Catalytic Upgrading of Acetaldehyde to Acetoin Using a Supported N-Heterocyclic Carbene Catalyst

We report the catalytic synthesis of 3-hydroxy-2-butanon (acetoin) from acetaldehyde as a key step in the synthesis of C4-molecules from ethanol. Facile C-C bond formation at the α-carbon of the C2 building block is achieved using an N-heterocyclic carbene (NHC) catalyst. The immobilization of the catalyst on a Merrifield's peptide resin and its spectroscopic characterisation using solid-state Nuclear Magnetic Resonance (NMR) is described herein. The immobilization of the NHC catalyst allows for process intensification steps and the reported catalytic system was subjected to batch recycling as well as continuous flow experiments. The robustness of the catalytic system was shown over a maximum of 10 h time-on-stream. Overall, high selectivity S>90 % was observed. The observed deactivation of the catalyst with increasing time-on-stream is explained by ex-situ 1H solution-state, as well as 13C and 15N solid-state NMR spectra allowing us to develop a deeper understanding of the underlying decomposition mechanism of the catalyst.

Construction of enantiopure imine bridged benzo[c]azepinones by a silver(i) and chiral N-heterocyclic carbene multicatalytic reaction sequence of N′-(2-alkynylbenzylidene)hydrazides and cyclopropanecarbaldehydes

A novel and efficient method for the synthesis of enantiopure bridged benzo[c]azepinone compounds has been developed by metal/N-heterocyclic carbene multicatalysis.

N-Heterocyclic Carbene/Palladium Cascade Catalysis: Construction of 2,2-Disubstitiuted Benzofuranones from the Reaction of 3-(2-Formylphenoxy)propenoates with Allylic Esters

The cascade catalysis involving N-heterocyclic carbene (NHC) and palladium/ligand was demonstrated. In the presence of a triazolium salt, palladium catalyst, and base, the reaction of 3-(2-formylphenoxy)propenoates and allylic esters proceeded efficiently under mild conditions to afford 2-allylbenzofuran-3-one-2-acetates in moderated to good yields. An asymmetric cascade catalysis was achieved when (R)-BINAP was employed as a chiral ligand, producing enantiomerically enriched 2,2-disubstitiuted benzofuran-3-one derivatives with an ee up to 81%.

Efficient Domino Hydroformylation/Benzoin Condensation: Highly Selective Synthesis of α-Hydroxy Ketones

An improved domino hydroformylation/benzoin condensation to give α-hydroxy ketones has been developed. Easily available olefins are smoothly converted into the corresponding α-hydroxy ketones in high yields with excellent regioselectivities. Key to success is the use of a specific catalytic system consisting of a rhodium/phosphine complex and the CO2 adduct of an N-heterocyclic carbene.