已经研究了在各个环位置被烷基取代的2-(苯磺酰基)-2-(4-(((三甲基甲硅烷基)甲基)-4-戊烯基)四氢吡喃自发分子内环化的立体选择性。对于4-和6-甲基衍生物,螺环中心的形成仅与甲基相反。5-甲基实例的结果是3.7:1 syn / anti拆分。对于反式4,6-二甲基衍生物,取代基以增强方式起作用,并且在一个方向上唯一地直接环化。顺式和反式双环醚均在中间体氧鎓离子的pi表面上与角氢同位而闭合。根据相关联的氧鎓离子的偏爱,可以通过椅子状或扭曲舟状过渡态进行亲核捕获,从而使结果合理化。
Acid-Triggered, Acid-Generating, and Self-Amplifying Degradable Polymers
摘要:
We describe the 3-iodopropyl acetal moiety as a simple cleavable unit that undergoes acid catalyzed hydrolysis to liberate HI (pK(a) similar to -10) and acrolein stoichiometrically. Integrating this unit into linear and network polymers gives a class of macromolecules that undergo a new mechanism of degradation with an acid amplified, sigmoidal rate. This trigger-responsive self amplified degradable polymer undergoes accelerated rate of degradation and agent release.