9 research outputs found
A Chiral Sulfoxide-Based CâH Acid
We report the design and synthesis of a strong, chiral, enantiopure sulfoxide-based CâH acid. Single crystal X-ray analysis confirms the proposed structure and its absolute configuration. The new motif shows a high acidity and activity in BrĂžnsted and Lewis acid catalyzed transformations. So far,only little to no enantioselectivities were achieved
1,1,3,3-Tetratriflylpropene (TTP): A Strong, Allylic CâH Acid for BrĂžnsted and Lewis Acid Catalysis
Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic CâH acid for BrĂžnsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, HosomiâSakurai, and FriedelâCrafts acylation reactions. X-ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP
Nitrone/Imine Selectivity Switch in BaseâCatalysed Reaction of Aryl Acetic Acid Esters with Nitrosoarenes: Joint Experimental and Computational Study
Approaching sub-ppm-level asymmetric organocatalysis of a highly challenging and scalable carbon-carbon bond forming reaction
The chemical synthesis of organic molecules involves, at its very essence, the creation of carbon-carbon bonds. In this context, the aldol reaction is among the most important synthetic methods, and a wide variety of catalytic and stereoselective versions have been reported. However, aldolizations yielding tertiary aldols, which result from the reaction of an enolate with a ketone, are challenging and only a few catalytic asymmetric Mukaiyama aldol reactions with ketones as electrophiles have been described. These methods typically require relatively high catalyst loadings, deliver substandard enantioselectivity or need special reagents or additives. We now report extremely potent catalysts that readily enable the reaction of silyl ketene acetals with a diverse set of ketones to furnish the corresponding tertiary aldol products in excellent yields and enantioselectivities. Parts per million (ppm) levels of catalyst loadings can be routinely used and provide fast and quantitative product formation in high enantiopurity. In situ spectroscopic studies and acidity measurements suggest a silylium ion based, asymmetric counter-anion-directed Lewis acid catalysis mechanism
Synthesis of Polyurethanes Using Organocatalysis: A Perspective
Organocatalysis has become an invaluable tool for polymer synthesis, and its utility has been demonstrated in ring-opening, anionic, zwitterionic, and group-transfer polymerizations. Despite this, the use of organocatalysis in other polymerization reactions such as step-growth polymerizations remains underexplored, relative to more traditional metal-based polymerizations. Recently, the use of organic bases such as guanidines, amidines, N-heterocyclic carbenes, and organic "strong or super-strong" Bronsted acids to catalyze the synthesis of metal-free polyurethanes has shown to be competitive to commercially widely used dibutyltin dilaurate and dibutyltin diacetate catalysts. This Perspective article highlights recent advances in organocatalyst design for isocyanate-based polyurethane synthesis with the aim of comparing the activity and selectivity of each of the new catalytic reactions to each other and the traditional metal-based catalysts. The article also draws attention to new trends in isocyanate-free polyurethane synthesis and the key role that organocatalysis is playing in these innovative polymerization processes