使用单一催化剂产生分子复杂性,其中必要的活化模式随着反应的进行而依次利用,是合成中一个有吸引力的指导原则。这要求每个底物转位都暴露出一种催化剂活化模式 (AM),所有先前或未来的中间体都对这种模式具有抵抗力。虽然麦克米伦将烯胺和亚胺离子活化的美丽结合体现了这一概念,但当代催化其他领域的例子仍然难以捉摸。在这里,我们将此策略扩展到有机光化学。通过利用 (-)-核黄素的两种离散光化学活化模式,可以分别通过能量转移 (ET) 和单电子转移 (SET) 激活途径依次诱导异构化和环化。这种催化方法已被用于模拟香豆素生物合成途径,该途径具有关键的光化学 E → Z 异构化步骤。由于随后的基于 SET 的环化消除了对预官能化芳环的需要,这构成了药学重要支架的新断开连接。
Development of a palladium catalyzed addition of boronic acids to alkynyl esters: synthesis of trisubstituted olefins as single isomers
作者:Alexander Graham Bush、Jojo Liu Jiang、Philippa R. Payne、William W. Ogilvie
DOI:10.1016/j.tet.2009.08.029
日期:2009.10
Very small phosphine ligands allow access to single isomer trisubstituted olefins from alkynyl esters with complete control of both stereochemistry and regiochemistry. This method provides a convenient synthesis of single isomer trisubstituted olefins without requiring olefin templates.
A Bio-Inspired, Catalytic<i>E</i>→<i>Z</i>Isomerization of Activated Olefins
作者:Jan B. Metternich、Ryan Gilmour
DOI:10.1021/jacs.5b07136
日期:2015.9.9
Herein, Nature's flavin-mediated activation of complex (poly)enes has been translated to a small molecule paradigm culminating in a highly (Z)-selective, catalytic isomerization of activated olefins using (-)-ribo-flavin (up to 99:1 Z/E). In contrast to the prominent Z -> E isomerization of the natural system, it was possible to invert the directionality of the isomerization (E -> Z) by simultaneously truncating the retinal scaffold, and introducing a third olefin substituent to augment A1,3-strain upon isomerization. Consequently, conjugation is reduced in the product chromophore leading to a substrate/product combination with discrete photophysical signatures. The operationally simple isomerization protocol has been applied to a variety of enone-derived substrates and showcased in the preparation of the medically relevant 4-substituted coumarin scaffold. A correlation of sensitizer triplet energy (ET) and reaction efficiency, together with the study of additive effects and mechanistic probes, is consistent with a triplet energy transfer mechanism.