Studies On Application Of Three Highly Reactive Intermediates:Arynes, β-Oxodithioesters And Isocyanides

Arynes are highly reactive intermediates poised to offer numerous applications in organic synthesis. Due to the presence of the C=C triple bond in a six-membered ring in arynes, the unhybridized p-orbitals are distorted and they are no longer parallel to each other as in normal alkynes. This strain created by the triple bond in the ring makes them highly reactive. The chemical properties of the β-oxodithioester can be determined by the presence of three nucleophilic and two electrophilic centres. Due to the presence of those active centres, the reactions of β-oxodithioesters with various dielectrophilic reagents resulted to the formation of various heterocyclic systems. Isocyanides have an almost unique set of properties, shared only with CO and carbenes, in that they can react with both nucleophiles and electrophiles on the same carbon atom.In the first chapter, we summarized the extensive applications of three highly reactive intermediates (arynes,β-oxodithioesters and isocyanides) in organic synthesis respectively.In the second chapter, a straightforward method was established to synthesize 2H-chromen-2-imine derivatives by starting with alkynes and β-oxo-N,S-acetal, which had not been reported in literatures. It is noteworthy that ort/?o-Quinone methides, arising from a formal [2+2] cycloaddition between arynes and DMF, were found to facilely undergo a [4+2] cycloaddition with β-oxo-N.S-acetal in this reaction. The optimized conditions for this reaction are as follows:2 equiv of arynes,1 equiv of β-oxo-N,S-acetal 4 equiv of KF, and DMF as the solvent at 80℃ under a N2 atmosphere.In chapter three, a facile and efficient method for the chemoselective synthesis of benzo[e]pyrazolo[1,5-c][1,3]thiazine derivatives has been developed by tandem Ullmann coupling reactions of β-oxodithioesters (ODEs) with 3-(2-bromoaryl)-1H-pyrazoles in C-S bond formation manner, in which ODEs play dual roles as both a substrate and a ligand. A series of benzo[e]pyrazolo[1,5-c][1,3]thiazine derivatives were provided in good to excellent yields with Cul as the copper source in the presence of NaOH in CH3CN at 80 ℃ under a N2 atmosphere.In chapter four, a novel Co(III)-catalyzed intermolecular Pauson-Khand-type reaction of two isocyanides with 2-alkynylaniline afforded pyrrolo[2,3-b]indole derivatives. In this reaction one isocyanide with 2-alkynylaniline in situ generated carbodiimide intermediates, and then carbodiimide intermediate reacted with another isocyanide to pyrrolo[2,3-b]indole derivatives in the Co(III)-catalyzed. The optimized conditions for this reaction are as follows:2.5 equiv of isocyanides,1 equiv of 2-alkynylaniline,1 equiv of Co(acac)3,1 equiv of Zn and DCE as the solvent at 80 ℃ under a O2 atmosphere.