Concave Imidazolinium Salts as Precursors to Concave N‐Heterocyclic Carbenes

Concave bimacrocyclic imidazolinium ions 8 have been synthesized as precursors for N‐heterocyclic carbenes 9 (NHC) in 13 to 29 % overall yields based on 2‐nitroresorcinol ( 1 ). As bridgeheads, 2,6‐bis(ω‐alkenyloxy)anilines 3 have been synthesized from 1 . Reaction of 3 with oxalyl chloride, reduction to respective diamines 5 , and ring closure with triethyl orthoformate gave N , N ‐diaryl‐substituted imidazolinium ions 6 . The terminal vinyl groups were connected by ring‐closing metathesis to give bimacrocyclic imidazolinium ions 7 , whose alkene functions were hydrogenated to give saturated bimacrocyles 8 . The structure of 8a was elucidated by X‐ray analysis. The respective NHC 9 was generated by deprotonation with potassium tert ‐butoxide, and 9 was scavenged with CS 2 to give adduct 10 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)