Photochemical Coupling Reaction Of Chromone And Uracil Iodide

Carbon-carbon bond formation is the core of organic synthesis and has been greatly changed in the last decades.The development of transition metal-catalyzed is indispensable in this processes,however it often has a poor atom economy and is carried out under rather harsh conditions.On the other hand,the increased attention to environmental problems requires some new methods to be evaluated.Photochemical reactions arise from electronically exicted states which is obtained by the absorption of a photon.In contrast to the most catalytic methods involve the use of toxic/polluting reagents,the photochemical reactions leave no residue,and in many cases,occur under unparalleled mild conditions and let deep-seated chemical transformations occurring in high yields and with high selectivity.Therefore,according to the principle of photochemical reactions to deisgn a more available synthetic sequence is worth considering.In the first part of this paper,we summarize the progress of photochemistry reaction and introduce the photo-induced coupling reaction,cyclization reaction,decarboxylation reaction and rearrangement reaction in detail.In the second part,3-iodoflavone and penta-heterocycles like N-methylpyrrole,pyrrole,furan,thiophene etc were irradiated in MeCN solvent under a high-pressure mercury lamp(500 W)for 7 h.The 19 kinds of heteroflavone were obtained directly and confirmed by FT-IR,1HNMR,13CNMR and HRMS.This method has many advantages such as mild reaction conditions,operational simplicity and friendly to environment.It is also the first time to cascade the photo coupling reaction of iodoflavone with rearrangement of dehydrogenation,realizing the cyclization and coupling cross of material in one step.The next chapter,we design a new method of photochemical syntheses of 3-heteroarylchromones compounds.3-iodochromone and heterocycles such as N-methylpyrrole,pyrrole,furan,thiophene,benzofuran etc were irradiated in MeCN solvent under ahigh-pressure mercury lamp(500 W)for 5 h.22 kinds of 3-heteroarylchromones compounds were obtained and characterized by hydrogen,carbon and mass spectra.The advandage of this method is operational simplicity,gentle reaction conditions,no metal residuce and environment friendly.In contrast to other photo-reaction,this synthesis is a green method as the operation was not protected by Ar and the solvent was not dehydrated.Afterwards,a new method of photocatalyzed syntheses of 5-aryluracil(uridine)was designed.5-iodouracil or 5-iodouridine and heterocycles such as N-methylpyrrole,pyrrole,furan,thiophene,benzene etc were irradiated in MeCN solvent under a high-pressure mercury lamp(500 W)for 7 h.Subsequently,12 kinds of 5-aryluracil and 5-aryluridine were obtained.Because of the pharmacological activities of 5-aryluracil(uridine),it is crucial for exploring this new synthetic method of these compounds.This method not only has the advantage of general photochemistry reaction but also has the special character no protecting group was requiredfor the hydroxyl of furanose and NH bond.It can simplify multi-step reaction to one step,improving the product yield and reducing the impurities.In the fifth part,the Stille coupling reaction was applied to synthesize the 3-thiophenchromonecompounds.Several substituted 3-iodochromone,tetrathiophentins,slight NaOAc and 0.5mol%of Pd/C were refluxed in ethanol for 4 h to synthesize the 3-thiophenchromone compounds which were confirmed by FT-IR,1HNMR,13CNMR and HRMS.In contrast with photochemistry reaction,the high yield is a significant advantage although there is no benefit to the environment.On the other hand,no dehydration for solvent and no protection by Ar were the other characteristic worth promoting in contrast to Suziki reaction.Hence,for this paper,the novel methods for syntheses of 3-arylchromones,5-aryluracil and heteroflavones have been developed via irradiating 3-iodochromones,5-iodouracil(uridine),3-iodoflavones and ?-excessive heteroarenes under high-pressure mercury lamp.Compared with other synthetic methods,the photochemical reactions have many advantages such as short route,operational simplicity and offers environmental protection,etc.These novel arylchromones and heteroflavones synthesized by photochemical reaction not only enriched their species and properties,more importantly,they provided the material basis for their studies and research.