Lead tetraacetate-iodine

Note 2. The molar ratios of lead tetraacetate iodine substate are 5.3 1.8 1. These ratios can be lowered and similar results obtained with ratios around 3 1.2 1. Excess iodine and lead tetraacetate react under the influence of light and heat to give methyl iodide and carbon dioxide. 

Note I. The ratio of lead tetraacetate iodine substrate is 2.85 1.31 1. A minimal amount of 1 mole of iodine per mole of substrate is necessary cf. procedure below). 

For effecting oxidative cyclizations of the types noted, superior results have been obtained with use of the combination lead tetraacetate-iodine, a method introduced by the Ciba-Basel group Ch. Meystre, Heusler, Kalvoda, P. Wieland, Anner, and Wettstein. Known as the hypoiodite reaction because the combination generates HOI, the method appears to be simpler and more efficient than lead tetraacetate alone, and than any of three other methods not employing lead tetraacetate. An improved procedure is as follows. Pregnenolone acetate (5) is first reduced with lithium tri-f-butoxyaluminum hydride in tetrahydrofurane to 3 8-acetoxy-20 -hydroxy-A -pregnene (6) the 20a-isomer is formed in minor amount. At the end... 

Mercuric oxide-iodine. This combination has been used as a possibly superior alternative to the lead tetraacetate-iodine reagent for oxidative attack of angular methyl groups. Thus a 6j8-hydroxysteroid (1) reacts with mercuric oxide and iodine in a light-induced reaction to give the 6,19-oxide (2) through an intermediate hypoiodite. ... 

Barton made two interesting applications of the lead tetraacetate-iodine method. One effects smooth decarboxylation of primary and secondary carboxylic acids to I he corresponding iodides, as in the examples formulated. A 5% suspension of lead tetraacetate in carbon tetrachloride is stirred and irradiated with a tungsten lamp. The carboxylic acid is added, followed by iodine until the color persists. If... 

Stereoisomeric ethyl 4,5-dimethylspiropentane-l-carboxylates 11 were prepared by copper-catalyzed addition of ethyl diazoacetate to cis- and tra .v-l,2-dimethyl-3-methylenecyclo-propane and by cyclopropanation of four isomeric ethyl 2-ethylidene-3-methylcyclopropane-l-carboxylates. The ethoxycarbonyl group was removed from the spiropentane system by saponification followed by treatment with lead tetraacetate, iodine and reaction with tributyltin hydride, both with irradiation. ... 

The acetoxylation of desmethyldiazepam (35) proceeds smoothly and hydrolysis of the product under nonaqueous conditions gives the 3-hydroxy compound. This is an alternative route to the lead tetraacetate-iodine mediated acetoxylation reaction at C-3 <79JHC1449>. 

In 1952, Frank B. Colton (1923-2003) at Searle synthesised and later patented norethynodrel, an isomer of norethisterone. An improved synthesis emerged, in which both compounds were obtained, while the aromatisation and Birch reduction could be avoided. [41,42] As starting point serves 5-androsten-3/l-ol-17-one acetate, to which hypochlorous acid is added. Notable is the thermal or photochemical functionalisation of C-19 with lead tetraacetate/iodine, [43] under formation of a cyclic ether. Hydrolysis ofthe ester and oxidation with chromium trioxide leads to a A -enedione, while HCI is eliminated. Reductive opening ofthe ether gives the 19-hydroxy-compound, which can be oxidised with chromium trioxide to the lOjS-carboxylic acid and then decarboxylated in... 

Lead tetraacetate iodine/irradiation y-Lactones from carboxylic acid amides... 

Lead tetraacetate/iodine/irradiation Cyclic ethers from alcohols 19-Norsteroids... 

The combination of organic hypervalent iodine compounds, such as (diacetoxyiodo)benzene (DIB) or iodosylbenzene. Phi = O, with iodine, proposed by Suarez in the mid 1980s, was extensively used by his group for the hypoiodite reaction. As in the case of lead tetraacetate-iodine, the alkyl hypoiodites were assumed to be formed by the reaction of alcohols with acetyl hypoiodite produced in situ by the reaction of DIB with iodine at room temperature. The reaction of the alcohols with acetyl hypoiodite generates the alkyl hypoiodite (Scheme 12). The acetoxy ion is occasionally incorporated into the reaction products. 

The billiard reaction, a second intramolecular hydrogen abstraction from a 1,3-diaxially located methyl group by a carbon-centered radical, initially generated by an alkoxyl radical was observed in the remote functionalization of certain triterpenoids and diterpenoids by a thermal hypoiodite reaction with lead tetraacetate-iodine by Wenkert and Milari in 1967. Recent work by Suarez indicates that similar results can be achieved by the photolysis of hypoiodites in the presence of (diacetoxyiodo)benzene-iodine (Scheme 21). Scheme 22 outlines the reaction path. 

Oxasteroids arising from tandem P-fragmentation and cyclization are products in the photolysis of the hypoiodites generated from 3-hydroxy-A -steroids and lead tetraacetate-iodine, as outlined in Scheme 84. The path of the formation of the oxasteroids is outlined in Scheme 85 one-electron oxidation of the intermediate radicals arising from the cyclization of allylic radicals generates the oxonium ions, which trap acetic acid to give the products. 

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