Studies Of Aryne Involved Reactions

Arynes are important intermediates in organic synthesis,which can be widely applied in the synthese of natural products,biological alkaloids and functional materials.However,the harsh reaction conditions for their preparations partially limited their applications in the organic synthesis.More recently,following the developments of mild preparation methods of arynes,the great interest has been aroused for the studies of novel aryne reactions.There are three main kinds of reaction patterns of arynes,namely precyclic reactions,nucleophilic additions and transition-metal catalyzed transformations.In the presenting dissertation,we investigated a variety of reactions involving arynes, which include:1.The tandem Diels-Alder cyeloaddtions of benzynes and substituted imidazolesA kind of reactions can be used for the preparations of 9-aminoanthracenes mediated by benzynes and substituted imidazoles will be reported in this chapter. The target products can be obtained in moderate yields when the reactions were conducted in 50℃for 12 h,and the great influence on the chemoselectivities arising from the ratio of the two rection substrates has been revealed.The tandem reaction has illustrated wide tolerance to various mono and disubstituted imidazoles. Mechanism investigation has revealed a kind of tandem Diels-Alder/retro-Diels-Alder/Diels-Alder reaction sequence to rationalize the experiment reasults,and the as-produced products have displayed great probabilities in the applications in the area of fluorescence materials.2.Palladium-Catalyzed tandem earbopalladation/C-H activation reaction of benzynesThe combination of aryne-mediated carbopalladation and C-H activaton of indoles has developed a kind of new reaction pathway can be used for the synthesis of the skeleton of benzophenathridines.The reaction can be carried out in high yield at 110℃in refluxing equivalent ratio mixture of acetonitrile and toluene in the presence of biphosphine ligand,and can tolerance various substituted indoles.Two hypothesis mechanisms have been brought forward to rationalize the experiment results,and the UV-vis adsorbed properties as well as fluorescent properties of the products has been measured and the result demonstrates that all the products own good fluorescent performances.3.The three-component reactions of benzyens,α-bromo-acetylbenzenes and pyridinesIn this chapter,we will reported a kind of new three component reaction mediated by benzynes under mild conditions,which can deliver the structure of pyrido[2,1-a]isoindoles.The final structure of the product has been confirmed by the monocrystal diffraction,and the reaction conditions have been optimized,as well as the scope and the limitations have been investigated under the optimized conditions. A plausible mechanism has been raised,which involving the 1,3-dipolar cycloadditon pathway of benzyne and the in-situ formed 1,3-dipole booting from pyridine andα-bromo-acetylbenzene.More interestingly,the pyrido[2,1-a]isoindole structure can isomerize into the charge separated form fully in some solvents,which can severely disturb the resolution of structure of the products.4.Copper catalyzed three component assembly of benzynes,terminal alkynes and allylic chloridesFor the first time,we report the copper-catalyzed reaction of arynes.Useful 1,6-enynes can be synthesized efficiently from benzyes,terminal alkynes and allylic chlorides through the copper catalyzed procedure.During the studies of this procedure,we find that the excess of allylic chlorides can suppress the formation of byproduct,and the addition of base can do a bigger favor to this suppression.Various allylic chloride can be used in the three component assembly,and so can various terminal alkynes.A postulated mechanism has been submitted to rationalize the reaction and can be described as below:the copper catalyst can react with the terminal alkynes to form the copper(Ⅰ)intermediated,and the following carbocupration of benzyne can deliver the arylcopper species;finally,the oxidative addition and reductive elimination sequence of allylic chlorides to the arylcopper can lead to the 1,6-enyne products.5.The cocatalyzed tandem reactions of terminal alkyne / benzyne / benzyne by copper and goldGold complex has been found catalyze the benzyne tranformations in cooperation with cuprous iodide.The same two components,namly termainal alkynes and benzynes,can be transformed into different products under different catalysts such as palladium,copper and gold,and in which it is the first time to report the Au/Cu cocatalyzed reactions of benzynes to generate the alkynlated biphenyl products.The reaction has been proved to be efficient towards many terminal alkynes and benzynes,and high yields can be obtained.A kind of mechanism containing the benzyne-Au complex has been postulated.The intramolecular hydroarylation of the as-described alkynlated biphenyl produnt has also been reported.6.The cycloaddtion reactions between benzynes and methylenecyclopropanesThe two reactive intermediates,namely arynes and methylenecyclopropanes, has been proved to react with each other under catalyst free conditions.The reaction can be conducted under room temperature but deliver low yields.Two types of reaction pathway can occur decided by the structure of methylenecyclopropanes.For the diaryl substituted methylenecyclopropanes,[4+2]cycloadditions will be in occurrance in contrast to the[2+2+2]cycloadditons leading by the monoaryl methylenecyclopropanes.The two different substitution-depended reaction pathway can be explained by two distinct mechanism,and the electron effect as well as the sterecally hindered effect of the second aryl group will be responsible for the reaction diversity.7.Tandem reaction of bromoacetynes and Oxazolidine-2-thionesThe unprecedented tandem reactions of bromoacetynes and Oxazolidine-2-thiones will constitute the main content of the eighth chapter.The tandem reaction can smoothly proceed with moderate yields at 140℃in dry xylene and critically impacted by the addition of diamine ligand.Wide substrate scope not only to bromoacetynes but also Oxazolidine-2-thiones has been illustrated.The precise structure of the product was confirmed by the ORTEP analysis and proved the reaction to be completely configuration retained pattern.The physiological activation analysis has revealed that these products possess some bacterium-inhibition effect to some extent.