Glycol-cleavage oxidation derivatives

The oxidation of cellulose, besides endgroups, may be discussed in three major types as illustrated in Fig. 11. The first type (A) is a glycol cleavage oxidation of a,(3-diol units with periodate giving the dialdehyde derivative... 

Although periodates also oxidize polycyclic aromatic hydrocarbons, phenols, hydrazines, active methylene compounds and sulfides, chemoselectivity can usually be achieved and glycol cleavage oxidation takes precedence. For example, the diol moiety in the diethyl dithioacetal derivative of o-glucose can be selectively oxidized in good yield (equation 6). In contrast, LTA is less selective dum periodate and oxidizes a far greater variety of oiganic compounds. Consequently, in order to minimize undesired reactions, it is customary to add LTA slowly to avoid contact of die initially formed products widi an excess of the oxidant (equation 7). ... 

For many purposes, these oxidants are interchangeable however, the fact that periodate functions best in water, and lead tetraacetate in organic solvents, makes glycol-cleavage oxidation possible with all types of carbohydrates and derivatives. For favorable examples, the behavior of the two reagents toward a given compound is sufficiently different to provide complementary information. 

Preparation. Fischer and Baer employed the glycol cleavage of l,2 5,6-di-0-isopropylidene-D-mannitol, followed by acid hydrolysis, to provide d-glyceraldehyde.13 A most convenient preparation is that of Perlin,14 who oxidized D-fructose with a limited proportion of lead tetraacetate, and hydrolyzed the resulting derivative. D-Glyceraldehyde 3-phosphate has been synthesized.15... 

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]. 

---