Decrypting Transition States by Light: Photoisomerization as a Mechanistic Tool in Brønsted Acid Catalysis
作者:Polyssena Renzi、Johnny Hioe、Ruth M. Gschwind
DOI:10.1021/jacs.7b02539
日期:2017.5.17
catalysis, experimental insight into transition states is very rare, and most of the mechanistic knowledge is gained by theoretical calculations. Here, we present an alternative approach (decrypting transition state by light = DTS-hν), which enables the decryption of the transition states involved in chiral phosphoric acids catalyzed addition of nucleophiles to imines. Photoisomerization of double bonds
尽管对映选择性布朗斯台德酸催化方法具有广泛的适用性,但对过渡态的实验性了解却很少,而且大部分机械知识是通过理论计算获得的。在这里,我们(由光= DTS-解密过渡态呈现的另一种方法ħ ν),这使得能够参与手性磷酸催化加成亲核试剂到亚胺过渡态的解密。双键的光异构化被用作机械工具。对于此类反应,可能存在四种途径(I Z型,I E型,II Z型,II E型),根据亚胺构型(E-或Z-亚胺)和亲核攻击位点(顶部或底部)。我们证明了亚胺双键可以在反应过程中被光(365 nm LED)异构化,从而导致反应速率和对映选择性变化的特征指纹图谱。该特征指纹图案直接与变换中涉及的过渡状态相关。I型ž和II型Ž被证明是酮亚胺的不对称转移氢化的竞争性途径,而在亲核加成乙酰丙酮到的Ñ -Boc保护的醛亚胺I型Ë和II型Ë活跃。对于酮亚胺的还原,观察到加速至高达177%的反应速率。我们的实验结果得到了量子化学计算和非共价相互作用分析的支持。