Shuai Yang, Wen-Jun Hua, Yanqi Wu
Jun 1, 2018
Citations
0
Influential Citations
16
Citations
Journal
Synfacts
Abstract
Significance: Reported is a palladium(II)-catalyzed synthesis of dibenzo[f,h]quinolines 3 by the reaction of 2-chloronicotinic acids 1 with dibenzo[b,d]iodol-5-ium triflates 2 through a decarboxylative annulation reaction. Compounds 1 and 2 bearing EDGs and EWGs (Me, t-Bu, MeO, CF3, F, Cl, CO2Et) were well tolerated and afforded the products 3 in yields of ≤86%. However, for polychlorinated 1 (R1 = 6-Cl), the chlorine next to the CO2H group gave products 3, indicating that the carboxylic group was the predominant ortho-directing group in the cross-coupling, rather than the strongly coordinating pyridine nitrogen. 2Chloroquinoline afforded the corresponding product 3 in 77% yield. Also, 3-chloroisonicotinic acids gave the corresponding isomers of products 3 (64–86% yield). The directed site-selective C–H activation/oxygenation of compounds 3 to give 4, followed by halogenation and arylation of 3a to 5a and 5b, respectively, demonstrated an application of the method. Comment: Dibenzoquinolines and their derivatives represent important scaffolds for materials chemistry (J. Wei, B. Han, Q. Guo, X. Shi, W. Wang, N. Wei Angew Chem. Int. Ed. 2010, 49, 8209), for which there are many available syntheses (see, for example: D. N. Nicolaides et al. J. Org. Chem. 1994, 59, 1083). The present method involves a simple one-step process from commercially or readily available substrates to give functionalized dibenzoquinolines 3. The uniqueness of the method is that it employs two cross-couplings between 1 and 2 in which the carboxylic acid of 1 acts as an ortho-directing group and 2 acts as a bis-electrophile. Although no possible mechanism is suggested, an analogous reaction of cyclic diaryliodonium salts has been previously reported and a mechanism proposed (see Review below). Some of the excessive optimization data might have been relegated to the supporting information.