Synthesis And Single-Electron Oxidation Cyclization Of (Z)-[3] Dendralenes Derivatives

Dendralenes are a kind of acyclic cross conjugated polyenes with branched chain skeleton.Since Paul et al.reported the first case of functionalized [3]dendralene in 1951,it has been considered as an unstable compound.However,with the discovery of dendralenes skeleton in natural products and the development of their synthesis methods,dendralenes chemistry has gradually become a research hotspot of chemists.In view of the similarity between the stereoscopic configuration of the dendralenes and the distribution of the leaves and stems of Euphorbiaceae,the research group gave its Chinese name " jixi " for the first time and reviewed its research progress in the past ten years in the journal Organic Chemistry.A variety of synthesis methods have been developed at present,and it has been proved that dendralenes have a broad development prospect.However,there are few reports on the stereoselective synthesis of dendralenes(Z/E),and the stereoselectivity or yield of most of this kind of structures are unsatisfying.Therefore,it is very important to develop a synthetic method with high stereoselectivity and good yields.In addition,except Diels-Alder reaction,alkenyl Nazarov cyclization and organic catalyzed domino cyclization,there are few reports on other derivatization reactions of dendralenes.How to maximize the application of[3]dendralenes skeleton in methodology system is still the direction of ongoing research.In this paper,based on the previous work of our research group and literature research,we carried out research on the synthesis and derivatization of(Z)-[3]dendralenes,and realized the high stereoselective synthesis and self cyclization of [3]dendralenes.The specific research contents are carried out from the following two aspects.1.Selective hydrogenation of phosphinyl conjugated enynesThe hydrogenation of phosphinyl conjugated enynes often require more stringent conditions.In this paper,the safe and clean borane is used as the hydrogen source to obtain the single target product with different hydrogenation sites by the catalysis of cobalt acetonate under mild conditions.The method has good functional group tolerance,high stereoselectivity and regional selectivity and good yields.In this paper,eleven unreported terminal alkene hydrogenation products and eight(Z)-[3]dendralenes products were synthesized.2.Study on single-electron oxidation cyclization of(Z)-[3]dendralenesAs the simplest dendralenes,[3]dendralenes meet the potential demand of efficient synthesis of complex molecules,and have attracted wide interest of synthetic chemists in the fields of polymer chemistry,electrochemistry,material chemistry and theoretical chemistry.In this paper,the self cyclization of(Z)-[3]dendralenes to polycyclic aromatic hydrocarbons catalyzed by aluminum chloride was studied.The substrates of this method are adaptable and can provide good to excellent yields.Sixteen(Z)-[3]dendralenes products and twenty-four six-membered ring closing products were successfully synthesized.All of them were new compounds synthesized for the first time.They were characterized by NMR(H,C,P,F),HRMS and single crystal diffraction.The yield of gram scale reaction can reach 78%.The results of the mechanism experiment show that the reaction may follow the free radical mechanism of one electron oxidation.