Deiodination radical

The first total synthesis of staurosporine and of e/it-staurosporine has been reported in full (see Vol. 29, p. 378). The glycal-derived epoxide 191 (from dimethyldioxirane epoxidation of the precursor glycal) was treated with the sodium salt of 190 and the product, 192, was then elaborated using iodoamina-tion as the the key cyclization step, radical deiodination then affording 193, an intermediate for synthesis of e r-staurosporine. ... 

The iodine atom in a 2-deoxy-2-iodo-gIycoside can be replaced by a hydroxyl group by radical deiodination in the presence of 2,2,6,6-tetramethylpiperidine-A -oxide, resulting in adducts such as 88 and its C-2 epimer, the N-0 bond in which can then be reductively cleaved (Zn, HOAc). ... 

Tri-O-acetyl-D-glucal is the starting material for a synthesis of lactone 108 via 104. Palladium catalysed allylic substitution at C4 to give 105, formed as a 72 28 mixture of epimers at the sulfonyl substituted centre, and desulfonation are the key steps. Intermediate 106 then undergoes iodoetherification giving 107 which is radically deiodinated to 108. This lactone is related to a precursor of thromboxane B2,109 (Scheme 23). ... 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

The cardiac agent API amiodarone was observed to deiodinate sequentially upon irradiation in deaerated ethanol to yield the mono iodo product and finally the des iodo product (Fig. 93) (136). Formation of aryl radicals during the de-iodination process was supported by a spin-trapping study. 

Ionized aniline possesses an isomeric stable species, the 4- (or 3-) dehydroanilinium distonic ions (m/z 93). It is thus expected that their identification could afford some additional pieces of information related to the localization of the initial site of protonation. The distonic ions can readily be prepared by protonation of iodoanilines followed by collisional deiodination. Such a protonation-deiodination sequence is also readily performed in the quadrupole-time of flight instrument and the CID spectra of all the m/z 93 ions are collected in Table 5. As a reference for aniline radical cations, AZ-methylaniline was used and was observed to intensively expel a methyl radical after protonation and excitation (high cone voltage). 

Deiodination occurs by irradiation of the antiarrhythmical and antianginal agent amiodarone in water (Paillous and Verrier, 1988). Contrary to the case of the C-F bond, C-I, and at least a part of C-Cl fragmentations are homolytic processes the products result from aryl radicals (Li and Chignell, 1987a). 

The atom transfer methodology is used in the formal total synthesis of racemic albene82. Addition of 1-butynyl radicals to an activated norbornene derivative occurs exclusively from the. w-face. and consecutive cyclization yields the rw-cvu-annulated system. Conversion of the anhydride to the dimethyl ether and reductive deiodination yields the intermediate diester. Further transformations give 3, a direct precursor to albene, in 32% overall yield. 

Radical-mediated deiodination, methanolysis of the acetate and subsequent oxidation of the resulting alcohol furnished the ketone 43 in 87% total yield. Transformation of 43 into the corresponding cyanohydrin acetate under ordinary conditions resulted in the formation of a diastereomeric mixture 44 and 45. However, only the kinetically favored cyanohydrin acetate 44 was obtained when treated with hydrogen cyanide and pyridine. Treatment of the nitrile 44 with HCl gas afforded the amide 46, which was subjected to alkaline hydrolysis followed by esterification of the resulting carboxyhc acid with diazomethane to furnish 5 in 11% overall yield from 27. 

The formation of the radical [91] is supported, first, by the fact that when the triple bond is flanked by two bulky substitutents, relatively stable acetylenyl radieals are detected (Tani et al., 1963), and, secondly, the formation of its dimer [92], perchloro-l,4-diphenylbutadiyne, in excellent yield by reductive deiodination of co-iodopentachlorophenylacetylene or by the oxidation of co//-pentachlorophenylacetylene by air (Cornet, 1977). It is also formed in the thermal decomposition of the co-iodo (165°C) and the cosilver (230°C) derivatives (95) (Tabernero, 1975). 

The applicability of tin-mediated radical cyclizations of non-isocyanides to form indoles has been pursued by several other investigators. Uneyama and colleagues reported the tin-mediated deiodination of imidoyl iodides and subsequent indolization (Scheme 1, equation 1) [1], This radical cyclization is also effected photochemically. Bowman and colleagues exploited the tin-promoted radical generation from imidoyl selanides and cyclization to form indoles... 

In an initial attempt, the B NMR spectrum showed almost quantitative formation of 1-methyl-o-carborane upon heating a toluene solution of l-Li-2-Me-3-I-l,2-C2BioH9 in the presence of 10mol % of Pd(PPh3)4. This catalytic deiodination process may be due to the thermal decomposition of Pd-2-methyl-1,3-dehydro-o-carborane presumably via a radical process under thermal conditions [14], in which the solvent acts as the hydrogen source. 

In the enantiospecific synthesis of ( )-bakkenolide III developed by Sha et al., the key step involved radical cyclization of the iodoketone 6 (Scheme 25.6), which afforded the cis-hydrindinane skeleton. Thus, exposure of 6 to pho-tolytic conditions in the presence of hexabutylditin led to an iodine ATRC, followed by deiodination with tributyltin hydride (TBTH) to generate vinylsilane 7. 

These reactions are relevant to this review in that they may be photoinduced, but as radical chain processes many of them can be initiated in other ways. Radical chain dehalogenation of aryl halides has been reviewed previously.The chain propagation sequence for the deiodination of aryl iodides with CH5O-/CH3OH is shown in Scheme 1. The species (Arl) is very short lived and deiodinates efficiently. Reactivity diminishes in the order Arl > ArBr > ArCl and is enhanced in cases where there is relief of steric strain. Photochemical dehalogenations of aryl halides with AIH4 and BH4 have been proposed to follow similar radical chain mechanisms. Evidence for electron transfer from BH4 to ArCl has been present by Freeman and Ramnath. ... 

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