Coupling Reactions of Anhydro-Aldose Tosylhydrazones with Boronic Acids

A catalyst-free coupling reaction between O-peracetylated, O-perbenzoylated, O-permethylated, and O-permethoxymethylated 2,6-anhydro-aldose tosylhydrazones (C-(β-d-glycopyranosyl)formaldehyde tosylhydrazones) and aromatic boronic acids is reported. The base-promoted reaction is operationally simple and exhibits a broad substrate scope. The main products in most of the transformations were open-chain 1-C-aryl-hept-1-enitol type compounds while the expected β-d-glycopyranosylmethyl arenes (benzyl C-glycosides) were formed in subordinate yields only. A mechanistic rationale is provided to explain how a complex substrate may change the well-established course of the reaction.     

Enantioselective Construction of Tertiary Boronic Esters by Conjunctive Cross‐Coupling

Catalytic enantioselective conjunctive cross‐coupling has been developed to construct tertiary alkylboronic esters. These reactions occur with good yield and enantioselectivity for a range of substrates. Mechanistic experiments reveal aspects of the catalytic cycle that allow hindered substrates to react without significant complicating side reactions.     

New Aspects in the Chemistry of Some Cyclic Esters of Alkylphosphonates

Abstract

Several new methods for the synthesis of 2-alkyl-2-oxo-1,3,2-dioxa-phosphorinane (1) and -phosphepane (2) were conducted based on Arbuzov rearrangement, alcoholysis of RP(o)Cl₂ with glycol using dilution method or alkylation of cyclic phosphite under PTC condition. The solvent effect on the ³¹P NMR chemical shift and the characteristic behaviours of the ¹³C NMR spectra of 1 was investigated. It was found that compd 1 with R=CH₃ existed in an equilibrium of e and a forms. The mass spectra of 1 and 2 showed that the ring opening was in competition with the cleavage of P-C bond. According to the fragmentation pathway, 1 can be classified in two categories involving ring opening and cleavage of C-C or P-C bond. For compd 2 the ring opening was a dominant process. Alkaline hydrolysis of 1 and 2 was studied in aqueous dioxane. The hydrolytic process is classified as an AE reaction. Quantitative structure-reactivity relationship was established by multiple regressionanalysis involving the rate constant and the structural parameters of the exocyclic substituents on phosphorus. The difference between the hydrolytic performance of cyclic alkylphosphonates and carboxylates was discussed in terms of various structural changes between ground state and transition state during the hydrolysis.     

New Reactions of Ortho Esters

Russian Journal of Organic Chemistry - A new reaction of triethyl orthoformate with ethyl butyrate has been revealed. It afforded diethoxymethyl butanoate and its hydrated form,...     

Divergent,Stereospecific Mono- and Difluoromethylation of Boronic Esters

There is considerable interest in incorporating fluorine into agrochemicals and pharmaceuticals to improve their biological properties. Whilst a number of methods have been reported for installing CH₂F and CHF₂ groups, they are mainly limited to radical reactions, which are invariably racemic. Herein, we report the divergent, stereospecific reaction of fluoroiodomethyllithium with boronic esters to give α-fluoro-boronic esters. These unique intermediates can be readily transformed into the corresponding mono- or difluoromethylated compounds through proto- or fluorodeboronation, respectively. The use of the highly unstable fluoroiodomethyllithium was key to allowing rapid 1,2-migration over competing decomposition of the carbanion. DFT calculations informed and supported the experimental findings.     

New Reactions with Cyanic Esters

The reactions of cyanic esters with acylating agents and the reactions of the resulting N-acyliminocarbonic ester halides are surveyed, and syntheses of heterocycles with cyanic esters and their reaction products are then reported.     

Stereodivergent Olefination of Enantioenriched Boronic Esters

A stereodivergent coupling reaction between vinyl halides and boronic esters is described. This coupling process proceeds without a transition‐metal catalyst, instead proceeding by electrophilic selenation or iodination of a vinyl boronate complex followed by stereospecific syn or anti elimination. Chiral, nonracemic boronic esters could be coupled with complete enantiospecificity. The process enables the highly stereoselective synthesis of either the E or Z alkene from a single isomer of a vinyl coupling partner.     

Synthesis and Utility of Dihydropyridine Boronic Esters

When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products.     

Stereospecific Couplings of Secondary and Tertiary Boronic Esters

This Minireview highlights advances in the Suzuki–Miyaura cross‐coupling of secondary boron reagents for the creation of C? C bonds with control of stereochemistry. It also includes non‐transition‐metal coupling of secondary and tertiary boronic esters to electron‐rich aromatics.     

Photoredox-Catalyzed Giese Reactions: Decarboxylative Additions to Cyclic Vinylogous Amides and Esters

An effective strategy has been developed for the photoredox-catalyzed decarboxylative addition of cyclic amino acids to both vinylogous amides and esters leading to uniquely substituted heterocycles. The additions take place exclusively trans to the substituent present on the dihydropyridone ring affording stereochemical control about the new carbon-carbon bond. These reactions are operationally simplistic and afford the desired products in good to excellent isolated yields.     

Divergent,Stereospecific Mono‐ and Difluoromethylation of Boronic Esters

There is considerable interest in incorporating fluorine into agrochemicals and pharmaceuticals to improve their biological properties. Whilst a number of methods have been reported for installing CH₂F and CHF₂ groups, they are mainly limited to radical reactions, which are invariably racemic. Herein, we report the divergent, stereospecific reaction of fluoroiodomethyllithium with boronic esters to give α‐fluoro‐boronic esters. These unique intermediates can be readily transformed into the corresponding mono‐ or difluoromethylated compounds through proto‐ or fluorodeboronation, respectively. The use of the highly unstable fluoroiodomethyllithium was key to allowing rapid 1,2‐migration over competing decomposition of the carbanion. DFT calculations informed and supported the experimental findings.     

Asymmetric Synthesis of Secondary and Tertiary Boronic Esters

Non‐racemic chiral boronic esters are recognised as immensely valuable building blocks in modern organic synthesis. Their stereospecific transformation into a variety of functional groups—from amines and halides to arenes and alkynes—along with their air and moisture stability, has established them as an important target for asymmetric synthesis. Efforts towards the stereoselective synthesis of secondary and tertiary alkyl boronic esters have spanned over five decades and are underpinned by a wealth of reactivity platforms, drawing on the unique and varied reactivity of boron. This Review summarizes strategies for the asymmetric synthesis of alkyl boronic esters, from the seminal hydroboration methods of H. C. Brown to the current state of the art.     

Decarboxylative Benzylation of Aryl and Alkenyl Boronic Esters

The copper‐catalyzed decarboxylative benzylation of aryl and alkenyl boronic esters with electron‐deficient aryl acetates is reported. The oxidative coupling proceeds under mild, aerobic conditions and tolerates a host of potentially reactive electrophilic functional groups that would be problematic with traditional benzylation methods (aryl iodides and bromides, protic heteroatoms, aldehydes, Michael acceptors). A reaction pathway in which a benzylic nucleophile is generated by aryl acetate decarboxylation and in turn is intercepted by the catalyst to form diarylmethane products is supported by mechanistic studies.     

多元硝酸酯热解反应的理论研究

运用SCF-MO－AM1方法，在RHF和UHF水平上，计算研究了四种多元硝酸酯在12种稳定构象下的热解反应．均裂氧硝基键（O-NO2）产生RCH2O·和·NO2的活化能较低，是硝酸酯热解的主要途径；通过α－H转移产生RCHO和HONO的环消除反应具有较高活化能均裂ONO2键的活化能与该键的Wiberg键级之间存在良好的线性关系     

Speciation Control During Suzuki–Miyaura Cross‐Coupling of Haloaryl and Haloalkenyl MIDA Boronic Esters

Boronic acid solution speciation can be controlled during the Suzuki–Miyaura cross‐coupling of haloaryl N‐methyliminodiacetic acid (MIDA) boronic esters to enable the formal homologation of boronic acid derivatives. The reaction is contingent upon control of the basic biphase and is thermodynamically driven: temperature control provides highly chemoselective access to either BMIDA adducts at room temperature or boronic acid pinacol ester (BPin) products at elevated temperature. Control experiments and solubility analyses have provided some insight into the mechanistic operation of the formal homologation process.     

Cyclic Elimination and Intramolecular Insertion Reactions of Thermally-Generated Monomeric Metaphosphoric Esters (Metaphosphates)

Abstract

2-Aryl-1,3,2-dioxaphospholanes (aryloxyphosphites) decompose thermally in the gas phase with loss of ethylene to generate aryl metaphosphates which cyclise by intramolecular insertion (phosphonylation) or abstract a β-hydrogen to form a terminal alkene by loss of HPO₃.     

Nickel‐Catalyzed Cross‐Coupling of Redox‐Active Esters with Boronic Acids

A transformation analogous in simplicity and functional group tolerance to the venerable Suzuki cross‐coupling between alkyl‐carboxylic acids and boronic acids is described. This Ni‐catalyzed reaction relies upon the activation of alkyl carboxylic acids as their redox‐active ester derivatives, specifically N‐hydroxy‐tetrachlorophthalimide (TCNHPI), and proceeds in a practical and scalable fashion. The inexpensive nature of the reaction components (NiCl₂?6 H₂O—$9.5 mol^?1, Et₃N) coupled to the virtually unlimited commercial catalog of available starting materials bodes well for its rapid adoption.