Applications Of Hydromagnesiation Reaction Of Alkynes In Stereoselective Synthesis Of Alkenes

This dissertation describes the preparation of the corresponding vinyl Grignard reagents by hydromagnesiation of alkynes and the applications of the corresponding vinyl Grignard reagents in high stereoselective synthetic reactions.The hydromagnesiation of alkynylsilanes in diethyl ether at 25℃in the presence of a catalytic amount of Cp2TiCl2 for 6 h give the (Z)-α-silylvinyl Grignard reagents. We studied the cross-coupling reaction of (Z)-α-silylvinyl Grignard reagents with (E)-α-iodovinyl sulfides catalyzed by Pd(PPh3)4, which provided a new route to stereoselective synthesis of (Z,Z)-2-silyl-3-arylthio- substituted 1,3-dienes. The present method has the advantages of readily available starting materials, straightforward and simple procedures, mild reaction conditions, high regio- and stereoselectivity, good yields.The hydromagnesiation of alkylarylacetylenes in diethyl ether at 25℃in the presence of a catalytic amount of Cp2TiCl2 for 2 h give the (E)-α-arylvinyl Grignard reagents. We studied the cross-coupling reaction of (E)-α-arylvinyl Grignard reagents with alkenyl halide catalyzed by Pd(PPh3)4. It was found that the reaction proceeded smoothly at room temperature, which provided a new route to stereoselective synthesis of (Z,E)-2-aryl-substituted 1,3-dienes. We also carried out the reaction of (E)-α-arylvinyl Grignard reagents with aldehydes or ketones in diethyl ether. It was found that the reaction also proceeded smoothly under mild reaction conditions in good yields, providing a new route to the stereoselective synthesis of (E)-2,3-disubstituted allylic alcohols. The present methods for synthesis of (Z,E)-2-aryl-substituted 1,3-dienes and (E)-2,3-disubstituted allylic alcohols have the advantages of readily available starting materials, straightforward and simple procedures, mild reaction conditions, high regio- and stereoselectivity , good yields.