Ni-Catalyzed Deprotection Of Olefinic Protecting Groups From Phenols/Alcohols

Phenols/alcohols are widely present in various natural compounds and are important intermediates in organic synthesis.The protection and deprotection of phenols/alcohols is an indispensable part of organic synthesis even more.The allyl protection method has many advantages such as low cost,good effect,strong acid-base tolerance,so it is an important phenols/alcohols protection method.In recent years,many researchers have reported deprotection methods for allyl protcting groups,which are mainly divided into non-catalytic method and transition metal catalytic method.The existing transition metal catalyzed method mainly uses metal palladium as the catalyst,but there are some problems such as high reaction cost and severe reaction conditions;at the same time,the deprotection method of long chain olefin protective groups of phenols is relatively single,and only the ruthenium metal has been reported.To solve the problem of removing olefin protective groups,a novel transition metal catalyzed method is used for the removal of olefinic protecting groups in this paper.After optimization tests of the catalyst,ligand,solvent and other conditions,it was found that the olefin protective groups can be efficiently removed under relatively mild reaction conditions by using 5%mol of NiC12(DME)as the catalyst and 10%mol of LI(6,6-dimethyl-2,2-bipyridine)as a ligand,1.5 times equivalent of B2Pin2 and 2.0 times equivalent of LiOtBu are added simultaneously.Meanwhile an appropriate amount of methanol is added,DMA and H2O are used as a mixed solvent,under the reaction at 30?.At the same time,the corresponding substrate and carbon chain length were expanded.The results show that the reaction conditions have strong functional group compatibility,which can be compatible with various electron-withdrawing and electron-donating functional groups,and can effectively remove an olefin protecting group of six carbon atomic length of phenols and allyl ethers of alcohols.Finally,the corresponding mechanism study is carried out.The results show that olefin is a necessary condition for removing the protecting group and the quaternary carbon atom cannot exist on the carbon chain.This mechanism may be due to the migration of alkenes in the molecules.