Study On The Synthesis Of Alkenyl Furans,Substituted And Sulfur-containing Heterocycle-fused ?-Pyrone Derivatives

In this paper,two aspects are studied.Firstly,2-diazo-?-pyrones as metal carbene precursors react with dithioacetals to regioselectively synthesize eight-membered sulfur-containing heterocycle-fused?-pyrones and 2-?1,4-dithianyl?-4-pyrones derivatives.On the basis of experimental data and references reported in literature,a possible reaction mechanism is proposed.Secondly,the cross-coupling reaction of ene-yne-ketones with phosphorus ylides is studied in the presence of silver-iodine double catalyst to produce?E?-?-alkenylfuran derivatives.The thesis divides into three parts and launches explaining.The synthesis and applications of?-pyrones,ene-yne-ketones and diazo compounds are reviewed in the first chapter.In the second chapter,a regioselective reverse strategy for the construction of eight-membered sulfur-containing heterocycle-fused?-pyrones and 2-?1,4-dithianyl?-4-pyrones starting from the identical starting materials,2-diazo-?-pyrones and dithioacetals,is achieved by using different catalysts for the first time.For Rh₂?OAc?₄,eight-membered sulfur-containing heterocycle-fused?-pyrones derivatives were obtained.For AgSbF₆/Rh₂?OAc?₄,2-?1,4-dithianyl?-4-pyrones are produced.The optimized conditions for the construction of eight-membered sulfur-containing heterocycle-fused?-pyrones are as follows:the use of 5 mol%Rh₂?OAc?₄ as catalyst,DCE as solvent at 80°C under nitrogen atmosphere.The optimal conditions for the formation of 2-?1,4-dithianyl?-4-pyrones are as follows:the use of AgSb F₆/Rh₂?OAc?₄?5 mol%?as co-catalysts,60°C and DCE as solvent under nitrogen atmosphere.When 2-diazo-?-pyrones bearing various substituents and different dithioacetals are used in the synthesis of eight-membered sulfur-containing heterocycle-fused?-pyrones compounds,only the dithioacetals of aryl,styryl and phenyl substituents as substrate have a poor reaction effect,and the yield of the remaining products is 70-90%.For the formation of 2-?1,4-dithianyl?-4-pyrones,only the dithioacetals of aryl substituent as a substrate has poor reactivity,and the yield of the remaining products is from 70%to 90%.In conclusion,we have successfully achieved the first Rh₂?OAc?₄-catalyzed cycle expansion of 2-diazo-?-pyrones with dithioacetals to afford eight-membered sulfur-containing heterocycle-fused?-pyrones.In the AgSb F₆/Rh₂?OAc?₄ system,a range of 2-?1,4-dithianyl?-4-pyrones was obtained in good yields starting from the identical starting materials.The novel strategy provides regioselective reversal construction of two heterocycle core skeletons in high isolated yields with total distereoselectivity.In the third chapter,we explored the synthesis of?E?-?-alkenylfuran derivatives starting from conjugated ene-yne-ketones and Wittig reagent in the presence of AgOTf and iodine.The optimized conditions for the construction of?E?-?-alkenylfuran derivative are as follows:AgOTf?10mol%?and I₂?10 mol%?as the catalyst,anhydrous DCE as solvent at80°C under nitrogen atmosphere.This method has some advantages such as simple,mild reaction conditions and high selectivity.