Aziridine ring rearrangement

Potassium hydroxide/alcohol Aziridine ring rearrangement with N-decarbalkoxylation... 

Thermal rearrangement of 2-vinylaziridine 203, with an electron-withdrawing substituent on the nitrogen atom, at reflux in decalin predominantly yielded 2-pyr-roline 204 along with some 3-pyrroline derivatives 205 (Scheme 2.50) [79]. A similar reaction was also observed with l-alkyl-2-phenyl-3-vinylaziridines 206 [80]. From these observations, the nature of the products formed depends on the natures of the substituents on the aziridine ring if the ring carbon carries a phenyl substituent, the thermolysis in most cases preferentially yields 2-pyrrolines. 

N-Acylaziridine-2-carboxylates readily rearrange to oxazolines under thennal, acidic, or nucleophilic conditions [91, 123-127]. Treatment of trans-aziridine-2-car-boxylate 176 (Scheme 3.63) with Nal in acetonitrile, for example, resulted in ring-expansion product 177 through the so-called Heine reaction. The reaction involves initial opening of the aziridine ring by iodide and subsequent oxazoline ring-closure by Sn2 displacement of the resultant iodide intermediate [127]. 

The aza-[2,3]-Wittig rearrangement [47] and the related aza-[3,3]-Claisen rearrangement [48] of vinylaziridines are elegant examples of expansion of the aziridine ring in a stereocontrolled fashion (Scheme 38). 

The adduct 65 of aziridine to the acetylenic phosphonium salt 64 readily rearranges to the enamine 66, which in refluxing acetonitrile is converted into the pyrroline derivative 68 by opening of the aziridine ring and recyclization of the resulting zwitterion 67 (equation 33)54. 

The 4-isoxazoline ring includes an N-O bond connected to a rt-system (N-O-vinyl functionality) that shows a low thermochemical stability allowing ring-rearrangement reactions. Aziridines are generally assumed to be involved in... 

Other cycliaationa- Oebromination converts (46) into the 2.6-diazasemibullvalene (47) nmr studies suggest that Cope rearrangement is rapid and that (47) is the predominant valence isomer.53 A new aziridine ring-forming reaction (from f-amine oxides and base) has been applied to the synthesis of (48).54 A novel route to the pavine skeleton (49)33 and regiospecific synthesis of (50) have been described. 

Carboxylic acids also add to the C=N double bond and the products rearrange to more stable compounds with opening of the aziridine ring. A method for peptide synthesis is based on these reactions [15] ... 

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