O-羧酸酐 (OCA) 的开环聚合可为聚酯提供多种官能团,而传统上这些官能团很难通过内酯聚合获得。典型的开环催化剂不可避免地会发生大多数 OCA 单体的外消旋化,这阻碍了高度等规结晶聚合物的合成。在这里,我们描述了一种有效的双功能单分子有机催化,用于无差向异构化的 OCA 选择性开环聚合。同一分子中两个活化基团的紧密相邻会产生放大的协同效应,从而允许使用温和的碱,从而使聚合的差向异构化最小化。由双功能单分子有机催化剂介导的 manOCA 单体(来自扁桃酸的 OCA)的开环聚合产生高度全同立构的聚(扁桃酸)(PMA),其分子量受控(高达 19.8 kg mol-1)。PMA 的两种对映异构体的混合在该区域产生了结晶立体复合物的第一个例子,它在 150 °C 左右显示出不同的 Tm 值。值得注意的是,双功能催化剂具有防潮、可回收和易于使用的特点,允许可持续和可扩展地合成有规立构功能聚酯。
Chemistry of cephalosporin antibiotics. 30. 3-Methoxy- and 3-halo-3-cephems
作者:Robert R. Chauvette、Pamela A. Pennington
DOI:10.1021/jm00238a017
日期:1975.4
the 3-hydroxy compounds to 3-methoxy-3-cephem derivatives. Removal of the ester-protecting group at the C4-carboxyl afforded a select group of cephalosporins with direct halo and methoxy substitution at C3. A number of these compounds are potent antibiotics.
Preparation of Stereoregular Isotactic Poly(mandelic acid) through Organocatalytic Ring-Opening Polymerization of a Cyclic<i>O</i>-Carboxyanhydride
作者:Antoine Buchard、David R. Carbery、Matthew G. Davidson、Petya K. Ivanova、Ben J. Jeffery、Gabriele I. Kociok-Köhn、John P. Lowe
DOI:10.1002/anie.201407525
日期:2014.12.8
as an organocatalyst for the ring‐opening polymerization (ROP) of the cyclic O‐carboxyanhydride (manOCA). Polymers with a narrow polydispersity index and excellent molecular‐weight control were prepared at ambient temperature. These highly isotactic chiral polymers exhibit an enhancement of the glass‐transition temperature (Tg) of 15 °C compared to the racemic polymer, suggesting potential future application
Optically active 3-substituted 2, 3-dihydro-1, 3, 4-thiadiazoles (2-5) were synthesized by the reaction of aldehyde methylthio(thiocarbonyl)hydrazones (1) and chiral 5-substituted 1, 3-dioxolane-2, 4-diones. The absolute configurations of compounds 2-5 were deduced from their circular dichroism spectra.
Neue β-Lactam-Antibiotika. Cephem-Derivate mit elektronenanziehenden Substituenten in 3-Stellung. Modifikationen von Antibiotika. 14. Mitteilung
作者:Heinrich Peter、Beat Müller、Hans Bickel
DOI:10.1002/hlca.19750580825
日期:1975.11.5
New β‐lactam antibiotics. Cephem derivatives with electron withdrawing substituents at position 3Oxidation of the 3‐formyl‐2‐cephem compound 1 according to Corey [6] gave 2‐cephem‐3‐carboxylic esters 4a, b, c (Scheme 1), which proved to be useful intermediates for the synthesis of cephalosporins bearing in position 3 a methoxycarbonyl group (10a, b, c, d / Scheme 2) or a carboxy group (20, 25, 30/Schemes 3, 4). The 3‐formyl‐3‐cephem compounds 31a, b could be transformed into cyano‐ (33a) or methoxyiminomethyl‐ (36a, c, d) cephems (Scheme 5), which represent further examples of cephalosporins with electron withdrawing groups in position 3.