The Cyclization Reactions Of Azides Initiated By Electrophiles

N-heterocycles, such as quinolines and indoles, are ubiquitously important organic compounds, which play vital role in pharmaceutical and agrochemical fields. A variety of reactions for synthesizing N-heterocycles, including condensation reaction, coupling reaction and cyclo-addition, have been achieved by using different nitrogen sources. Azide, performing nucleophilic character due to the nucleophilicity of the terminal nitrogen atom, is commonly used as an important nucleophiles.There are many kinds of electrophiles which can react effectively with nucleophiles. Diarylhypervalent iodine reagents belong to them, and usually can work as aromatic reagent to develop aromatic moiety. Protonic acids also show good electrophilic nature, and can provide proton to synthesize N-H indole compound.In this work, an efficient method was described to construct N-heterocycles by using copper catalyst, which induced diarylhypervalent iodine reagent to generate electrophilic moiety to cyclize with alkyne and azide. Protonic acid was also found to be able to induce the cascade cyclization to yield a variety of indoles without the assistance of transition-metal catalyst.Via the optimization of catalyst, solvent, temperature and reaction time, the scope of substrates was explored. The products are also determinded by the structure and character of substrates.An efficient copper-catalyzed intermolecular reaction had been developed for synthesis of quinoline derivatives. This method used Cu（I） salt as catalyst, ω-azide-1-alkyne as starting material, diarylhypervalent iodine reagent as electrophile, and the correspongding five-, six-, and seven-member ring fused quinoline products could be obtained in moderate to excellent yields and good selectivity. Mechanistically, the aryl cation generated from diarylhypervalent iodine reagent was supposed to undergo electrophilic attack to azide and subsequently alkyne to give the products.A convenient one-pot Cu（II）-catalyzed intermolecular reaction among diarylhypervalent iodine reagents, alkyne and arylazide to synthesize isoindole derivatives had been developed, which underwent [3+2] cascade cyclization. The mechanism may involve the procedures of alkyne activation, attack towards azide, cation migration, and sequentially Friedel-Crafts cyclization. This novel method proceeded with high regioselectivities, moderate yields and was tolerant with a broad scope of substrates.A one-pot metal-free electrophilic cyclization enabled by HNTf₂ has been developed to obtain indole derivatives in mild reaction conditions. This reaction gave moderate yields and high regionselectivities, which provides a new route to the formation of indole. HNTf₂ is determined in activating the alkyne and azide.Under mild conditions, the alkyne and azide could be activated smoothly by readily available electrophilic reagents of diarylhypervlent iodine reagent or protonic acid to obtain N-heterocycles. Hopefully, more effective electrophilic reagents should be explored to build significant N-heterocycles in the future.