Stereospecific Oxycyanation of Alkenes with Sulfonyl Cyanide

Oxycyanation of alkenes would allow the direct construction of useful β-hydroxy nitrile scaffolds. However, only limited examples of such reactions have been reported, and some problems including limited substrate scope and the lack of diastereocontrol in the case of the oxycyanation of internal alkenes have arisen. We herein report on the intermolecular oxycyanation of alkenes using p-toluenesulfonyl cyanide (TsCN) in the presence of tris(pentafluorophenyl)borane (B(C₆ F₅ )₃ ) as a catalyst, affording products that contain a sulfinyloxy group and a cyano group at the vicinal position. The reaction features a stereospecific syn-addition. The reaction also shows a broad substrate scope with good functional group tolerance. Mechanistic investigations by experimental studies and density functional theory (DFT) calculations revealed that the reaction proceeds via an unprecedented stereospecific mechanism through the electrophilic cyanation of alkenes, in which B(C₆ F₅ )₃ efficiently activates TsCN through the coordination of the cyano group to the boron center.

A Stereospecific Alkene 1,2-Aminofunctionalization Platform for the Assembly of Complex Nitrogen-Containing Ring Systems

TFA promoted deprotection of O-Ts activated N-Boc hydroxylamines triggers aminofunctionalization-based polycyclizations of tethered alkenes. The processes involve intramolecular stereospecific aza-Prilezhaev alkene aziridination in advance of stereospecific C-N cleavage by a pendant nucleophile. Using this approach, a wide range of fully intramolecular alkene anti-1,2-difunctionalizations can be achieved, including diaminations, amino-oxygenations and amino-arylations. Trends associated with the regioselectivity of the C-N cleavage step are outlined. The method provides a broad and predictable platform for accessing diverse C(sp³ )-rich polyheterocycles of relevance to medicinal chemistry.

Rhodium-Catalyzed Chemo-, Regio-, Diastereo-, and Enantioselective Intermolecular [2+2+2] Cycloaddition of Three Unsymmetric 2π Components

We have developed the Rh⁺ /H₈ -binap-catalyzed chemo-, regio-, diastereo-, and enantioselective intermolecular [2+2+2] cycloaddition of three unsymmetric 2π components. Thus, two arylacetylenes react with a cis-enamide to yield a protected chiral cyclohexadienylamine. Moreover, replacing one arylacetylene with a silylacetylene enables the [2+2+2] cycloaddition of three distinct unsymmetric 2π components. These transformations proceed with excellent selectivity (complete regio- and diastereoselectivity and up to >99 % yield and >99 % ee). Mechanistic studies suggest the chemo- and regioselective formation of a rhodacyclopentadiene intermediate from the two terminal alkynes.

Late-Stage Modification of Drugs via Alkene Formal Insertion into Benzylic C-F Bond

C-F insertion of carbon-atom units is underdeveloped although it poses significant potential applications in both drug discovery and development. Herein, we report a photocatalytic protocol for late-stage modification of trifluoromethyl aromatic drugs involving formal insertion of abundant alkene feedstocks into a benzylic C-F bond selectively. This redox-neutral transformation features mild conditions and extraordinary functional group tolerance. Preliminary studies are consistent with this transformation involving a radical-polar crossover pathway. Additionally, it offers an alternative strategy for difunctionalization of alkenes via quenching of the carbocation intermediate with nucleophiles other than external fluoride.

Intertwining Olefin Thianthrenation with Kornblum/Ganem Oxidations: Ene-type Oxidation to Furnish α,β-Unsaturated Carbonyls

A widely applicable, practical, and scalable synthetic method for efficient ene-type double oxidation of alkenes is reported via a two-step alkenyl thianthrenium umpolung/Kornblum-Ganem oxidation strategy. This chemo- and stereoselective procedure allows easy access to various α,β-unsaturated carbonyls that may be otherwise difficult or cumbersome to synthesize by conventional methods. For α-olefins, this metal-free transformation can be tuned according to synthetic needs to produce either the elusive (Z)-unsaturated aldehydes or their (E) counterparts. Moreover, this strategy has enabled streamlined synthesis of distinct butadienyl pheromones and kairomones.

α-Acylation of Alkenes by a Single Photocatalyst

A direct strategy for the difunctionalization of alkenes, with acylation occurring at the more substituted alkene position, would be attractive for complex ketone synthesis. We report herein a reaction driven by a single photocatalyst that enables α-acylation in this way with the introduction of a fluoromethyl, alkyl, sulfonyl or thioether group at the β-position of the alkene with high chemo- and regioselectivity under extremely mild conditions. Crucial to the success of this method are rate differences in the kinetics of radical generation through single-electron transfer (SET) between different radical precursors and the excited photocatalyst (PC*). Thus, the β-position of the alkene is first occupied by the group derived from the radical precursor that can be generated most readily, and α-keto acids could be used as an electrophilic reagent for the α-acylation of alkenes.

Sonochemically-Induced Reduction of Alkenes to Alkanes with Ammonia

With the progressive defossilization of our industry, hydrogen (H₂ ) has been identified as a central molecule to store renewable electricity. In this context, ammonia (NH₃ ) is now rapidly emerging as a promising hydrogen carrier for the future. This game change indirectly impacts the field of fine chemistry where hydrogenation reactions are widely deployed. In particular, the possibility of performing hydrogenation reactions using ammonia directly instead of hydrogen has become highly desirable but it remains a very difficult scientific task, which we address in this communication. Here we show that the N-H bond of NH₃ can be cleaved within cavitation bubbles, generated by ultrasonic irradiation at a high frequency, leading to the in situ formation of a diimide, which then induces the hydrogenation of alkenes. Advantageously, this work does not involve any transition metal and releases N₂ as a sole co-product.

Picolinamides and Iodoalkynes Enable Palladium-Catalyzed syn-Aminoalkynylation of Di- and Trisubstituted Alkenes to Give Pyrrolidines

Palladium-catalyzed aminoalkynylation of electronically unbiased olefins with iodoalkynes is reported. The picolinamide auxiliary enables for the first time the syn-selective aminoalkynylation of mono-, di- and trisubstituted alkenes to afford the corresponding pyrrolidines in up to 97 % yield and as single diastereomers. Furthermore, through a C-H activation approach, the picolinamide allows the rapid synthesis of functionalized olefins, which are suitable cyclization precursors. Facile and orthogonal deprotection of the amides and Siⁱ Pr₃ -acetylenes in the products, and a subsequent Pictet-Spengler reaction is demonstrated.

Ligand-Controlled NiH-Catalyzed Regiodivergent Chain-Walking Hydroalkylation of Alkenes

A NiH-catalyzed migratory hydroalkylation of alkenyl amines with predictable and switchable regioselectivity is reported. By utilizing a ligand-controlled, directing group-assisted strategy, various alkyl units are site-selectively installed at inert sp³ C-H sites far away from the original C=C bonds. A range of structurally diverse α- and β-branched protected amines are conveniently synthesized via stabilization of 5- and 6-membered nickelacycles respectively. This method exhibits broad scope and high functional group tolerance, and can be applied to late-stage modification of medicinally relevant molecules.

Intermolecular Carbosilylation of α-Olefins with C(sp3 )-C(sp) Bond Formation Involving Silylium-Ion Regeneration

A regioselective addition of alkynylsilanes across unactivated, terminal alkenes is reported. The reaction is initiated by the capture of a sterically unhindered silylium ion by a silylated phenylacetylene derivative to form a bis(silylated) ketene‐like carbocation. This in situ‐generated key intermediate is the actual catalyst that maintains the catalytic cycle by a series of electrophilic addition reactions of silylium ions and β‐silicon‐stabilized carbocations. The computed reaction mechanism is fully consistent with the experimental findings. This unprecedented two‐component carbosilylation establishes a C(sp³)−C(sp) bond and a C(sp³)−Si bond in atom‐economic fashion.

Organophotocatalytic Regioselective C-H Alkylation of Electron-Rich Arenes Using Activated and Unactivated Alkenes

Direct alkylation of the C-H bond arenes in a selective manner is a long-standing challenge. Herein, a metal-free photocatalytic regioselective C-H alkylation method for electron-rich arenes with both activated and unactivated alkenes was developed. The reaction tolerates a wide range of aromatic rings with diverse substitution patterns, as well as terminal and internal alkenes, providing a general and straightforward metal-free method for C-C bond formation from inert C-H bonds. Moreover, alkynes are also compatible to give the C-H vinylation of electron-rich arenes.

Electrocatalytic Allylic C-H Alkylation Enabled by a Dual-Function Cobalt Catalyst

The direct functionalization of allylic C-H bonds with nucleophiles minimizes pre-functionalization and converts inexpensive, abundantly available materials to value-added alkenyl-substituted products but remains challenging. Here we report an electrocatalytic allylic C-H alkylation reaction with carbon nucleophiles employing an easily available cobalt-salen complex as the molecular catalyst. These C(sp³ )-H/C(sp³ )-H cross-coupling reactions proceed through H₂ evolution and require no external chemical oxidants. Importantly, the mild conditions and unique electrocatalytic radical process ensure excellent functional group tolerance and substrate compatibility with both linear and branched terminal alkenes. The synthetic utility of the electrochemical method is highlighted by its scalability (up to 200 mmol scale) under low loading of electrolyte (down to 0.05 equiv) and its successful application in the late-stage functionalization of complex structures.

Organic matter quality by pyrolysis-gas chromatography/mass spectrometry and lead and arsenic adsorption

The organic soils (Histosols) are important as filters for organic and inorganic pollutants, mainly because they are usually located on the banks of rivers and lakes. The aim of this study was to evaluate which functional groups of soil organic matter (SOM) most contribute for the Pb²⁺ and H₂AsO₄^- adsorption in Histosols. This study used 20 samples (160 ~ 290 g kg^-1 of organic carbon (OC) collected at 0-5 cm in five areas of Histosols from Curitiba, Southern of Brazil. Hydrofluoric acid (10%) was used to solubilize minerals to concentrate organic matter (391 to 510 g kg^-1 of OC) in the samples. Samples having been submitted to pyrolysis in combination with gas chromatography (Py-GC/MS) that identified 186 organic compounds grouped based on their chemical similarity. The samples were saturated separately with Pb²⁺ and H₂AsO₄^- under acid conditions (pH 4.0). The exchangeable (electrostatic interactions with SOM charges) and nonexchangeable (complexed to SOM) Pb²⁺ and H₂AsO₄^- were determined for sequential methods (Ca(NO₃)₂ and EPA 3051A, respectively. Positive correlations occurred between exchangeable Pb²⁺ and phenolic compounds (r = 0.6, p < 0.05), lignin phenols (r = 0.5, p < 0.05), and sterols (r = 0.6, p < 0.05). For nonexchangeable Pb²⁺, there was a significant correlation with alkenes (r = 0.8, p < 0.01), alkanes (r = 0.8, p < 0.01), and methyl ketones (r = 0.7 p < 0.01). The exchangeable H₂AsO₄^- is related to alkanes, alkenes, and methyl ketones. Therefore, in acid Histosols constituted of aliphatic organic matter tend to have less environmental fragility, due to the lesser transportation of these contaminants to other compartments like surface and subsurface waters.

Reductive Alkylation of Alkenyl Acetates with Alkyl Bromides by Nickel Catalysis

Catalytic alkylation of stable alkenyl C-O electrophiles is synthetically appealing, but studies to date have typically focused on the reactions with alkyl Grignard reagents. We report herein a cross-electrophile reaction of alkenyl acetates with alkyl bromides. This work has enabled a new method for the synthesis of aliphatic alkenes from alkenyl acetates to be established that can be used to add more structural complexity and molecular diversity with enhanced functionality tolerance. The method allows for a gram-scale reaction and modification of biologically active molecules, and it affords access to useful building blocks. Preliminary mechanistic studies reveal that the Ni^I species plays an essential role for the success of the coupling of these two reactivity-mismatched electrophiles.

Modular synthesis of non-conjugated N-(quinolin-8-yl) alkenyl amides via cross-metathesis

We report a direct and modular method to access non-conjugated alkenyl amides containing the 8-aminoquinoline (AQ) directing auxiliary and related groups via cross-metathesis. In this way, readily available, AQ-containing, terminal β,γ-unsaturated amides can be coupled with various terminal alkenes to furnish internal alkene products that are otherwise difficult to prepare. The value of this family of products stems from their ability to participate in a number of directed alkene functionalization reactions.

Palladium/norbornene-catalyzed distal alkenyl C-H arylation and alkylation of cis-olefins

In this full article, a detailed study of a distal alkenyl C-H arylation and alkylation through the palladium/norbornene (NBE) cooperative catalysis is described. Both aminopyridine- and oxime ether-type directing groups have been found effective for this transformation, allowing functionalization of diverse allyl amines and homoallyl alcohols. In addition, the C5,C6-substititued NBEs show optimal reactivity and selectivity. Various cis-olefins can be transformed to the corresponding arylated or alkylated trisubstituted alkenes with excellent regio- and stereoselectivity. Preliminary mechanistic studies support the Catellani pathway instead of the Heck pathway.

Realization of Anti-Markovnikov Selectivity in Pd-Catalyzed Oxidative Acetalization and Wacker-Type Oxidation of Terminal Alkenes

Catalytic oxidative acetalization and Wacker-type oxidation of terminal alkenes normally proceed with Markovnikov selectivity to afford internally oxyfunctionalized compounds, such as internal acetals and ketones. Thus, the realization of anti-Markovnikov (AM) selectivity in these reactions is challenging. This account focuses on our recent development of Pd-catalyzed AM oxidation of terminal alkenes (mainly styrenes and aliphatic alkenes), that is, oxidative acetalization (oxidation to terminal acetals) and Wacker-type oxidation (oxidation to aldehydes). The key factors that enhance the yield and AM selectivity of the products found in our studies are: 1) the steric bulkiness of the oxygen nucleophiles that attack on the coordinated alkenes, 2) the electron-deficient cyclic alkenes as additives that withdraw electrons from Pd, 3) the slow addition of substrates in the case of the aliphatic alkenes, which suppresses the isomerization of the terminal alkenes into internal alkenes, and 4) the halogen directing groups in the case of aliphatic alkenes.

Pd-Catalyzed C-C, C-N, and C-O Bond-Forming Difunctionalization Reactions of Alkenes Bearing Tethered Aryl/Alkenyl Triflates

Over the past few years our group has described a new type of alkene difunctionalization reaction in which aryl or alkenyl triflates bearing tethered alkenes are coupled with various nucleophiles to afford carbocyclic products. The products are formed in moderate to good chemical yield, with generally high levels of stereoselectivity. Our progress to date in this area, which includes reactions of amine, alcohol, enolate, and indole nucleophiles, is described in this review.

Influence of hydrocarbons on hydrogen chloride removal from refinery off-gas by zeolite NaY derived from rice husks

The removal of gaseous hydrochloric acid (HCl) in refineries and petrochemical plants is essential to prevent potential catalyst poisoning, equipment corrosion, and several associated public health and environmental hazards when the acid contaminates the hydrogen-hydrocarbon feedstock. In the present work, the effect of alkanes, alkenes, and liquid aromatic hydrocarbons on the removal of HCl from refinery off-gas using zeolite NaY was evaluated. Zeolite NaY was synthesized from rice husks via a hydrothermal route. Adsorbent characterization analyses such as XRD, SEM-EDS, FT-IR, BET and particle size distribution were employed. Fixed-bed experiments were operated under feed condition of 600 ppm HCl and gas hourly space velocity of 640 mL/h·cm³. Gaseous HCl was combined with H₂, H₂-alkanes and H₂-alkenes to simulate the main components of refinery-off gas. Experimental breakthrough curves were used to determine the adsorption capacities of zeolite NaY pellets at breakthrough and saturation. HCl removal by fresh zeolite NaY was inhibited by light alkanes but improved in the presence of alkenes. The adsorption capacity at breakthrough for fresh zeolite with combined hydrogen and light alkenes was measured at 0.1507 g/g. In the presence of aromatics, significant reduction in adsorption capacities to 0.1247, 0.1379 and 0.1437 g/g were obtained for adsorbents subjected to H₂, H₂-alkanes and H₂-alkenes respectively. Zeolite NaY consistently showed higher performance for HCl removal in the presence of H₂ feed mixed with light hydrocarbons compared with a commercial adsorbent.

Quantitative Structure-Property Relationship study for Prediction of boiling point and enthalpy of vaporization of alkenes

INTRODUCTION

Quantitative structure- property relationships (QSPRs) models have been widely developed to derive correlation between chemical structures of molecules to their known properties. In this study, QSPR models have been carried out on 91 alkenes to develop a robust model for the prediction of enthalpy of vaporization at standard condition (∆H°vap/kJ.mol-1) and normal temperature of boiling points (T˚bp /K) of alkenes.

METHODS

A training set of 81 structurally diverse alkenes was randomly selected and used to construct QSPR models. These models were optimized using backward -multiple linear regression (MLR) analysis. The Genetic algorithm and multiple linear regression analysis (GA-MLR) were used to select the suitable descriptors derived from the Dragon software.

RESULTS

The multicollinearity properties of the descriptors contributed in the QSPR models were tested and several method were used for testing the predictive models power such as Leave-One-Out (LOO) crossvalidation(Q2 LOO), the five-fold cross-validation techniques, external validation parameters (Q2F1, Q2F2, Q2F3), the concordance correlation coefficient (CCC) and the predictive parameter R2m .

CONCLUSION

The predictive ability of the models were found to be satisfactory, and the five descriptors in three blocks namely connectivity, edge adjacency indices and 2D matrix-based descriptors could be used to predict the mentioned properties of alkenes.

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings

Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2 ]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3 , DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.

Assembling the prenylneoflavone system through a Pechmann condensation/Mitsunobu reaction/Claisen rearrangement/olefin cross-metathesis sequence

Abstract

The multistep synthesis of a prenylneoflavone through a sequence of the Mitsunobu reaction/Claisen rearrangement/olefin cross-metathesis reaction has been accomplished in 5% yield over six steps starting from commercially available 3-methoxyacetophenone. The sequence is shown to be compatible with a Pechmann condensation which proved to be a robust and cost-effective method for the assembling of the α-pyrone core. The results open doors to a general approach to the prenylneoflavone system starting from phenol and acetophenone derivatives.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s00706-020-02584-8) contains supplementary material, which is available to authorized users.

Oxidative Cleavage of Alkene C=C Bonds Using a Manganese Catalyzed Oxidation with H2O2 Combined with Periodate Oxidation

A one‐pot multi‐step method for the oxidative cleavage of alkenes to aldehydes/ketones under ambient conditions is described as an alternative to ozonolysis. The first step is a highly efficient manganese catalyzed epoxidation/cis‐dihydroxylation of alkenes. This step is followed by an Fe(III) assisted ring opening of the epoxide (where necessary) to a 1,2‐diol. Carbon–carbon bond cleavage is achieved by treatment of the diol with sodium periodate. The conditions used in each step are not only compatible with the subsequent step(s), but also provide for increased conversion compared to the equivalent reactions carried out on the isolated intermediate compounds. The described procedure allows for carbon–carbon bond cleavage in the presence of other alkenes, oxidation sensitive moieties and other functional groups; the mild conditions (r.t.) used in all three steps make this a viable general alternative to ozonolysis and especially for use under flow or continuous batch conditions.

Stereocontrolled synthesis of bicyclic ureas and sulfamides via Pd-catalyzed alkene carboamination reactions

The synthesis of bicyclic ureas and sulfamides via palladium-catalyzed alkene carboamination reactions between aryl/alkenyl halides/triflates and alkenes bearing pendant cyclic sulfamides and ureas is described. The substrates for these reactions are generated in 3-5 steps from commercially available materials, and products are obtained in good yield with up to >20:1 diastereoselectivity. The stereochemical outcome of the sulfamide alkene addition is consistent with a mechanism involving anti-aminopalladation of the alkene, whereas the stereochemical outcome of the urea alkene addition is consistent with a syn-aminopalladation mechanism.

Bromofluorination of Unsaturated Compounds using DMPU/HF as a Fluorinating Reagent

Bromofluorination reactions were performed by treating of a variety of unsaturated compounds with N-bromosuccinimide (NBS) and DMPU/HF as the fluorinating reagent. The DMPU/HF complex showed to be an efficient fluorinating reagent to convert alkenes into their corresponding bromofluoro compounds. It showed to have high reactivity and the process afforded bromofluorinated products with good Markovnikov regioselectivity. These fluorinated compounds are useful starting materials and serve as building blocks for many fluorinated biologically active molecules.