Ytterbium-catalyzed Furan Dearomatization To Construct Fused-ring Triazoles

Our basic energy resources will inevitably undergo a restructuring from fossil resources to renewable resources.In the near future,we will face a great challenge to develop adaptive new energy utilization systems,or to use existing comprehensive energy strategies to adapt to new energy requirements.At present,the biomass furan obtained by the biological finishing processing of lignocellulose is considered as one of the plant-based and inedible renewable resources and an attractive chemical and chemical raw material in the post-fossil era.Therefore,it is very important to develop a synthesis strategy based on furan.Triazole is a class of very important compounds,they are stable to light,water,oxygen,and can be stable in the body for metabolic degradation.It can also be combined with target biomolecules by hydrogen bond.Fused 1,2,3-triazole has a large three-dimensional diversity and is widely found in small molecules with biological activity.This kind of heterocyclic compounds not only have shown anti-hiv,anti-allergy,anti-fungal,anti-virus and other activities,but also are widely used in industry,such as dyes,corrosion inhibitors,light stabilizers,photographic materials and agricultural chemicals.However,it has long been challenging to develop synthetic methods for polydense triazole.Over the past few decades,chemists have developed many synthetic strategies for the synthesis of fused triazole compounds.But most of the synthetic strategies depend on Cu(I)catalytic acetylene-organic azide[3+2]cycloaddition.Although this is an efficient synthesis strategy,the cytotoxic Cu catalyst greatly limits its application in drug synthesis.Therefore,it is of great significance to develop a novel and efficient method for the synthesis of fused triazole without Cu.A method for synthesis of dense fused triazole based on biofuran opening-ring strategy and ytterbium salt catalysis was developed.The cheap rare earth metal salt ytterbium trifluoromethylsulfonate was used instead of the toxic copper catalyst used in the husgen cyclization reaction,and the strong Lewis acid catalyst needed for the strategy of furan ring opening synthesis developed by our group before.The reaction conditions were simple,mild and easy to operate.A series of fused triazole compounds were synthesized successfully,including double-ring system,three-ring system,screw-ring system and bridge-ring system.These fused triazoles are new compounds that have not been reported.And the Z/E configuration of the side chain of the enone was effectively controlled by using different solvents.After most reactions are completed,clean products can be obtained without column chromatography purification,and the yield is high.We also found that the gram-scale synthesis of triazole compounds could be achieved when the catalyst dosage was reduced to lmol%.At the same time,the mechanism of Z/E configuration selectivity was studied by in situ 1HNMR.