Oxidation imidazole diol

A bimetallic Pt/Bi/C catalyst was used for the oxidation of imidazole diol to give imidazole-4,5-dicarbaldehyde, a key step in the synthesis of pro-drugs of hepatitis C virus replicase inhibitors (Scheme 11). ... 

Acyloins are useful starting materials for the preparation of a wide variety of heterocycles (e.g., oxazoles and imidazoles ) and carbocyclic compounds (e.g., phenols ). Acyloins lead to 1,2-diols by reduction, and to 1,2-diketones by mild oxidation. 

Iodination reagents combined with aryl phosphines and imidazole can also effect reductive conversion of diols to alkenes. One such combination is 2,4,5-triiodoimidazole, imidazole, and triphenylphosphine.215 These reagent combinations are believed to give oxyphosphonium intermediates which then serve as leaving groups, forming triphenylphosphine oxide as in the Mitsunobu reaction (see Section 3.2.4). The iodide serves as both a... 

A modification of GSR has been reported by Classon and co-workers.190 The idea remains the same create a covalently bound phosphorus cation and displace with a nucleophile—in this case, a halogen. Both bromine and iodine have been used.190 Three different systems were evaluated (1) chlorodiphenylphophine, iodine-bromine, and imidazole (2) p-(dimethylamino)phenyldiphenylphosphine, iodine-bromine, and imidazole or (3) polymer-bound triphenylphosphine, iodine-bromine, and imidazole. The last two were found to be very similar to just triphenylphosphine itself, and displayed reactivity inferior to the first system. The polymer-bound reagent does allow for easier removal of triphenylphosphine oxide produced in the course of the reaction. As with the original procedure, and consistent with a Sn2 mechanism, inversion of configuration occurred. Again, as with the original method vicinal diols were readily converted into alkenes.191 This... 

Another immobilized system was recently reported by Wei and Liu [64] using amphiphilic coblock polymers consistent of ethylene glycol and methyl acrylate monomers that had been functionalized with imidazole groups. In combination with oxone (KHS05) as the oxidant in an ethyl acetate/water mixture, this system yields the 1,2-diol product in 62% yield, which is probably formed by ring opening of the epoxide by the acidic oxone. 

Catalytic amounts of camphor-10-sulfonic acid (CSA) in methanol and dichloro-methane smoothly cleave the orthoester function in 23, giving the intermediate y-lactone-l,3-diol. Subsequent protection of the primary alcohol function with di-methylphenylchlorosilane (TPSCl) in dimethylformamide with imidazole as the base and of the secondary alcohol function via alcoholate with benzylbromide (BnBr) following WiLLlAMSON s ether synthesis yields the y-lactone 24. Its reduction with lithiumaluminumhydride leads to two vicinal primary alcohol groups. Thereafter, camphor-10-sulfonic acid (CSA) in dichloromethane selectively cleaves the TBS ether and catalyzes the transketalization with acetone dimethyUcetal to the precursor 25 of the aldehyde 8. Smooth oxidation of the primary alcohol function in 25 is achieved with tetrapropylammoniumperruthenate (TPAP) and A-methyl-morpholine-A-oxide (NMO) in acetonitrile. 

Scheme 11 Oxidation of imidazoie diol to give imidazole-4,5-dicarbaldehyde. ...

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