Studies On The Cascade Or Multicompo-nent Reactions Of Arynes

It has been paid much attention to obtain complex molecules in one-pot without isolation of intermediates employing commercial or easily prepared reagents. The highly reactive arynes tend to react with electron-rich molecules, which usually afford reactive intermediates. Further transformations of the intermediates with inter- or intramolecular reagents could result in the formation of more stable structures, which imply the feasibility to realize the cascade or multicomponent reactions (MCRs) involving arynes in one-pot.Due to the harsh generation conditions of arynes from the traditional precursors, the application of arynes had been limited. Since the inovation of mild generation conditions of arynes induced by fluoride ions, the nucleophilic additions, pericyclic reactions and transition-metal-catalyzed reactions of arynes have been developed in the recent years. Basing on the nucleophilic additions and pericyclic reactions of arynes, we developed some cascade and MCRs involving arynes generated from 1,2-eliminations of ortho-silylaryl triflates induced by fluorides. By these functional groups-tolerable procedures, benzocarbo- or heterocycles could be synthesized efficiently, which were difficult to obtain via other protocols. In the dissertation, we mainly focused on the subjects listed as below:1. Aryne insertions into the carbon carbonσbonds between Cαand carbonyl groups of acyclicβ-arylsulfonyl carbonyl compounds have been realized which were based on the nucleophilic additions of carbon nucleophiles with arynes. Employing cyclicβ-arylsulfonyl ketones instead of acyclic ones, the aim of ring expansions of cyclic moieties could be achieved. After the subsequent desulfonylation of the ring expansion products by Raney nickel reagent, seven- to ten-membered benzocyclic ketones could be obtained.2. Next, we developed the multicomponent reactions of pyridine derivatives,α-bromo carbonyl compounds and arynes which were based on the 1,3-dipolar cycloadditions of azomethine ylides with arynes. Pyrido[2,1-a]isoindoles or isoindolo[2,1-a]isoquinolines could be obtained via this one pot protocol. 3. Subsequently, a facile synthesis of 9-functionalized xanthenes and acridines based on the cascade nucleophilic addition-cyclic Michael addition process of arynes with phenols/anilines substituted withα,β-unsaturated groups at the ortho positions has been researched. The reaction has also been successfully extended to the synthesis of 9-spiro-xanthene and acridine derivatives with potential biochemical importance.4. Furthermore, a facile synthesis of 2H-chromenes and 9-functionalized phenanthrenes has been developed, which involves annulations of arynes with a,β-unsaturated compounds bearing different electron-withdrawing groups (EWGs). Depending on the nature of different EWGs, the reaction proceeds via different pathways:enals react with arynes through a tandem [2+2] cycloaddition-thermal electrocyclic ring-opening-6π-electrocyclization course to afford 2H-chromenes, while theβ-aroyl/acetyl/ethoxycarbonyl/cyano styrenes undergo a Diels-Alder reaction with arynes followed by aromatization to afford 9-functionalized phenanthrenes. To study the mechanism of the cascade reaction, the isotopic distribution reaction was conducted to reveal thatα,β-unsaturated compounds play important roles in dehydrogenation aromatization by abstracting hydrides from the intermediates of the initial Diels-Alder reactions.