Sequential Norrish TypeII Photoelimination and Intramolecular Aldol Cyclization of -Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives
Sequential Norrish TypeII Photoelimination and Intramolecular Aldol Cyclization of -Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives
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DOI：
10.1002/chem.201301230
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发表时间：
2013-07-29
影响因子：
4.3
通讯作者：
Suarez, Ernesto
中科院分区：
文献类型：
--
作者：
Alvarez-Dorta, Dimitri;Leon, Elisa I.;Suarez, Ernesto
nono-2，3-diulose衍生物的最内层羰基的激发通过用可见光照射引发连续的Norrish II型光消除和羟醛环化过程，最终得到多官能化的环庚醇。重排已被证实，通过分离稳定的无环photoenol中间体，可以独立地环化热5-（enolexo）-exo-esterol非催化的羟醛缩合反应，具有高的非对映选择性。在这最后一步中，发现的1，5-氢原子转移的大氘动力学同位素效应似乎表明，羟醛缩合反应通过协调周环机制运行。由于各种构型的吡喃糖的现成可用性，该方案已被用于研究吡喃糖环取代基对羟醛缩合环化反应的非对映选择性的影响。与其他吡喃糖环收缩方法相比，不需要过渡金属试剂，并且通过使用可见光和适度加热（0至60摄氏度）简单地发生顺序重排。
The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish typeII photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 degrees C).