Ultrasound- and microwave-assisted preparation of lead-free palladium catalysts: effects on the kinetics of diphenylacetylene semi-hydrogenation

The effect of environmentally benign enabling technologies such as ultrasound and microwaves on the preparation of the lead-free Pd catalyst has been studied. A one-pot method of the catalyst preparation using ultrasound-assisted dispersion of palladium acetate in the presence of the surfactant/capping agent and boehmite support produced the catalyst containing Pd nanoparticles and reduced the number of pores larger than 4 nm in the boehmite support. This catalyst demonstrated higher activity and selectivity. The comparison of kinetic parameters for diphenylacetylene hydrogenation showed that the catalyst obtained by using the one-pot method was seven times as active as a commercial Lindlar catalyst and selectivity towards Z-stilbene was high. Our work also illustrated that highly selective Pd/boehmite catalysts can be prepared through ultrasound-assisted dispersion and microwave-assisted reduction in water under hydrogen pressure without any surfactant

Catalyst Repurposing Sequential Catalysis by Harnessing Regenerated Prolinamide Organocatalysts as Transfer Hydrogenation Ligands

A catalyst repurposing strategy based on a sequential aldol addition and transfer hydrogenation giving access to enantiomerically enriched α-hydroxy-γ-butyrolactones is described. The combination of a stereoselective, organocatalytic step, followed by an efficient catalytic aldehyde reduction induces an ensuing lactonization to provide enantioenriched butyrolactones from readily available starting materials. By capitalizing from the capacity of prolineamides to act as both an organocatalyst and a transfer hydrogenation ligand, catalyst repurposing allowed the development of an operationally simple, economic, and efficient sequential catalysis approach

Biotin – The Chiral Challenge

In this contribution, the first examples of the catalytic highly enantioselective reduction of cyclic meso-anhydrides to lactones and of thioanhydrides to thiolactones are described. The N-benzyl protected key building blocks in the industrial synthesis of (+)-biotin were so far only accessible by usage of expensive reagents in multi-step procedures. In contrast, homogeneous catalytic enantioselective hydrogenation of the corresponding meso-anhydride mediated by a metal phosphane complex proceeds with high optical induction (ee >95%) and excellent yield. The catalytic system provides a generally applicable new method for the preparation of lactones from cyclic anhydrides

Large-Scale Production of Bioactive Ingredients as Supplements for Healthy Human and Animal Nutrition

In this review, synthetic strategies and the development of environmentally benign methods for the production of economically important vitamins, carotenoids, and nutraceuticals used as food and feed supplements are illustrated by selected examples. The application of efficient catalytic transformations in multi-step chemical syntheses of such natural products enables technically feasible and cost-effective processes. For the preparation of fat-soluble (isoprenoid) vitamins A and E and the water-soluble vitamin (+)-biotin, homogeneous metal catalysis, including enantioselective transformations, heterogeneous and enzymatic catalysis serve as key methodologies. In the area of carotenoids, general building concepts and coupling methods for the total synthesis of ?-carotene and astaxanthin are discussed. Biotechnological methods and isolation from natural sources are also employed successfully, as exemplified for the xanthophyll lutein and the antioxidant (–)-epigallocatechin gallate. Lastly, key steps of the chemical synthesis of the polyphenol resveratrol are highlighted