title: Synthesis of Naphtho[1',2':4,5]imidazo[1,2-a]pyridines and Imidazo[5,1,2-cd]indolizines Through Pd-Catalyzed Cycloaromatization of 2-Phenylimidazo[1,2-a]pyridines with Alkynes.
abstract: In this paper, palladium-catalyzed oxidative cycloaromatization of 2-phenylimidazo[1,2-a]pyridine (PIP) with internal alkyne is studied. From this reaction, two classes of fused N-heterocycle, naphtho[1',2':4,5]imidazo[1,2-a]pyridine (NIP) and imidazo[5,1,2-cd]indolizine (IID), were formed through dehydrogenative coupling featured with cleavage of the C-H bonds located on different moiety of the PIP substrates. Moreover, when 5-methyl-2-phenylimidazo [1,2-a]pyridine or 2-mesitylimidazo[1,2-a]pyridine was used, either NIP or IID could be obtained as an exclusive product with good efficiency. Intriguingly, Pd(II) showed different action mode in promoting this reaction compared with Rh(III) and led to the formation of NIP with reversed regio-selectivity for the reaction of asymmetrical alkyne.
authors.affiliation: School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Normal University, Xinxiang, Henan 453007, China.
authors.forename: Peiyuan
authors.initials: P
authors.lastname: Li
authors.affiliation: School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Normal University, Xinxiang, Henan 453007, China.
authors.forename: Xinying
authors.initials: X
authors.lastname: Zhang
authors.affiliation: School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Normal University, Xinxiang, Henan 453007, China.
authors.forename: Xuesen
authors.initials: X
authors.lastname: Fan
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D007212:Indolizines / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000480:Alkynes; D007093:Imidazoles; D007212:Indolizines; D011725:Pyridines; D010165:Palladium; C023666:pyridine