Glucitol. acetalation

Once again, efforts have been made to find neutral conditions that can modulate the course of the reaction. For instance, use of 2,2-diincthoxypropane in solution in 1,2,-dimethoxyethane (which probably plays a role through its interaction with polyols) has been suggested as a reagent for acetalation in neutral conditions (no catalyst) of D-mannitol [42] and o-glucitol [43],... 

Bicyclic trans diacetals with one axial residue will be considerably less stable than the acetals with equatorial residues this is shown by the absence of 3,5 4,6-diacetals of glucitol, 1,3 2,4-diacetals of mannitol and 2,4 3,5-diacetals of arabitol from the products of acetalation of the free glycitols. However, by suitable masking of hydroxyl groups, some trans diacetals with axial substituents should be obtainable. The most interesting will be 2,4 3,5-di-0-methylene-D-talitol (LIII), in which one terminal group is axial and the other equatorial (see p. 43). 

Figure 6.34 (Top) Equilibrium proportions of acetal products from benzalation of glycerol. (Bottom) Major kinetic and thermodynamic product from acetalation of glucitol with aliphatic aldehydes.

Acetalation of l,6-anhydro-l(6)-thio-D-glucitol with acetone, formaldehyde, or benzaldehyde furnished 2,3 4,5-diacetals whose structures, after desulphurization, were established by m.s. On partial hydrolysis of the 2,3 4,5-di-0-isopropylidene derivative, one of the isopropylidene groups was removed and the other migrated to 0-3 and -4 to give the monoacetal (53). 

The acetalation of l,6-anhydro-l(6)-thio-D-glucitol with acetone, formaldehyde, or benzaldehyde to give 2,3 4,5-diacetals has been noted in Chapter 5. ... 

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