有机合成中的高价碘应用

高价碘化物作为一种性能温和、选择性强及环境友好的氧化试剂在有机合成中得到了广泛的应用。近年来,各种不同结构的高价碘试剂和各种新的反应及应用大量涌现出来,使它们的应用领域从传统的醇类氧化扩展到一些结构复杂化合物的合成领域当中。本文以最常用和研究较多的几个高价碘化合物为例,对它们用于有机合成反应,如氧化、加成、取代和重排的最新进展进行了概述,对本研究小组重点研究的五价碘化合物邻羟基苯碘酰与酮类化合物的取代反应和烯烃化合物的加成反应也作了介绍。     

PhI Catalyzed Acetoxyselenylation and Formyloxyselenylation of Alkenes

With PhI as catalyst and m CPBA as oxidant, a novel and efficient catalytic procedure has been developed for the acetoxyselenylation and formyloxyselenylation of alkenes. In this protocol, PhI is first oxidized into hypervalent iodine intermediate, which promotes the cleavage of Se–Se bond in diselenides. The in situ generated electrophilic selenium species then reacts with alkenes, affording 2‐acetoxy‐1‐selenides and 2‐formyloxy‐1‐selenides in high regioselectivity and good yields.     

Electrophilic trifluoromethylation by copper-catalyzed addition of CF3-transfer reagents to alkenes and alkynes

Regio- and stereoselective Cu-catalyzed addition of the above hypervalent iodine reagent to alkynes and alkenes was achieved. In the presence of CuI, the reaction is suitable to perform trifluoromethyl-benzoyloxylation and trifluoromethyl-halogenation of alkenes and alkynes. Electron-donating substituents accelerate the process, and alkenes react faster than alkynes emphasizing the electrophilic character of the addition reaction.     

烯酸在碘化铵催化作用下的卤代内酯化反应

研究了不饱和烯酸在碘化铵催化作用下的溴代和氯代内酯化反应.通过该反应,4-戊烯酸等不饱和烯酸在催化剂碘化铵和氧化剂间氯过氧苯甲酸作用下很容易与溴化锂和氯化锂反应,常温下短时间内即可得到良好产率的溴/氯甲基γ-丁内酯化合物,从而建立了一个简单快速合成溴/氯甲基γ-丁内酯的新方法.考察了反应条件对反应的影响,提出了该反应是经过有机高价碘中间体而进行的反应机理.     

A Cooperative Strategy for the Highly Selective Intermolecular Oxycarbonylation Reaction of Alkenes using a Palladium Catalyst

A novel method for intermolecular functionalization of terminal and internal alkenes has been designed. The electrophilic reagent, hypervalent iodine, plays a key role in this process by activating the alkene C=C bond for nucleophilic addition of the palladium catalyst. This process generates an iodonium‐containing palladium species which undergoes CO insertion. The new approach, intermolecular oxycarbonylaton reactions of alkenes, has been achieved and carried out under mild reaction conditions to produce the corresponding β‐oxycarbonylic acids with excellent efficiencies and levels of regio‐ and diastereoselectivity.     

烯烃二胺化反应制备邻二胺化合物的研究进展

介绍了通过烯烃二胺化反应路线制备邻二胺化合物的研究工作,对烯烃二胺化反应的类型及催化体系进行了综述,钯、铜金属催化剂及超价碘(Ⅲ)试剂对烯烃二胺化反应具有普适性,环境友好的铜及非金属催化剂是未来研究的热点。     

Iodine(III)-Promoted Intermolecular Diamination of Alkenes

A rapid and productive vicinal diamination of alkenes takes place in the presence of a hypervalent iodine(III) reagent and bissulfonimides as nitrogen sources. A total of more than 60 examples are presented. The reaction is characterized by its robustness and its wide substrate scope: it proceeds selectively with both terminal and internal alkenes and tolerates a range of functional groups.     

有机高价碘化学简介及其应用

近几十年来,有机高价碘化学蓬勃发展,有机高价碘试剂也受到化学合成工作者的广泛关注,关于有机高价碘试剂的反应性研究也获得了迅猛发展。有机高价碘试剂作为绿色、高效、多功能化的氧化剂,通常容易制备且操作简单,与已有的合成方法相比,该类试剂参与的反应表现出了许多独特的优点,并且具有与汞、铬、铅、铊等重金属试剂类似的反应性,但却没有这些试剂所带来的毒性和环境污染问题。本文介绍了有机高价碘化学的起源与发展,高价碘试剂的结构特点与分类,高价碘试剂在有机合成、材料化学及工业合成中的应用。     

烯酸在有机高价碘试剂催化下的氯代内酯化反应

研究了不饱和烯酸在有机高价碘催化剂和间氯过氧苯甲酸作用下与氯化锂的反应. 通过该反应, 4-戊烯酸等可在常温下短时间内得到良好产率的氯代γ-丁内酯化合物, 提供了简单快速合成氯代γ-丁内酯的新方法. 考察了反应条件的影响, 并提出了可能的反应机理.     

Catalytic Hypervalent Iodine Promoters Lead to Styrene Dimerization and the Formation of Tri‐ and Tetrasubstituted Cyclobutanes

Reported herein is that the use of catalytic quantities of hypervalent iodine reagents (phenyliodine diacetate or Dess–Martin periodinane) allows the rapid and stereoselective formation of cyclobutanes under very mild reaction conditions. The presence of a fluorinated solvent is essential for the success of these reactions which form unsymmetrical tri‐ and tetrasubstituted cyclobutanes through a heterodimerization process involving two different alkenes.     

Pd-catalyzed C-h fluorination with nucleophilic fluoride

The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.     

Efficient One-Pot Synthesis of Benzimidazoles Under Solvent-Free Conditions

A green, efficient method for the synthesis of various 2-aryl-benzimidazoles in the presence of hypervalent iodine as the oxidant at room temperature under solvent-free conditions is reported. The salient features of this method include mild conditions, short reaction times (3–5 min), excellent yields, and simple procedure.     

Organo‐Iodine(III)‐Catalyzed Oxidative Phenol–Arene and Phenol–Phenol Cross‐Coupling Reaction

The direct oxidative coupling reaction has been an attractive tool for environmentally benign chemistry. Reported herein is that the hypervalent iodine catalyzed oxidative metal‐free cross‐coupling reaction of phenols can be achieved using Oxone as a terminal oxidant in 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP). This method features a high efficiency and regioselectivity, as well as functional‐group tolerance under very mild reaction conditions without using metal catalysts.     

N-tosyloxycarbamates as a source of metal nitrenes: rhodium-catalyzed C-H insertion and aziridination reactions

The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C-H insertion or aziridination reaction is described. Aliphatic N-tosyloxycarbamates produce oxazolidinones with high yields and stereospecificity through insertion in benzylic, tertiary, and secondary C-H bonds. Intramolecular aziridination occurs with allylic N-tosyloxycarbamates to produce aziridines as single diastereomers. The reaction proceeds at room temperature using a rhodium catalyst and an excess of potassium carbonate and does not require the use of strong oxidant, such as hypervalent iodine reagents. A rhodium nitrene species is presumably involved, as both reactions are stereospecific.     

Photoinduced Aerobic Iodoarene‐Catalyzed Spirocyclization of N‐Oxy‐amides to N‐Fused Spirolactams**

Iodoarene catalysis is a powerful methodology that usually requires an excess of oxidant, or of redox mediator if the terminal oxidant is dioxygen, to generate the key hypervalent iodine intermediate to proceed efficiently. We report that, using the spiro‐cyclization of amides as a benchmark reaction, aerobic iodoarene catalysis can be enabled by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalysts under very mild operating conditions.     

Strategies to Control Hypervalent Iodine – Primary Amine Reactions

The field of hypervalent iodine chemistry has been prevalent since 1886. Its journey from obscurity to coming into the limelight has witnessed many effective transformations which have benefited the synthetic community at large. The reactivity of primary amines with hypervalent iodine reagents causes difficulty in synthetic outcome or not feasible due to high exothermicity of amine iodine which is an acid base reaction. This minireview highlights the worthwhile reactivity of hypervalent iodine reagents with aromatic and aliphatic primary amines. Some recent literature has been discussed to make a clear understanding on how such high reactivity of primary amine is controlled by introducing modulation in either substrate or reaction conditions, most of which are carried out under ambient reaction conditions.     

Hypervalent‐Iodine‐Mediated Cascade Annulation of Diarylalkynes Forming Spiro Heterocycles under Metal‐Free Conditions

An unusual reaction featuring the cascade annulation of internal alkynes to afford spiro heterocycles as the products has been realized for the first time with a hypervalent iodine reagent as the only oxidant. This unprecedented process encompasses not only two sequential C?N/C?O‐bond formations, but also the insertion of a carbonyl oxygen, all in one pot under metal‐free conditions.     

The Multiple Facets of Iodine(III) Compounds in an Unprecedented Catalytic Auto‐amination for Chiral Amine Synthesis

Iodine(III) reagents are used in catalytic one‐pot reactions, first as both oxidants and substrates, then as cross‐coupling partners, to afford chiral polyfunctionalized amines. The strategy relies on an initial catalytic auto C(sp³)?H amination of the iodine(III) oxidant, which delivers an amine‐derived iodine(I) product that is subsequently used in palladium‐catalyzed cross‐couplings to afford a variety of useful building blocks with high yields and excellent stereoselectivities. This study demonstrates the concept of self‐amination of the hypervalent iodine reagents, which increases the value of the aryl moiety.     

Synthesis,characterization, and initial reaction study of two new bicyclic hypervalent iodine(III) reagents

The synthesis of two new bicyclic hypervalent iodine(III) reagents 5 and 6 is described along with their corresponding X-ray crystal structures for the first time. A detailed comparison in the bond lengths and bond angles of reported bicyclic hypervalent iodine(III) reagents is also presented. Furthermore, an initial study shows that these two hypervalent iodine(III) reagents could promote the dipeptide coupling reaction.     

Direct cyanation of heteroaromatic compounds mediated by hypervalent iodine(III) reagents: In situ generation of PhI(III)-CN species and their cyano transfer

Hypervalent iodine(III) reagents mediate the direct cyanating reaction of a wide range of electron-rich heteroaromatic compounds such as pyrroles 1, thiophenes 3, and indoles 5 under mild conditions (ambient temperature), without the need for any prefunctionalization. Commercially available trimethylsilylcyanide is usable as a stable and effective cyanide source, and the reaction proceeds in a homogeneous system. The N-substituent of pyrroles is crucial to avoid the undesired oxidative bipyrrole coupling process, and thus a cyano group was introduced selectively at the 2-position of N-tosylpyrroles 1 in good yields using the combination of phenyliodine bis(trifluoroacetate) (PIFA), TMSCN, and BF3.Et2O at room temperature. In the reaction mechanism, cation radical intermediates of heteroaromatic compounds are involved as a result of single electron oxidation, and the key to successful transformations seems to depend on the oxidation potential of the substrates used. Thus, the reaction was also successfully extended to other heteroaromatic compounds having oxidation potentials similar to that of N-tosylpyrroles such as thiophenes 3 and indoles 5. However, regioisomeric mixtures of the products derived from the reaction at the 2- and 3-positions were obtained in the case of N-tosylindole 5a. Further investigation performed in our laboratory provided insights into the real active iodine(III) species during the reaction; the reaction is induced by an active hypervalent iodine(III) species having a cyano ligand in situ generated by ligand exchange reaction at the iodine(III) center between trifluoroacetoxy group in PIFA and TMSCN, and effective cyanide introduction into heteroaromatic compounds is achieved by means of the high cyano transfer ability of the hypervalent iodine(III)-cyano intermediates. In fact, the reaction of N-tosylpyrrole 1a with a hypervalent iodine(III)-cyano compound (e.g., (dicyano)iodobenzene 8), in the absence of TMSCN, took place to afford the 2-cyanated product 2a in good yield, and an effective preparation of the intermediates is of importance for successful transformation. 1,3,5,7-Tetrakis[4-{bis(trifluoroacetoxy)-iodo}phenyl]adamantane 12, a recyclable hypervalent iodine(III) reagent, was also comparable in the cyanating reactions as a valuable alternative to PIFA, affording a high yield of the heteroaromatic cyanide by facilitating isolation of the cyanated products with a simple workup. Accordingly, after preparing the active hypervalent iodine(III)-CN species by premixing of a recyclable reagent 12, TMSCN, and BF3.Et2O for 30 min in dichloromethane, reaction of a variety of pyrroles 1 and thiophenes 3 provided the desired cyanated products 2 and 4 in high yields. The iodine compound 13, recovered by filtration after replacement of the reaction solvent to MeOH, could be reused without any loss of activity (the oxidant 12 can be obtained nearly quantitatively by reoxidation of 13 using m-CPBA).