attack onto alkynes. This minireview ...     

Pd-catalysed regioselective C-H functionalisation of 2-pyrones

A new synthetic methodology for the catalytic C-H functionalisation of 2-pyrones is described which proceeds regioselectively at the C3 position, mirroring the observed regioselectivity in 6π-electrocyclisation/oxidative aromatisation reactions of related compounds. Insight into the reaction mechanism is provided, with support for a neutral palladium(II) pathway. Cationic palladium(II) complexes possessing 2-pyrones are unstable and readily undergo Pd(II)→P transfer at ambient temperature resulting in phosphonium salt formation (and Pd(0)L(n) species).     

Ferrocenyl iminophosphine ligands in Pd-catalysed Suzuki couplings

A mixture of Pd₂(dba)₃/{η-C₅H₄CHN[CH(CH₃)(Nap)]}Fe[η-C₅H₄P(^tBu)₂] efficiently catalyzes the Suzuki reactions of a variety of bulky aryl halides and aryl- and alkyl-boronic acids, affording the desired cross-coupling biaryl products in quantitative isolated yields under mild conditions and at low (1 × 10⁻⁶-1 mol%) Pd loadings. Spectroscopic (NMR & ESI) analysis of the mixture of Pd₂(dba)₃, the hybrid [P,N] ligands, and aryl halides revealed different structural forms of oxidative addition products that are dependent on the substituent on the imino nitrogen.     

P-Stereogenic monophosphines in Pd-catalysed enantioselective hydrovinylation of styrene

Two groups of P-stereogenic monodentate phosphines containing pendant groups bearing functionalities capable of having secondary interactions, PArPhR (Ar = 2-[(2′,6′-dimethoxy)-1,1′-biphenylyl] and R = OMe (6) or Me (8)) and PMeR(CH₂R′) (13, R = t-Bu or 14 R = Fc and R′ = SiMe₃ (a), SiMe₂Ph (b) or CH₂(2-naphthyl) (c)) have been prepared in enantiomerically pure form by the Jugé and Evans methodologies and characterised, including the crystal structure for the borane adduct of 12b. Reaction of the phosphines with the Pd dimer [Pd(η³-2-Me-allyl)(μ-Cl)]₂ produced neutral allylic complexes C [PdCl(η³-2-Me-C₃H₄)P1], which have been characterised in solution and shown to be a mixture of isomers with different absolute configuration at the Pd atom. After abstraction of the chloride ligand by AgBF₄, the solutions of cationic complexes have been used as catalyst precursors in the hydrovinylation of styrene under mild conditions. Very good activities (up to 1015 h^?1), moderate to good selectivities to 3-phenyl-1-butene and low to moderate enantioselectivities (<45% ee) have been found. Deep differences in the activity and enantioselectivity have been found depending on the structure of the ligand. In spite of that the results did not permit to confirm the improvement of the selectivities of the reaction by stabilization of the catalyst through secondary coordination with the potentially hemilabile ligands.     

Z-Stereoselective Peterson olefination of ketones

A highly-stereoselective method (90 % of theZ-isomer) was developed for the Peterson olefination of ketones with nerylacetone (1) as an example. The method is based on the introduction of a PhS group, which is removed after completion of the reaction, at the ketone C(3) atom.DeceasedFor the perliminary communication, see Ref. 10.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 509–516, March, 1995.The authors are grateful to the Russian Foundation for Basic Research (grant No. 94.03.08904) and the International Science Foundation (grant NGO000) for financial support of this work.     

Freons in catalytic olefination reaction. Synthesis of fluorinated compounds from the products of olefination

Application of freons in catalytic olefination for production of fluorinated alkenes is discussed and also the synthesis of versatile fluorinated compounds on this basis.     

Pd-catalysed asymmetric mono- and bis-alkoxycarbonylation of vinylarenes

The asymmetric alkoxycarbonylation of vinylarenes catalysed by palladium complexes bearing chiral phosphine ligands has attracted much attention over the last decades. The products of both mono- and bis(alkoxycarbonylation) reactions are important intermediates in the syntheses of pharmaceuticals such as 2-arylpropionic acids, the most important class of non-steroidal anti-inflammatory drugs. In this article, a general overview of the topics will be presented and the recent advances in this field will be particularly detailed. Besides the term alkoxycarbonylation, hydroesterification and hydroalkoxycarbonylation are also used in the literature to describe this reaction. Furthermore, more specific terms such as methoxycarbonylation can be found. In this report, the term alkoxycarbonylation will be used as the general term, and specific terms will be used to unambiguously define which reaction is meant.     

A one-pot silyl-Reformatsky olefination

A novel one-pot olefination reaction has been developed, involving the stereoselective formation of (E)-α,β-unsaturated esters/ketones from the reaction of α-bromocarbonyl compounds with aromatic aldehydes. The reactions use a reagent combination of trichlorosilane, and triethylamine and may proceed via the in situ formation of a trichlorosilyl ketene acetal. The general procedure offers key advantages (high conversions, low quantities of organic soluble by-products) over the conventional Wittig reaction.     

Metallophthalocyanine catalyzed olefination of aldehydes

The Wittig reaction to synthesize olefins is a very attractive method in organic synthesis. Recently, this methodology has been achieved utilizing simple metal catalysts and diazo compounds in addition to a phosphine and an aldehyde. The following work investigates the use of a variety of metallophthalocyanines (MPc’s) to catalyze Wittig-like reactions from ethyldiazoacetate. We also examine the influence of substitution on the aromatic ring of the aldehyde as well as various phosphines, arsines and antimony complexes. We have been able to exclusively synthesize the trans-olefins in excellent yields in short periods of time (1?h).     

Wittig-type olefination catalyzed by PEG-telluride

Soluble poly(ethylene glycol) (PEG)-supported telluride 2 was designed and synthesized for catalytic Wittig-type reactions. It was found that the catalytic loading could be reduced from 20 to 2 mol % by the introduction of PEG (even to 0.5 mol % when some telluride salts were used as the catalyst). Under the catalytic reaction conditions, a wide variety of aldehydes with different structures could react with bromoacetate to afford beta-substituted or alpha,beta-disubstituted unsaturated esters in high yields with excellent E-stereoselectivity. The modified process, by using sodium bisulfite instead of triphenyl phosphite, represented a very simple product isolation procedure. The roles of PEG for promoting the ylide formation and stabilizing the catalytic species were disclosed. The mechanism was also studied.     

Pd-catalyzed aerobic direct olefination of polyfluoroarenes

The first example of Pd-catalyzed aerobic direct olefination of polyfluoroarenes has been developed. The reaction makes use of molecular O₂ as terminal oxidant, and provides a cost-efficient and environmentally benign access to polyfluoroarene–alkene structures that are of interest in life and material sciences.     

Catalytic ketone olefination with methyltrioxorhenium

Methyltrioxorhenium (MTO) catalyses the olefination of ketones with ethyl diazoacetate in the presence of triphenylphosphane. Unactivated ketones require the addition of 0.5 equiv of benzoic acid to achieve good yields, while trifluoromethyl ketones require no co-catalyst. The optimised system allows the olefination of aromatic, aliphatic, unsaturated, cyclic and trifluoromethyl ketones.     

Nickel-catalyzed olefination of unactivated aliphatic dithioacetals

[reaction: see text] Olefination of aliphatic dithioacetals with Grignard reagents is catalyzed by Ni(acac)(2) in the presence of an appropriate trialkylphosphine ligand.