Facile Access to Libraries of Diversely Substituted 2-Aryl-Benzoxazoles/Benzothiazoles from Readily Accessible Aldimines via Cyclization/Cross Coupling in Imidazolium-ILs with Pd(OAc)2 or NiCl2 (dppp) as Catalyst

Abstract A two-step protocol involving Pd-catalyzed cyclization of readily accessible p-bromophenyl-aldimines to 2-bromophenyl-benzoxazole/benzothiazole in [BMIM][PF6] or [BMIM][BF4] as solvent, followed by the Suzuki, Heck, and Sonogashira cross-coupling reactions catalyzed by Pd or Ni is described that generates libraries of diversely substituted 2-aryl-/heteroaryl-benzoxazoles/benzothiazoles in respectable isolated yields under mild reaction conditions. The feasibility to perform the two-steps in sequence in one-pot starting from the aldimines is also demonstrated and the potential for recycling/reuse of the IL solvent is also shown.