Ab‐initio‐Studien anN‐ Acyliminium‐Ionen

Ab initioStudies onN‐Acyliminium Ions The geometric and electronic structure and reactivity of theN‐formylmethyleneiminium ion are calculated in different conformations byab initiomethods and compared to those ofN‐methylformamide and the methyleneiminium ion. The known preferred attack of the C(5) of 3‐acyl‐2,3‐dihydro‐1,3‐oxazoles by electrophiles is explained by the lower (calculated) energy of the corresponding acyliminium ion relative to that of the oxenium ion. The stereoselectivity of additions to these acyliminium ions can not be explained by our calculations.Ab initiocalculations of the subsystems acyliminium and oxenium ion show that the reactivity can be predicted from investigation of these much simpler systems and make us suppose that a nitro instead of an acyl group will reverse the regioselectivity of the addition to 2,3‐dihydro‐1,3‐oxazoles.