Oxiranes, amino functionalization

Numerous carbacyclic, or sulfur-containing, analogues of mono- and difluoronucleo-sides have been synthesized as potential antivirals. In the carbacyclic series, the starting compound is hydroxymethylcyclopentene oxide. Rearrangement of this oxirane creates a new unsaturation that can be oxidized further into another epoxide. An amino function can then be introduced on the 4 position and can be used to build the base (Figure 6.13). 

By analogy with cyclopropanes and oxiranes, 2-acylaziridines, aziridine-2-carboxylic esters and amides, are also suitable substrates for one-electron reductive ring cleavage. This is an efficient and highly regioselective method for the synthesis of yS-amino carbonyl compounds. Vinylogous substrates are, furthermore, transformed into <5-amino y8,y-unsaturated carbonyl derivatives azetidines can also be used to achieve y-amino functionalization (Scheme 19) [72]. 

The products presented in scheme 5 show that it should be possible by subsequent introduction of amino groups through halogen or oxirane functionalities, to get an efficient entry into a series of polyhydroxylated piperidines (azasugars) [6,7,30] by intramolecular reductive amination. This class of compounds gained much interest recently because of its biological activity as potential glycosidase inhibitors [31-33]. In scheme 8 novel substitution patterns of polyhydroxy piperidines (boxed), which we synthesized stereoselectively by our own new procedures [34], are compared with known compounds derived from natural sources. 

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