Pd/Cu Synergistic Borylation Of Allenylic Carbonates:Efficient Synthesis Of 2-Boryl 1,3-Butadienes

2-Boryl 1,3-butadiene compounds are important synthetic reagents in organic synthesis.They have been successfully used in the synthesis of various organic compounds and are also widely used in the synthesis of natural drug molecules.Therefore,the development of efficient methods for the synthesis of 2-boryl 1,3-butadiene derivatives has always been one of the hot topics in the synthetic chemistry community.This dissertation mainly studies the synthesis of2-boryl 1,3-butadiene from 2,3-alienol derivatives.In recent years,the use of 2,3-alienols to synthesize molecular backbones with a wide range of applications has become a popular synthetic strategy.Among them,2-boronyl-1,3-butadiene was successfully synthesized by copper-catalyzed S_N2’boronation.However,this method has the following two disadvantages:1)The reaction conditions are not easy to achieve,and the method must use NHC carbene ligand catalyst,which is expensive and not a commercial reagent,and needs to be synthesized by itself,which greatly reduces the universality of the reaction;2)When asymmetric 2,3-allyl alcohol derivatives are used,the stereoselectivity is relatively low or relies on sterically bulky substituents,limiting the applicable scope of the reaction.Therefore,there is an urgent need to develop synthetic methods that are more universal and have better stereo control.In this paper,we adopted a Pd/Cu bimetallic synergistic catalysis mechanism,using isopropyl 2,3-alienol carbonate as the substrate,B₂pin₂ as the double boron reagent,and P（OEt）₃as the ligand.Synthesis of 2-boryl 1,3-butadiene under neutral conditions with high yield and good selectivity.The reagents required for this reaction are all commercial reagents and are readily available.The experimental study showed that for the symmetric 2,3-alienol isopropyl carbonate substrate（1.0 equiv.）,the optimal reaction conditions were:strictly anhydrous and oxygen-free environment,Pd₂dba₃（2.5 mol%）,Cu I（5 mol%）,B₂pin₂（1.5 equiv）,P（OEt）₃（15mol%）,activated 3?MS 4 grains,THF（0.1 M）at room temperature After 24 hours of reaction,the reaction has a good substrate scope and high yield;for asymmetric 2,3-alienol isopropyl carbonate substrate（1.0 equivalent）,the optimal reaction:strictly anhydrous and anoxic Ambient,Pd₂dba₃（2.5 mol%）,Cu I（10 mol%）,B₂pin₂（1.5 equiv）,P（OEt）₃（15 mol%）,activated 3?MS 4 granules,THF（0.1 M）,reacted at room temperature for 24 hours,with good selectivity,only Z-form 2-boryl 1,3-butadiene was formed.