Triaziridine. 4. Mitteilung . Synthese von cis ‐2,3‐Diisopropyltriaziridin‐1‐carbonsäureestern

Triaziridines. Synthesis of cis ‐2,3‐Diisopropyltriaziridine‐1‐carboxylic Esters Irradiation of the ( Z )‐azimines 1a , b in Et 2 O with a Hg high pressure lamp through Corex yielded (besides 30% of the previously described trans ‐triaziridines 3a , b ) 15% of the new cis ‐triaziridines 4a , b . The same irradiation of the ( E )‐azimines 2a , b afforded only 15–18% of 3a , b but 20–23% of 4a , b . Thus, these azimine photocyclizations show some stereospecificity. The triaziridines 3a , b and 4a , b formed in this way were always accompanied by the same three types of by‐products, namely 10–15% of the ‘triazones’ 5a , b , 11–20% of the carbamic esters 6a , b , and 5–10% of the ether/nitrene insertion products 7a , b . The constitution and configuration of the new cis ‐triaziridines 4 followed from their spectral properties. Of particular interest are the symmetry properties of 4 derived from the 1 H‐, 13 C‐, and 15 N‐NMR spectra: The stereoisomers 3 and 4 differ only in that the isochronicity of the two constitutionally equivalent molecular halves is temperature dependent in 3 but independent in 4 . Both triaziridines 3 and 4 exhibit the IR CO band at (for carbamates) remarkably high frequency. The results confirm that the alkyl‐substituted N‐atoms of triaziridines are pyramidally stable, that the corresponding acyl‐substituted N‐atoms (N(1)) are also pyramidal, but can invert more readily, and that rotation around the N(1), C(O) bond is rapid. Thus, there can be only little amide‐type delocalization between a triaziridine N‐atom and an acyl substituent of the carbamate type attached to it.