Iodine compounds heterocycles

Iodosyl compounds can be converted by sulfur tetrafluoride at —20 to — IOC into the corresponding difluoroiodides 24. These same products, e.g. 25, can also be obtained by treatment of bis(trifluoroacetoxy)iodine compounds with sulfur tetrafluoride at 70CC. The reactions are general and may be used for the preparation of aliphatic, aromatic and heterocyclic difluoroiodides.223-224... 

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... 

Polyvalent iodine compounds in the oxidation of heterocycles 02CRV2523. 

Organohypervalent iodine compounds in the synthesis of heterocycles 01SL565. 

Of the methods of iodination described in section (a) on page 152, the old procedure with iodine and yellow HgO can, inter alia, be applied for iodination of heterocycles. The compound to be iodinated, or its solution in alcohol, glacial acetic acid, benzene, or light petroleum (b.p. 100-120°) is shaken or rapidly stirred with iodine (1 mole) and HgO (0.6-1.0 mole) the iodine and HgO are added in alternate small portions, and in most cases red Hgl2 is formed already at room temperature. A detailed description of the preparation of 2-iodothiophene is given in Organic Syntheses.12 This derivative can also be obtained by treating thiophene with iodine and concentrated nitric acid.729... 

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]. 

The first six-membered iodine(III) heterocycle, the cyclic tautomer of 2-iodosylphenylacetic acid, 221, was reported in 1963 by Leffler and coauthors [342]. This compound was synthesized by chlorination of 2-iodophenylacetic acid (220) followed by hydrolysis of the initially formed, unstable 2-(dichloroiodo)phenylacetic acid (Scheme 2.67). Compound 221 is stable at room temperature but decomposes in solution at 80-100 °C the proposed cyclic structure 221 is in agreement with its relatively low acidity (pXa = 7.45) [342]. 8-Iodosyl-l-naphthoic acid (222) was prepared by the peracetic oxidation of 8-iodo-1-naphthoic acid [343]. Anions of 2-iodosylphenylacetic acid (221) [328] and 222 [343] have a moderate reactivity in the cleavage of phosphate esters in aqueous micellar solution. The chiral, enantiomerically pure substituted 2-iodosylphenylacetic acid derivatives 223 and 224 were synthesized from the corresponding aryl iodides by oxidation with dimethyldioxirane [344]. 

Preparation of the first example of a six-membered iodine(III) heterocycle, the cyclic tautomer of 2-iodosylphenylacetic acid 192, was reported in 1963 by Leffler and coauthors (1962JA3443). This compound was synthesized by chlorination of 2-iodophenylacetic acid 191 followed by hydrolysis of the initially formed, unstable 2-(dichloroiodo)phenylacetic acid (Scheme 41). Compound 192 is stable at room temperature but decomposes in solution at 80—100 °C the proposed cyclic structure 192 is in agreement... 

The five-membered pentavalent iodine heterocycles represent a particularly important class of hypervalent iodine compounds. Cyclic iodine(V) compounds, such as IBX 212 and DMP 213, have found broad practical application as mild and selective reagents for the oxidation of alcohols and some other useful oxidative transformations. Several comprehensive reviews of the chemistry and synthetic applications of IBX and DMP have been published (2011JOC1185, 2006ARK26, 2010T7659, 2011AGE1524, 2001ACE2812). 

Togo, H., Aoki, M., and Yokoyama, M., Facile radical decarboxylative alkylation of heteroaromatic bases using carboxylic acids and trivalent iodine compounds, Tetrahedron Lett., 32, 6559, 1991. Togo, H., Aoki, M., and Yokoyama, M., Alkylation of aromatic heterocycles with oxalic acid monoalkyl esters in the presence of trivalent iodine compounds, Chem. Lett., 1691,1991. Vismara, E., Torri, G., Pastori, N., and Marchiandi, M., A new approach to the stereoselective synthesis of C-nucleosides via homolytic heteroaromatic substitution. Tetrahedron Lett., 33, 7575, 1992. 

The first representatives of this group of compounds, 1,5-benzotelluroazepinones 57, have been prepared in 17% yield by the reaction between 2-iodopropyolanilides and NaHTe (98H631). The reaction proceeds, most probably, as nucleophilic substitution of the iodine, resulting in telluroles 58 and the subsequent nucleophilic addition of a hydrotelluride group to the triple bond. An alternative mechanism involving initial addition of NaTeH to the triple bond followed by the nucleophilic substitution of the iodine atom was mled out because the anilides PhNHCOC=CR do not react with NaTeH under the conditions at which the heterocycles 57 were obtained. Neither of the adducts PhNHCOCH=C(R)TeH or [PhNHCOCH=C(R)Te]2 was isolated. 

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

Radical reactions of Hoffmann-Loffler-Freytag type with participation of iodine(III) compounds leading to five-member N-heterocycles 97YGK90. 

Of the several syntheses available for the phenothiazine ring system, perhaps the simplest is the sulfuration reaction. This consists of treating the corresponding diphenylamine with a mixture of sulfur and iodine to afford directly the desired heterocycle. Since the proton on the nitrogen of the resultant molecule is but weakly acidic, strong bases are required to form the corresponding anion in order to carry out subsequent alkylation reactions. In practice such diverse bases as ethylmagnesium bromide, sodium amide, and sodium hydride have all been used. Alkylation with (chloroethyl)diethylamine affords diethazine (1), a compound that exhibits both antihista-minic and antiParkinsonian activity. Substitution of w-(2-chloroethyl)pyrrolidine in this sequence leads to pyrathiazine (2), an antihistamine of moderate potency. 

---