| The seven-membered oxygen-containing cyclic substructure is the core skeleton of many natural products and drug molecules,and its synthesis has always been a hot spot in organic chemistry.The intermolecular [3+4] cycloaddition reaction is a straightforward and efficient method in seven-member ring synthesis.Vinylcyclopropane can be acted as a 1,3-dipole under the catalysis of transition metals and Lewis acids,and reacts with aldehydes,imines and electron-deficient olefins to obtain many compounds containing five or six membered rings.However,ortho-Quinoe Methide is generated in situ from phenolic derivatives under mild conditions such as acid and base,it can be regarded as an oxadien to participate in various [4+n]-annulation reactions.In this paper,the combination of alkali-promoted ortho-quinoe Methide and palladium(0)-catalyzed annulation of vinylcyclopropane.aromatization is the driving force for the [3+4]-annulation reaction of vinylcyclopropane with in situ generated ortho-quinoe Methide.The reaction includes a Michael addition/aromatization/palladium catalyzed O-allylation process,which provides a new method for the synthesis of multi-substituted 1-benzoxanthine compounds.In addition,it has also been discovered that dearomatization [3+2]-annulation reaction of some weakly aromatic reactants. |
