Tandem [8 + 2] cycloaddition--[2 + 6 + 2] dehydrogenation reactions involving imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines.
The reaction between benzynes and imidazo[1,2-a]pyridines (pyrimidines) to form benzo[a]imidazo[5,1,2-cd]indolizines and 2,3,9c-triazocyclopenta[j,k]fluorenes has been studied computationally and experimentally. It is found that these reactions take place via tandem [(pi)8(s) + (pi)2(s)] and [(sigma)2(s) + (pi)6(s) + (sigma)2(s)] processes. The [8 + 2] cycloaddition steps are essentially barrierless, and the aromatization steps occur via highly synchronous aromatic transition structures. From an experimental standpoint, the reaction is feasible under microwave irradiation and using 2-(trimethylsilyl)phenyl triflates as benzyne precursors. Depending on the substitution pattern in the starting triflate a complete regiocontrol of the reaction can be achieved. The tetracyclic compounds thus prepared emitted blue light when excited at 365 nm and exhibited interesting photophysical properties.
Aginagalde
Maialen
M
Kimika Organikoa I Saila, Universidad del País Vasco-Euskal Herriko Unibertsitatea (UPV-EHU), P. K. 1072, 20018 San Sebastián-Donostia, Spain.
Vara
Yosu
Y
Arrieta
Ana
A
Zangi
Ronen
R
Cebolla
Vicente L
VL
Delgado-Camón
Arantzazu
A
Cossío
Fernando P
FP
D001555:Benzene Derivatives / Q000737:chemistry; D003500:Cyclization; D005449:Fluorenes / Q000737:chemistry; D006865:Hydrogenation; D007093:Imidazoles / Q000737:chemistry*; D007212:Indolizines / Q000737:chemistry; D008872:Microwaves; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*
D001555:Benzene Derivatives; D005449:Fluorenes; D007093:Imidazoles; D007212:Indolizines; D011725:Pyridines; D011743:Pyrimidines; C524146:benzyne; C041509:fluorene