Metal-Free And Solvent-Free Synthesis Of M-Terphenyls Through Tandem Cyclocondensation Of Aryl Methyl Ketones With Triethyl Orthoformate

In organic synthesis,m-terphenyl plays an important role because of its unique molecular arrangement,the m-terphenyl ligand is a monanionic ligand,in most case,substitution in the 1 position of the central phenyl group is facile and often proceeds.Substituents in this position are effectively in a ‘pocket’ between the two ortho aryl groups and they can often experience strong associations to the ortho aryl groups via a p-arene interaction.M-terphenyls have highly photophysical and optical properties,and have been extensively applied in material science,such as conducting polymers,OLEDs,heat storage and transfer agents,laser dyes,and textile dye carriers.In addition,terphenyl scaffolds are also found in several naturally occurring compounds with interesting biological properties.As a consequence,significant attention has been paid to the synthesis of m-terphenyl and its derivatives.The simplest m-terphenyl,1,3-diphenylbenzene,was firstly synthesized by the addition of the Grignard agent to 1,3-cyclohexanedione.Till now,Various methods have been reported to construct m-terphenyl frameworks.Among these methods,the transition metal-catalyzed coupling reactions have been the most widely used approaches.However,these methods are generally associated with various drawbacks,which include harsh reaction conditions,expensive metal catalysts,limited substrate scope,and poor chemo-or regioselectivity.Thus,there is still a great demand to develop simple,efficient and regioselective methods for the synthesis of m-terphenyls.We have found an efficient method for the prepartion of a large range of m-phenyls through cyclocondensation reaction of aryl methyl ketones with triethyl orthoformate.Aryl methyl ketones and triethyl orthoformate were readily condensed to their corresponding m-phenyls in good to excellent yields with high regioselectivity.Importantly,most of these condensation reactions proceeded remarkably fast at mild temperature.