自组装的超分子主体[Ga 4 L 6 ] 12−(1 ; L = N,N‐双(2,3-‐二羟基苯甲酰基)‐1,5‐二氨基萘)催化Nazarov环化1,3-戊二烯醇的过程高效率。催化反应的进行速度比背景反应快一百万倍,与某些酶体系中观察到的增加相当。进行了详细的研究以阐明戊二烯醇的催化的和未催化的纳扎罗夫环化的反应机理。动力学分析和18O交换实验暗示了一种机制,其中包封,质子化和从基质中流失的水分是可逆的,然后进行不可逆的电环化。尽管在未催化反应中电环化是决定速率的,但在组装催化反应中水损失和电环化的障碍几乎相等。对催化和未催化反应的能量学分析表明,过渡态稳定化显着促进了催化反应速率的显着提高。
Enzymelike Catalysis of the Nazarov Cyclization by Supramolecular Encapsulation
摘要:
The water-soluble, self-assembled, tetrahedral assembly K12Ga4L6 (L = 1,5-biscatecholamidenaphthalene) catalyzes the Nazarov cyclization of 1,3-pentadienols with extremely high levels of efficiency. The catalyzed reaction proceeds over a million times faster than the background reaction, an increase comparable to those observed in some enzymatic systems. This catalysis operates under aqueous conditions at mild temperatures and pH, and the reaction is halted by the addition of an appropriate inhibitor. This unprecedented rate enhancement is attributed to both the stabilization of protonated reaction intermediates and the effect of constrictive binding on the bound guest.
Enzyme-like Control of Carbocation Deprotonation Regioselectivity in Supramolecular Catalysis of the Nazarov Cyclization
作者:Courtney J. Hastings、Mikael P. Backlund、Robert G. Bergman、Kenneth N. Raymond
DOI:10.1002/anie.201105325
日期:2011.11.4
The kinetically controlled, regioselectivedeprotonation of cyclopentenyl cations is mediated by encapsulation within a metal–ligand assembly. The regiochemistry of the deprotonation step determines which one of two possible products is formed. Moreover, subtle differences in the stereochemistry of the encapsulated cation switch the selectivity of this process (see scheme).