Aziridine-ring cleavage regioselectivity

Unsubstituted benzyl 4-(9-benzyl-2,3-dideoxy-2,3-epimino-(3-D-/yv o- (341) and -ot-D-n )o-pyranoside (342) have been used by Paulsen and Patt in 1981 in cleavage reactions with azide. By the action of a mixture of sodium azide and ammonium chloride in a butanol-water system, the aziridine-ring cleavage proceeded exclusively at C-3, thus exhibiting anti-Furst-Plattner regioselectivity for both epimines. No explanation for this preference was given in the paper. 

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 Fiirst Plattner rule can be used only for predicting the regioselectivity of kinetically controlled cleavage reactions. If thermodynamic control takes place and the initially formed diaxial isomer is able reversibly to close back to the aziridine ring, the diequatorial isomer can begin to accumulate in the reaction mixture and is isolated either as the sole product or in a mixture " with the diaxial isomer. 

Exocyclic aziridines react without the influence of a tetrahydropyran or tet-rahydrofuran ring on the regioselectivity, and thus these epimines resemble nonsugar aziridines in their cleavage reactions. 

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