Allylic Cleavage Research Articles

Thermal decomposition of alkenes: role of allylic C-C bond cleavage

Thermal decomposition of alkenes is critical in many chemical processes. In the alkene moiety, allylic CC bonds are significantly weaker than alkylic and vinylic CC bonds. To address literature discrepancies in the rate of allylic CC bond cleavage, the current work investigates the thermal decomposition of two prototype molecules, namely 1-hexene (k1) and 4-methyl-1-pentene (k2). The formation of product allyl radicals is tracked using a highly sensitive UV laser diagnostic to determine the rate coefficients of k1 and k2 over 1178–1359 K in a shock tube. Both reactions exhibit a positive Arrhenius temperature dependence, with the decomposition of 4-methyl-1-pentene occurring 1.5–3 times faster than that of 1-hexene. Values of k1 adopted in literature models vary by an order of magnitude.By integrating our previous measurements of 1-butene and 1-pentene decomposition (Zhou et al., 2024), this work establishes a comprehensive set of rate rules that encompasses the decomposition of allylic-primary (P), allylic-secondary (S21 and S22), and allylic-tertiary (T) CC bonds. At 1200 K, the decomposition of a tertiary allylic CC bond (kT) occurs 42 times faster than that of the primary CC bond (kP). Notably, our established rate rules caution against commonly adopted analogies between the rate coefficients of the thermal decomposition of 1-butene and 1-pentene, as kS21 proceeds 3–7 times faster than kP.The implementation of these rate rules in various kinetic models of alkenes and biofuels greatly enhances the accuracy of their predictions. This work thus contributes to a deeper understanding of the mechanisms underlying soot formation during from the combustion of unsaturated fuels.

Dual derivatization strategy for the comprehensive quantification and double bond location characterization of fatty acids by ultra-high performance liquid chromatography-tandem mass spectrometry

Comprehensive analysis of fatty acids (FAs) has long been challenging due to their poor ionization efficiency, lack of characteristic fragment ions and difficulty of identifying C=C bond locations. In this study, a high coverage ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was established for the quantification and C=C bond location characterization of FAs using two structural analogues, 2-hydrazinyl-4,6-dimethylpyrimidine (DMP) and 2-hydrazinylpyrimidine (DP), as dual derivatization reagents. DP-labeled FA standards were used as internal standards to reduced matrix effects, which guaranteed the accurate quantification of FAs. The derivatization yields of FAs were larger than 99% and the sensitivities were increased by 400-fold compared with non-derivatized FAs. Pretreatment and instrumental analysis of FAs can be completed in 20 minutes. Only 5 μL rat plasma can satisfy the quantification of 36 FAs with good linearity (r>0.99). Both intra-day and inter-day accuracies were in the range of 85-105%, and the precisions were less than 15%. The extraction recoveries were investigated to be in the range of 88-112%. No obvious matrix effects were observed for the derivatized FAs. In addition, the locations of C=C bonds in DMP-derivatized FAs could be identified by diagnostic fragment ions generated from 1,4-hydrogen elimination and allylic cleavage under low energy collision induced dissociation (CID). The new method was finally employed for FA profiling in plasma from rats with moxifloxacin-induced liver injury. Significant downregulation of butyric acid was observed in moxifloxacin treated model rats, which was believed to be related to the liver injury.

Silver(I)-Catalyzed Deprenylation of Allylsulfonamide Derivatives

The silver(I)-catalyzed deprenylation of sulfonamide bearing prenyl functional groups on the nitrogen atom has been developed. In this reaction, the prenyl moiety was selectively eliminated without allyl or benzyl cleavage on the nitrogen atom. In addition, geranyl was also applicable for this elimination reaction. Furthermore, sulfonamide possessing two prenyl groups underwent a double deprenylation to form the corresponding deprenylated sulfonamide. Thus, a novel reactivity between the silver cation and double bond was observed.

A mild copper catalyzed method for the selective deprotection of aryl allyl ethers

Copper boryl reagents enable the selective cleavage of aryl allyl ethers to the corresponding phenols in good to moderate yields.

ChemInform Abstract: Synthesis of Oxetane‐3‐carboxaldehyde and Methyl Oxetane‐3‐carboxylate via Homologation of Oxetane‐3‐one.

Abstract A 4-pot telescoped procedure to prepare oxetane-3-carboxaldehyde and methyl oxetane-3-carboxylate was developed using readily available starting materials. Classical homologation methods applied to oxetane-3-one proved challenging due to the sensitivity of the oxetane ring toward strongly oxidative, basic and acidic conditions. Subsequently, a mild homologation sequence was developed. The key steps involve a Tsuji hydrogenolysis of an allylic acetate, osmium-free dihydroxylation and oxidative cleavage. Although methyl oxetane-3-carboxylate is marketed by a small number of specialty chemical companies, this work represents the first published preparation of this vital building block.

Synthesis of oxetane-3-carboxaldehyde and methyl oxetane-3-carboxylate via homologation of oxetane-3-one

A 4-pot telescoped procedure to prepare oxetane-3-carboxaldehyde and methyl oxetane-3-carboxylate was developed using readily available starting materials. Classical homologation methods applied to oxetane-3-one proved challenging due to the sensitivity of the oxetane ring toward strongly oxidative, basic and acidic conditions. Subsequently, a mild homologation sequence was developed. The key steps involve a Tsuji hydrogenolysis of an allylic acetate, osmium-free dihydroxylation and oxidative cleavage. Although methyl oxetane-3-carboxylate is marketed by a small number of specialty chemical companies, this work represents the first published preparation of this vital building block.

Application of a new phosphorus-free palladium heterogeneous nanocatalyst supported on modified MWCNT the highly selective and efficient cleavage of propargyl, allyl, and benzyl phenol ethers under mild conditions.

A stable and efficient phosphorus-free, low Pd-loading heterogeneous nanocatalyst comprising palladium and a multi-walled carbon nanotube was prepared and characterized by various techniques such as SEM, TEM, AFM, FT-IR, and Raman spectrometry, N2 adsorption isotherm and thermogravimetric analysis. This catalyst was used for the deprotection of phenol ethers. The catalyst selectivity for deprotection of between propargyl, allyl, and benzyl, as a protecting group, was studied. Also, the presence of different functional groups was studied to establish the scope and limitations of this method. The catalytic activity of recycled catalyst was evaluated. The results indicated that the catalyst is heterogeneous, stable, and very active under the established conditions, and it could be reused up to five times without any significant leaching. In addition, according to ICP analysis, low leaves of leaching of palladium from the catalyst was observed, which indicates that anthraquinone has an excellent ability to coordinate with palladium.

The Dimethoxyphenylbenzyl Protecting Group: An Alternative to the p-Methoxybenzyl Group for Protection of Carbohydrates

A reliable reagent system for the cleavage of 4-(3,4-dimethoxyphenyl)benzyl (DMPBn) ethers under acidic conditions has been established. Treatment of DMPBn-protected mono- and pseudodisaccharides with TFA in anhydrous CH2Cl2 and 3,4-(methylenedioxy)toluene as a cation scavenger resulted in the selective cleavage of the DMPBn ether giving the corresponding deprotected products in moderate to high yields. Examples are reported which show that allyl, benzyl, and p-bromobenzyl ethers, esters, and glycosidic linkages are stable to these reaction conditions. The selective cleavage of allyl, p-bromobenzyl, and PMB ethers in protected carbohydrates containing DMPBn ethers are also demonstrated. This work establishes the 4-(3,4-dimethoxyphenyl)benzyl ether as an effective and robust alternative to p-methoxybenzyl as a protecting group for alcohols.

Approach for expanding triterpenoid complexity via divergent Norrish-Yang photocyclization.

Triterpenoids comprise a very diverse family of polycyclic molecules that is well-known to possess a myriad of medicinal properties. Therefore, triterpenoids constitute an attractive target for medicinal chemistry and diversity-oriented synthesis. Photochemical transformations provide a promising tool for the rapid, green, and inexpensive generation of skeletal diversity in the construction of natural product-like libraries. With this in mind, we have developed a diversity-oriented strategy, whereby the parent triterpenoids bryonolic acid and lanosterol are converted to the pseudosymmetrical polyketones by sequential allylic oxidation and oxidative cleavage of the bridging double bond at the B/C ring fusion. The resultant polyketones were hypothesized to undergo divergent Norrish-Yang cyclization to produce unique 6/4/8-fused triterpenoid analogues. The subtle differences between parent triterpenoids led to dramatically different spatial arrangements of reactive functionalities. This finding was rationalized through conformational analysis to explain unanticipated photoinduced pinacolization, as well as the regio- and stereochemical outcome of the desired Norrish-Yang cyclization.

Highly practical iron-catalyzed C–O cleavage reactions

Facile iron-catalyzed cleavage of various allyl, cinnamyl and benzyl C–O linkages has been effected in the presence of ethylmagnesium chloride. The protocol is operationally simple (xylene–THF, r.t., 1 h), requires low catalyst loading (1 mol% FeCl2) and tolerates halides, esters, amines, ethers and olefins. The allyl moiety is converted to volatile hydrocarbons which renders laborious product separation unnecessary.

Elaboration of the ether cleaving ability and selectivity of the classical Pearlman's catalyst [Pd(OH)2/C]: concise synthesis of a precursor for a myo-inositol pyrophosphate

The cleavage of propargyl, allyl, benzyl, and PMB ethers by Pd(OH)2/C can be tuned in that order, by varying the reaction conditions. Other moieties such as C–C double bonds, esters, trityl ether, p-bromo and p-nitrobenzyl ethers are stable to these reaction conditions. Cleavage of allyl ethers can be made catalytic by using 1:1 mixture of Pd(OH)2/C and Pd/C. The synthetic potential of the selective ether cleaving ability of Pd(OH)2/C, essentially under neutral conditions, has been demonstrated by an efficient synthesis of a precursor for the preparation of an inositol pyrophosphate derivative.

Palladium‐Mediated Phosphine‐Dependent Chemoselective Bisallylic Alkylation Leading to Spirocarbocycles

Cycles everywhere: The selectivity in the transformations of 1,3-diones to carbocycles by palladium-catalyzed bisallylic alkylations is strongly dependent on the phosphine that is employed. Moreover, synthesized vinylcyclopentenes can be easily transformed into cycloheptadiene derivatives through a carbon-carbon allylic bond cleavage.

ChemInform Abstract: Catecholborane Reductive Cleavage of Allyl and Propargyl Acetals and Ketals: A Simple Route to Allyl and Prop-2-ynyl Ethers.

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Double Bond Migration to Methylidene Positions During Electron Ionization Mass Spectrometry of Branched Monounsaturated Fatty Acid Derivatives

Electron ionization mass spectra of several monounsaturated methyl-branched fatty acid methyl and trimethylsilyl esters were examined. These spectra exhibited some intensive fragment ions, whose formation could be explained after double-bond migration to methylidene position. This preferential migration (substantiated by deuterium labeling) acts significantly in the case of monounsaturated fatty acid methyl and trimethylsilyl esters possessing a methyl branch localized between the penultimate and the C(4) positions (relative to the ester group), whatever the position of the double-bond. Allylic cleavage and gamma-hydrogen rearrangement of the ionized methylidene group thus formed afforded very interesting fragment ions, which could be particularly useful to determine branching positions of monounsaturated methyl-branched fatty acid methyl and trimethylsilyl esters without additional treatment.

Remarkable Solvent Effect on Pd(0)-Catalyzed Deprotection of Allyl Ethers Using Barbituric Acid Derivatives: Application to Selective and Successive Removal of Allyl, Methallyl, and Prenyl Ethers

Pd(0)-catalyzed deprotection of allyl ethers using barbituric acid derivatives in protic polar solvent such as MeOH and aqueous 1,4-dioxane proceeds at room temperature without affecting a wide variety of functional groups. Control of the reaction temperature allows selective and successive cleavage of allyl, methallyl, and prenyl ethers. A study of ligand effects on the deprotection reveals that the improved reactivity in MeOH results from the accelerated oxidative addition to Pd(0).

Selective Cleavage of Allyl and Propargyl Ethers to Alcohols Catalyzed by Ti(O‐i‐Pr)4/MXn/Mg.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Hydrosilylation of allyl glycidyl ether with triethoxysilane

Hydrosilylation of allyl glycidyl ether with triethoxysilane in presence of Speier’s catalyst leads to triethoxy(3-glycidoxypropyl)silane and triethoxy(2-glycidoxy-1-methylethyl)silane and is accompanied by isomerization of allyl glycidyl ether and cleavage of the oxirane ring and the ether bond. An effect of admixtures in allyl glycidyl ether on the process is revealed. Some other hydrosilylation catalysts and additives to Speier’s catalyst are studied

Stereoselective syntheses of (−)-tetrahydrolipstatin via Prins cyclisations

Stereoselective syntheses of (−)-tetrahydrolipstatin have been achieved via two divergent approaches through Prins cyclisations as the key steps. PCC mediated oxidative cleavage, Frater alkylation, Keck allylation, Sharpless asymmetric epoxidation and allylic cleavage were the other key steps employed.

Gas chromatography–mass spectrometry determination of metabolites of conjugated cis-9, trans-11, cis-15 18:3 fatty acid

Structural determination of polyunsaturated fatty acids by gas chromatography–mass spectrometry (GC–MS) requires currently the use of nitrogen containing derivatives such as picolinyl esters, 4,4-dimethyloxazoline or pyrrolidides derivatives. The derivatization is required in most cases to obtain low energy fragmentation that allows accurate location of the double bonds. In the present work, the following metabolites of rumelenic ( cis-9, trans-11, cis-15 18:3) acid, from rat livers, were identified: cis-8, cis-11, trans-13, cis-17 20:4, cis-5, cis-8, cis-11, trans-13, cis-17 20:5, cis-7, cis-10, cis-13, trans-15, cis-19 22:5, and cis-4, cis-7, cis-10, cis-13, trans-15, cis-19 22:6 acids by GC–MS as their 4,4-dimethyloxazoline and methyl esters derivatives. Specific fragmentation of the methyl ester derivatives revealed some similarity with their corresponding DMOX derivatives. Indeed, intense ion fragments at m/ z = M + − 69, corresponding to a cleavage at the center of a bis-methylene interrupted double bond system were observed for all identified metabolites. Moreover, intense ion fragments at m/ z = M + − 136, corresponding to allylic cleavage of the n-12 double bonds were observed for the C20:5, C22:5, C22:6 acid metabolites. For the long chain polyunsaturated fatty acids from the rumelenic metabolism, we showed that single methyl esters derivatives might be used for both usual quantification by GC–FID and identification by GC–MS.

Ruthenium‐Catalyzed Chemoselective N‐Allyl Cleavage: Novel Grubbs′ Carbene Mediated Deprotection of Allylic Amines.

A novel application of the Grubbs carbene complex has been discovered. The first examples of the catalytic deprotection of allylic amines with reagents other than palladium catalysts have been achieved through Grubbs carbene mediated reaction. Significantly, the catalytic system directs the reaction toward the selective deprotection of allylic amines (secondary as well as tertiary) in the presence of allylic ethers. A variety of substrates, including enantiomerically pure multifunctional piperidines, are also usable. The new method is more convenient, chemoselective, and operationally simple than the palladium-catalyzed method. The current mechanistic hypothesis invokes a nitrogen-assisted ruthenium-catalyzed isomerization, followed by hydrolysis of the enamine intermediate. We believe that the reactive species involved in the reaction may be an Rubond;H species rather than the Grubbs carbene itself. Thus, the isomerization may occur according to the hydride mechanism. The synthetic utility of this ruthenium-catalyzed allyl cleavage is illustrated by the preparation of indolizidine-type alkaloids.