Neighbouring Ester (Amide) Groups-participated Selective Functionalization Of Aryl Acetylenes

Alkyne-based precursor is an important research topic in modern organic chemistry.Notable examples include the industrial materials and pharmaceutical molecules that synthesized by alkyne-based transformations.The functionality of alkynes is highlighted by its capability to activate C-C triple bond using precious metal or Lewis acid as catalyst.Over the past years,studies of alkyne functionalization such as alkyne intramolecular cyclization and carbonylation reaction have sparked considerable interests in synthetic chemistrys.Significantly,selective functionalization of aromatic alkynes through neighboring group-participation is widely considered as a effective strategy.In this work,We have successfully developed a novel method for neighbouring ester（amide）groups-participated and selective functionalization of aryl acetylene in a metal-free condition.The main are as follows:1.Neighbouring ester-participated the dicarbonylation of aryl acetyleneWe report herein a neighboring ester-participated dicarbonylation of aryl acetylene in a metal-free catalyzing condition.Benzil-o-carboxylates is an important oxygen-hybrid intermediates.To promote the conversion of o-alkynylbenzoates into benzyl-o-carboxylates,we employed Tetrabutylammonium bromide（TBAB）used as the bromine source and potassium peroxymonosulfonate（Oxone）used as the oxidant,respectively.The resulting diketone compounds in the synthesis of quinoxalines could be achieved by a one-pot reaction of o-alkynylbenzoate and o-phenylenediamine.Mechanistic studies suggest that the whole process is composed of the bromocyclic intermediates generated from an electrophilic bromide-mediated neighboring ester-participating bromocyclization and the ring-opening dibromohydrative compounds.The source of oxygen in the dicarbonylation of alkynes has been confirmed by H₂O¹⁸-tracing experiments.Whereas silica gel-based hydrolysis of the dibromohydrative products and water are found to be the main and secondary sources,respectively.2.Neighboring ester-participated 2,4-dibromohydration of conjugated enynesWe have developed a regioselective neighboring ester-participating 2,4-dibromohyd-ration of conjugated enynes for the synthesis of 2-（2,4-dibromobut-2-enoyl）benzoate in the presence of TBAB and Oxone.2,4-dibromohydration compounds is recognized as an important synthon towards phthalazin-1（2H）-one and the natural product Shihunine.H₂O¹⁸-tracing experiments indicated that the neighboring ester group is participated in the 2,4-dibromohydration of conjugated enynes.While the oxygen atom of ester is transferred into the C-C triple bond to form the keto carbonyl group in the product.The method has the advantages of short reaction time,high selectivity and mild conditions.In addition,we pioneered the construction of a new 2,4-dibromohydration compound skeleton method.3.Neighboring amide-participated 5-exo-dig cyclization of aryl acetyleneWe have developed a regioselective amide-participating 5-exo-dig oxo-cyclization of aryl acetylene.The use of TBAB in combination with Oxone,resulted in 5-exo-dig bromocyclization of o-alkynylbenzamide to form tproceeded for the synthesis of isobenzofuran-1-imine and isobenzofuranones derivatives at a given temperature.Additionally,the resulting isobenzofuranones was used as an intermediate of drug molecules and natural products to synthesize phthalazin-1（2H）-ones and various substituted isobenzofuranones derivatives.The reaction is composed of amidyl oxygen radical derived from single electron oxidation of neighboring amide,as well as isobenzofuran-1-imine radical intermediate derived by amidyl oxygen radical.The radial and radial intermediate subsequently added to the triple bond in a fashion of 5-exo-dig.The reaction is demonstrated to be metal-free,environmentally friendly and highly regioselectivity.