Visible Light Induced Brønsted Acid Assisted Pd-Catalyzed Alkyl Heck Reaction of Diazo Compounds and N-Tosylhydrazones

A mild visible light-induced palladium-catalyzed alkyl Heck reaction of diazo compounds and N-tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acid-assisted generation of hybrid palladium C(sp³)-centered radical intermediate, which allowed for new selective C?H functionalization protocol.     

1,3-Diynes: A Versatile Precursor in Transition-Metal Catalyzed (Mediated) C−H Functionalizations

Transition metal-catalyzed C−H functionalization of diverse arenes with alkyne units has attracted enormous attention for decades since they provide straightforward access to various functionalization/annulations, which are commonly present in bioactive compounds and natural products. Recently, conjugated alkynes (1,3-diynes) have been utilized as key coupling partner in many C−H activation reactions due to their versatile characteristic properties. The presence of two C≡C bonds in conjugated 1,3-diyne brings the new diversity in synthetic transformations, such as chemo-, regioselective pathways, mono-bis functionalizations, cascade annulations, etc. Herein, we summarized the latest developments in the realm of transition-metal-catalyzed C−H functionalizations of diverse arenes with 1,3-diynes. Moreover, we highlighted the diverse transformations, conditions, mechanisms and applications of the corresponding reaction in detail.     

配体促进的过渡金属催化芳烃远程meta-C—H键官能化反应研究进展

过渡金属催化C—H活化反应中,配体能够对催化中心的空间及电子效应进行调控,从而实现芳烃C—H键的选择性官能化.近年来,配体促进芳烃远程C—H键官能化反应研究有了新的进展.对近几年来配体促进的过渡金属催化芳烃远程meta-C—H键选择性官能化反应进行了系统总结,并对该研究领域的局限性和未来的发展前景进行总结和展望.     

Ruthenium(II)‐Catalyzed C−H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate‐Controlled Synthesis of Indoles and 3H‐Indoles

Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor–acceptor diazo compounds were developed that afforded NH indoles and 3H‐indoles under ruthenium catalysis. The coupling of α‐diazoketoesters afforded NH indoles by cleavage of the C(N₂)?C(acyl) bond whereas α‐diazomalonates gave 3H‐indoles by C?N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium‐catalyzed C?H activation.     

Catalytic multicomponent reactions for the synthesis of N-aryl trisubstituted pyrroles

Dirhodium(II) salts efficiently catalyze the three-component assembly reaction of an imine, diazoacetonitrile (DAN), and an activated alkynyl coupling partner to form substituted 1,2-diarylpyrroles in moderate to good yields. The transition-metal-catalyzed decomposition of the diazo compound in the presence of the imine presumably generates a transient azomethine ylide that undergoes cycloaddition with dipolarophiles in a highly convergent manner.     

How Nucleophilic Are Diazo Compounds?

The kinetics of the reactions of benzhydryl cations with eight diazo compounds 1 a-g were investigated photometrically in dichloromethane. The nucleophilicity parameters N and slope parameters s of these diazo compounds were derived from the equation log k (20 degrees C)=s (E+N) and compared with the nucleophilicities of other pi systems (alkenes, arenes, silyl enol ethers, silyl ketene acetals). It is shown that the nucleophilic reactivities of diazo compounds cover more than ten orders of magnitude, being comparable to that of styrene on the low reactivity end and to that of enamines on the high reactivity end. The rate-determining step of these reactions is the electrophilic attack at the diazo-carbon atom to yield diazonium ions, which rapidly lose nitrogen.     

Unusual Reaction of Diazo Compounds with Enamines

Transition metal catalyzed decomposition of diazo compounds and consequent transformations constitute various synthetic useful reactions in the past decades. The catalytic addition of diazo compounds to olefins generally provides cyclopropanes in high yield. However the reaction of electron-rich enamines with diazo compounds gave variable results. Wenkert et al. reported the reaction of enamines with ethyl diazoacetae (EDA) in the presence of cuprous chloride or silver oxide unexpectedly gave…     

A Photoenzymatic Strategy for Radical-Mediated Stereoselective Hydroalkylation with Diazo Compounds

Carbene insertion reactions initiated with diazo compounds have been widely used to develop unnatural enzymatic reactions. However, alternative functionalization of diazo compounds in enzymatic processes has been unexploited. Herein, we describe a photoenzymatic strategy for radical-mediated stereoselective hydroalkylation with diazo compounds. This method generates carbon-centered radicals through an ene reductase catalyzed photoinduced electron transfer process from diazo compounds, enabling the synthesis of γ-stereogenic carbonyl compounds in good yields and stereoselectivities. This study further expands the possible reaction patterns in photo-biocatalysis and offers a new approach to solving the selectivity challenges of radical-mediated reactions.     

Cross‐Coupling of α‐Carbonyl Sulfoxonium Ylides with C−H Bonds

The functionalization of carbon–hydrogen bonds in non‐nucleophilic substrates using α‐carbonyl sulfoxonium ylides has not been so far investigated, despite the potential safety advantages that such reagents would provide over either diazo compounds or their in situ precursors. Described herein are the cross‐coupling reactions of sulfoxonium ylides with C(sp²)−H bonds of arenes and heteroarenes in the presence of a rhodium catalyst. The reaction proceeds by a succession of C−H activation, migratory insertion of the ylide into the carbon–metal bond, and protodemetalation, the last step being turnover‐limiting. The method is applied to the synthesis of benz[c]acridines when allied to an iridium‐catalyzed dehydrative cyclization.     

多功能氧酰胺导向基在碳氢键活化反应中的研究进展

近年来,通过导向基团进行碳氢键活化构建C―C键及C―X键的方法得到了快速发展,已成为有机合成的重要手段之一。在碳氢键活化中,作为多功能导向基团之一的氧酰胺,由于其独特的性质,引起了科学家们的广泛关注。氧酰胺中O―N键的氧化性替代外部氧化剂,使反应处于氧化还原中性。加入化学计量的外部氧化剂,通常可以使O―N键得到保留。在不同的溶剂中,能够表现出不同的区域选择性和立体选择性;皆体现了氧酰胺作为导向基团的独特之处。本文综述了N-苯氧基酰胺作为底物进行碳氢键活化的研究进展,同时根据现有的实验和理论研究结果对不同反应的机理进行了探讨。     

High Selective and Catalyst-directed Addition of Diazo Compounds to Imines

Transition metal-catalyzed decomposition of diazo compounds and subsequent transformations constitute vast synthetically useful reactions. Recently the catalytic approaches to ylide generation and reaction leading to heterocycle compounds from diazo compounds have achieved remarkable successes.     

1,2-Thio group migration in Rh(II) carbene reactions

[reaction: see text] A series of beta-thio group substituted alpha-diazo carbonyl compounds have been prepared by nucleophilic substitution reactions of thiophenol, thionaphthol, or benzyl mercaptan with beta-acetoxy-alpha-diazo carbonyl compounds. The diazo decomposition of these diazo carbonyl compounds with various transition metal catalysts, including Rh(II) carboxylates and Cu(I) and Cu(II) complexes, has been investigated. It was found that the diazo decomposition of these compounds gave 1,2-thio group migration products. No 1,2-hydride or 1,2-aryl migration products were observed in all cases.     

A novel one-pot method for the preparation of pyrazoles by 1,3-dipolar cycloadditions of diazo compounds generated in situ

A convenient one-pot procedure for the preparation of pyrazoles by 1,3-dipolar cycloaddition of diazo compounds generated in situ has been developed. Diazo compounds derived from aldehydes were reacted with terminal alkynes to furnish regioselectively 3,5-disubstituted pyrazoles. Furthermore, the reaction of N-vinylimidazole and diazo compounds derived from aldehydes gave exclusively 3-substituted pyrazoles in a one-pot process.     

N-氟代苯磺酰亚胺参与的过渡金属催化C-H氟化和胺化的研究进展

众多胺类及含氟化合物具有重要的生理活性,在医药领域均具有不可替代的作用.过渡金属催化的C-H胺化及氟化反应因其高反应效率及原子经济性,受到了合成化学家的关注,为生物碱类天然产物及含氟分子的合成提供了便利.N-氟代双苯磺酰胺(NFSI)兼有氟原子及含氮官能团,可以在过渡金属催化下参与多种类型的有机反应,实现C-H键的氟化或胺化.因此,探索NFSI参与的C-H键直接氟化或胺化反应具有重要意义.综述了近十年NFSI参与的C-H活化构建C-N键和C-F键方法的研究进展,围绕各类方法的反应机理和应用范围进行阐述,同时对该领域的局限性和发展前景进行总结和展望.     

Chemistry of Phosphorus Ylides. Part 40. Synthesis of Pyrazoles by the [3 + 2] Cycloaddition of Diazo Compounds with Wittig Reagents as Antimicrobial Compounds

A comparative study between the reactions of active phosphacumulenes and stabilized phosphonium ylides on some diazo compounds have been performed. A number of substituted phosphanylidene spiro pyrazoles have been synthesized from the reaction of the active phosphacumulenes and the diazo derivatives. On the other hand, treatment of the diazo substrates with the stabilized phosphonium ylides led to the formation of the corresponding ylidenes and diazenyl phosphanylidenes. The antimicrobial activities for the new compounds are also reported.     

Tandem cycloaddition reactions of allenyl diazo compounds forming triquinanes via trimethylenemethane diyls

A tandem reaction strategy for forming triquinanes from linear allenyl diazo compounds through an intramolecular 1,3-dipolar cycloaddition reaction of an allenyl diazo group that generates a trimethylenemethane (TMM) diyl followed by an intramolecular [2 + 3] TMM diyl cycloaddition reaction has been developed. The new tandem cycloaddition reaction is readily applicable to the synthesis of complex molecules with high versatility and efficiency.     

Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis‐Aziridines from One Enantiomer of the Catalyst

Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl‐ and alkyl‐substituted imines, alkynyl imines react to give cis‐substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis‐aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si‐face to Re‐face addition to the imine, which in turn is related to a switch from reaction with an E‐imine in the former and a Z‐isomer of the imine in the latter.     

BER催化还原一些含氮功能基化合物的研究

用强碱性阴离子交换树脂制备了硼氢阴离子交换树脂还原剂(BER),使其在氯化铜等金属化合物的催化下还原一些芳香硝基、氰基、氮氮双键等含氮功能基化合物.还研究了BER的制备条件:如温度、溶剂、不同金属化合物对还原反应的影响,并初步探讨其反应机理.     

Diazo preparation via dehydrogenation of hydrazones with "activated" DMSO

[reaction: see text] We report that "activated" dimethyl sulfoxide efficiently dehydrogenates hydrazones to the respective diazo species at -78 degrees C. Under optimized conditions, triethylamine hydrochloride is removed quantitatively by vacuum filtration to provide solutions of diazo compounds. Stable diazo species can be isolated in high yield, or alternatively, the direct treatment of these solutions with carboxylic acids provides esters.     

Light‐Induced CH Arylation of (Hetero)arenes by In Situ Generated Diazo Anhydrides

Diazo anhydrides (Ar?N?N?O?N?N?Ar) have been known since 1896 but have rarely been used in synthesis. This communication describes the development of a photochemical catalyst‐free C?H arylation methodology for the preparation of bi(hetero)aryls by the one‐pot reaction of anilines with tert‐butyl nitrite and (hetero)arenes under neutral conditions. The key step in this procedure is the in situ formation and subsequent photochemical (>300 nm) homolytic cleavage of a transient diazo anhydride intermediate. The generated aryl radical then efficiently reacts with a (hetero)arene to form the desired bi(hetero)aryls producing only nitrogen, water, and tert‐butanol as byproducts. The scope of the reaction for several substituted anilines and (hetero)arenes was investigated. A continuous‐flow protocol increasing selectivity and safety has been developed enabling the experimentally straightforward preparation of a variety of substituted bi(hetero)aryls within 45 min of reaction time.