5 research outputs found
Prevalence of Diarylprolinol Silyl Ethers as Catalysts in Total Synthesis and Patents
Diarylprolinol silyl ethers are among the most utilized stereoselective organocatalysts for the construction of complex molecules. With their debut in 2005, these catalysts have been applied in numerous method developments primarily leveraging enamine and iminium-ion catalysis. These strategies have extended into the preparation of complex molecules in both academic and industrial settings. This Review intends to give an overview of the application of the diarylprolinol silyl ether catalysts in total synthesis. Furthermore, integration of these catalysts in patent literature is also disclosed highlighting the versatility of the catalytic system
Iron-Catalyzed Hydrogenation of Amides to Alcohols and Amines
This article describes
the iron-catalyzed hydrogenation of unactivated
amides. Under the optimal conditions, a PNP-ligated Fe catalyst affords
25–300 turnovers of products derived from C–N bond cleavage.
This reaction displays a broad substrate scope, including a variety
of 2° and 3° amide substrates. The reaction progress of <i>N,N</i>-dimethylformamide hydrogenation has been monitored in
situ using Raman spectroscopy. This technique enables direct comparison
of the relative activity of the Fe-PNP catalyst to that of its Ru
analogue. Under otherwise identical conditions, the Fe and Ru catalysts
exhibit rates within a factor of 2
Tandem Amine and Ruthenium-Catalyzed Hydrogenation of CO<sub>2</sub> to Methanol
This Communication describes the
hydrogenation of carbon dioxide
to methanol via tandem catalysis with dimethylamine and a homogeneous
ruthenium complex. Unlike previous examples with homogeneous catalysts,
this CO<sub>2</sub>-to-CH<sub>3</sub>OH process proceeds under basic
reaction conditions. The dimethylamine is proposed to play a dual
role in this system. It reacts directly with CO<sub>2</sub> to produce
dimethylammonium dimethylcarbamate, and it also intercepts the intermediate
formic acid to generate dimethylformamide. With the appropriate selection
of catalyst and reaction conditions, >95% conversion of CO<sub>2</sub> was achieved to form a mixture of CH<sub>3</sub>OH and dimethylformamide
Base-Free Iridium-Catalyzed Hydrogenation of Esters and Lactones
Half-sandwich iridium bipyridine
complexes catalyze the hydrogenation
of esters and lactones under base-free conditions. The reactions proceed
with a variety of ester and lactone substrates. Mechanistic studies
implicate a pathway involving rate-limiting hydride transfer to the
substrate at high pressures of H<sub>2</sub> (≥50 bar)
An Asymmetric SN2 Dynamic Kinetic Resolution
The SN2 reaction exhibits the classic Walden inversion, indicative of the stereospecific backside attack of the nucleophile on the stereogenic center. Observation of the inversion of the stereocenter provides evidence for an SN2-type displacement. However, this maxim is contingent on substitution proceeding on a discrete stereocenter. Here we report an SN2 reaction that leads to enantioenrichment of product despite starting from a racemic mixture of starting material. The enantioconvergent reaction proceeds through a dynamic Walden cycle, involving an equilibrating mixture of enantiomers, initiated by a chiral aminocatalyst and terminated by a stereoselective SN2 reaction at a tertiary carbon to provide a quaternary carbon stereocenter. A combination of computational, kinetic, and empirical studies elucidates the multifaceted role of the chiral organocatalyst to provide a model example of the Curtin–Hammett principle. These examples challenge the notion of enantioenriched products exclusively arising from predefined stereocenters when operating through an SN2 mechanism. Based on these principles, examples are included to highlight the generality of the mechanism. We anticipate the asymmetric SN2 dynamic kinetic resolution to be used for a variety of future reactions