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4.1 Introduction<br />
There are only a few approaches that describe the direct synthesis of 2aminoimidazoles<br />
and their biological activity 1-5 . The earliest method involves<br />
condensation of α-aminocarbonyl compounds with cyanamide or their synthetic<br />
equivalents 6,7 . This method is most commonly used for the direct construction of the<br />
2-aminoimidazole ring. Other general applicable strategies are cyclocondensation of<br />
α-bromoketone with N-acetylguanidine in acetonitrile 8 , iminophosphorane-mediated<br />
cyclization of α –azido esters 9 , ammonolysis of 2-amino-1,3-oxazol-3-iumsalts 10 ,<br />
sequential functionalization of 1,2-diprotected imidazole ring with different<br />
electrophiles 11 . Most of them involve long experimental procedures, the use of<br />
unstable precursors and tiresome workup process. Accordingly, the development of<br />
straightforward and general procedures for the synthesis of diversely substituted 2aminoimidazoles<br />
from readily available precursors is highly warranted. Herein, we<br />
report a rapid and highly efficient Cu-mediated synthesis of 2-aminoimidazoletriazole<br />
framework via click reaction and dimorth rearrangement.<br />
“Click chemistry” has emerged as a fast and efficient approach to synthesis of novel<br />
compounds with desired function making use of selected “near perfect” reactions. 12<br />
(very fast, selective, high-yield, and wide scope).<br />
The Dimroth rearrangement 13 is an isomerization of heterocycles that consists in a<br />
translocation of endo- or exocyclic heteroatoms through a ring-opening-ring-closure<br />
sequence. It can be catalyzed by acids, bases, heat or light.<br />
Recently group of Erik 14 reported a new one pot microwave assisted synthesis of<br />
substituted 2-amino-1H- imidazoles from readily available 2-aminopyrimidine (1) and<br />
α-bromoketone (2). The first step was performed by heating N-(3azidopropyl)pyrimidin-2-amine<br />
(1) and 2-bromo-1-phenylethanone (2) at 75 o C for 3<br />
h resulting in the formation of hydroxyl salt (3) which undergoes dimorth type<br />
rearrangement by 7 equiv of NH2NH2.H2O resulting in the formation of N-(2-azido)-<br />
1H-imidazol-2-amine. Final step of click reaction was performed under microwaveirradiation<br />
using phenylacetylene (1.5.equiv), Cu(Oac)2 (10 mol %)as catalyst at 100<br />
o<br />
C 10 min with a maximum power of 40W to obtain 2-AI-T scaffold (5). (Scheme 1)