Synthesis Of Pyrrole Heterocyclic Compounds With The Participation Of Alkynes

Many natural products,active molecules,pesticides and functional materials have a pyrrole ring skeleton structure in the center of the structure.It is of great significance to realize the synthesis of heterocyclic compounds containing pyrrole ring structure with high efficiency,low price and environmental protection.Cyclization reactions involving alkynes in heteroatom-containing substrates have always been an important method for the construction of heterocyclic compounds.As a good C1 and N1 donor,isocyanides can be used to synthesize pyrrole heterocycles;the ipso-cyclization reactions of benzenes are also powerful tool for the synthesis of spiro products.In this paper,the palladium-catalyzed[2+2+1]cyclization reaction of isocyanides and alkynes and the ipso-cyclization reaction of N-（prop-2-yn-1-yl）aniline are mainly studied.This paper mainly includes as follows:1.Palladium-catalyzed imidoylation-triggered[2+2+1]cyclization of internal alkyne with isocyanidesA palladium-catalyzed[2+2+1]cyclization of internal alkynes with double isocyanides is described.Under 5 mol%of tetrakis（triphenylphosphine）palladium,2equivalents of cesium carbonate,toluene and protection of nitrogen,N-propynyl-2-halogenanilines can be convert into desired compounds for 8-12 h,at110℃.This facile procedure is efficient for synthesizing various pyrrolo[3,2-c]quinolin-2-amine compounds（21 examples）for the first time with a yield of 29%-74%.In addition,under 5 mol%of palladium trifluoroacetate,3equivalents of cesium carbonate,10 mol%of N-（p-methoxyphenyl）-2-acetyl acetamide,and 1,1-dichloroethane,1-alkynyl-8-halogen naphthalenes can be convert into various acenaphtho[1,2-b]pyrrole-8-amines（21 examples）by reacting for 10-12 h at 90℃under the protection of nitrogen.The reaction worked well with a broad reaction scope.In the process,it is believed that sequential double isocyanide insertion,6-exo-dig cyclization of alkyne,and addition of an imino group are involved.2.ZnBr₂/Oxone-mediated ipso-cyclization of N-（prop-2-yn-1-yl）anilineThe selective synthesis of 1-azaspiro[4.5]deca-3,6,9-trien-8-ones from N-p-methylbenzenesulfonyl-N-（propyl-2-yne-1-yl）aniline was developed（17examples）.The transformation proceeds smoothly in a mixed solvent including CH₃CN and deionized water when 1 equivalent ZnBr₂ and 2 equivalents of Oxone are employed,and the corresponding spiro compound can be prepared with a yield of50%-77%.Mechanism studies show that the reaction proceeds in a regioselective manner via a radical ipso-cyclization pathway.