Addition To Olefins Research Articles

A quantum chemical study of the mechanisms of olefin addition to group 9 transition metal dioxo compounds.

The mechanistic aspects of ethylene addition to MO2(CH2)(CH3) (M=Co, Rh, Ir) have been investigated with a Hartree–Fock/DFT hybrid functional at the MO6/LACVP* and B3LYP/LACVP* levels of theory to elucidate the reaction pathways on the singlet, doublet and triplet potential energy surfaces (PES). In the reaction of the IrO2CH2CH3 complex with ethylene, [3 + 2]C,O addition is the most plausible pathway on the singlet PES, the [3 + 2]O,O addition is the most favoured pathway on the doublet surface whiles the stepwise [1 + 1] addition involving the oxygen atom of the complex in the first step and the carbon atom of the complex in the second step is the most plausible pathway on the triplet PES. For the reaction of the RhO2(CH2)(CH3) complex, the [2 + 2]Rh,O addition pathway is the most favoured on the singlet surface, the [2 + 2]Rh,C is the most plausible pathway on the triplet PES and [3 + 2]C,O is the most plausible on the doublet surface. For the reactions of the CoO2(CH2)(CH3) complex, the [1 + 2]O addition is the most plausible on the singlet PES, [3 + 2]C=Co=O cycloaddition to form the five–membered intermediate is the most preferred pathway on the doublet PES, whiles on the triplet PES the preferred pathway is the [3 + 2] addition across the O=Co=O bond of the metal complex. The reactions of olefins with the Co dioxo complex have lower activation barriers for the preferred [3 + 2] and [2 + 2] addition pathways as well as fewer side reactions than those of the rhodium and iridium systems. This could imply that the cobalt dioxo complexes can efficiently and selectively catalyze specific reactions in oxidation of olefins than Rh and Ir oxo complexes will do and therefore Co oxo complexes may be better catalysts for specific oxidation reactions of olefins than Rh and Ir complexes are. The activation barriers for the formation of the four—or five-membered metallacycle intermediates through [2 + 2] or [3 + 2] cyclo-addition are lower on the triplet PES than on the singlet PES for the formation of similar analogues. There are fewer competitive reaction pathways on the triplet surface than on the singlet PES. Also, cycloadditions that seem impossible on the singlet PES seem possible on the doublet and or triplet PESs, this is the case typically for the Rh and Co complexes, illustrating the importance of multiple spin states in organometallic reactions.Graphical Table of Contents Synopsis: A study of the mechanism of ethylene addition to MO2(CH2)(CH3)(M=Co,Rh,Ir) shows the reactions of the Co complex have lower activation barriers for the preferred [3+2] and [2+2] addition pathways and fewer side reactions than those of Rh and Ir. Reactions are more feasible and selective on the triplet PES than on the singlet PES. These illustrate the importance of multiple spin states in organometallic reactions and shows catalyst activity and selectivity decreases down the group.

Nucleophile-Assisted Alkene Activation: Olefins Alone Are Often Incompetent

Emerging work on organocatalytic enantioselective halocyclizations naturally draws on conditions where both new bonds must be formed under delicate control, the reaction regime where the concerted nature of the AdE3 mechanism is of greatest importance. Without assistance, many simple alkene substrates react slowly or not at all with conventional halenium donors under synthetically relevant reaction conditions. As demonstrated earlier by Shilov, Cambie, Williams, Fahey, and others, alkenes can undergo a concerted AdE3-type reaction via nucleophile participation, which sets the configuration of the newly created stereocenters at both ends in one step. Herein, we explore the modulation of alkene reactivity and halocyclization rates by nucleophile proximity and basicity, through detailed analyses of starting material spectroscopy, addition stereopreferences, isotope effects, and nucleophile-alkene interactions, all obtained in a context directly relevant to synthesis reaction conditions. The findings build on the prior work by highlighting the reactivity spectrum of halocyclizations from stepwise to concerted, and suggest strategies for design of new reactions. Alkene reactivity is seen to span the range from the often overgeneralized "sophomore textbook" image of stepwise electrophilic attack on the alkene and subsequent nucleophilic bond formation, to the nucleophile-assisted alkene activation (NAAA) cases where electron donation from the nucleophilic addition partner activates the alkene for electrophilic attack. By highlighting the factors that control reactivity across this range, this study suggests opportunities to explain and control stereo-, regio-, and organocatalytic chemistry in this important class of alkene additions.

Difunctionalization of Alkenes Using 1-Chloro-1,2-benziodoxol-3-(1H)-one.

Difunctionalization of alkenes with 1-chloro-1,2-benziodoxol-3-(1H)-one (1) was investigated. Various additional nucleophiles were tested, and oxychlorination, dichlorination, azidochlorination, chlorothiocyanation, and iodoesterfication were demonstrated. The oxychlorination product was obtained efficiently when the reaction was operated in water. Dichlorination occurred in the presence of a Lewis basic promoter, such as 4-phenylpyridine N-oxide, as an additive. The reaction with in situ-generated azido anion afforded azidochlorinated compounds with a chlorine atom at the terminal position, while the reaction with trimethylsilyl isothiocyanate produced chlorothiocyanation adducts with a chlorine atom at the benzylic position. On the other hand, when 1 was treated with tetra-n-butylammonium iodide prior to the addition of alkenes, only iodoesterification occurred selectively. These mild reactions enable convenient site-selective difunctionalizations of substrates having two alkene moieties. NMR experiments suggested that the electrophilic reactive species in each reaction varied depending on the nature of the added nucleophile.

Generation of Aryl Radicals through Reduction of Hypervalent Iodine(III) Compounds with TEMPONa: Radical Alkene Oxyarylation.

A novel method for selective generation of aryl radicals from diaryliodonium salts and iodanylidene malonates with sodium 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONa) as a single-electron transfer (SET) reducing reagent is described. In the presence of various alkenes, aryl radicals formed after SET-reduction of hypervalent iodine compounds undergo alkene addition and the adduct radicals that are thus generated are efficiently trapped by the concomitantly generated TEMPO radical to eventually afford oxyarylated products in moderate to very good yields. The efficiency of aryl radical generation of various iodine(III) reagents is studied and the generation of an iodanylidene malonate aryl radical is also investigated by computational methods.

ChemInform Abstract: Palladium‐Catalyzed 6‐endo‐Selective Oxycyclization—Alkene Addition Cascades of ortho‐Alkynylarylcarboxamides and α,β‐Unsaturated Carbonyl Compounds.

AbstractThis cascade reaction does not require protic solvents and needs only substoichiometric amounts of KI additive.

ChemInform Abstract: Silver‐Mediated Thio‐Acetoxylation and TFA Triggered Cyclization of Amino Disulfides with Unactivated Alkenes: Synthesis of 3‐Aryl/Alkyl‐1,4‐benzothiazines.

A convenient strategy for the synthesis of 3-aryl/alkyl-1,4-benzothiazines has been developed. This reaction proceeds via 1,2-thioacetoxylation of an alkene with silver acetate and acetic acid as an additive, followed by cyclization using TFA. The addition of alkene took place in a regioselective manner, forming exclusively one regioisomer, which was confirmed by a single crystal X-ray study. Various differently substituted alkenes, such as aromatic and aliphatic olefins, were coupled with amino disulfides to form a library of benzothiazine derivatives.

Commercial Organophosphorus Chemicals: Status and New Developments

By definition, organophosphorus chemicals are those with at least one P-C-bond. They all are downstream-products of elemental phosphorus – mostly of the P4-allotrope – though with very few exceptions they cannot be synthesized directly from phosphorus element; instead, use has to be made of P4-derivatives, such as PCl3, PH3 or sodium hypophosphite (SHP). By the end of the 90th and the early 2000 novel processes for the production of organophosphorus chemicals and their transformation, resp., were developed and partly commercialized. Examples are olefin addition reactions to SHP, leading to novel flame retardants (EXOLIT® OP-types, Clariant), or to a new way of making a well-known extraction agent for the separation of Cobalt and Nickel (IONQUEST® 290, Rhodia, now Solvay). Various methods to produce organophosphorus chemicals in commercial scale are described. Using the example of methylphosphonous acid, existing and new routes are shown to synthesize that key intermediate for herbicide BASTA® (Bayer) and flame retardants like EXOLIT® OP (Clariant).

Catalytic nucleophilic addition of olefinic C[sbnd]H bond to α,β-unsaturated-γ-lactams

A novel catalytic nucleophilic addition of olefins to α,β-unsaturated-γ-lactams has been developed with a cyclic N-acyliminium ion as a key intermediate. It provides an efficient approach to 5-alkenyl-2-pyrrolidinones from simple and readily available starting materials and the desired products could be obtained in moderate to good yields (23–85%).

Palladium‐Catalyzed 6‐endo‐Selective Oxycyclization–Alkene Addition Cascades of ortho‐Alkynylarylcarboxamides and α,β‐Unsaturated Carbonyl Compounds

AbstractRegio‐ and chemoselective palladium‐catalyzed cyclization–coupling cascade reactions between ortho‐alkynylarylcarboxamides and methyl vinyl ketone or acrylaldehyde are described. An initial 6‐endo‐oxypalladation of the triple bond is followed by a C–C coupling to give structurally diverse isochromenimines (and related heterosubstituted derivatives), in which the α,β‐unsaturated carbonyl moiety is incorporated as an alkyl‐type exocyclic side chain. The coupling products were obtained in 76–97 % yield (average 86 % yield) without significant interference from Heck or alternative regiochemical pathways. In contrast to related cases, these cascade reactions do not require the use of protic solvents and excess amounts of halide additives, and they proceed effectively under either PdCl2 catalysis in the presence of substoichiometric amounts of added KI or PdI2 catalysis without any additive.

ChemInform Abstract: Development of Novel Cyclizations via Rhodacycle Intermediate and Its Application to Synthetic Organic Chemistry

AbstractReview: 64 refs.

Catalytic cracking of n-alkane naphtha: The impact of olefin addition and active sites differentiation

An extended dual kinetic model allows to fit the n-heptane cracking results working in a wide range of reaction conditions. The duality of the model is provided by the contribution of monomolecular and bimolecular cracking mechanisms. It takes into account the role played by the olefins formed on the global cracking or added within the feed. Furthermore by means of this model and the kinetic parameters obtained when cracking n-heptane on ZSM-5, it has been observed that, while some characterization techniques show a homogeneous zeolite surface from the point of view of the active sites, rigorous kinetic experiments point to the possibility that the reactant sees a heterogeneous surface with, at least, two groups of cracking active sites. Those differentiated active sites give different cracking rates and different activation energies for the process and, in the case of ZSM-5, could be assimilated to sites pointing to the 10R channels and sites pointing into the crossing of the 10R channels, mainly due to differences in acid site location and confinement effects.

Predicting rate constants of hydroxyl radical reactions with alkenes and aromatics

The radicals obtained from the additions of alkenes with the hydroxyl radical (•OH) and from the H-atom abstraction of aromatics initiated by the OH radical were, respectively, used to calculate quantum chemical descriptors for quantitative structure-activity relationship (QSAR) models for the rate constants (kOH) of the reactions of alkenes and aromatics with the OH radical in the troposphere. Quantum chemical descriptors used as the inputs for the support vector machine (SVM) models were calculated with the unrestricted hybrid density functional theory (DFT), at the UB3LYP level of theory with 6-31G(d) basis set. The average root-mean-square errors (RMSE) for 70 alkenes and 80 aromatics are 0.101 and 0.236 log units, respectively, which show the SVM models in this paper are accuracy and acceptable. To develop QSAR models for kOH, calculating quantum chemical descriptors from the reaction radicals of alkenes and from aromatic radicals formed by the H-atom abstraction is feasible.

ChemInform Abstract: Synthesis of 2‐Nitro‐1H‐benzo[f]chromenes.

The reaction of Mannich bases derived from 2-naphthol with 4-(2-nitrovinyl)morpholine or N,N-di-methyl(2-nitrovinyl)amine in acetic anhydride gives 2-nitro-1H-benzo[f]chromenes. This reaction may be regarded formally as the addition of a push-pull olefin acting as a 1,2-ambiphile with naphthalenic o-quinone methide acting as a 1,4-ambiphilic reagent.

Development of efficient processes for multi-gram scale and divergent preparation of fluorous-Fmoc reagents

An optimized, multi-gram scale synthesis of fluorous-Fmoc reagents is described. Fmoc reagents bearing C3F7, C4F9, and C6F13 chains were prepared on multi-gram scale (ca. 1.0–7.0 g) in eight steps with overall yields of 73%, 60%, and 90%, respectively. The order of addition of the fluorous alkenes in a one-pot double tagging Heck reaction was also investigated in order to conduct an encoded mixture synthesis of f-Fmoc reagents. The target f-Fmoc reagents bearing C3F7, C4F9, and C6F13 chains could be effectively separated based on the fluorine content of the molecules.

Kinetics of the Addition of Olefins to Si-Centered Radicals: The Critical Role of Dispersion Interactions Revealed by Theory and Experiment

Solution-phase rate constants for the addition of selected olefins to the triethylsilyl and tris(trimethylsilyl)silyl radicals are measured using laser-flash photolysis and competition kinetics. The results are compared with predictions from density functional theory (DFT) calculations, both with and without dispersion corrections obtained from the exchange-hole dipole moment (XDM) model. Without a dispersion correction, the rate constants are consistently underestimated; the errors increase with system size, up to 10(6) s(-1) for the largest system considered. Dispersion interactions preferentially stabilize the transition states relative to the separated reactants and bring the DFT-calculated rate constants into excellent agreement with experiment. Thus, dispersion interactions are found to play a key role in determining the kinetics for addition reactions, particularly those involving sterically bulky functional groups.

Brønsted Acid Catalyzed [4+2] Addition of Alkenes with ortho-Quinone Methides

Key words chromanes - hetero-Diels–Alder reaction - N-triflylphosphoramides

ChemInform Abstract: Iron‐Catalyzed Alkenylation of Isochroman Acetals with Simple Alkenes.

AbstractIron(III) p‐toluenesulfonate is found to be an efficient and inexpensive catalyst for the nucleophilic addition of alkenes to 1‐methoxyisochromans under redox‐neutral conditions.

Polydicyclopentadiene aerogels from first- versus second-generation Grubbs’ catalysts: a molecular versus a nanoscopic perspective

Polydicyclopentadiene (pDCPD) aerogels obtained via ring-opening metathesis polymerization using the first-generation Grubbs’ catalyst (GC-I) are well-shaped monoliths; those obtained from the second-generation Grubbs’ catalyst (GC-II) were severely deformed. At lower densities, materials from either catalyst consisted of entangled nanofibers, turning into random aggregates of nanoparticles as density increased. Nanoscopically, all those microstructures consisted of similar mass-fractal aggregates of secondary particles (by rheology), which in turn are closely packed assemblies of primary particles (by SAXS). Soluble oligomers along gelation were observed only with GC-II (by 1H NMR); nevertheless, all monomers were eventually incorporated in the skeletal framework of both materials (gravimetrically). The extent of cross-linking by olefin addition (via solid-state 13C NMR) was in the same range with both catalysts (19–25 % of pendant cyclopentenes). The only significant difference in the two kinds of aerogels was in the cis versus trans configuration of the polymeric backbone (by IR and solid-state 13C NMR). Deformation of GC-II-derived aerogels has been rectified by filling the empty space among primary particles (about 36 % v/v) with a hard polymer. Those aerogels have the same mechanical properties with those derived from GC-I, meaning that deformation is due to rearrangement at a level below the load-bearing macroporous network. Thus, a self-consistent model for deformation calls for primary particles of mostly trans pDCPD (via GC-I) being more rigid and more difficult to squeeze; thus, higher mass-fractal aggregates of secondary particles do not penetrate into the empty space of one another. Conversely, primary particles of more malleable cis/trans pDCPD (via GC-II) are squeezable, allowing higher aggregates to partially penetrate into one another. This model may also be related to frequently noted drying shrinkage of wet-gels even after converting the pore-filling solvent into a supercritical fluid, whereas all surface tension forces should have been eliminated.

ChemInform Abstract: Syntheses of Chiral Ferrocenophanes and Their Application to Asymmetric Catalysis.

AbstractChiral N‐substituted azaferrocenophanes are prepared and evaluated in the Cu(I)‐catalyzed asymmetric oxidative homocoupling of naphthol derivatives and in the asymmetric Michael addition of nitro olefins to ketones.

ChemInform Abstract: Novel and Convenient Acetoxyselenenylation of Alkenes Catalyzed by Potassium Iodide.

With KI as catalyst and m-chloroperbenzoic acid as the oxidant in acetic acid, a novel and efficient catalytic procedure has been developed for acetoxyselenenylation of alkenes, which providing a series of 2-acetoxy-1-selenenylation compounds with high regioselectivity and good yields in mild conditions. In this protocol, KI is first oxidized by m-chloroperbenzoic acid into acetylhypoiodite, which rapidly reacts with diselenide to form the active electrophilic selenenylating reagent, following an electrophilic addition of alkenes and 2-acetoxy-1-selenenylation compounds are obtained. The suitable equivalent ratio of alkene to diselenide is 1.2.