Enantioselective Dreiding-Schmidt reactions: asymmetric synthesis and analysis of α-methylene-γ-butyrolactones
摘要:
The zinc/silver-graphite mediated Dreiding-Schmidt reactions between aldehydes and the 2-bromomethyl-acrylate derived sultamamides (+)/(-)-28 or (+)/(-)-30 gave the corresponding substituted alpha-methylene-gamma-butyrolactones with ee's up to 90%. Enantiomerically pure compounds were obtained by semipreparative HPLC using a chiral stationary phase. (C) 1997 Elsevier Science Ltd.
Lewis Acid Catalyzed Allylboration: Discovery, Optimization, and Application to the Formation of Stereogenic Quaternary Carbon Centers
作者:Jason W. J. Kennedy、Dennis G. Hall
DOI:10.1021/jo049773m
日期:2004.6.1
A full account of the development of the first catalytic manifold for the additions of allylboronates to aldehydes is described. The thermal additions (both diastereospecific and enantioselective) of 2-carboxyester 3,3-disubstituted allylboronates 1 to both aromatic and aliphatic aldehydes give biologically and synthetically important exo-methylene butyrolactones 2 containing a β-quaternary carbon
Brønsted Acid-Catalyzed Allylboration: Short and Stereodivergent Synthesis of All Four Eupomatilone Diastereomers with Crystallographic Assignments
作者:Siu Hong Yu、Michael J. Ferguson、Robert McDonald、Dennis G. Hall
DOI:10.1021/ja054171l
日期:2005.9.1
structures brings an end to the ambiguity of the original stereochemical assignments. Further to the TfOH-catalyzed allylboration, the synthetic route featured a number of remarkable observations: the surprising reactivity of 2-bromo-3,4,5-trimethoxybenzaldehyde, the subtle reagent control observed in the hydrogenation of an alpha-exo-methylene lactone intermediate, and the success of a difficult case of
本研究描述了一种新的 Brønsted 酸催化烯丙基硼酸化方法,适用于最困难的、电子失活的烯丙基硼酸酯和醛底物。该方法避免使用金属离子,而是使用简单且廉价的催化剂三氟甲磺酸。它作为一种互补的烯丙基硼化变体的有用性通过四步、立体发散合成从单一烯丙基硼酸酯中合成 eupomatilone-6 的所有四种非对映异构体。多达五个 X 射线晶体结构支持的立体化学的彻底证明结束了原始立体化学分配的模糊性。除了 TfOH 催化的烯丙基硼化反应之外,该合成路线还具有许多值得注意的观察结果:2-溴-3,4,5-三甲氧基苯甲醛的惊人反应性,
Triflic Acid-Catalyzed Additions of 2-Alkoxycarbonyl Allylboronates to Aldehydes. Study of Scope and Mechanistic Investigation of the Reaction Stereochemistry
作者:Tim G. Elford、Yuichiro Arimura、Siu Hong Yu、Dennis G. Hall
DOI:10.1021/jo062151b
日期:2007.2.1
The substrate scope and the effect of substrate on the observed inversion of stereoselectivity in the triflic acid-catalyzed allylboration reaction between 2-alkoxycarbonyl allylboronates and aldehydes are presented. A mechanisticinvestigation is described so as to confirm the involvement of a carbocation intermediate as the source of stereochemical inversion. This methodology allows a facile access