Studies On Some Fluorine Chemistry And Free Radical Addition Reactions Ofallenes

Allenes are a class of compounds with a cumulated three-carbon unit bearing a remarkable substituent-loading capability. Much effort has already been made towards the nucleophilic additions, electrophilic additions, free radical additions, transition metal-catalyzed cyclizations, and enzyme-catalyzed reactions of allenes in our group. Based on these studies, the main theme of my dissertation may be divided into the following two parts:Part â… :Studies on some fluorine chemistry of allenes1. We have developed an efficient methodology for preparation of multi-substituted2-perfluoroalkyl furans and furan-2-yl perfluoroalkyl ketones:(a)2-perfluoroalkyl furans or furan-2-yl perfluoroalkyl ketones could be obtained highly selectively by adjusting the reaction conditions, such as the dosage of TfOH and H2O, and reaction temperature, from fully-substituted allenyl perfluoroalkyl ketones.(b)2-perfluoroalkyl furans could be efficiently prepared from cycloisomerization of tri-substituted allenyl perfluoroalkyl ketones with AuCl as the catalyst; in the spirit of the two-steps in one pot synthetic strategy, addition of TfOH and water into the same vessel would generate corresponding furan-2-yl perfluoroalkyl ketones through the tandem cycloisomerization-hydrolytic defluorination of allenyl perfluoroalkyl ketones. The oxygen atom of the carbonyl group of the newly formed furan-2-yl perfluoroalkyl ketones originates from the water according to the18O isotopic study.2. We have developed a highly regioselective iodofluorination reaction of mono-substituted and geminally disubstituted allenes, affording2-iodoallylic fluorides which have been demonstrated to be very attractive building blocks in organic synthesis. Part II:Studies on the free radical addition reactions of allenesWe have developed a highly regio-and stereoselective nitro-oxoamination reaction of mono-allenes via a radical process to form C-N and C-O bonds in one step, which could tolerate various functional groups and heterocycles affording a series of useful building blocks. This conversion would offer a practical strategy for the synthesis of intricate structure.In addition, we have realized the efficient preparation of perfluoroalkyl ketones via the1,2-addition reactions of alkenoates, alkynoates, and normal carboxylic acid esters with perfluoroalkyl Grignard reagents based on the synthetic methodology developed previously by Dr. He Guangke in our group.