Aziridine-ring cleavage

Aziridine-ring cleavage of A-substituted methyl 4,6-0-benzylidene-2,3-di-deoxy-2,3-epimino-a-D-mannopyranosides by either sodium azide alone or in admixture with ammonium chloride leads to the formation of the diaxial azido derivative and the corresponding oxazoline (see Table I for details). 

All produets had eonfigurations as predieted by the Furst Plattner rule, whieh implies that fission of the benzylidene group had to take plaee after aziridine-ring cleavage. 

The reactions of V-substituted D-allo epimines with HCl and HI proceeded trans-diaxially in all cases where the biased conformation of the tetrahydropyran ring was maintained. In the reaction, where 4,6-O-benzylidene group was hydrolyzed prior to aziridine-ring cleavage, mixtures of stereoisomers were formed. ... 

A -Benzylepimine 160 reacted with a mixture of ammonium and tetrabutyl-ammonium bromide or iodide to give the respective diequatorial bromo (193) or iodo (194) derivatives as the sole products. This formation is the result of an equilibrium between the starting epimine and the diaxial halo derivative, which is formed initially by aziridine-ring cleavage. This equilibrium could be set up readily because of the instability of the diaxial halo derivatives and their tendency to undergo back-cyclization of the aziridine ring. To prove the existence of the equilibrium, the diaxial bromo derivative 191 was prepared by the action... 

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. 

Dauban and coworkers published a detailed study on the reactivity of 2,3-epimino-2,3-dideoxy-D-lyxono-1,4-lactone derivatives 370, 380 with both soft (RSH, AcOH, LiBr) and hard (ROH, BnNH2) nucleophiles. Reactions of the epimines with soft nucleophiles proceeded by direct aziridine-ring cleavage to give predominantly C-2 regioisomers. 

J. Kroutil, T. Trnka, M. Budesinsky, and M. Cerny, Aziridine ring cleavage by nucleophiles in epimino derivatives of 1,6-anhydro-P-D-hexopyranoses, Eur. J. Org. Chem. (2002) 2449-2459. 

A quinoxaline-related system can emerge upon the expansion not only of a five- but also a three-membered heterocycle. New frani-perhydroquinoxalin-2(lfl)-ones were prepared by the reaction of aziridines 449 with a-amino acids 312a, f as a result of the aziridine ring cleavage and pyrazine ring formation (Scheme 2.91) (Rees 1987). Note that the reaction is non-stereoselective and gives a mixture of products 450 and 451. 

The N-protected-2-aryl aziridines react smoothly with various thiols to afford the corresponding (3-aminosulfides (Fig. 9). In the cleavage of A/-benzyl- and Af-tosyl-2-aryl aziridines, preferential cleavage is at the benzylic position of the aziridine ring, whereas (V-tosyl-2-alkyl aziridines cleaves at the less hindered (terminal) aziridine-ring carbon. 

Three N-C bond-cleavage processes are shown here. Dealkylation of 260 was carried out in two steps (Equation 49) <1987H(26)1503>, and the benzoxycarbonyl protective group was removed with a Lewis acid (Equation 50) <1994ACS517>. The aziridine ring of 201 was cleaved with acid (Equation 51) <2007S225>. 

Azetidine can be considered as a fairly typical cyclic amine. Strain in the four-membered ring is less than that in the three-membered aziridine system, and as a result azetidines show few, if any, of the exceptional properties associated with aziridines. Thus, ring cleavage reactions occur with greater ease than in larger ring cyclic amines, but much less readily than with aziridine for example, unlike aziridines, azetidines do not function as alkylating... 

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