Anhydrosugars yields

Polymer-supported glucal 37 was converted to the protected thioethyl glucosyl donor 39 as outlined in Scheme 2.11. Compound 37 was first epoxidized by the action of DMDO. The resulting 1,2-anhydrosugar was opened by a mixture of ethanethiol and dichloromethane (1 1) in the presence of a trace of trifluoroacetic acid. Polymer-bound 38 was thus obtained in 91% yield. This was a substantial improvement over the 78% yield obtained by the same protocol in solution. Protection by reaction with pivaloyl chloride occurred in quantitative yield to furnish 39a. 

The stereoselective glycosidation of the secoaglycon 1338 was achieved by reaction of the sodium salt of 1338 with the a-l,2-anhydrosugar 1339 to give the p-glucopyranoside 1340 in 48% yield. After the removal of the SEM protecting group with TBAF, the photocyclization of compound 1341 afforded the indolocarbazole... 

Perfluorinated oxaziridines epoxidize glycols to give the corresponding 1,2-anhydrosugars in high yield and moderate to complete diastereoselection <1995CC901>. For example, treatment of 226 with 80 in chloroform afforded 227 in >90% yield and >98% de. 

A subsequent study, reported by Dunkerton, et al.,21 showed that the above described chemistry was also applicable to l-O-acetyl-2,3-anhydrosugars. The results, directly analogous to the use of phenolic glycosides shown in Scheme 4.3.2, are illustrated in Scheme 4.3.4. As shown, excellent yields and high anomeric selectivity was observed with a net retention of the anomeric configuration. Although complementary to similar C-glycosidations discussed thus far, it should be noted that the applications of this specific reaction type is limited with low yields observed when substituents are present at C4 of the substrate. 

Further research into the types of substrates available for transition metal mediated C-glycosidations demonstrated the utility of glycosyl carbonates. As shown in Scheme 4.3.5, Engelbrecht, et al.,22 effected the formation of glycosyl carbonates on reaction of anhydrosugars with isobutyl chloroformate and pyridine. Under these conditions, the a glycosyl carbonate was isolated in 75% yield. Subsequent treatment with diethyl malonate in the... 

Cycloaddition between CSI and polymer bound vinyl ethers, for example 152 and 155, followed by the intramolecular alkylation provided mixtures of corresponding clavams 121/153 or cephams 115/116 [144]. In all cases, reactions proceeded with a lower yield and stereoselectivity than the corresponding sequences of reactions performed in solution. Moreover, in both cases formation of anhydrosugars 154 and 156 was observed [144,145]. It should be, however, pointed out that the same reactions performed with soluble polymer proceeded similarly to those carried out in solutions [ 145). 

Optical resolution of racemic /3-lactam has also been achieved by Bose and his collaborators via a stereospecific glycosylation. Thus, reaction of racemic 7.1.22 with the anhydrosugar 7.1.21 gave the desired /3-lactam 7.1.23 in 24% yield along with 36% of the other diastereomer (250). 

We are investigating various pretreatment processes to increase the pyrolytic yield of levoglucosan from herbaceous biomass. This work is motivated by our effort to convert lignocellulosic material into simple sugars suitable for fermentation. In particular, we are investigating thermal depolymerization of com stover and switchgrass into anhydrosugars and their subsequent hydrolysis and fermentation to lactic acid. 

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