Hypervalent iodine heterocycles

The five-membered hypervalent iodine heterocycles, benziodoxoles, are commonly used as convenient radical precursors [3,33]. The main advantage of benziodoxoles over the non-cyclic hypervalent iodine reagents is the higher thermal stability allowing the preparation of otherwise unstable derivatives with I-Br, I-OOR, I-N3, and I-CN bonds. The stable cyanobenziodoxoles 36-38 are prepared in one step by the reaction of cyanotrimethylsilane with the respective hydroxybenziodoxoles 35 (Scheme 16) [34, 35], or from acetoxybenziodoxole... 

Polymer-supported hypervalent iodine heterocyclic reagents 02SL1966. 

Arylsilanols, aryltributylstannanes, and arylantimony chlorides " are suitable coupling partners. When a hypervalent iodine heterocycle undergoes ring opening upon coupling, an aryl iodide is left behind that can be further manipulated. ... 

An unusual fused hypervalent iodine heterocycle (234) has been prepared by oxidative cyclization of 3-iodo-3-hexene-2,5-diol 233 with neat rerr-butyl hypochlorite (Scheme 2.70) [352,353]. 

The first representatives of fused hypervalent iodine heterocycles with an iodine atom at a ring junction were described by Agosta in 1965 (1965TL2681). Compounds 200 and 201 were originally prepared by oxidation of the corresponding iodides 199 and 201 with peracetic acid... 

Chemical transformations of heterocycles induced by hypervalent iodine reagents 97T1179. 

Synthesis of heterocyclic compounds using hypervalent iodine reagents 98AHC(69)1. 

The use of the hypervalent iodine reagent [bis(trifluoroacetoxy)iodo]benzene has been reported to be effective in the synthesis of C-nucleoside-like compounds. Radical decarboxylation of a suitably protected uronic acid, initiated photochem-ically, followed by addition of a heterocyclic base provided the C-nucleoside in high yield.154 The mode of action involves initial radical formation of 122 (Scheme 33), followed by introduction of the base and radical coupling.155 The anomeric selectivity was high in some examples, and low in others—lepidine gave the highest proportion of the ( anomer. Isolated yields were poor to moderate. 

Diaryliodonium salts, with few exceptions, are stable compounds towards heat, oxygen and humidity they are mildly light-sensitive and should be stored in the dark, without refrigeration. Generally, their reactivity is less pronounced than that of other hypervalent iodine compounds. Indeed, in several of their reactions relatively drastic conditions may be necessary, especially for the least reactive heterocyclic iodonium salts. The search for optimum conditions is often desirable even for well-established reactions, by applying new findings concerning the use of specific... 

Oxidative heterocyclization using hypervalent iodine 90S431. 

Development of novel oxidation reactions in water using /,(9-heterocycles with hypervalent iodine as oxidants 04YGK116. 

For reactions of hypervalent iodine reagents in the synthesis of heterocyclic compounds, see Prakash, O. Singh, S.P. 

Kita Y, Egi M, Okajima A, Ohtsubo M, Takada T, Tohma H (1996) Hypervalent iodine(lll) induced intramolecular cyclization of substituted phenol ethers bearing an alkyl azido side-chain - a novel synthesis of quinone imine ketals. Chem Commun 1491-1492 Kita Y, Egi M, Ohtsubo M, Saiki T, Takada T, Tohma H (1996) Novel and efficient synthesis of sulfur-containing heterocycles using a hypervalent iodine(lll) reagent. Chem Commun 2225-2226... 

Hypervalent iodine chemistry (1-heterocycles and s5mthesis of heterocycles) 05AC(E)3656. 

Figure 2.9 Known hypervalent iodine(lll) five-membered heterocyclic systems.

Azidobenziodoxoles The noncyclic azido X -iodanes, for example, PhI(N3)OAc or PhI(N3)2, in general lack stability and rapidly decompose at -25 to 0 °C with the formation of iodobenzene and dinitrogen (Section 2.1.12.1). The incorporation of hypervalent iodine atom into a five-membered heterocycle leads to a significant stabilization of the azidoiodane. Stable azidobenziodoxoles 122-124 can be prepared by the reaction of hydroxybenziodoxoles 121 with trimethylsilyl azide in acetonitrile [251, 292], or by treatment of acetoxybenziodoxoles 125 with trimethylsilyl azide in dichloromethane in the presence of catalytic trimethylsilyl triflate (Scheme 2.43) [259]. All three azides 122-124 were isolated as thermally stable, non-explosive, microcrystalline solids that can be stored indefinitely in a refrigerator. 

Trifluoromethylbenziodoxoles The noncyclic CF3-substituted X -iodanes in general lack stability and cannot be isolated at room temperature however, the incorporation of a hypervalent iodine atom into a five-membered heterocycle has a significant stabilization effect. The first synthesis of stable trifluoromethylbenziodoxoles 157 and 159-161 by treatment of corresponding methoxybenziodoxole 156 or acetoxybenziodoxole 158 with trimethyl(trifluoromethyl)silane was reported by Togni and coworkers in 2006 (Scheme 2.52) [248]. 

Owing to the nature of hypervalent bonding and the T-shaped geometry of the iodine(ni) center, the formation of six-membered iodine heterocycles is highly unfavorable. Several such compounds have been reported in the literature [328,342-346] however. X-ray structural data on six-membered iodine(III) heterocycles is not available. Moreover, based on the available X-ray single-crystal data for several pseudocyclic six-membered iodine(V) derivatives (Section 2.2.2), it can be expected that these compounds may exist as their noncyclic tautomers [345]. 

Within the broad field of hypervalent iodine chemistry, five-membered iodine(V) heterocycles occupy a special place. There has been significant interest in the cyclic X -iodanes, mainly 2-iodoxybenzoic acid (IBX)... 

The oxidative spirocyclization of phenolic substrates containing an internal nitrogen nucleophile provides a useful tool for the construction of nitrogen heterocycles [287, 315-318], For example, the hypervalent iodine-induced cyclization of phenolic oxazolines 251 affords the synthetically useful spirolactam products... 

Cationic cyclizations, induced by hypervalent iodine reagents, are particularly useful in the synthesis of het-erocycles. Tellitu and Dominguez have developed a series of [bis(trifluoroacetoxy)iodo]benzene-promoted intramolecular amidation reactions, generalized in Scheme 3.134, leading to various five, six and seven-membered heterocycles 335 [388,389]. Experimental evidence supports the ionic mechanism of these reactions, involving A -acylnitrenium intermediates 334 generated in the initial reaction of the amide 333 with the hypervalent iodine reagent [390]. 

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