The Research Of Some New Reactions With High Atom-Utilization

This thesis focuses on exploiting some new reactions with high atom-utilization, which includes the highly atom-economical acid-catalyzed Friedel-Crafts reaction of a-hydroxyesters or a-hydroxyketones with electron-rich (hetero)arenes, tandem Wittig/conjugate reduction sequence which internally utilizes the by-product Ph3PO as the catalyst, and the development of chiral pyridinebisoxazolines bearing a C4 bulky shielding group for the highly enantioselective copper-catalyzed cycloaddition of phosphole-based dialkynes with azides.First, a highly atom-economical Friedel-Crafts reaction of a-hydroxyesters or a-hydroxyketones with electron-rich (hetero)arenes is developed, affording α-quaternary carbonyl compounds in rich diversity. Cheap and easily available HCIO4 (70%, aq) is used as the catalyst. This method tolerates a variety of (hetero)aromatic compounds, such as anisoles, thiophenes, pyrroles and indoles. The thus obtained products can be readily elaborated. Under the same condition, a-hydroxyesters react with substituted phenols to furnish various unsymmetrical 3,3-diaryl or 3-aryl-3-alkyl benzofuranones through a tandem Friedel-Crafts/lactonization reaction, which is confirmed by NMR studies.Second, a tandem Wittig/conjugate reduction reaction from phosphorane and ethyl trifluoropyruvate is established, allowing highly chemoselective synthesis of a-CF3-y-keto esters. Internally recycling by-product Ph3PO to activate HSiCl3 plays the key role in the chemoselective conjugate reduction of β-CF3-β-ester substituted enones. This tandem reaction can be further extended for the facile synthesis of 6-substituted 4,5-dihydro-3-trifluoromethyl pyridazinones.’A tandem Wittig/conjugate reduction/Paal-Knorr reaction from phosphorane and 1,2-dicarbonyl compounds is also developed, which provides an efficient method for the synthesis of di-or trisubstituted furans. This sequence first utilizes the by-product Ph3PO from Wittig step to catalyze the 1,4-reduction of enone intermediate using HSiCl3, and then recycles the by-product HCl generated in quenching trichlorosilyl ether intermediate to promote the Paal-Knorr reaction. The whole atom-utilization of the process is improved by using by-products twice.Third, chiral pyridinebisoxazolines bearing a C4 bulky shielding group are developed, which proves to be powerful for the highly enantioselective copper-catalyzed cycloaddition of phosphole-based dialkynes with azides. The chiral Cu(Ⅰ) complex derived from newly developed ligand and CuBr not only allows the efficient synthesis of P-stereogenic phospholes bearing a terminal alkyne and a 1,2,3-triazole moiety, but also suppresses the formation of undesired diazole effectively. The thus obtained chiral phospholes can be readily elaborated via transformations based on the alkyne group and P=O double bond.