Vinyl Oxiranes Research Articles

DMAP Catalyzed Ring-Opening/Cycloaddition of Vinyl Oxiranes with Activated Ketone Compounds to Construct the 1,3-Dioxolane Skeletons.

The present work develops a DMAP-catalyzed [3 + 2] cycloaddition of vinyl oxiranes with activated ketone compounds, affording dioxolane derivatives with moderate to excellent yields. This approach represents the first Lewis base (LB)-catalyzed ring-opening reaction of vinyl epoxides, simultaneously providing a rare oxygen-containing active intermediate in this field. The gram-scale preparation and facile derivatization of the cycloadduct highlight the significant synthetic potential of this strategy.

Recent Progress in (3+3) Cycloadditions of Bicyclobutanes to Access Bicyclo[3.1.1]heptane Derivatives

AbstractThe synthesis of bicyclo[3.1.1]heptane (BCHeps) derivatives, which serve as three-dimensional (3D) bioisosteres of benzenes and are the core skeleton of several terpene natural products, is garnering growing interest. The (3+3) cycloadditions of bicyclobutanes (BCBs) represent an attractive method for efficiently accessing (hetero)BCHep skeletons with 100% atom economy. Herein, we give a brief summary of recent achievements in this approach for the synthesis of diverse BCHep derivatives, emphasizing our recent progress in the initial palladium-catalyzed (3+3) cycloadditions of bicyclobutanes with vinyl oxiranes.1 Introduction2 Radical (3+3) Cycloaddition Reaction3 Polar (3+3) Cycloaddition Reaction4 Palladium-Catalyzed Enantioselective (3+3) Cycloaddition Reaction5 Conclusion

The Ligand is in Control: Pd-Catalyzed (5+3) or [2σ+2σ] Cycloadditions of Bicyclobutanes and Vinyl Oxiranes

The Ligand is in Control: Pd-Catalyzed (5+3) or [2σ+2σ] Cycloadditions of Bicyclobutanes and Vinyl Oxiranes

Microwave Spectroscopy of Chiral Astrochemical Candidate Vinyloxirane: The Missing Gauche Conformer.

The recent detection of a chiral molecule, propylene oxide, in the interstellar medium provides impetus for investigation of related analogues as candidates for discovery of a second chiral species. Vinyloxirane (VO) shares many of the characteristics of propylene oxide that favored its remote detection such as modest size, appreciable dipole moment and modest adsorption to water ice. The microwave spectrum of vinyloxirane at room temperature has been studied in the 18 - 26 GHz region. Rotational transitions of the previously undetected gauche-1 conformer have been assigned and fitted. The quantum number range of anti conformer transitions has been greatly expanded, providing improved molecular constants. Vibrational satellite transitions were assigned and fitted for the lowest frequency ν27 torsion mode, for 2ν27, and for the ν26 C=CC bend of anti VO, along with ν27 satellites of gauche-1. The rovibrational analyses were assisted by anharmonic vibrational calculations at B3LYP-D3/aug-cc-PVTZ, B2PLYPD3/cc-pVTZ, and DSDPBEP86/cc-pVTZ levels. Experimental peak intensities provide a population ratio Ngauche-1/Nanti of 0.36 ± 0.06, corresponding to a Gibbs free energy difference of 2.5 ± 0.4 kJ mol-1 in favor of the anti conformer, in agreement with the density functional theory results. In the gauche-1 conformer, the torsional angle between vinyl group and oxirane ring, τC=CCM, is optimized at -35° to favor an intramolecular CvinylH11...O interaction. The gauche-2 conformer with τC=CCM of + 74° suffers from CvinylH11...HCcyclopropyl repulsion so that it is calculated to be 8-9 kJ mol-1 higher than gauche-1. Reinterpretation of earlier Raman spectra suggests that the gauche-2 conformer had not been observed as reported.

Palladium-Catalyzed Ligand-Controlled Switchable Hetero-(5 + 3)/Enantioselective [2σ+2σ] Cycloadditions of Bicyclobutanes with Vinyl Oxiranes.

For nearly 60 years, significant research efforts have been focused on developing strategies for the cycloaddition of bicyclobutanes (BCBs). However, higher-order cycloaddition and catalytic asymmetric cycloaddition of BCBs have been long-standing formidable challenges. Here, we report Pd-catalyzed ligand-controlled, tunable cycloadditions for the divergent synthesis of bridged bicyclic frameworks. The dppb ligand facilitates the formal (5+3) cycloaddition of BCBs and vinyl oxiranes, yielding valuable eight-membered ethers with bridged bicyclic scaffolds in 100% regioselectivity. The Cy-DPEphos ligand promotes selective hetero-[2σ+2σ] cycloadditions to access pharmacologically important 2-oxabicyclo[3.1.1]heptane (O-BCHeps). Furthermore, the corresponding catalytic asymmetric synthesis of O-BCHeps with 94-99% ee has been achieved using chiral (S)-DTBM-Segphos, representing the first catalytic asymmetric cross-dimerization of two strained rings. The obtained O-BCHeps are promising bioisosteres for ortho-substituted benzenes.

Metal-Free, Photoinitiated Cationic Terpolymerization of Vinyl Ethers, Oxiranes, and Ketones: Simultaneous Control of Monomer Sequence and Molecular Weight by the Formation of Long-Lived Propagating Species

Metal-Free, Photoinitiated Cationic Terpolymerization of Vinyl Ethers, Oxiranes, and Ketones: Simultaneous Control of Monomer Sequence and Molecular Weight by the Formation of Long-Lived Propagating Species

Vinyl and Alkynyl Substituted Heterocycles as Privileged Scaffolds in Transition Metal Promoted Stereoselective Synthesis.

ConspectusBiologically active compounds and pharmaceutically relevant intermediates often feature sterically congested stereogenic centers, in particular, carbon stereocenters that are either tertiary tetrasubstituted ones or quaternary in nature. Synthons that comprise such bulky and often structurally complex core units are of high synthetic value and represent important incentives for communities connected to drug discovery and development. Streamlined approaches that give access to a diverse set of compounds incorporating acyclic bulky stereocenters are relatively limited, though vital. They enable further exploration of three-dimensional entities that can be designed and implemented in discovery programs, thereby extending the pool of molecular properties that is inaccessible for flat molecules. However, the lack of modular substrates in particular areas of chemical space inspired us to consider functionalized heterocycles known as cyclic carbonates and carbamates as a productive way to create sterically crowded alkenes and stereocenters.In this Account, we describe the major approximations we followed over the course of 8 years using transition metal (TM) catalysis as an instrument to control the stereochemical course of various allylic and propargylic substitution processes and related transformations. Allylic substitution reactions empowered by Pd-catalysis utilizing a variety of nucleophiles are discussed, with amination being the seed of all of this combined work. These procedures build on vinyl-substituted cyclic carbonates (VCCs) that are simple and easy-to-access precursors and highly modular in nature compared to synthetically limited vinyl oxiranes. Overall these decarboxylative conversions take place with either "linear" or "branched" regioselectivities that are ligand controlled and offer access to a wide scope of functional allylic scaffolds. Alternative approaches, including dual TM/photocatalyzed transformations, allowed us to expand the repertoire of challenging stereoselective conversions. This was achieved through key single-electron pathways and via formal umpolung of intermediates, resulting in new types of carbon-carbon bond formation reactions significantly expanding the scope of allylic substitution reactions.Heterocyclic substrate variants that have triple bond functional groups were also designed by us to enable difficult-to-promote stereoselective propargylic substitution reactions through TM catalysis. In these processes, inspired by the Nishibayashi laboratory and their seminal findings in the area, we discovered various new reactivity patterns. This provided access to a range of different stereodefined building blocks such as 1,2-diborylated 1,3-dienes and tetrasubstituted α-allenols under Cu- or Ni-catalysis. In this realm, the use of lactone-derived substrates gives access to elusive chiral γ-amino acids and lactams with high stereofidelity and good structural diversity.Apart from the synthetic efforts, we have elucidated some of the pertinent mechanistic manifolds operative in these transformations to better understand the limitations and opportunities with these specifically functionalized heterocycles that allowed us to create complex synthons. We combined both theoretical and experimental investigations that lead to several unexpected outcomes in terms of enantioinduction models, catalyst preactivation, and intermediates that are intimately connected to rationales for the observed selectivity profiles. The combined work we have communicated over the years offers insight into the unique reactivity of cyclic carbonates/carbamates acting as privileged precursors. It may inspire other members of the synthetic communities to widen the scope of precursors toward novel stereoselective transformations with added value in drug discovery and development in both academic and commercial settings.

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds.

This present review delineates the repertoire of vinyl cyclopropanes and their stuctural analogues to accomplish a wide array of oxa-cycles, aza-cycles, and thia-cycles under transition metal catalysis and metal-free approaches from early 2019 to the present date. The generation of electrophilic π-allyl intermediates and 1-3/1-5-dipolarophile chemistry originating from VCPs are always green, step- and atom-economical and sustainable strategies in comparsion with prefunctionalized and/or C-H activation protocols. Here, the strained ring-system extends its applicability by relieving the strain to undergo a ring-expansion reaction to accomplish 5-9 membered carbo- and heterocyclic systems. The availability of chiral ligands in the ring-expansion reaction of VCPs and their analogues has paved the way to realizing asymmetric synthetic transformations.

The C2H4O isomers in the oxidation of ethylene

A combined rotational spectroscopy, thermochemistry, and kinetic modeling study explores the mechanism of acetaldehyde (ethanal), vinyl alcohol (ethenol), and ethylene oxide (oxirane) formation in the oxidation of ethylene (ethene). Multiplexed quantitative detection of oxidation intermediates and products exiting a SiO2/SiC microreactor at 1700 K is demonstrated with the BrightSpec W-band chirped-pulse Fourier transform millimeter-wave spectrometer. The broadband rotational spectrum contains transitions of formaldehyde (CH2O), methoxy (CH3O), methanol (CH3OH), ketene (CH2CO), acetaldehyde (CH3CHO), syn-vinyl alcohol (syn-CH2CHOH), anti-vinyl alcohol (anti-CH2CHOH), oxirane (c-CH2OCH2), propyne (CH3CCH), and syn-propanal (syn-CH3CH2CHO). We focus on the three C2H4O species and deduce their concentration ratio [CH3CHO]:[CH2CHOH]:[c-CH2OCH2] = 1:0.7(2):0.06(2) by comparing the observed line intensities to those simulated with the PGOPHER software. Detailed thermochemistry of the C2H4O isomers and conformers is provided by Active Thermochemical Tables. The observed excess concentrations of vinyl alcohol and oxirane relative to the more stable acetaldehyde compared to the equilibrium ratio at 1700 K (1:0.087:0.000024), point to direct chemical pathways to these higher energy isomers. The mechanism for the formation of the three C2H4O isomers is analyzed using a 0-D homogenous reactor kinetics simulation for ethylene oxidation. The ratios of the C2H4O isomers concentrations predicted by the kinetic model are compared to the experimental values.

Palladium‐ and Iridium‐Catalyzed Deracemization of Allylic Oxygen Compounds with Oxygen Nucleophiles

AbstractAllylic oxygen compounds (AOCs) are an important class of versatile building blocks in natural and non‐natural product synthesis. Catalytic in‐situ deracemization is an attractive means for their enantioselective synthesis. Particularly attractive is the deracemization of AOCs through transition metal‐catalyzed dynamic kinetic asymmetric transformation (DYKAT) with oxygen nucleophiles (ONus). This review describes pertinent aspects of the palladium‐catalyzed DYKAT of racemic allylic carboxylates, vinyl oxiranes and vinyl dioxolanones with carboxylates, hydrogen carbonate, alcohols, phenols, oximes, diosphenols and water and the iridium‐catalyzed DYKAT of racemic allylic alcohols, imidates and carboxylates with alcohols and carboxylic acids. Included in the discussion is the palladium‐catalyzed desymmetrization ofmeso‐cycloalkene bis(carboxylates) with hydrogen carbonate. While Trost's bisphosphinobenzamides, Zhou's spiro‐phosphoramidite and Feringa's BINOL‐phosphoramidite are highly efficient ligands in palladium‐catalyzed DYKAT, Carreira‐Dorta's BINOL‐phosphoramidite‐olefin is an excellent ligand in iridium‐catalyzed DYKAT. This review also discusses mechanistic and structural aspects of η3‐allylpalladium‐bisphosphinobenzamide and η3‐allyliridium‐BINOL‐phosphoramidite‐olefin complexes and of the corresponding catalysts.

Vacuum-ultraviolet absorption cross-sections of functionalized four-carbon species

Absorption cross-sections were measured in the vacuum ultraviolet from 5.17 – 9.92 eV using differential absorption spectroscopy for 33 four-carbon species: n-butane, trans-2-butene, cis-2-butene, butanal, butyric acid, ethyloxirane, trans-2,3-dimethyloxirane, cis-2,3-dimethyloxirane, 2-methyloxetane, 2,2′-bioxirane, vinyl oxirane, 3,4-epoxybutan-2-one, diacetyl, diethyl ether, ethyl vinyl ether, vinyl acetate, acetic anhydride, 1-butanol, 3-buten-1-ol, 1‑hydroxy-butan-2-one, 1‑hydroxy-butan-3-one, 2,3-epoxybutan-1-ol, 3,4-epoxybutan-1-ol, 2-oxetanemethanol, butanone, methyl vinyl ketone, 4H-1,3-dioxine, allyl formate, 2-oxobutanal, 4-hydroxybutanal, 2-methyloxetan-3-one, cis‑but-2-en-1-ol, and trans-2‑but-enal. Uncertainties were quantified in all cases by accounting for errors in gas-phase concentration, experimental repeatability, and signal-to-noise ratio as a function of photon energy. With the exception of 2-oxobutanal, which is reported with an uncertainty of 10%, convolving the sources of error using the root-sum-square method led to an upper limit of 5% uncertainty above the detection limit, which is largely attributable to chemical purity.The primary objective of the present work is to provide absolute cross-sections along with quantified uncertainty limits. The majority of the absorption spectra, which reflect electronic transitions such as σ → σ* and n → σ*, are reported for the first time and provide insight into fundamental chemical physics, such as vibrational band structure and Rydberg transitions. The quantitative spectra in the present work facilitates the discovery of chemical intermediates that support improvement in the accuracy of computational models for low-temperature combustion and atmospheric chemistry.

Copolymerizability Evaluation in Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes: Effects of Bulkiness and the Number of Substituents Introduced into Oxiranes

Copolymerizability Evaluation in Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes: Effects of Bulkiness and the Number of Substituents Introduced into Oxiranes

Iridium‐Catalyzed [4+3] Cyclization of ortho‐Tosylaminophenyl‐Substituted para‐Quinone Methides with Vinylic Oxiranes/Vinyl Aziridines

AbstractAn Iridium‐catalyzed [4+3] cyclization of ortho‐tosylaminophenyl‐substituted para‐quinone methides with vinylic oxiranes or vinyl aziridines has been successfully developed. In the presence of [Ir(cod)Cl]2 and a suitable base, this unprecedented cascade reaction occurs readily in good yield (up to 97%) and high diastereoselectivity (dr>20 : 1), providing a highly efficient synthetic approach to synthetically valuable seven‐membered heterocyclic frameworks.

3 + 1 + 1] cyclization of vinyl oxiranes with azides and CO by tandem palladium catalysis: efficient synthesis of oxazolidinones

An efficient [3 + 1 + 1] cyclization of vinyl oxiranes for the synthesis of oxazolidinones has been developed via tandem palladium catalysis.

Tert-Butyl Esters as Potential Reversible Chain Transfer Agents for Concurrent Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes.

tert-Butyl esters are demonstrated to function as chain transfer agents (CTAs) in the cationic copolymerization of vinyl ether (VE) and oxirane via concurrent vinyl-addition and ring-opening mechanisms. In the copolymerization of isopropyl VE and isobutylene oxide (IBO), the IBO-derived propagating species reacts with tert-butyl acetate to generate a copolymer chain with an acetoxy group at the ω-end. This reaction liberates a tert-butyl cation; hence, a polymer chain with a tert-butyl group at the α-end is subsequently generated. Other tert-butyl esters also function as CTAs, and the substituent attached to the carbonyl group affects the chain transfer efficiency. In addition, ethyl acetate does not function as a CTA, which suggests the importance of the liberation of a tert-butyl cation for the chain transfer process. Chain transfer reactions by tert-butyl esters potentially occur reversibly through the reaction of the propagating cation with the ester group at the ω-end of another chain.

Chemical kinetics study of 1,3-butadiene + HȮ2; implications for combustion modeling and simulation

Detailed reaction kinetics for the system of 1,3-butadiene + hydroperoxyl radical (HȮ2) and its application in combustion modeling have been investigated in this work. Zero-point energy (ZPE) corrected potential energy surfaces (PESs) for the title reactions have been obtained using high-level ab initio electronic structure methods of ROCCSD(T)/CBS//BHandHLYP/6–311++G(d,p), and the energies relative to the reactants for all stationary points were used in the kinetic calculations. Pressure- and temperature-dependent rate constants for each individual reaction pathway have been calculated by solving the Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) implemented in the Master Equation System Solver (MESS) program. The bimolecular pathways forming vinyl oxirane, (CYOC)CC, and hydroxyl radical (ȮH) from the reactants are found to be dominant in the temperature range of 800–2000 K below 1 atm, and keep competitive when temperature is higher than 1000 K at 100 atm. At elevated pressures, the stabilizations of the two entrance channels forming radicals of 1-hydroperoxy-3-buten-2-yl (C4H61–3OOH4) and 3-butenyl-2-peroxy (C4H71-OO3) are more important than the formation of bimolecular products (CYOC)CC + ȮH at temperatures below 1000 K. Temperature-dependent thermochemical properties for important species on the PESs of 1,3-butadiene + HȮ2 have also been calculated. The kinetics and thermochemistry data for the title reaction system calculated in this work have been incorporated into AramcoMech 3.0 mechanism and their influence on the performance of AramcoMech 3.0 in simulating the combustion properties of 1,3-butadiene, including ignition delay times and species profiles against temperature or time, has been investigated. This is a first-time study on the reaction kinetics between HȮ2 radical and species including two double bonds.

ABC Pseudo-Periodic Sequence Control by Cationic Orthogonal Terpolymerization of Vinyl Ether, Oxirane, and Ketone

For the purpose of achieving ABC-type periodic terpolymers, various vinyl ethers (VEs), oxiranes, and ketones were examined in the cationic vinyl-addition, ring-opening, and carbonyl-addition terpo...

Synthesis of Highly Functionalized Allylic Alcohols from Vinyl Oxiranes and N-Tosylhydrazones via a Tsuji-Trost-Like "Palladium-Iodide" Catalyzed Coupling.

An unprecedented efficient palladium(0)-catalyzed reaction of vinyl oxiranes with N-tosylhydrazones, affording "skipped" allylic alcohols in total regioselectivity and stereoselectivity, with excellent functional-group compatibility, is reported. In this Tsuji-Trost-like allylation, we propose the use of N-tosylhydrazones as a synthetic equivalent of α-styryl anions. More than 20 new products are described, including naturally occurring derivatives. A catalytic system involving an iodide (I-) source is necessary to sustain the catalytic cycle.

Catalytic Nucleophilic Allylation Driven by the Water-Gas Shift Reaction.

The ruthenium-catalyzed allylation of aldehydes with allylic pro-nucleophiles has been demonstrated to be an efficient means to form carbon-carbon bonds under mild conditions. The evolution of this reaction from the initial serendipitous discovery to its general synthetic scope is detailed, highlighting the roles of water, CO, and amine in the generation of a more complete catalytic cycle. The use of unsymmetrical allylic pro-nucleophiles was shown to give preferential product formation through the modulation of reaction conditions. Both (E)-cinnamyl acetate and vinyl oxirane were efficiently used to form the anti-branched products (up to >20:1 anti/syn) and E-linear products (up to >20:1 E/Z) in high selectivity with aromatic, α,β-unsaturated, and aliphatic aldehydes, respectively. Attempts to render the reaction enantioselective are highlighted and include enantioenrichment of up to 75:25 for benzaldehyde.

Efficient Access to All-Carbon Quaternary and Tertiary α-Functionalized Homoallyl-type Aldehydes from Ketones.

β,γ-Unsaturated aldehydes with all-carbon quaternary or tertiary α-centers were rapidly assembled from ketones through a unique synthetic operation consisting of 1) C1 homologation, 2) Lewis acid mediated epoxide-aldehyde isomerization, and 3) electrophilic trapping. The synthetic equivalence of a vinyl oxirane and a β,γ-unsaturated aldehyde is the key concept of this previously undisclosed tactic. Mechanistic studies and labeling experiments suggest that an aldehyde enolate is a crucial intermediate. The homologating carbenoid formation plays a critical role in determining the chemoselectivity.