34982-21-3Relevant academic research and scientific papers
Hexameric resorcinarene capsule is a bronsted acid: Investigation and application to synthesis and catalysis
Zhang, Qi,Tiefenbacher, Konrad
supporting information, p. 16213 - 16219 (2013/11/19)
Molecular capsules have attracted interest as simple enzyme mimetics and several examples of catalytic transformations in water-soluble metal-ligand based systems have been reported. This is not the case for hydrogen-bond based molecular capsules, which in contrast can be employed in organic solvents. We describe herein our investigations of such a system: The resorcin[4]arene hexamer is one of the largest hydrogen bond-based self-assembled capsules and has been studied intensively due to its ready availability. We present evidence that the capsule acts as a reasonably strong Bronsted acid (pK a approximately 5.5-6). This finding explains the capsule's high affinity toward tertiary amines that are protonated and therefore encounter cation-π interactions inside the cavity. We were able to translate this finding into a first synthetic application: A highly substrate-selective Wittig reaction. We also report that this property renders the capsule an efficient enzyme-like catalyst for substrate selective diethyl acetal hydrolysis.
Comparison between electron transfer and nucleophilic reactivities of ketene silyl acetals with cationic electrophiles
Fukuzumi,Ohkubo,Otera
, p. 1450 - 1454 (2007/10/03)
The products and kinetics for the reactions of ketone silyl acetals with a series of p-methoxy-substituted trityl cations have been examined, and they are compared with those of outer-sphere electron transfer reactions from 10,10′-dimethyl-9,9′, 10, 10′- tetrahydro-9,9′-biacridine [(AcrH)2] to the same series of trityl cations as well as other electron acceptors. The C-C bond formation in the reaction of β,β-dimethyl-substituted ketene silyl acetal (1: (Me2C=C(OMe)OSiMe3) with trityl cation salt (Ph3C+ClO4-) takes place between 1 and the carbon of para-positon of phenyl group of Ph3C+, whereas a much less sterically hindered ketene silyl acetal (3: H2C=C(OEt)OSiEt3) reacts with Ph3C+ at the central carbon of Ph3C+. The kinetic comparison indicates that the nucleophilic reactivities of ketene silyl acetals are well correlated with the electron transfer reactivities provided that the steric demand at the reaction center for the C-C bond formation remains constant.
