Convergent Versus Divergent Three-Step Synthesis of the First (4-Aminophenoxy)alkanoic Acid–Based Tripodal Melamines

Starting from N-(4-hydroxyphenyl)acetamide (Paracetamol, convergent approach) or from cyanuric chloride in reaction with 4-aminophenol (divergent approach), two synthetic routes toward novel tripodal N-substituted melamines as s-triazine derivatives of (4-aminophenoxy)acetic acid or of 4-(4-aminophenoxy)butyric acid are comparatively defined. The key steps consist of Williamson etherification of N-masked forms of 4-aminophenol and acidic hydrolysis of the N- and/or O-protected (4-aminophenoxy)alkanoic segments.     

Highly Efficient Etherification and Oxidation of Aromatic Alcohols Using Supported and Unsupported Phosphorus Pentoxide as a Heterogeneous Reagent

A highly efficient procedure for etherification and oxidation of aromatic alcohol is described using unsupported and supported P₂O₅ on alumina and/or silica gel. The silica gel and alumina proved to be the most suitable support among the supports examined in our experiments. It was illustrated that the etherification and oxidative performance in reactions depend largely upon variables including reaction temperature, the nature of the P₂O₅ used (supported or unsupported P₂O₅), and whether solvent-free conditions are applied. It was shown that P₂O₅ not only can convert the aromatic alcohols into corresponding ethers and/or aldehyde and ketone but also can convert aromatic ethers into aldehyde or ketone via oxidative cleavage. Finally, quantum mechanical calculations were performed to rationalized these events, and it was indicated that aldehyde and ketone are more favorable products on the basis of the heat of formation (ΔH_f).

Synthesis of (S)-3-hydroxytetrahydropyran from l-glutamic acid

A concise synthesis of (S)-3-hydroxytetrahydropyran from natural l-glutamic acid has been developed. The intramolecular etherification starting from 1,5-diol was promoted by trifluoromethanesulfonic anhydride. The clinnamates of the alcohols were prepared for accurately determining the optical purity by HPLC method.     

负载铯催化剂上苯酚与甲醇醚化制苯甲醚

研究了不同酸碱中心、载体、前躯体和负载量对负载铯催化剂上苯酚与甲醇醚化制苯甲醚反应行为的影响。结果表明,碱性中心比酸性中心具有更高的苯甲醚选择性,碱性中心的阳离子影响催化剂的苯甲醚选择性。载体影响铯离子的电子结合能,从而影响催化剂的醚化活性;铯离子的电子结合能越低,催化剂醚化活性越低;载体影响催化剂强碱性位数量,从而影响苯甲醚选择性;强碱性位数量越多,副反应越容易发生,苯甲醚选择性越低。不同前躯体制备的Cs/Si O2由于表面相对铯原子数量不同而活性不同;Cs/Si O2的单层负载量为1.0 mmol/g,超过单层负载量后催化剂的平均活性显著下降。     

Carbohydrate O-benzylation through trialkylsilane-mediated reductive etherification

Abstract

Trialkylsilane-mediated reductive etherification has been actively used in carbohydrate O-benzylation since it emerged decades ago. In this review, we first trace the origin, development, and possible reaction mechanism of trialkylsilane-mediated reductive etherification, then focus on its typical applications in carbohydrate synthesis including regioselective protection, one-pot combinatorial protection, and one-pot protection-glycosylation. At the end, we discuss its limitations and potentials in global benzylation.     

微波促进姜黄素羟乙基醚化反应

在微波加热条件下,研究了姜黄素与2-氯乙醇亲核取代反应中辐射时间、辐射温度、溶剂种类、缚酸剂种类与用量、反应浓度以及反应物用量比因素对该羟乙基醚化反应的影响.研究结果表明:当该反应在水介质中使用底物用量3倍的KOH为反应的缚酸剂以及使用底物用量2.2倍的2-氯乙醇时,在95℃下微波辐射6min可获得最佳的反应结果,此时,姜黄素双羟乙基醚的产率达76.4%.研究结果为姜黄素双羟乙基醚的快速制备提供了一条有效的途径.