Stereocontrol of Novel Radical Reactions

1.在Et_3B存在下，三(2-呋喃)锗能有效地与烯烃发生加成反应。将三(2-呋喃)锗加成到硅烯醇酸盐上，然后消除了硅氧基和硅氧基，为酮转化为烯烃提供了一条新的途径。芳基镁化合物与四氢呋喃通过碘代烷-乙基四氢呋喃体系的简单偶联反应得到2-芳基四氢呋喃。此外，在二甲醚中用乙基溴化镁处理烯丙基β-碘缩醛，得到四氢呋喃甲基镁化合物。Schwartz试剂是一种在三乙基硼烷存在下还原有机卤化物的有效自由基链载体。用Cp_2Zr(H)Cl对卤代缩醛进行还原自由基环化反应，得到了产率较高的环化产物。Cp_2ZrCl_2与红铝和三乙基硼烷的催化反应也是成功的。有机卤化物在乙醇水溶液中，在自由基引发剂和碱的存在下与膦酸反应，以高产率产生相应的还原产物。此外，氚代膦酸是有机卤代反应的有效链状载体。碘乙酸烯丙酯在水中的原子转移自由基环化反应比在苯中的环化反应更有效。通过从头计算，揭示了水在碘乙酸烯丙酯环化反应中溶剂效应的来源。在Ni(II)催化剂存在下，溴化乙烯发生两电子还原反应和三氟化乙烯酯发生两电子还原反应，可以实现卤代乙烯的立体选择性羧化反应生成α，β-不饱和酸。作为此类研究的一部分，我们还开发了一种新的简便的方法，利用微波辐射立体选择性地合成(E)和(Z)-卤化乙烯。

1. Tri(2-furyl)germane in the presence of Et_3B adds to alkenes efficiently. The addition of tri(2-furyl)germane to silyl enolates followed by elimination of germyl and siloxy moieties provides a new route for the conversion of ketones into alkenes.2. A facile coupling reaction between arylmagnesium compounds and THF by an iodoalkane-EtMgBr system provides 2-aryltetrahydrofurans. In addition, treatment of allyl β-iodoacetals with ethylmagnesium bromide in DME provides tetrahydrofuranylmethylmagnesium compounds.3. Schwartz reagent is 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 provides the cyclized products in good to excellent yields. Reaction employing a catalytic amount of Cp_2ZrCl_2 combined with Red-Al and triethylborane is also successful.4. Treatment of organic halides with phosphinic acid in aqueous ethanol in the presence of a radical initiator and a base yields the corresponding reduced products in high yields. In addition, deuterated phosphinic acid is an efficient chain carrier for the radical deuteration of organic halides.5. Atom transfer radical cyclization of allyl iodoacetate is much more efficient in water than in benzene. Ab initio calculation was conducted to reveal the origin of the solvent effect of water in the cyclization of allyl iodoacetate.6. Stereoselective carboxylation of vinyl halides to give α,β-unsaturated acids could be achieved by two-electron reduction of vinyl bromides in the presence of Ni(II) catalyst and by two-electron reduction of vinyl triflates using an electrochemical method. As one of such studies, we also developed a new and convenient method for a stereoselective synthesis of (E)- and (Z)-vinyl halides by using microwave irradiation.