Efficient Synthesis Of Fused Oxa-Heterocycles Via Cascade Annulation Of Cyclic 1,3-Dicarbonyl Compounds With Propargylic Alcohols

The oxa-fused heterocyclic structure is widely present in various natural products and biologically active molecules.The development of new heterocyclic synthesis methods is one of the important tasks of synthetic chemistry.The cycloaddition reaction of propargyl precursors and carbonyl compounds is an effective method for synthesizing heterocycles,especially oxygen heterocycles.Under the promotion of metal reagents,4H-pyrans,polysubstituted furans and 2H-pyrans can be obtained smoothly.Molecular iodine is both a mild Lewis acid catalyst and a commonly used electrophile.It can trigger various reactions of propargyl derivatives,such as iodine cyclization,iodine Meyer-Schuster rearrangement,and dihalogen cyclization.As a Lewis acid,molecular iodine can not only promote the formation of carbocations from propargyl alcohol,but also activate the acetylene bond for electrophilic addition.Use suitable bis-nucleophiles to capture the carbocation,and then initiate a cyclization reaction,which can efficiently synthesize cyclic compounds.In this thesis,different cyclic 1,3-diketones are used as bis-nucleophiles.After the dual effects of elemental iodine catalysis and iodine cyclization,the benzofuran skeleton and pyrano [ 2,3-b]Selective synthesis of chroman-5-one skeleton.In previous reports,4H,5H-pyrano[2,3-b]chroman-5-one is often a side effect of the synthesis of 4H,5H-pyrano[3,2-c]chroman-5-one.The product,this work has realized the selective synthesis of this heterocyclic structure for the first time.In addition,through the triple relay catalysis of Lewis acid,elemental iodine and visible light,this work achieved the first three-step one-pot method to efficiently catalyze the synthesis of 2-position acylated 6,7-dihydrobenzofuran-4(5H)ketone.The post-modification of the above-mentioned framework can facilitate the acquisition of some biologically active molecules.A new method was developed to regulate the regioselective synthesis of oxa-fused rings by nucleophiles.