Aminations, using hypervalent iodine reagents

Mechanism of C—H Amination using Hypervalent Iodine Reagents... 

A reaction of considerable interest is the Hofmann type degradation of primary carboxamides to amines. Several examples have been reported of such efficient conversions, notably with the system IOB in formic acid (in water of acetonitrile), which forms in situ PhI(OOCH)2 [44], Other hypervalent iodine reagents have also been used extensively for these transformations (Sections 4.4.1 and 7.4.1). Yields may vary widely as illustrated for three similar amines obtained from the corresponding carboxamides with IOB-formic acid and with [hydroxy-(tosyloxy)iodo]benzene [45] ... 

The aimnation of benzylic C—H bonds proceeds in good yields using 1 equiv of amine and alkane in the presence of 2 equiv of the hypervalent iodine reagent. However, insertion in tertiary and secondary C-H bonds requires 5 equiv of substrate to undergo complete conversion (Eq. (5.15)). 

The development of in situ procedures to prepare iminoiodinanes from amine precursors and hypervalent iodine reagents has had a significant impact on the progress made towards C—H amination reactions. However, there are some drawbacks associated with the use of hypervalent iodine reagents, in particular, their cost... 

In the presence of a chiral catalyst such as rhodium(II) (5)-/V l,8-naphthanoyl-tert-leucinate dimer, Troc-amino indane was produced with 56% yield and 2.57 1 enantiomeric ratio. In contrast to other methods, no hypervalent iodine reagent (typically used stoichiometrically or in excess and forming iodobenzene as by-product) is required for oxidation of the amine component. However, a slight excess of the aromatic alkane component (5 equiv) must be used to achieve good conversions. The reactivity of rhodium nitrenes generated from 2,2,2-trichloroethyl-/V-tosyloxycarbamate with aliphatic alkanes is similar to the one observed with metal nitrenes obtained from the oxidation of sulfamate with hypervalent iodine reagent. Troc-protected amino cyclohexane and cyclooctane were obtained, respectively, in 73 and 62% yields when 2 equiv of alkanes was used, whereas yields up to 85% were observed with 5 equiv (eq 3). 

This review is devoted to an overview of phenol dearomatization and its application in natural product synthesis through the use of a special class of phenolophile reagents that has attracted much attention in recent years, the hypervalent iodine reagents. These polyvalent iodine compounds, also called iodanes, are oxidizing electrophiles that can mediate a wide number of diverse chemical transformations not only of (hetero)aromatic compounds, but also of inter alia alkenes, alkynes, alcohols, sulfides, amines and amides, (enolizable) carbonyl... 

In addition, the reaction between hypervalent iodine reagents such as iodosyl-benzene or its diacetate derivative with molecular iodine has been employed frequently in aliphatic amination reactions. These processes start from an initial formation of an alkyl hypoiodite derivative, which can promote subsequent radical amination pathways. An excellent use of this concept is the Suarez methodology for the generation of diversified aminated carbohydrate structures [80-86]. Although the hypervalent iodine reagent is not directly involved in the amination reaction, the efficiency of the method deserves mentioning within the present chapter. It was recently extended to catalytic transformations [87],... 

Zhu C, Sun C, Wei Y (2010) Direct oxidative conversion of alcohols, aldehydes and amines into nitriles using hypervalent iodine(III) reagent Synthesis 24 4235-4241... 

A metal-free direct oxidative preparation of amides 107 from aldehydes 105 and amines 106 using the ion-supported hypervalent iodine(III) reagent S>9 as a recyclable oxidant under mild conditions has been reported (Scheme 5.35) [100]. The oxidant and its reduced form 108 are completely insoluble in diethyl ether consequently, products 107 can be extracted directly from the reaction mixture and the reagent 99 can be easily recycled. 

Despite the demonstrated success of NBS and the hypervalent iodine compounds as modem HR reagents, the classical variant lead tetraacetate continues to find synthetic applications. A synthesis of the carbocyclic nucleoside (-)-aristeromycin features the conversion of amide 122 to Boc-protected amine 123. Similar tactics are used for syntheses of 6 - 3-... 

PhI(OTf)2 is an effective oxidant for the direct formation of bicyclic diazenium salts from a variety of linear hydrazone precursors. This oxidative cyclization is postulated to occur by the iodine(III)-mediated formation of an l-aza-2-azoniaallene salt intermediate. A direct intermolecular allylic amination has been achieved with up to 99% yields using metal-free conditions. The reaction employs a hypervalent iodine(lll) reagent as an oxidant and bistosylimide as a nitrogen source. Mechanistic studies including isotope labelling and Hammett correlation indicated that depending... 

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