Glucitol formation

Sugihara and Schmidt49 reported the isolation of 2,5-anhydro-D-glucitol in crystalline form its preparation on a relatively large scale has been described in the patent literature,50 and consists in the thermal dehydration of D-mannitol. The process leads to the formation of 1,4-anhydro-D-mannitol, 1,5-anhydro-D-mannitol, 1,4 3,6-dianhydro-D-mannitol, and 2,5-anhydro-D-glucitol, which is isolated as the crystalline 1,3-O-isopropyIidene derivative (35). 

Intramolecular cyclization can also be effected with acyclic intermediates derived from such readily available alditols as D-mannitol. Kuszmann and Vargha63 reported the formation of 2,5-anhydro-l,6-dibromo-l,6-dideoxy-4-0-(methylsulfonyl)-D-glucitol (63), in 73% yield, by boiling 3,5-di-0-acetyl-l,6-dibromo-l,6-dideoxy-2,4-di-0-... 

Miiller and Vargha65 reported that treatment of 1,6-di-O-benzoyl-D-mannitol (29) with p-toluenesulfonyl chloride gave 2,5-anhydro-l,6-di-0-benzoyl-3,4-di-0-p-tolylsulfonyl-D-glucitol (67). The formation of this compound may be the result of a favored p-toluenesulfonyla-tion at the 2(5)-hydroxyl group, followed by intramolecular cycliza-tion and subsequent esterification by the excess of the reagent. This... 

It is probable that the two 1,3-anhydro compounds just described are anhydrides of the same alditol. The compound of Ustyuzhanin and coworkers50 is unequivocally a 1,3-anhydro-D-glucitol derivative, because the hydroxyl groups at C-2, 4,5, and 6 were protected prior to the ring formation. Positive identity of the two would have been achieved by converting the monomethyl ether obtained by Haslam... 

Jackson and Hayward59hydroxyl group in l,4 3,6-dianhydro-D-glucitol is preferentially sulfonylated prior to conversion into the mixed ester is incorrect. They based their conclusions on studies of the rate of replacement of p-tolylsulfonyloxy group by iodide in the three dianhydro stereoisomers. However, their proof of structure was questioned by Lemieux and Mclnnes59acetoxonium intermediate prior to attack by the iodide ion. 

Brigl and coworkers9 discovered the first example showing that the formation of aldose amides is not restricted to the degradation of acylated nitriles of aldonic acids. By ammonolysis of 2,3,4,5,6-penta-O-benzoyl-aldehydo-n-glucose (16), they obtained l,l-bis(benz-amido)-l-deoxy-D-glucitol (17). 

The presence of alkoxide ion would enhance the rate of ammonolysis, and the formation of bis(amido) derivatives by an ortho-ester mechanism (see Section VI, p. 110) would be partially suppressed in the competitive set of reactions. Thus, ammonolysis of penta-O-benzoyl-D-glucose in the presence of 5 mmolar proportions of sodium meth-oxide showed a decrease of 11% in the yield of the bis(benzamido)-glucitol derivative as compared with the same reaction conducted without added methoxide ion.47... 

Contribution (Moles/mole) of Each Benzoyl Group to the Migration, With Formation of l,l-Bis(benzamido)-l-deoxy-D-glucitol s... 

The formation of a small proportion of the glucitol 138 is explained in terms of further reduction of the phosphinyl group of 131a to the 5-phosphino compound by an excess of SDMA, followed by intramolecular oxygen-transfer similar to that described in Scheme 2 for the formation of 96. 

This last reaction (RM) enables us to understand the formation of products containing 3 carbon atoms (glycerol, 1,2-propanediol) from glucitol (sorbitol) but is always in competition with the two other ones (DOH, RC). The ratio of these three reactions, determining the conversion selectivity, depend widely on the copper origin (Raney, deposited on a support, impurities, activation process). So, we studied the influence of additives deposited on Raney copper on these reaction selectivities. 

Protonation occurs preferentially at the primary hydroxyl group. The first dehydration step can also take place between the 3- and 6-position, leading to the 3,6-monoanhydro derivative 41. The second water-elimination step from the 1,4-, as well as from the 3,6-, anhydro-D-glucitol, leads to the formation of D-isosorbide. However, kinetic studies showed94 that the proportion of the 3,6-anhydro isomer is low compared to that of the 1,4-anhydride. An investigation giving similar results is described in Ref. 95. 

All synthetic efforts directed towards the synthesis of L-ascorbic acid that have thus far been presented began with the reduction of D-glucose (8) to D-glucitol (24), followed by oxidation atC-5 and C-6. An alternative approach to the synthesis of L-ascorbic acid is first to convert D-glucose (or its equivalent) into D-glucuronic acid (54) (or its equivalent), followed by reduction of 54 at G-1 and then oxidation at C-5, or oxidation of 54 first at C-5 and then reduction at C-l. These options are shown in Scheme 7 in both, formation of L-oty/o-2-hexulo-sonic acid (28) (or its equivalent) results. In this Section, several approaches to the synthesis of L-ascorbic acid that proceed through an intermediate equivalent to 55 will be presented. 

Further studies verified the intermediate formation of free radicals, as demonstrated by the electron-spin resonance spectra obtained during autooxidation of cellulose,75 and hydrogen peroxide was identified as a byproduct in the autooxidation of D-glucitol. Similar oxidations of cellulose in the presence of alkenic monomers afforded graft copolymers. The autooxidation of cellulose and of the cello-oligosaccharides was shown to be more extensive in the presence of transition-metal cations. 

The favored formation of acetylated l-a-deuterio-l,5-anhydro-D-glucitol 78 in labeling experiments has been put forward to support the occurrence of carbohydrate radicals as intermediates in the photolytic decomposition of glucopyranosyl phenyl sulfone acetates104 as well as the Cp2TiBD4193 and zinc-silver/graphite-197 mediated reduction of glycosyl halides. Cationic intermediates would have favored the opposite stereochemistry 26... 

---