Alcohol hypoiodites

Cascade Radical Rearrangement Triggered by a Selective P-Fragmentation of Alkoxyl Radicals Generated by the Photolysis of Cyclic Alcohol Hypoiodites... 

The intramolecular additions of alkoxyl groups to carbon-carbon double bonds to give P-iodo-alkyl ethers from alkyl hypoiodites under photolytic conditions have been reported. Suginome and collaborators found that the formation of a-iodoepoxides arising from an intramolecular a, P-addition of an allylic alkoxyl radical is a major general process in the photolysis of tertiary and some secondary allylic alcohol hypoiodites in the presence of mercury (11) oxide and iodine in benzene. Thus, 5-hydroxy-SP-cholest-3-ene gave epimeric a-iodoepoxides in a ratio of 10 1 in 86% yield as outlined in Scheme 86. Similar reaction of l-alkylcyclohex-2-en-l-ols gave a mixture of cis- and tr s-a-iodoepoxides (Scheme 87). The addition of pyridine dramatically enhanced the yield of the addition product. The yields of the a-iodoepoxides obtained from the photolysis of l-alkylcyclohex-2-en-l-ols and the ratios of cis- to trans-isomers are summarized in Table 109.1. 

Suginome, H. and Wang, J.B., Intramolecular P,y-addition of allylic alkoxyl radicals. A new general synthesis of a-iodoepoxides by photolysis of allylic alcohol hypoiodites in the presence of mer-cury(II) oxide, iodine and pyridine in benzene, /. Chem. Soc., Chem. Commun., 1629,1990. Suginome, H., Isayama, S., Maeda, N., Furusaki, A., and Katayama, C., Photo-induced transformations. 57. The formation of bridged oxabicycHc compounds by intramolecular radical addition of oxyl radicals generated from some A-homo-4a-cholesten-3-ol hypoiodites, /. Chem. Soc., Perkin Trans. 1, 2963,1981. 

Similarly, bromofomi [75-25-2] CHBr, and iodoform [75-47-8] CHI, are obtained from sodium hypobromite and hypoiodite, respectively. Ethyl alcohol is the only primary alcohol that undergoes this reaction. 

Although such alkoxides have never been isolated it is assumed that with bulky alcohols such as steroidal alcohols, the main contributing structure in such an equilibrium (especially when excess lead tetraacetate is present) is the one in which n = 1. An advantage of this procedure held in common with the hypoiodite reaction is the fact that the alcohol derivative is formed in situ. Intermolecular hydrogen abstraction e.g., reaction with solvent)... 

A considerable extension of the synthetic utility of the hypoiodite reaction is achieved if the steroid hypoiodite (2) is generated from the alcohol and acetyl hypoiodite and then decomposed in a nonpolar solvent. In this case ionic hydrogen iodide elimination in the 1,5-iodohydrin intermediate (3) is slow, thereby allowing (3) to be converted into an iodo hypoiodite (5). 

The procedure described here is a modification of one involving the thermal fragmentation of 1-adamantyl hypoiodite and cycliza-tion of the resulting iodo ketone/ By means of this procedure, 4-protoadamantanone is obtained from 1-adamantanol with consistent yields in the range of 71 to 82% and a purity greater than 98%. This method is also applicable to the preparation of other polycyclic ketones from the related bridgehead alcohols with a-bridges of zero, one, or two carbon atoms (see Table I). 

XVIII has now been excluded,42 since the methyl glycoside of the sugar reacts rather rapidly with one mole of periodate per mole furthermore, in contrast to the behavior of mycaminose (XXI), no moiety with one carbon atom less has been isolated from the products of periodate oxidation. Oxidation of mycarose with hypoiodite affords a crystalline lactone with the empirical formula C7H12O4 this observation eliminates the possibility of the keto structure XX. Thus, mycarose appears to be a 2,6-dideoxy-3-C -methylhexose (XIX). In the original compound, the isovaleryl group must be esterified to the alcohol function at C4, since the methyl glycoside isovalerate obtained from carbomycin is only attacked by periodate after alkaline hydrolysis. 

This hypoiodite reaction can also be used for ring expansion of cyclic ketones.2 Thus Barbier cyclization of a-(w-iodopropyl)cyclododecanone (3) furnishes the bicyclic alcohol 4, which undergoes regioselective cleavage to a 15-membered iodo... 

For the substitution of the angular methyl groups in steroids five methods are known (a) homolysis of N-chloramines [Loffier-Freytag reaction (only C-18)] (b) oxidation of alcohols with lead tetraacetate (c) photolysis of nitrite esters (d) homolysis of hypochlorites (e) the hypoiodite reaction. ... 

Ganter has developed three different approaches to tricyclo[5.2.1.0 ]decane (403), yet another of the nineteen isomeric hydrocarbons of adamantaneland As seen in Scheme XXXIII, the routes involve intramolecular cyclization of keto tosylate 399 followed by Wolff-Kishner reduction of the resulting ketone, thermo-cyclization of 400 and subsequent dechlorination, hydrogenation, and photocycli-zation of aldehydes 401. Majerski s approach involved hypoiodite cleavage of alcohol 402... 

Chemistry of the Tetracyclic Diterpenoids.—The transannular hypoiodite reactions of 6-hydroxy-17-norkauranes have been studied with the object of functionalizing the methyl groups of ring A. Whereas the 6a-alcohols afford the 6—20 ethers, the 6/3-alcohols produce substitution at C-19. 

Hypohalites IRO-Hal) are similar to nitrates (see p. 155 in their photochemical behaviour. Ultraviolet irradiation gives an (n,Ji > excited state that cleaves to form an alkoxy radical and a halogen atom. The radical may undergo alpha-cleavage before recombination with the halogen atom occurs, and this accounts for the formation of 5-iodopentanal (5.69) from the hypoiodite of cydopentanol such hypoiodites are generated in situ from the alcohol. Iodine and merturyfll oxide. In open-chain systems the alkoxy radical can... 

This photocyclization proceeds in a one pot reaction with photolytic cleavage of the intermediate carbone-mercury bond and subsequent hydrogen abstraction through a probable hypoiodite intermediate 6 [15 a]. With secondary alcohols (R = H), the reaction is less efficient than with primary ones (R = H), and mainly undergoes a retention of configuration at the anomeric carbon [15 b] by abstraction of the a-anomeric hydrogen. 

Bromine (hypobromite) and hypoiodite oxidations are particularly useful for the preparation of aldonic acids from aldoses and of aldaric acids from glycuronic acids. Primary alcohol groups also undergo oxidation by these reagents, although this conversion is of less value glycosides can thus be converted into glycosiduronic acids, and alditols into aldoses and aldonic acids. 

Instead of alkyl nitrite, other alkoxyl radical precursors such as ROOH, ROOR, ROI, ROC1, etc. can also be used for the same type of reaction. The high reactivity of these compounds comes from the weak bond dissociation energies in O-O, 0-1, and O-Cl bonds. Another simple method is as follows. Photolytical treatment of alcohol (5) with NIS (AModosuccinimide) provides the tetrahydrofuran skeleton (6), through the formation of alkyl hypoiodite (ROI), homolytic cleavage of the 0-1 bond to form an alkoxyl radical, 1,5-H shift to form a carbon-centered radical, reaction with ROI to form 8-iodoalcohol, and finally ionic cyclization to form a tetrahydrofuran skeleton, together... 

Of great synthetic importance is the generation of aikoxy radicals from alcohols DIB reacts first with elemental iodine to form acetyl hypoiodite which in the presence of an alcohol is converted into alkyl hypoiodite upon irradiation with visible light the aikoxy radical is generated ... 

The reaction is the same as that involved in the usual chemical preparation of iodoform, whereby a colorless solution of hypoiodite (obtained by dissolving iodine in a sufficient quantity of potassium-hydroxide solution) is made to react with alcohol. The decomposition potential of potassium iodide, investigated by Dony-Henault,2 show s that the iodine as such does not act on the alcohol, but only after its conversion into hypoiodite. The iodine ions are set free at the same anode potential no matter if alcohol is added or not. The alcohol does not act as a depolarizer towards the iodine ion the electrical iodoform synthesis is a typical secondary process. 

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