Bildung von 4‐, 5‐ und 6gliedrigen Heterocyclen durch ambidoselektive Ringschlüsse von Enolat‐Ionen

Formation of 4‐, 5‐ and 6‐membered heterocycles by ambidoselective cyclization of enolate anions N ‐Acylmethyl‐ N ‐chloracetyl‐2,6‐dimethylanilines 4 were cyclized with base to 4‐, 5‐ or 6‐membered ring compounds, depending on the substituent R 2 ( Scheme 2 ). All products can be rationalized as derived from the intermediate enolate anions a and b . The enolate anion a reacts by intramolecular alkylation to yield either 1, 4‐oxazines 5 or azetidines 6 ( Schemes 1, 3 and 7 ). The regioselectivity observed is expected on the basis of the allopolarization principle. The enolate anion b reacts only with formation of a new CC bond (Scheme 5) . Comparison with the behaviour of the 2, 6‐unsubstituted anilines 9, 1a and 12 , shows a strong dependence not only on electronic but also on steric factors ( Scheme 4 and 6 ).