Highly Efficient Bond-Forming Reactions utilizing Ynolates

我们发现烯醇酸酯与酮反应生成β-内酯烯醇酸酯，烯醇酸酯开环形成四取代烯烃。在这个研究项目中，我们研究了通过油酸酯进行烯烃的细节，包括范围和限制。1)芳基烷基酮、芳基芳基酮和烷基烷基酮的烯烃化：芳基烷基酮的烯烃化使产物具有e选择性。在芳基芳基酮的情况下，富电子芳基倾向于被定位为反式到羧基。Pinacolon使烯烃具有z选择性。2)烷基硅烷的烯烃化：实现了完美的z选择性。乙烯基硅烷的这种烯烃化是第一次成功的高效烯烃化，得到了具有高通用性的四取代烯烃。产物很容易转化为其他四取代烯烃。例如，乙烯基硅烷与碘化芳基的Hiyama偶联成功地提供了不加氟的偶联产物。由于羰基氧的配位更容易形成高价硅烷，因此硅碳键被激活。利用这种活化作用，发现了通过亲电裂解C-Si键合成硅内酯的新方法。3)酯类的烯化：由于酯类羰基的亲性较差，用常规试剂如Wittig试剂等难以烯化酯类羰基。烯醇酯很容易与酯反应生成烯烃产物（烯醇醚），收率高，e -选择性高。E/Z选择性是由β-内酯烯醇酯开环（电环反应）中的扭矩选择性决定的。转矩选择性由跃迁态的2^<和>轨道相互作用决定。理论计算揭示了几种轨道相互作用：芳基的π轨道和碳氢键的σ轨道稳定了过渡态中断开的碳氧键的σ^*轨道，使其向外旋转；C-Si、C-O和C-C键的σ^*轨道稳定了断开的碳氧键的σ轨道，使其向内旋转。少

We have found that ynolates react with ketones to afford β-lactone enolates, which are ring-opened to form tetrasubstituted olefins. In this research project, we investigated the details of the olefinations via ynolates including scope and limitations.1)Olefination of aryl alkyl ketones, aryl aryl ketones, and alkyl alkyl ketones : the olefination of aryl alkyl ketones gave the products with E-selectivity. In the case of aryl aryl ketones, the electron-rich aryl groups preferred to be positioned to be trans to carboxyl groups. Pinacolon furnished the olefin with Z-selectivity.2)Olefination of acylsilanes : Perfect Z-selectivity was achieved. This olefination giving vinylsilanes is the first successful efficient olefination giving tetrasubstituted olefins with high generality. The products are easily converted into other tetrasubstituted olefins. For examples, Hiyama coupling of the vinylsilanes with aryl iodide successfully provided the coupling products without adding fluoride. Becaus … More e of formation of hypervalent silanes by coordination of carbonyl oxygen, the Si-C bond is activated. Taking advantage the activation, novel synthesis of silalactones via electrophilic cleavage of C-Si bonds was found.3)Olefination of esters : it has been difficult in olefination of ester carbonyls by conventional reagents like Wittig reagents, due to the poor electrophlicity of the carbonyls. Ynolates easily react with esters to give the olefinated products (enol ethers) in good yield with high E-selectivity.The E/Z selectivity is determined by torquoselectivity in ring-opening (electrocyclic reactions) of the β-lactone enolates. The torquoselectivity is governed by 2^<nd> orbital interactions in the transition states. Theoretical calculations disclosed several orbital interactions : π-Orbitals of aryl groups and σ-orbitals of C-H bonds stabilize the σ^* orbital of the disconnecting C-O orbital in the transition states to make them rotate outward, σ^* Orbitals of C-Si, C-O, and C-C bonds stabilize the σ orbital of the disconnecting C-O bond to make them rotate inward. Less