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1.
Jayabrata Das Pravas Dolui Wajid Ali Jyoti Prasad Biswas Hediyala B. Chandrashekar Gaurav Prakash Debabrata Maiti 《Chemical science》2020,11(35):9697
Lactones comprise a class of valuable compounds having biological as well as industrial importance. Development of a methodology to synthesize such molecules directly from readily available materials such as aliphatic carboxylic acid is highly desirable. Herein, we have reported synthesis of δ-lactones and ε-lactones via selective γ-C(sp3)–H activation. The γ-C–H bond containing aliphatic carboxylic acids provide six or seven membered lactones depending on the olefin partner in the presence of a palladium catalyst. A mechanistic investigation suggests that C–H activation is the rate-determining step. Further transformations of the lactones have been carried out to showcase the applicability of the present strategy.Six and seven membered lactones have been synthesized directly from readily available aliphatic acids. 相似文献
2.
This work emphasizes easy access to α-vinyl and aryl amino acids via Ni-catalyzed cross-electrophile coupling of bench-stable N-carbonyl-protected α-pivaloyloxy glycine with vinyl/aryl halides and triflates. The protocol permits the synthesis of α-amino acids bearing hindered branched vinyl groups, which remains a challenge using the current methods. On the basis of experimental and DFT studies, simultaneous addition of glycine α-carbon (Gly) radicals to Ni(0) and Ar–Ni(ii) may occur, with the former being more favored where oxidative addition of a C(sp2) electrophile to the resultant Gly–Ni(i) intermediate gives a key Gly–Ni(iii)–Ar intermediate. The auxiliary chelation of the N-carbonyl oxygen to the Ni center appears to be crucial to stabilize the Gly–Ni(i) intermediate.We have developed Ni-catalyzed reductive coupling of N-carbonyl protected α-pivaloyloxy glycine with Csp2-electrophiles that enabled facile preparation of α-amino acids, including those bearing hindered branched vinyl groups. 相似文献
3.
A dual photochemical/nickel-mediated decarboxylative strategy for the assembly of C(sp3)–C(sp2) linkages is disclosed. Under light irradiation at 390 nm, commercially available and inexpensive Hantzsch ester (HE) functions as a potent organic photoreductant to deliver catalytically active Ni(0) species through single-electron transfer (SET) manifolds. As part of its dual role, the Hantzsch ester effects a decarboxylative-based radical generation through electron donor–acceptor (EDA) complex activation. This homogeneous, net-reductive platform bypasses the need for exogenous photocatalysts, stoichiometric metal reductants, and additives. Under this cross-electrophile paradigm, the coupling of diverse C(sp3)-centered radical architectures (including primary, secondary, stabilized benzylic, α-oxy, and α-amino systems) with (hetero)aryl bromides has been accomplished. The protocol proceeds under mild reaction conditions in the presence of sensitive functional groups and pharmaceutically relevant cores.This works demonstrates the implementation of an electron donor–acceptor (EDA) complex platform toward Ni-catalyzed C(sp3)–C(sp2) bond formation, circumventing the need for exogenous photocatalysts, additives, and stoichiometric metal reductants. 相似文献
4.
Yulong Kuang Hui Cao Haidi Tang Junhong Chew Wei Chen Xiangcheng Shi Jie Wu 《Chemical science》2020,11(33):8912
Deuterium labelled compounds are of significant importance in chemical mechanism investigations, mass spectrometric studies, diagnoses of drug metabolisms, and pharmaceutical discovery. Herein, we report an efficient hydrogen deuterium exchange reaction using deuterium oxide (D2O) as the deuterium source, enabled by merging a tetra-n-butylammonium decatungstate (TBADT) hydrogen atom transfer photocatalyst and a thiol catalyst under light irradiation at 390 nm. This deuteration protocol is effective with formyl C–H bonds and a wide range of hydridic C(sp3)–H bonds (e.g. α-oxy, α-thioxy, α-amino, benzylic, and unactivated tertiary C(sp3)–H bonds). It has been successfully applied to the high incorporation of deuterium in 38 feedstock chemicals, 15 pharmaceutical compounds, and 6 drug precursors. Sequential deuteration between formyl C–H bonds of aldehydes and other activated hydridic C(sp3)–H bonds can be achieved in a selective manner.A selective hydrogen deuterium exchange reaction with formyl C–H bonds and a wide range of hydridic C(sp3)–H bonds has been achieved by merging tetra-n-butylammonium decatungstate photocatalyst and a thiol catalyst under 390 nm light irradiation. 相似文献
5.
A dual catalytic decarboxylative allylation and benzylation method for the construction of new C(sp3)–C(sp3) bonds between readily available carboxylic acids and functionally diverse carbonate electrophiles has been developed. The new process is mild, operationally simple, and has greatly improved upon the efficiency and generality of previous methodology. In addition, new insights into the reaction mechanism have been realized and provide further understanding of the harnessed reactivity.A dual catalytic decarboxylative allylation and benzylation method for the construction of new C(sp3)–C(sp3) bonds between readily available carboxylic acids and functionally diverse carbonate electrophiles has been developed. 相似文献
6.
Kang-Jie Bian Yan Li Kai-Fan Zhang Yan He Tian-Rui Wu Cheng-Yu Wang Xi-Sheng Wang 《Chemical science》2020,11(38):10437
As an alternative approach to traditional C–H activation that often involved harsh conditions, and vicinal or primary C–H functionalization, radical relay offers a solution to these long-held problems. Enabled by 1,n (n = 5, 6)-hydrogen atom transfer (HAT), we use a most prevalent moiety, alkene, as the precursor to an sp3 C-centered radical to promote selective cleavage of inert C(sp3)–H bonds for the generation of azidotrifluoromethylated molecules. Mild conditions, broad scope and excellent regioselective control (>20 : 1) are observed in the reactions. Deuterium labelling studies disclose the kinetic characteristics of the transformations and verify a direct 1,n-HAT pathway. The key to this C-centered radical relay is that iron plays a dual role as a radical initiator and terminator to incorporate the azide functionality through radical oxidation via azido–ligand-transfer. The methods and the later derivatization promise expeditious synthesis of CF3-containing organic azides, γ-lactam and triazoles that are widely used in designing new fluorescent tags and functional materials.Remote functionalization of inert C(sp3)–H bonds is described via iron-catalyzed sp3 C-centered radical relay. 相似文献
7.
Xi-Shang Sun Xing-Heng Wang Hai-Yan Tao Liang Wei Chun-Jiang Wang 《Chemical science》2020,11(40):10984
In this study, we developed an efficient Ir-catalyzed cascade umpolung allylation/2-aza-Cope rearrangement of tertiary α-trifluoromethyl α-amino acid derivatives for the preparation of a variety of quaternary α-trifluoromethyl α-amino acids in high yields with excellent enantioselectivities. The umpolung reactivity empowered by the activation of the key isatin-ketoimine moiety obviates the intractable enantioselectivity control in Pd-catalyzed asymmetric linear α-allylation. In combination with quasi parallel kinetic resolution or kinetic resolution, the generality of this method is further demonstrated by the first preparation of enantioenriched quaternary trifluoromethyl β-, γ-, δ- and ε-amino acid derivatives.In this study, we developed an efficient Ir-catalyzed cascade umpolung allylation/2-aza-Cope rearrangement for the preparation of a variety of quaternary trifluoromethyl α-ε-amino acids in high yields with excellent enantioselectivities. 相似文献
8.
α-Arylated carboxylic acids, esters and amides are widespread motifs in bioactive molecules and important building blocks in chemical synthesis. Thus, straightforward and rapid access to such structures is highly desirable. Here we report an organophotocatalytic multicomponent synthesis of α-arylated carboxylic acids, esters and amides from exhaustive defluorination of α-trifluoromethyl alkenes in the presence of alkyltrifluoroborates, water and nitrogen/oxygen nucleophiles. This operationally simple strategy features a unified access to functionally diverse α-arylated carboxylic acids, esters, and primary, secondary, and tertiary amides through backbone assembly from simple starting materials enabled by consecutive C–F bond functionalization at room temperature. Preliminary mechanistic investigations reveal that the reaction operates through a radical-triggered three-step cascade process, which involves distinct mechanisms for each defluorinative functionalization of the C–F bond.Here we report an organophotocatalytic synthesis of α-arylated carboxylic acids, esters and amides from exhaustive defluorination of α-trifluoromethyl alkenes in the presence of alkyltrifluoroborates, water and nitrogen/oxygen nucleophiles. 相似文献
9.
Zhoulong Fan Shuai Zhao Tao Liu Peng-Xiang Shen Zi-Ning Cui Zhe Zhuang Qian Shao Jason S. Chen Anokha S. Ratnayake Mark E. Flanagan Dominik K. Klmel David W. Piotrowski Paul Richardson Jin-Quan Yu 《Chemical science》2020,11(45):12282
DNA-encoded library (DEL) technology has the potential to dramatically expedite hit identification in drug discovery owing to its ability to perform protein affinity selection with millions or billions of molecules in a few experiments. To expand the molecular diversity of DEL, it is critical to develop different types of DNA-encoded transformations that produce billions of molecules with distinct molecular scaffolds. Sequential functionalization of multiple C–H bonds provides a unique avenue for creating diversity and complexity from simple starting materials. However, the use of water as solvent, the presence of DNA, and the extremely low concentration of DNA-encoded coupling partners (0.001 M) have hampered the development of DNA-encoded C(sp3)–H activation reactions. Herein, we report the realization of palladium-catalyzed C(sp3)–H arylation of aliphatic carboxylic acids, amides and ketones with DNA-encoded aryl iodides in water. Notably, the present method enables the use of alternative sets of monofunctional building blocks, providing a linchpin to facilitate further setup for DELs. Furthermore, the C–H arylation chemistry enabled the on-DNA synthesis of structurally-diverse scaffolds containing enriched C(sp3) character, chiral centers, cyclopropane, cyclobutane, and heterocycles.DNA-compatible C(sp3)–H activation reactions of aliphatic carboxylic acids, amides, and ketones were developed for efficient access to DEL synthesis. 相似文献
10.
Pd-catalyzed C(sp3)–H oxygenation has emerged as an attractive strategy for organic synthesis. The most commonly proposed mechanism involves C(sp3)–H activation followed by oxidative addition of an oxygen electrophile to give an alkylpalladium(iv) species and further C(sp3)–O reductive elimination. In the present study of γ-C(sp3)–H acyloxylation of amine derivatives, we show a different mechanism when tert-butyl hydroperoxide (TBHP) is used as an oxidant—namely, a bimetallic oxidative addition-oxo-insertion process. This catalytic model results in an alkoxypalladium(ii) intermediate from which acyloxylation and alkoxylation products are formed. Experimental and computational studies, including isolation of the putative post-oxo-insertion alkoxypalladium(ii) intermediates, support this mechanistic model. Density functional theory reveals that the classical alkylpalladium(iv) oxidative addition pathway is higher in energy than the bimetallic oxo-insertion pathway. Further kinetic studies revealed second-order dependence on [Pd] and first-order on [TBHP], which is consistent with DFT analysis. This procedure is compatible with a wide range of acids and alcohols for γ-C(sp3)–H oxygenation. Preliminary functional group transformations of the products underscore the great potential of this protocol for structural manipulation.Alkoxypalladium(ii) species lead to γ-C(sp3)–H acyloxylation and alkoxylation products using tert-butyl hydroperoxide as the oxidant. 相似文献
11.
Suresh Rajamanickam Mayank Saraswat Sugumar Venkataramani Bhisma K. Patel 《Chemical science》2021,12(46):15318
An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is γ to the appended group and decreases by moving from γ → δ → ε positions. In –COO– linked alkyl chains, the same distal γ-selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N–H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote Csp3–H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > α to keto > distal methylene (γ > δ > ε). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.An intermolecular amination at the distal methylene carbon has been realized in an appended alkyl chain with electron withdrawing groups. Traceless remote Csp3–H functionalization has been accomplished using borate esters. 相似文献
12.
Kedong Yuan Taisiia Feoktistova Paul Ha-Yeon Cheong Ryan A. Altman 《Chemical science》2021,12(4):1363
PdII/CuI co-catalyze an arylation reaction of gem-difluoroalkenes using arylsulfonyl chlorides to deliver α,α-difluorobenzyl products. The reaction proceeds through a β,β-difluoroalkyl–Pd intermediate that typically undergoes unimolecular β-F elimination to deliver monofluorinated alkene products in a net C–F functionalization reaction. However to avoid β-F elimination, we offer the β,β-difluoroalkyl–Pd intermediate an alternate low-energy route involving β-H elimination to ultimately deliver difluorinated products in a net arylation/isomerization sequence. Overall, this reaction enables exploration of new reactivities of unstable fluorinated alkyl–metal species, while also providing new opportunities for transforming readily available fluorinated alkenes into more elaborate substructures.PdII/CuI co-catalyze a desulfitative arylation of aliphatic gem-difluoroalkenes in a radical arylation/migratory insertion sequence that avoids β-F elimination. 相似文献
13.
Thirupathi Gogula Jinquan Zhang Madhava Reddy Lonka Shuaizhong Zhang Hongbin Zou 《Chemical science》2020,11(42):11461
Transition metal-catalysed C–H bond functionalisations have been extensively developed in organic and medicinal chemistry. Among these catalytic approaches, the selective activation of C(sp3)–H and C(sp2)–H bonds is particularly appealing for its remarkable synthetic versatility, yet it remains highly challenging. Herein, we demonstrate the first example of temperature-dependent selective C–H functionalisation of unactivated C(sp3)–H or C(sp2)–H bonds at remote positions through palladium catalysis using 7-pyridyl-pyrazolo[1,5-a]pyrimidine as a new directing group. At 120 °C, C(sp3)–H arylation was triggered by the chelation of a rare [6,5]-fused palladacycle, whereas at 140 °C, C(sp2)–H arylation proceeded instead through the formation of a 16-membered tetramer containing four 7-pyridyl-pyrazolo[1,5-a]pyrimidine–palladium chelation units. The subsequent mechanistic study revealed that both C–H activations shared a common 6-membered palladacycle intermediate, which was then directly transformed to either the [6,5]-fused palladacycle for C(sp3)–H activation at 120 °C or the tetramer for C(sp2)–H arylation at 140 °C with catalytic amounts of Pd(OAc)2 and AcOH. Raising the temperature from 120 °C to 140 °C can also convert the [6,5]-fused palladacycle to the tetramer with the above-mentioned catalysts, hence completing the C(sp2)–H arylation ultimately.Unprecedented 16-membered tetramer or [6,5]-fused palladacycle, mutually shadowboxing-like transformed from the shared common intermediate, accomplishes the Pd-catalysed temperature-dependent selective arylation of C(sp2)–H or C(sp3)–H. 相似文献
14.
Shengfei Jin Hang T. Dang Graham C. Haug Viet D. Nguyen Hadi D. Arman Oleg V. Larionov 《Chemical science》2020,11(34):9101
Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.α-Branched carboxylic acids and other carbonyls are readily accessed by a metal- and base-free deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls via boron enolates, resulting in a tricomponent coupling with unconventional electrophiles. 相似文献
15.
Sergei V. Lepeshkevich Igor V. Sazanovich Marina V. Parkhats Syargey N. Gilevich Boris M. Dzhagarov 《Chemical science》2021,12(20):7033
Picosecond to millisecond laser time-resolved transient absorption spectroscopy was used to study molecular oxygen (O2) rebinding and conformational relaxation following O2 photodissociation in the α and β subunits within human hemoglobin in the quaternary R-like structure. Oxy-cyanomet valency hybrids, α2(Fe2+–O2)β2(Fe3+–CN) and α2(Fe3+–CN)β2(Fe2+–O2), were used as models for oxygenated R-state hemoglobin. An extended kinetic model for geminate O2 rebinding in the ferrous hemoglobin subunits, ligand migration between the primary and secondary docking site(s), and nonexponential tertiary relaxation within the R quaternary structure, was introduced and discussed. Significant functional non-equivalence of the α and β subunits in both the geminate O2 rebinding and concomitant structural relaxation was revealed. For the β subunits, the rate constant for the geminate O2 rebinding to the unrelaxed tertiary structure and the tertiary transition rate were found to be greater than the corresponding values for the α subunits. The conformational relaxation following the O2 photodissociation in the α and β subunits was found to decrease the rate constant for the geminate O2 rebinding, this effect being more than one order of magnitude greater for the β subunits than for the α subunits. Evidence was provided for the modulation of the O2 rebinding to the individual α and β subunits within human hemoglobin in the R-state structure by the intrinsic heme reactivity through a change in proximal constraints upon the relaxation of the tertiary structure on a picosecond to microsecond time scale. Our results demonstrate that, for native R-state oxyhemoglobin, O2 rebinding properties and spectral changes following the O2 photodissociation can be adequately described as the sum of those for the α and β subunits within the valency hybrids. The isolated β chains (hemoglobin H) show similar behavior to the β subunits within the valency hybrids and can be used as a model for the β subunits within the R-state oxyhemoglobin. At the same time, the isolated α chains behave differently to the α subunits within the valency hybrids.O2 rebinding and conformational relaxation following O2 photodissociation were studied on picosecond to millisecond time scale in the α and β subunits within human hemoglobin in the quaternary R-like structure. 相似文献
16.
Precise structural modifications of amino acids are of importance to tune biological properties or modify therapeutical capabilities relevant to drug discovery. Herein, we report a ruthenium-catalyzed meta-C–H deaminative alkylation with easily accessible amino acid-derived Katritzky pyridinium salts. Likewise, remote C–H benzylations were accomplished with high levels of chemoselectivity and remarkable functional group tolerance. The meta-C–H activation approach combined with our deaminative strategy represents a rare example of selectively converting C(sp3)–N bonds into C(sp3)–C(sp2) bonds.Precise structural modifications of amino acids are of importance to tune biological properties or modify therapeutical capabilities relevant to drug discovery. 相似文献
17.
Directing group assistance provided a paradigm for controlling site-selectivity in transition metal-catalyzed C–H functionalization reactions. However, the kinetically and thermodynamically favored formation of 5-membered metallacycles has greatly hampered the selective activation of remote C(sp3)–H bonds via larger-membered metallacycles. Recent development to achieve remote C(sp3)–H functionalization via the C–H metallation process largely relies on employing specific substrates without accessible proximal C–H bonds. Encouragingly, recent advances in this field have enabled the selective functionalization of remote aliphatic C–H bonds in the presence of equally accessible proximal ones by taking advantage of the switch of the regiodetermining step, ring strain of metallacycles, multiple non-covalent interactions, and favourable reductive elimination from larger-membered metallacycles. In this review, we summarize these advancements according to the strategies used, hoping to facilitate further efforts to achieve site- and even enantioselective functionalization of remote C(sp3)–H bonds.Recent advances in site-selective functionalization of remote aliphatic C–H bonds in organometallic pathways are summarized. 相似文献
18.
The radical cations of tertiary amines (R3N) have been well-established as the precursors of HAT reagents in photochemical transformations. Similarly, thiols and thioacids bearing SH groups have also been widely applied as HAT reagents. Despite the fact that sulfoxides (R2SO) and sulfides (RSR) also bear lone pairs of electrons, these compounds have been barely reported as HAT reagents in photocatalysis. On the other hand, the α-C–H 4-pyridylation of O or N-containing compounds has been documented, whereas 2-pyridylation remains challenging. However, the antihistamine and anticholinergic agent carbinoxamine is an ether bearing 2-pyridyl, which has not been obtained by the existing α-photoarylation of ether. In this work, we report the discovery of a non-donor–acceptor (D–A) type organic photoreductant CBZ6 and sulfoxide/sulfide synergistically catalyzed general α-C(sp3)–H arylation of ethers, thioethers and amines. By using as low as 1 mol% of CBZ6 as a recyclable organic photoreductant and sulfoxides or sulfides as a new type of HAT reagent, the 2- or 4-pyridylation of O, N, or S-containing compounds has been accomplished. This is the first base-free version of α-C–H 2-/4-pyridylation of O, N, or S-containing compounds. It is the first example of sulfoxides or sulfides working as HAT reagents. It is also the first general method for photocatalytic HAT 2-pyridylation of various ethers, amines or thioethers.We report the discovery of a non-donor–acceptor (D–A) type organic photoreductant CBZ6 and sulfoxide/sulfide synergistically catalyzed general α-C(sp3)–H arylation of ethers, thioethers and amines. 相似文献
19.
The advent of saturated N-heterocycles as valuable building blocks in medicinal chemistry has led to the development of new methods to construct such nitrogen-containing cyclic frameworks. Despite the apparent strategic clarity, intramolecular C–H aminations with metallonitrenes have only sporadically been explored in this direction because of the intractability of the requisite alkyl nitrenes. Here, we report copper-catalysed intramolecular amination using an alkyl nitrene generated from substituted isoxazolidin-5-ones upon N–O bond cleavage. The copper catalysis exclusively aminates aromatic C(sp2)–H bonds among other potentially reactive groups, offering a solution to the chemoselectivity problem that has been troublesome with rhodium catalysis. A combined experimental and computational study suggested that the active species in the current cyclic β-amino acid synthesis is a dicopper alkyl nitrene, which follows a cyclisation pathway distinct from the analogous alkyl metallonitrene.Copper-catalysed conditions have been developed for the chemoselective synthesis of cyclic β-amino acids. 相似文献
20.
Vera A. Vil' Yana A. Barsegyan Leah Kuhn Maria V. Ekimova Egor A. Semenov Alexander A. Korlyukov Alexander O. Terent'ev Igor V. Alabugin 《Chemical science》2020,11(20):5313
How far can we push the limits in removing stereoelectronic protection from an unstable intermediate? We address this question by exploring the interplay between the primary and secondary stereoelectronic effects in the Baeyer–Villiger (BV) rearrangement by experimental and computational studies of γ-OR-substituted γ-peroxylactones, the previously elusive non-strained Criegee intermediates (CI). These new cyclic peroxides were synthesized by the peroxidation of γ-ketoesters followed by in situ cyclization using a BF3·Et2O/H2O2 system. Although the primary effect (alignment of the migrating C–Rm bond with the breaking O–O bond) is active in the 6-membered ring, weakening of the secondary effect (donation from the OR lone pair to the breaking C–Rm bond) provides sufficient kinetic stabilization to allow the formation and isolation of stable γ-hydroperoxy-γ-peroxylactones with a methyl-substituent in the C6-position. Furthermore, supplementary protection is also provided by reactant stabilization originating from two new stereoelectronic factors, both identified and quantified for the first time in the present work. First, an unexpected boat preference in the γ-hydroperoxy-γ-peroxylactones weakens the primary stereoelectronic effects and introduces a ∼2 kcal mol−1 Curtin–Hammett penalty for reacquiring the more reactive chair conformation. Second, activation of the secondary stereoelectronic effect in the TS comes with a ∼2–3 kcal mol−1 penalty for giving up the exo-anomeric stabilization in the 6-membered Criegee intermediate. Together, the three new stereoelectronic factors (inverse α-effect, misalignment of reacting bonds in the boat conformation, and the exo-anomeric effect) illustrate the richness of stereoelectronic patterns in peroxide chemistry and provide experimentally significant kinetic stabilization to this new class of bisperoxides. Furthermore, mild reduction of γ-hydroperoxy-γ-peroxylactone with Ph3P produced an isolable γ-hydroxy-γ-peroxylactone, the first example of a structurally unencumbered CI where neither the primary nor the secondary stereoelectronic effect are impeded. Although this compound is relatively unstable, it does not undergo the BV reaction and instead follows a new mode of reactivity for the CI – a ring-opening process.Protecting stereoelectronic effects prevent Baeyer–Villiger rearrangement and stabilize γ-OX-γ-peroxylactones (X = H, OH), the previously elusive non-strained Criegee intermediates. 相似文献