( E,Z )‐Gleichgewichte, 15. Synthesen und erhöhte Konfigurationslabilität von 2‐Iminoindan‐Derivaten mit Vorderseitenspannung

( E,Z ) Equilibria, 15 [1] . – Syntheses and Lability of the Configuration of 2‐Iminoindan Derivatives with Front Strain Syntheses and properties are described for sterically shielded imines R 2 C = NR ( 3c, e, g–k ), which are rather inert toward nucleophiles. Nucleophilic attack at the nitrogen atom of 3k is indicated by the formation of the azine 4 . ( E,Z ) Configurational diastereotopomerization ( anti/syn ) is strongly dependent on N substituents [CH 3 , phenyl, 1‐naphthyl, acetyl, Si(CH 3 ) 3 , cyano, SC 6 H 5 , SOC 6 H 5 , SO 2 C 6 H 5 , and nitro]. It is accelerated by front strain along the CN bond in 3a–c, e, g, h, j , and k and provides an energetic basis (by Δ G ≠ and ΔΔ G ≠ values) for the gauging of force‐field parameters. This ( E,Z ) stereo‐mutation is characterized by a vanishing solvent dependence and a positive volume of activation (+10.2 cm 3 mol ‐1 for 3a ). In contrast to other π acceptor substituents, the N ‐nitro group in 31 retards ( E,Z ) interconversion.