Faile Synthesis Of Dihydropyran And Biphenyl Compounds Via An Intramolecular Alkene-carbonyl Cyclization Reaction

Biaryl and dihydropyran compounds are important chemical raw materials.These aromatic carbocycles and oxygen-containing heterocycles are widely found as key structural motifs in a variety of natural products and pharmacologically active drugs,which also have broad application prospects in material science,biochemistry,and others,such as luminous polymers,liquid crystals,and organic semiconductors.At present,biaryls are mostly prepared by the coupling reactions of substituted aromatic compounds catalyzed by precious metals.Although such cross-coupling reactions provide efficient pathways for production of biphenyl compounds in both laboratory and industry,however,there are some disadvantages in these methods,such as using of expensive catalyst,complex preparation of raw materials,harsh reaction conditions,and poor regioselectivity.The synthesis of biaryls using acyclic compounds as starting materials through cascade intra-or intermolecular cyclization/aromatization reactions has also attracted a lot of interest from chemists,but so far,only a few examples of such reactions have been reported.In this paper,we have developed a new catalytic method for the synthesis of biaryl compounds,which uses allyl substituted ?-ketone esters,or aldehydes and ketones as the starting materials and a super acid as the catalyst,a series of biaryl derivatives can be prepared by an intramolecular alkene-carbonyl Prins reaction and a cascade aromatization reaction.The reaction has the characteristics of cheap raw materials,mild reaction conditions and convenient to operate.In the process of optimizing the reaction conditions for preparation of biaryls,we found that the dihydropyran products can also be obtained from this reaction by controlling the reaction temperature.Since dihydropyran compounds are important chemical materials,we have conducted a simple study on the preparation of such derivatives.The results show that this catalytic reaction can also be used efficiently to synthesize dihydropyran compounds.Further mechanistic studies have found that dihydropyran compounds can be converted into corresponding biaryls at higher reaction temperature.Therefore,dihydropyran compounds may be the active intermediates in this reaction.Based on the above experimental phenomena,a possible reaction mechanism was speculated.In addition,the reaction can also be used to prepare polycyclic aromatic hydrocarbons and bicyclic compounds by regulating the structure of the starting materials.In summary,a new method for the synthesis of biaryls and dihydropyran compounds has been successfully developed,via a systematic study on the catalytic system and the substrate universality of the reaction.A series of biaryl and dihydropyran derivatives with different structures were obtained.The method has a good application prospects in organic synthesis because of its some advantages such as mild reaction conditions,simple reaction operation,good universality of substrate,and environmental friendliness.