Glycols aldehydes, cleavage

Aqueous periodic acid can be used to achieve glycol cleavage, combined with anodic oxidation of the iodate, which is formed, back to periodate [70]. Oxidation of iodate is catalysed at a lead dioxide anode [71] but at the potentials required, aldehydes are oxidised to the corresponding acids. Due to this further reaction, the redox-mediated cleavage of diols to form an aldehyde may be difficult to achieve witli a catalytic amount of periodic acid. Cleavage using a stoichiometric amount of periodic acid, followed by recovery of the iodic acid and then its electochemical oxidation, has been achieved [72]. 

Lewis acid catalyzed oxidations.2 Oxidations with C6H5I02 alone generally proceed rather slowly at room temperature, but are strongly catalyzed by various l.cwis acids. Thus, in the presence of acetic acid, benzylic alcohols are oxidized to aldehydes a-naphthol can be oxidized to theo-quinone under these conditions. Glycol cleavage occurs efficiently with trichloroacetic acid catalysis. 

Conversion of the cryrtro-aldols to eryrAro-a-inethyl-/J-hydroxy aldehydes is effected by reduction with LiAlH4 to a mixture of isomeric diols followed by glycol cleavage by sodium periodate in aqueous methanol.3... 

Oxidation of 12 with excess Collins Reagent in methylene chloride yields the sensitive keto aldehyde 13. A pinacol cyclization of the keto aldehyde 13. to the tricyclic intermediate 14 is accomplisehd by reaction with finely powdered metallic Titanium inTHF. 2, 13 Oxidation to the ketol without appreciable glycol cleavage can be readily accomplished via an oxysulfonium intermediate. 14, 15 "phe ketol can then be converted to the MEM ether derivative by treatment with MEM chloride and diisopropylethylamine in methylene chloride at reflux to give the MEM ether derivative 15. ... 

An easy deprotection of the isopropyhdene residue in 1 and glycolic cleavage of the diol 2 to the aldehyde 3, or glycolic cleavage followed by the oxidation to the carboxylic function and formation of the ester 4, provide particularly attractive synthons (Scheme 2). Dirhodium complexes derived from difluoro-azetidinones, obtained in this way, were used as chiral catalysts for enantioselective decomposition of diazocompounds and cyclopropanation, to show, however, a moderate selectivity (Scheme 3) [26]. 

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