Development of new radical reactions in aqueous media

点击翻译按钮获取中文摘要

Triethylborane-induced hydrometalation of alkynes proceeds in an anti manner to afford the corresponding (Z)-alkenylmetal compounds stereoselectively, where dichloroindium hydride would play a key role. A variety of functional groups including hydroxy, carbonyl, and carboxy groups were tolerant under the reaction conditions. Following iodolysis and cross-coupling reaction of the (Z)-alkenylmetal species show the usefulness of this strategy.An allylgallium reagent is found to be effective for radical allylation of α-iodo or α-bromo carbonyl compounds. Treatment of benzyl bromoacetate with allylgallium, prepared from allylmagnesium chloride and gallium trichloride, in the presence of triethylborane in THF provided benzyl 4-pentenoate in good yield. The addition of water as a cosolvent improved the yields of allylated products. It was revealed that the allylgallium species resists immediate decomposition on exposure to water.Bis (cyclopentadienyl) zirconium chloride hydride (Schwartz reagent) proved to be an efficient radical chain carrier for the reduction of organic halides in the presence of triethylborane. Reductive radical cyclization of halo acetals with Cp_2Zr(H)Cl generated in situ from Cp_2ZrCl_2 and sodium bis (2-methoxyethoxy) aluminium hydride (Red-Al) provided the cyclized products in good to excellent yields. Reaction employing a catalytic amount of Cp_2ZrCl_2 combined with Red-Al and triethylborane was also successful.