isobutyric anhydride in the presence of 10 mol % of a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at -50 degrees C gave the 4-O-isobutyryl derivative as the sole product in 98% yield. Thus, chemoselective acylation, favoring a secondaryhydroxylgroup in the presence of a free primary hydroxylgroup, and regioselective acylation, favoring one of three secondaryhydroxylgroups, took place
D-glucopyranoside with isobutyric anhydride in the presence of the catalysts gave the 6- O-acylate as the major product via acylation of a primary hydroxylgroup. On the other hand, the 4- O-acylate was obtained as the major product in 66% regioselectivity via acylation of the secondaryhydroxylgroup at C-4 on treatment of octyl β- D-glucopyranoside with isobutyric anhydride in the presence of a PPY catalyst. Use
Carboxylate Anions Accelerate Pyrrolidinopyridine (PPy)-Catalyzed Acylation: Catalytic Site-Selective Acylation of a Carbohydrate by in Situ Counteranion Exchange
Acylpyridinium ions have been known as catalytically active species in acylation reactions catalyzed by 4-dimethylaminopyridine and its analogues. Acylpyridinium carboxylates were found to be 800–1300 times more reactive than the corresponding acylpyridinium chlorides. A catalytic cycle was developed, in which acylpyridinium carboxylates were generated by in situ counteranion exchange from the acylpyridinium
A Pyridine‐Acetylene‐Aniline Oligomer: Saccharide Recognition and Influence of this Recognition Array on the Activity as Acylation Catalyst
作者:Yuki Ohishi、Toshikazu Takata、Masahiko Inouye
DOI:10.1002/cplu.202000603
日期:2020.12
of foldamer‐type hosts, various kinds of recognition arrays are expected to be developed. Here, a pyridine‐acetylene‐aniline unit is presented as a new class of a saccharide recognition array. The conformational stabilities of this array were analyzed by DFT calculation, and suggested that a pyridine‐acetylene‐aniline oligomer tends to form a helical structure. An oligomer of this array was synthesized
为了创建折叠式主机的新功能,预计将开发各种识别阵列。在这里,吡啶-乙炔-苯胺单元被作为一种新型的糖类识别阵列。通过DFT计算分析了该阵列的构象稳定性,表明吡啶-乙炔-苯胺低聚物趋于形成螺旋结构。合成了该阵列的低聚物,并通过1 H NMR测量证实了其与辛基β -D-吡喃葡萄糖苷的缔合。UV / Vis,圆二色性和荧光滴定实验表明,它对非极性溶剂中的辛基糖苷具有很高的亲和力(K a = 10 4至10 5 M -1)。该低聚物在碱性条件下相对稳定,因此预期该阵列可用于糖的衍生化。一种由4-(二烷基氨基)吡啶连接的吡啶-乙炔-苯胺低聚物被证明催化辛基糖苷的酰化作用。
Perfectly regioselective acylation of a cardiac glycoside, digitoxin, via catalytic amplification of the intrinsic reactivity
作者:Keisuke Yoshida、Takumi Furuta、Takeo Kawabata
DOI:10.1016/j.tetlet.2010.07.036
日期:2010.9
Organocatalytic regioselective acylation of digitoxin has been developed. This method provides the 4'''-O-manoacylate as the sole product without the concomitant formation of diacylates. The extremely high regioselectivity was assumed to be the result from the combined effects of the high intrinsic reactivity of C(4''')-OH and catalyst-promoted regioselective acylation of the same hydroxy group. (C) 2010 Elsevier Ltd. All rights reserved.