Organoselenium Reagent-mediated Hydroseleno Functionalization And The Synthesis Of 2-benzoxepin And Isochromene Compounds

Organoselenium compounds have medicinal activities such as antioxidant,anti-tumor,anti-cancer,and elimination of inflammation activities,etc.Since the 1929 patent described the use of selenium compounds as antioxidants,how to introduce selenium-containing functional groups into the molecular skeleton of the compounds has become a research hotspot in selenium chemistry.The hydroseleno group on the amino acid molecular is the active center of mammalian selenoenzyme,which can catalyze the decomposition of hydrogen peroxide in the organism by glutathione as the reducing agent.Compounds containing 2-benzoxepin and isochromene skeletons usually have certain antidepressant and antibacterial activities and can be used to treat neuronal degenerative diseasesIn this paper,N,N,N-triphenylselenoisocyanuric acid is used as the electrophilic organoselenium reagent,and a Lewis acid and a high-valent iodine reagent as the catalysts.The hydroseleno functionalization of benzyl cinnamate and the highly selective 7-endo and 6-exo carbocyclizations of cinnamyl benzyl ethers were performed to produce 2-hydroseleno-3,4,5-trimethoxybenzyl cinnamate,2-benzoxepin,1,3-dihydrobenzoxepin,and isochromene compounds respectively,in high yields and with high regio-and stereoselectivitiesIn the presence of ZnCl2 catalyst,N,N,N-triphenylselenoisocyanuric acid-induced hydroseleno functionalization of 3,4,5-trimethoxybenzyl cinnamate was performed at 40℃ for 4 h to produce eighteen 2-hydroseleno-3,4,5-trimethoxybenzyl cinnamate compounds.The advantages of this method include high yield and regiospecificity,mild reaction conditions,and easy operation.Moreover,the key of this reaction is that in the absence of a reducing agent,the phenylselenyl group can be converted into the hydroseleno group by using the electrophilic organoselenium reagent.Actually,in this one-pot procedure,the valence of selenium is reversed from+2 to-2 via the phenylselenylation and dephenylation reactions of the substratesIn the presence of bistrifluoroacetyl iodobenzene,phenylselenium ion intermediate can be generated in situ from diphenyl diselenide which is easily available By optimizating the reaction conditions such as the amount of diphenyl diselenide and bistrifluoroacetyl iodobenzene,reaction temperature and charging sequence of the substrate and reagents,the same cinnamyl benzyl ether compound can respectively undergo a 7-endo carbocyclization,a sequence of 7-endo carbocyclization and deselenenylation,and a 6-exo carbocyclization to obtain 2-benzoxepins,1,3-dihydrobenzoxepins,and isochromenes respectively,48 products in total.The key of this method is that the 7-endo carbocyclization products and the deselenenylization products can be obtained respectively by adding equivalent or catalytic amount of PhSeSePh whereas the 6-exo carbocyclization products can be produced by changing the charging sequence of the substrate and reagent.Moreover,the advantages of this method include no metal participation,mild reaction conditions,easy operation,convenient purification of the products,broadly functional group tolerance of the substrate,good to high yield and high regio-and stereoselectivity.