Hydroxyl groups removal, deoxygenation reactions

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Radical chemistry has been widely exploited for the modification of carbohydrates. In particular, tributyltin hydride-promoted deoxygenation provides a convenient method for the effective removal of hydroxyl groups without intervention of other functionalities. Stereoselective carbon-carbon bond formation at the anomeric center has also revealed its apphcability for the preparation of carbon analogues of 0-glycosides. The majority of this work has been reviewed in earlier publications and hence will not be covered in this account. Instead a selection of newer appHcations is provided here, which have been categorized according to the type of radical reaction carried out. 

R.H. Schlessinger et al. have successfully synthesized the a,(3-unsaturated octenoic acid side chain of zaragozic acid, which contains acyclic skip 1,3 dimethyl stereocenters. Their approach utilized the Barton radical deoxygenation reaction in the last step of the total synthesis for the removal of the unnecessary hydroxyl group. 

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