Synthesis of Differentially Substituted 2-Aminoimidazolidines via a Microwave-Assisted Tandem Staudinger/Aza-Wittig Cyclization

A new route for the construction of 2-aminoimidazolidines including analogues of the α2 adrenergic agonist drug clonidine is elaborated. The key step is an intramolecular microwave-assisted Staudinger/aza-Wittig cyclization of an in situ generated urea intermediate (formed by the reaction of β-amino azide and isocyanate) upon treatment with Bu3P or polymer-supported phosphine reagent, allowing the introduction of various substituents at the N1 and the 2-amino function. Furthermore, a useful one-pot Staudinger/aza-Wittig/Buchwald-Hartwig protocol leading to bicyclic guanidines has been elaborated.