Hydrogen-Bonding-Assisted Hydrochlorination Of Unactivated Alkynes

Chlorination has become a very important conversion in organic chemistry because of the large number of applications of chloride in production and life.Vinyl chloride is one of the most important group of chlorine-containing compounds.Vinyl chlorides are widely found in natural products,pharmaceuticals and agrochemicals,and also are valuable coupling partners in coupling reactions such as Stille coupling,Suzuki coupling,Sonogashira coupling,and Buchwald-Hartwig amination.In view of the important role of vinyl chlorides,organic chemists have paid great attention to their preparation methods.The traditional syntheses of vinyl chlorides include halogenations of carbonyl compounds and electrophilic chlorination of alkynes.They are not suitable for industrial applications due to the large amount of waste generated or the use of hazardous reagents.Subsequently,the indirect hydrochlorination strategies for activated alkynes,using acid chlorides,trimethylchlorosilanes(TMSCl)or metal chlorides as chlorine sources were reported.Recently,the mode of activating hydrogen halide using noble metal catalyst,such as ruthenium,palladium or gold and so on,have been greatly developed.However,all of the above methods require precious metal catalysts or activated alkynes,which do not conform to the principle of green and economy.Therefore,it is particularly urgent to find a simple,efficient,safe and green method for synthesizing vinyl chlorides.In addition,hexafluoro-2-propanol(HFIP)as a strong hydrogen bond donor solvent can form a hydrogen bond network or cluster,increasing the reaction rate.Moreover,the network has the advantages of being environmentally friendly and having high functional group resistance as compared with the using transition metals or super acid reagent.In this paper,the unactivated alkyne is used as substrate,and the hydrogen bond network formed by the HFIP in the solution is used to assist the reaction with TMSCl to directly realize the hydrochlorination reaction of the unactivated alkyne.The advantages of this work are as follows:Firstly,the hydrogen bond network is used to assist the reaction to achieve metal-free catalysis;Secondly,the experimental operation is simple,and the substrate range is broad(including terminal alkyne and internal alkynes);Morever,the product yield is extremely high,and the selectivity is good;In addition,the hydrogenation reaction of other halogens can also be achieved by this method.In addition,the reaction mechanism of this method is novel.In the other reaction modes of alkyne hydrochlorination reported,the general mechanism is that metal ions(M~+)or hydrogen protons(H~+)preferentially add to the alkyne,and the synergistic addition mechanism has never been reported.Here,we first proposed a novel synergistic addition reaction mode,which is different from the traditional metal cation(M~+)or hydrogen ion(H~+)first to the carbon-carbon bond addition reaction mode.