Diols with sodium hypochlorite

A variation of this route was applied to the preparation of a-methylenecyclo-pentane 179, an intermediate that was employed for the synthesis of prostaglandin PGF2o, (180) (Scheme 6.82). The acetonide-protected oxime-diol 175 [derived from propanal (174)] was treated with sodium hypochlorite without the addition of base. This led to the tricyclic adduct 176 with high stereoselectivity. One of the side chains was subsequently elaborated and the fully protected cyclopentano-isoxazo-line (177), when exposed to Raney Ni/boron trichloride, gave the 2-hydroxymethyl-cyclopentanone (178). This compound was dehydrated using mesyl chloride/ pyridine to furnish enone (179) (324). In another related synthesis of PGF2q, the p-side-chain (3-hydroxyoctenyl) was introduced prior to the cycloaddition (325). 

The reaction was conducted at room temperature, and with H2O2 only moderate yields of 46% were achieved. With sodium hypochlorite, yields of diol of 90% were obtained after a 4 h reaction time. Nevertheless, this system is not very efEdent, since good results can only be achieved with a non-environmentally friendly oxidant... 

The sequence has been applied to the synthesis of 1,4-cyclohexanedione from hydroquinone 10), using W-7 Raney nickel as prepared by Billica and Adkins 6), except that the catalyst was stored under water. The use of water as solvent permitted, after hltration of the catalyst, direct oxidation of the reaction mixture with ruthenium trichloride and sodium hypochlorite via ruthenium tetroxide 78). Hydroquinone can be reduced to the diol over /o Rh-on-C at ambient conditions quantitatively (20). 

In another procedure, oxidation is carried out in the presence of chloride ions and ruthenium dioxide [31]. Chlorine is generated at the anode and this oxidises ruthenium to the tetroxide level. The reaction medium is aqueous sodium chloride with an inert solvent for the alkanol. Ruthenium tetroxide dissolves in the organic layer and effects oxidation of the alkanol. An undivided cell is used so that the chlorine generated at the anode reacts with hydroxide generated at the cathode to form hypochlorite. Thus this electrochemical process is equivalent to the oxidation of alkanols by ruthenium dioxide and a stoichiometric amount of sodium hypochlorite. Secondary alcohols are oxidised to ketones in excellent yields. 1,4- and 1,5-Diols with at least one primary alcohol function, are oxidised to lactones while... 

Approximately 1.05 3a equivalents of sodium hypochlorite (MW = 74.44) in an aqueous ca. 1.8 M b solution are slowly added over 15-30 min.c to a ca. 0.6 1.4 M stirred solution of the diol in acetic acid. When most of the starting alcohol is consumed,d a saturated NaHCCF aqueous solution is added and the resulting mixture is extracted with an organic solvent such as ether or CH2C12. The organic phase is washed with water, dried (MgS04) and concentrated, providing a hydroxyketone that may need further purification. 

Oxidation of alcohols is often aeeomplished conveniently by or via hypochlorites in sueh Ireatment of primary-seeondary diols, a selectivity of 1 7-20 is reached for the seeondary hydroxyl group. In general, sodium hypochlorite in acetic acid solution is used for this purpose (25). We obtained very good results, based on chlorine or trichloroisocyanuric acid (TCIA) in methanol in acid-buffered medium. The hy-droxyketone [7] can be formed reliably with a selectivity of 1 50-65. The improved selectivity is based on the use of the lowest convenient temperature and on the Promotion of the exchange of positive chlorine between primary and secondary alcohol positions (including from relatively stable methyl hypochlorite). 

Oxidative Methods.—A convenient and inexpensive procedure for the oxidation of secondary alcohols to ketones, applicable to multi-mole preparations, uses aqueous sodium hypochlorite in acetic acid/ Selective oxidation of secondary alcohols is possible as primary alcohols are oxidized much more slowly. Alcohol oxidations with molecular bromine in combination with nickel(ll) benzoate in acetonitrile are remarkably free from competing reactions. However, 1,4-diols yield butyrolactones. ... 

Other alternatives for the oxidant for stoichiometric oxidations include the use of a selenoxide [99], including a photochemical oxidation of catalytic selenium [100], iodine [101], sodium chlorite [102], hypochlorite [103], and electrochemical methods [101,104]. Even air can be used as the oxidant [99,100], but care has to be taken with regard to the choice of solvent as cleavage of the product 1,2-diol can occur, especially when the alkene has an aryl substituent [53, 105, 106]. 

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