Diastereoface Selectivity During Pthalimidonitrene Additions to ( E )‐and ( Z )‐configurated α, β‐unsaturated esters, induced by a chiral center in the γ‐position

In ‐ situ ‐generated phthalimidonitrene was added to five α, β‐unsaturated esters containing a chiral secondary O‐function at C (γ). The additions were fully suprafacial, inasmuch as the (E)‐isomers 1 afforded only the trans ‐aziridines 2 and 3 (J(β, γ) = 4.8−5.1 Hz) and the (Z)‐isomers 4 only the cis ‐ aziridines 5 and 6 (8.2−8.5 Hz). The products 2 , 3 , 5 , and 6 where shown to possess the arabino ‐, xylo ‐, ribo ‐, and lyxo ‐ configuration , respectively, by X‐ray structure analysis of 2b , 2d , and 6a . The diastereoface selectivity of the nitrene additions, induced by the chiral substructure around C(γ), resulted in more 2 than 3 from 1 , but more 6 than 5 from 4 , which means that the preference of attack at the double bond switches from one side to the other depending on the C=C configuration. The preferences were higher at lower temperature. The aziridines 2a , 2d , and 3d exhibit 1 H‐NMR‐visible isomerism at the ring N‐atom; the major (78−95 %)invertomer A is always the one with the phthalimido group in trans ‐position to the (larger) substructure around C (γ). The other aziridines only show 1 H‐NMR signals of one invertomer, which – by steric reasoning ‐ ought to be A ; this is confirmed by a 1 H‐NMR argument for 3a , 5a , 6a , 5c , and 6c .