Aziridines cleavage

Aziridine cleavage based on an Sn2 reaction was used for the synthesis of peptides bearing E alkene dipeptide isosteres, a novel class of potent bombesin receptor antagonists [62]. Treatment of the vinylaziridine 86 (Scheme 9.19) with isobutyl and isopentyl magnesiocyanocuprates in THF at —78 °C for 30 min. stereospecifi-cally gave the desired E alkene isosteres 87 in high isolated yields [63]. 

Aziridine cleavage. Cob(I)alamin is prepared in situ by Zn reduction of hy-droxocob(III)alamin HCl in the presence of NH4CI. Fused mcso-aziridines are cleaved to chiral allylic amines. 

Oxidative cleavage of P-aminoacyl complexes can yield P-amino acid derivatives (320,321). The rhodium(I)-catalyzed carbonylation of substituted aziridines leads to P-lactams, presumably also via a P-aminoacyl—metal acycHc compound as intermediate. The substituent in the aziridine must have 7T or electrons for coordination with the rhodium (322,323). 

For most common amides cleavage is quite difficult, but in the case of an aziridine (which exhibited reduced participation significantly in amide resonance because of the nonplanar amide moiety ) hydrolysis is much simpler, as shown in the following illustration ... 

Amino alcohols are also good substrates for aziridination under Mitsunobu conditions. The rfs-1,4-amino alcohols 48, obtained by reductive cleavage of the nitrogen-oxygen bonds of the hetero Diels-Alder adducts 47, underwent syn-SN2 -type displacement on treatment with PPh3 and DEAD to give cyclic vinylaziridines 49 (Scheme 2.15) [27]. 

Intramolecular and intermolecular 1,3-dipolar cycloadditions of aziridine-2-car-boxylic esters with alkenes and alkynes have been investigated [131, 132]. Upon heating, aziridine-2-carboxylates undergo C-2-C-3 bond cleavage to form azome-... 

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