A gold-triggered dearomative spirocarbocyclization/Diels-Alder reaction cascade towards diverse bridged N-heterocycles

A rapid approach for the diversity-oriented synthesis of complex bridged polycyclic N-heterocycles from readily available starting materials in two operational steps has been developed. This strategy firstly introduces molecular diversity by an Ugi four-component reaction, and then achieves these bridged N-heterocycles via an efficient gold-triggered chemo- and diastereoselective cascade non-oxidative ortho-dearomative spirocarbocyclization/Diels-Alder reaction sequence. The application of microwave irradiation for this cascade process efficiently shortens the reaction time to 10 minutes and improves the diastereoselectivity.status: publishe

Hydrogen borrowing : towards aliphatic tertiary amines from lignin model compounds using a supported copper catalyst

Upcoming biorefineries, such as lignin-first provide renewable aromatics containing unique aliphatic alcohols. In this context, a Cu-ZrO2 catalyzed hydrogen borrowing approach was established to yield tertiary amine from the lignin model monomer 3-(3,4-dimethoxyphenyl)-1-propanol and the actual lignin-derived monomers, (3-(4-hydroxyphenyl)-1-propanol and dihydroconiferyl alcohol), with dimethylamine. Various industrial metal catalysts were evaluated, resulting in nearly quantitative mass balances for most catalysts. Identified intermediates, side and reaction products were placed into a corresponding reaction network, supported by kinetic evolution experiments. Cu-ZrO2 was selected as most suitable catalyst combining high alcohol conversion with respectable aliphatic tertiary amine selectivity. Low pressure H2 was key for high catalyst activity and tertiary amine selectivity, mainly by hindering undesired reactant dimethylamine disproportionation and alcohol amidation. Besides dimethylamine model, diverse secondary amine reactants were tested with moderate to high tertiary amine yields. As most active catalytic site, highly dispersed Cu species in strong contact with ZrO2 is suggested. ToF-SIMS, N2O chemisorption, TGA and XPS of spent Cu-ZrO2 revealed that imperfect amine product desorption and declining surface Cu lowered the catalytic activity upon catalyst reuse, while thermal reduction readily restored the initial activity and selectivity demonstrating catalyst reuse

Tertiary Amines from RCF Lignin Mono- and Dimers: Catalytic N-Functionalized Antioxidants from Wood

Functionalization of bio-based aromatics offers an appealing opportunity toward a renewable way of fulfilling our current needs for chemicals and materials. Here, an atom-efficient Cu-catalyzed hydrogen borrowing strategy is presented, which successfully functionalizes aliphatic alcohols in aromatic monomers and dimers, derived from lignin by the reductive catalytic fraction (RCF), into tertiary dimethylamines. Kinetic experiments and ToF-SIMS analysis of the supported copper catalyst demonstrated a reduced catalytic activity for monomeric methoxyphenolics, such as guaiacol and syringols, relative to phenolic and nonphenolic model compounds. This is explained by the formation through demethylation and the adsorption of strong coordinating catechol species. The nature of the catalyst support proved to be key to cope with the catechol deactivation and keep high catalytic activity, with Cu supported on SiO2 outperforming earlier reported Cu-ZrO2. The hydrogen borrowing method was extended to real spruce wood-derived RCF lignin oil fractions, containing both phenolic mono- and oligomers. Special effort was done to identify the composition and molecular structure of the resulting phenolic dimer amines by GC × GC-TOF/MS and 1H-13C-NMR techniques. The stable lignin-derived tertiary amines displayed excellent antioxidant activity during an ABTS assay, highlighting the added value of the products obtained by the hydrogen borrowing upgrading strategy