extremely facile and rapid C-Si bondcleavage in supercritical water. The rapid C-Si bondcleavage occurred even with robust unactivated tetraalkylsilanes. The control experiments revealed the dramatic difference between supercritical and subcritical conditions and that between supercritical water and supercritical methanol, attesting to a unique reactivity of supercritical water in C-Si bondcleavage.
Stereospecific lithium-halogen exchange of alkenyl iodides was performed upon treatment with butyllithium in non-polar solvents such as hexane, benzene, and toluene at 25 °C to provide alkenyllithiums quantitatively with retention of the configuration. Metal-iodine exchange of allenyl iodides with n-BuLi, i-PrMgBr or Et2Zn was also performed effectively to afford the corresponding allenylmetallic reagents
Olefination of carbonyl compounds with gem-dizincioalkanes, bis(iodozincio)methane, 1,1-bis(iodozincio)ethane, and bis(bromozincio)methyltrimethylsilane, afforded the corresponding olefins in good to excellent yields.
Partial reduction of alkynes to (Z)-alkenes is achieved with the low-valent group 5 metal reagents prepared from MtlCl5 (Mtl = Nb or Ta) and zinc in a mixed solvent of DME (or THF) and benzene.
The reduction of alkenyl halides with tributyltinhydride in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium has been studied. Alkenyl iodides reacted easily with tributyltinhydride at 25°C to give the corresponding hydrocarbons stereoselectively. However, the reaction of alkenyl bromides were sluggish at 25°C and needed heating at 75°C to complete.