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 1H‐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 1H‐NMR signals of one invertomer, which – by steric reasoning ‐ ought to be A; this is confirmed by a 1H‐NMR argument for 3a, 5a, 6a, 5c, and 6c.