Alkylation of dianhydrohexitols

Alkylation of dianhydrohexitols under phase-transfer catalysis (PTC) conditions... 

A series of new ethers has been obtained by alkylation of dianhydrohexitols (i. e. iso-sorbide, isomannide, isoidide) under the action of microwave irradiation and PTC conditions. Yields exceeded 90%, a dramatically improvement compared with those from conventional heating, despite similar temperature profiles. The best yields, for example from isosorbide, were obtained in the presence of a small amount of xylene and TBAB as catalyst at 140 °C (Eq. 9 and Tab. 5.6) [20],... 

Loupy et al. [84] have synthesized new diethers by alkylation of dianhydrohexitol under the action of irradiation with PTC conditions. The yields were very good (>90%) within a few minutes. Even when similar temperature profiles were used the yields were much lower under the action of conventional heating (Scheme 8.60). 

Alkylation of dianhydrohexitols under the action of Phase-transfer Catalysis (PTC) conditions Dianhydrohexitols, important by-products of biomass (Scheme 4.13) derived from com starch, were dialkylated under PTC conditions in the presence of a small amount of xylene. 

The double dehydration of sorbitol yields D-isosorbide (l,4 3,6-dianhydrohexitol), a white, biodegradable, nontoxic solid. It is used in medicine to treat glaucoma. Other medications are derived from isosorbide, including isosorbide dinitrate and isosorbide mononitrate used to treat angina pectoris. The high thermal stability makes isosorbide interesting as a monomeric building block for thermoplastic polymers such as polyester and polycarbonates. The electrophilic alkylation of isosorbide with dimethyl sulfate yields dimethyl isosorbide, a colorless liquid which is used as a plasticizer for vinyl polymers and as a solvent in pharmaceutical and cosmetic preparations. 

The exception noted for hydroxyl ions in rule (2) is well established for other sulfonic esters of carbohydrates, which therefore differ from simple alkyl sulfonates. An example of hydrolysis of an exo sulfonyloxy group is provided by the compound described as methanesulfonyl-monochloro-l,4 3,6-dianhydrosorbitol which must now be designated 1,4 3,6-dianhydro-5-chloro-5-deoxy-2-0-mesyl-L-iditol reaction with sodium hydroxide affords the free, hydroxy compound of the same configuration. Examples of the hydrolysis of endo sulfonyloxy groups are not available in the dianhydrohexitols, but the endo tosyloxy group in the stereochemically equivalent 3,6-anhydro-l, 2-0-isopropylidene-5-0-tosyl-D-glucofuranose (LXVII) is hydrolyzed by sodium hydroxide to the corresponding hydroxyl... 

In an analogous manner, the selectively obtained exo mono-benzylated isosorbide [69] was alkylated by use of alkyl dibromides to afford new ethers from dianhydrohexitols moieties separated by ether functions (Eq. (47), Table 6.17) [70]. Tosylates seemed to be a better leaving group for minimizing competitive j8-elimination [71]. 

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