Study On The Functionalizaton Of Haloalkynes

Alkynes are one of the most important raw materials in organic synthesis, especially the development of the terminal alkynes have attracted the interest of the chemical researchers. Recently, several mild and convenient methods have been reported and thus have increased the attractiveness of haloalkynes in organic synthesis. This type of reaction has signicant advantages, the alkyne proceeds the coupling reaction with the halogen atom as the leaving group. Halogen atom could activate the triple bond and as the directing group, the triple bond occurs the electrophilic addition reaction. The halogen atom as the protective group replaces the terminal alkyne which proceeds the carbon-hydrogen functionalization reactions.Our objectives are to develop catalytic system or transiton-metal-free conditions to selectively form C-C, C-N, C-O and C-halogen bonds to create useful molecules such as the alkenes wih sp2 carbon-halogen bond and heterocycle compound, from readily available terminal alkynes or haloalkynes. Our research on activation and functionalisation of alkynes has led to a series of new results which will be presented in the following six chapters.In Chapter 1, we have introduced the reaction features of haloalkynes, the effective synthesis methods and the progress on selective C-C, C-N, C-O, C-halogen bond formation from haloalkyns, and introduces the significane of this research subject.In Chapter 2, we have presented the first example of a silver-catalyzed highly regio- and stereoselective difunctionalization reaction using simple terminal alkynes, which are easily available from commercial vendors, to afford the (Z)-β-haloenol acetate derivatives efficiently. The products could be functionalized through transition-metal-catalyzed reactions, such as Sonogashira reactions. The reaction affords the corresponding haloalkynes from terminal alkynes first and then transforms to the products via electrophilic addition with acetic anhydride through silver-catalysis.In Chapter 3, 2,5-disubstituted 3-iodofurans are readily prepared under very mild reaction conditions by the palladium/copper-catalyzed cross-coupling of (Z)-β-bromoenol acetates and terminal alkynes, followed by iodocyclization. The useful intermediates conjugated enyne acetates are obtained in high yields in the transformation. Aryl- and alkyl-substituted alkynes undergo iodocyclization in good yields. The resulting iodine-containing furans can be readily elaborated to 2,3,5-trisubstituted furans.In Chapter 4, a convenient and practical route to synthetically useful (Z)-2-halo-1-iodoalkene from the simple terminal alkynes in high regio- and stereoselectivity is described. The method shows excellent functional group compatibility, and high yields of the products are observed. Moreover, the useful intermediate is briefly transformed to the conjugated (Z)-haloenyne and (Z)- asymmetric enediyne in good yields.In Chapter 5, we have successfully developed an efficient synthetic approach to symmetrical 1,3-diynes from 1-haloalkynes under transition-metal-free conditions in DMF solvent. Especially, the homocoupling of 1-iodoalkynes are more effective for synthesis of the symmetrical 1,3-diynes. Although the haloalkynes are usually prepared from terminal alkynes by halogenation, the absence of any transition-metal and base can make the method more valuable. The mechanism shows that the reactions proceeded via radical coupling or redox-radical coupling way.In Chapter 6, a general and efficient method for the synthesis of a wide range of amides is described here. The reactions are conducted under convenient conditions and provides secondary and tertiary amides in moderate to excellent yields. A variety of amines and substituted alkynyl bromides are used to proved the scope of the reactions. Moreoverα-ketoamides could be readily achieved in DMF solvent.Finally the research summary, research achievements, and acknowledgement are introducted successively.