1,4:3,6-Dianhydrohexitols

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

Dianhydrohexitols, important by-products of biomass (Scheme 3.10), were dialky-lated under PTC conditions in the presence of a small amount of xylene. 

Tab. 3.14 Yield (%) from dialkylation of dianhydrohexitols under 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],... 

Synthesis of Diethers and New Diols Derived from Dianhydrohexitols... 

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). 

In the same way, new diols have been obtained from dianhydrohexitol ethers [85],... 

Montgomery and Wiggins47 have studied the reaction of D-mannitol with hydrochloric acid in detail and the results throw some light on the mode of formation of isomannide from D-mannitol. When D-mannitol is heated under reflux with hydrochloric acid for several days, isomannide results in about 35-40% yield. But when D-mannitol is heated under pressure with fuming hydrochloric acid l,6-dichloro-l,6-didesoxy-D-mannitol (40% yield) and very little isomannide are formed. On examination of the residues after separation of isomannide from the first reaction mentioned above, no fewer than two monoanhydrohexitol derivatives and three new dianhydrohexitol derivatives were encountered. The products isolated are summarized in Table II. 

One of the dianhydrohexitols, B, was identified with l,5 3,6-dianhy-dro-D-mannitol (neomannide, see below), but the other two, A and C, remain of unknown structure. An interesting observation concerning the dianhydride A has been made.48 When l,6-dichloro-l,6-didesoxy-D-mannitol was treated with sodium methoxide a new crystalline dianhydrohexitol was obtained. This had m. p. 118-119° but showed la]D + 33.6°. It was therefore the enantiomorph of dianhydride A. Furthermore, when dichloro-didesoxy-D-mannitol is treated with sodium amalgam yet another dianhydride was isolated. This had m. p. 118-119° and fa]D + 93.6° and is doubtless identical with the /3-mannide of Siwoloboff.49... 

Since no other stereoisomer but that of iditol, mannitol or sorbitol can exist in the as-fused ring series of l,4 3,6-dianhydrohexitols and since amination experiments on the ditosyl derivatives of each isomer have given three different amino derivatives, it is reasonable to assume that the two diamines which have been isolated are of the same configuration as their parent dianhydrohexitols. These two diamines LXXIV and LXXV on treatment with nitrous acid suffered deamination as expected but instead of obtaining in one case isomannide and in the other isosorbide, only one dianhydrohexitol was isolated and that was dian-hydro-L-iditol. The deamination must of course lead to the transitory carbonium cation LXXVIII and this on hydroxylation can take on any of the configurations, L-iditol, D-mannitol or D-sorbitol. That it preferentially takes on the configuration of L-iditol indicates that this is in some ways a more stable structure than the others. This behavior is paralleled... 

Two other dianhydrohexitols are known. One was prepared over sixty years ago by Siwoloboff66 and was named /3-mannide and the other, neomannide, was prepared by Hockett and Sheffield68 in 1946. The... 

The acetates of the l,4 3,6-dianhydrohexitols may also be useful as plasticizers both 2,5-diacetyl-l,4 3,6-dianhydro-D-mannitol and the analogous D-sorbitol derivative have been described.97... 

Keywords a,co-Alkanediamines, l,4 3,6-Dianhydrohexitols, Aldaric acids, Aldo-nolactones, Aminoalditols, o-Glucitol, Diaminoalditols, D-Mannitol, D-Xyhtol application, Erythritols, Isoidide, Isomannide, Isosorbide, L-Arabinitol, Lipase-catalysis, Polyamides, Polycarbonates, Polyesteramides, Polyesters, Polyethers, Polyureas, Polyurethanes, Super-acid, Tartaric acids... 

In 1984 Thiem et al. [50, 51] prepared polyterephthalates 64 of low molecular weight by melting condensation of terephthalic acid dichloride with 1,4 3,6-dianhydrohexitols. With labile isosorbide (1) polymers of cross-linked character were obtained. Later, Storbeck et al. [52] reinvestigated these polyterephthalates. The reaction conditions were optimized, and pyridine was found to be the most useful acceptor of hydrogen chloride. 

Stoicheiometric RuOyCCl was also used to oxidise several furanoses, partially acylated glycosides and l,4 3,6-dianhydrohexitols [317] pyranosides to pyrano-siduloses [313] methyl 2,3,6-tri-O-benzoyl-a-D-glucopyranoside and its C-4 epimer to the a-D-xy/o-hexapyranosid-4-ulose (Table 2.3) [317], and methyl 2,3,6-trideoxy-a-D-e 7f/tro-hexapyranoside to the -a-D-,g/yceri9-hexa-pyranosid-4-ulose, an intermediate in the synthesis of forosamine [318], It was also used to oxidise benzyl 6-deoxy-2,3-0-isopropylidene-a-L-mannopyranoside to the a-L-/yxo-hexapyranosid-4-ulose [319] and for oxidation of isolated secondary alcohol functions, e.g. in the conversion of l,6-anhydro-2,3-0-isopropylidene-P-D-man-nopyranose to the-P-D-/yxo-hexa-pyranos-4-ulose mannopyranose (Fig. 2.16, Table 2.3 [20, 320, 324]). 

Of all the anhydrohexitols currently known, the structure of two dianhydrohexitols (reported by Wiggins57) remain unresolved. The two dianhydrides were obtained on heating D-mannitol with hydrochloric acid one had m.p. 118° and [a]D —34°, and the second was isolated only as its dimethanesulfonate, m.p. 113-114°. The apparent enantiomorph of the first was formed on treating l,6-dichloro-l,6-dideoxy-D-mannitol with sodium methoxide. 

Circular dichroism of the nitrato (ONO) chromophore of the mono- and di-nitric esters of l,4 3,6-dianhydrohexitols was found to consist of two dichroic bands, one weak and positive, at about 265 nm, and a stronger band at —228 nm, which was positive for the endo-(R)-nitrato chromophore and negative for the exo-(S)-nitrato group.68 However, for l,4 3,6-dianhydro-D-glucitol dinitrate, which has both an endo and an exo nitrato group, both bands were positive, but [ ]ma r (+ 7,260) for the band at 225 nm was about half of the algebraic sum of this band for the di-endo (+ 18,400) and di-exo (—4,460) compounds. 

Micellar Behavior of Monostearates of Dianhydrohexitols in Benzene Solution... 

The three l,4 3,6-dianhydrohexitols show the shielding effect of the cts-fused oxolane ring on their di-O-sulfonyl derivatives. As C-2 and C-5 of 1,4 3,6-dianhydro-D-mannitol 2,5-di-p-toluene-sulfonate and 2,5-dimethanesulfonate are open to attack from the exo direction, they react readily with such nucleophilic reagents as benzoate in /V,iV-dimethylfoimainide,94 acetate in acetone,93 thioacetate,95 phthalimide in A/,JV-dimethylformamide,93 and iodide in acetic anhy-dride.59<6) Inversion occurs at these positions and the L-iditol configuration results, as pointed out in the several examples in Table V. However, hydroxide ion may merely saponify,92 with retention of configuration.93... 

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