Studies On The Addition And Cyclization Reactions Of Electron-deficient Allenes And Alkynes

Great efforts have already been made on the cyclization of functionalized allene in our group. Based on these research findings, the main theme of my dissertation is on the cyclization reaction of electron-deficient allenes, including electrophilic addition cyclizations of 2,3-allenoates and 1,2-allenyl ketones and coupling cyclization reactions of 2,3-allenoic acids and 2,3-allenamides. The chemoselective control of these reactions has been achieved. Besides, the fixation of carbon dioxide with 2,3-allenamides and alkynamides has also been developed.1. In the electrophilic addition reaction of 2,3-allenoates with PhSeCl, water was proved to be the crucial factor in control of chemoselectivity. Butenolides and 4-oxo-2(E)-alkenoates could be obtained respectively with high selectivity by adjusting reaction conditions.2. Furans or 2,5-dihydrofuran-2-ols could be obtained in the electrophilic cyclization reaction of 1,2-alkenyl ketones with iodine when different substrates were used. Allenyl prerfluoroalkyl ketones showed higher reactivity and gave higher yields as compared to ordinary allenyl alkyl ketones.3. Coupling cyclization reactions of 2,3-allenoic acids in the presence of electron-deficient alkynes were continuously studied based on the research of Dr. Zhenhua Gu. When alkynones were used as substrates, a one-pot synthesis of E-4-(3'-oxo-1'-alkenyl)-2-(5H)-furanones was established. Though a mixture of Z/E isomers was obtained in the first step, it could be converted to the thermodynamically stable E isomer by heating in DMSO. When propiolates served as the substrates, a 1:1 adduct product could be formed by controlling reaction conditions. For alkynyl phosphonate, only E isomer of the 1:1 adduct product was observed.4. We have developed a PdCl2/NaI/K2CO3-catalyzed highly stereoselective homodimeric coupling-cyclization reaction of 2,3-allenamides. The addition of K2CO3 plays an important role in this transformation. Additionally, we have established a protocol of the Pd-catalyzed coupling reaction of 2,3-allenamides with propargylic carbonates affordingβ-allenyl furanamines. Preliminary mechanism study showed that this reaction was probably initiated by the Pd(0) species. Furanamine-type products were obtained indicating that both of the two reactions proceeded through the O-attack pathway.5. In the fixation and transformation of carbon dioxide, we developed a very simple and mild protocol for the reaction of carbon dioxide with 2,3-allenamides. In the absence of metal catalyst, the starting materials were converted into 1,3-oxazine-2,4-diones with a CO2 balloon. On the basis of this report, the fixation of carbon dioxide with 2-alkynamides was also established. Meanwhile, a one pot three-component reaction of alkynamides, CO2 and electrophilic agents such as NIS and NBS was developed to afford halogen-substituted oxazoles.