Studies On Hydration And Cycloaddition Reactions Of Electron-Deficient Allenes

Allenes show high reactivity in organic synthesis due to the presence of the cumulated dienes structure. Their diverse reaction patterns are mainly influenced by the different substituents on each of the terminal carbon atoms. In this thesis, we focused on the studies on hydration and cycloaddition reactions of electron-deficient al enes.Part one: The hydration of unsaturated compounds represents one of the most attractive methods for the construction of carbonyl group. The developed methods mainly require transition- metals, ligands as well as strong acid catalysts. Allenes are also employed as the substrates in hydration, however, the substrate scope is very limited to the electron-rich allenes, including the requirement of transition-metals and Br?nsted acid catalysts. We developed a protocol for the hydration of electron-deficient allenic esters and ketones by employing O xone as the reagent. A wide range of 1,3-dicarbonyl compounds could be obtained in 54-85% yields. This reaction has the character of the nontoxic and recoverable reagents, mild conditions and easy operation.Part two: Diazo compounds are a class of compounds with high reactivity. They are used as the metal carbene precursors to form C-X?X = C, N, O, S, Si? bonds through transition- metal-catalyzed X-H bond insertion. In addition, they are used as the 1,3-dipoles, which could undergo cycloaddition with a variety of unsaturated compounds to form heterocyclic compounds. We recently developed a cycloaddition of trifluorodiazoethane with various electron-deficient allenes, giving the trifluoromethylpyrazoles in high yields. In this thesis, we continued to investigate the cycloaddition reaction of non-trifluoromethyl-substituted diazo compounds with electron-deficient allenes. In the presence of Et₃N, a highly chemo- and regioselective [3+2] cycloaddition was achieved, affording a wide range of multi-substituted pyrazoles in 70-95% yields.