From Tree to Tape: Direct Synthesis of Pressure Sensitive Adhesives from Depolymerized Raw Lignocellulosic Biomass

We report a new and robust strategy toward the development of high-performance pressure sensitive adhesives (PSAs) from chemicals directly obtained from raw biomass deconstruction. A particularly unique and translatable aspect of this work was the use of a monomer obtained from real biomass, as opposed to a model compound or lignin-mimic, to generate well-defined and nanostructure-forming polymers. Herein, poplar wood depolymerization followed by minimal purification steps (filtration and extraction) produced two aromatic compounds, 4-propylsyringol and 4-propylguaiacol, with high purity and yield. Efficient functionalization of those aromatic compounds with either acrylate or methacrylate groups generated monomers that could be easily polymerized by a scalable reversible addition–fragmentation chain-transfer (RAFT) process to yield polymeric materials with high glass transition temperatures and robust thermal stabilities, especially relative to other potentially biobased alternatives. These lignin-derived compounds were used as a major component in low-dispersity triblock polymers composed of 4-propylsyringyl acrylate and <i>n</i>-butyl acrylate (also can be biobased). The resulting PSAs exhibited excellent adhesion to stainless steel without the addition of any tackifier or plasticizer. The 180° peel forces were up to 4 N cm^–1, and tack forces were up to 2.5 N cm^–1, competitive with commercial Fisherbrand labeling tape and Scotch Magic tape, demonstrating the practical significance of our biomass-derived materials

Aerobic Oxidative C–H Olefination of Cyclic <i>N</i>‑Sulfonyl Ketimines Catalyzed by a Rhodium Catalyst

A useful method for the synthesis of <i>ortho</i>-olefinated ketimines from readily accessible cyclic <i>N</i>-sulfonyl ketimines and various olefins has been achieved. The reactions proceeded by Rh­(III)-catalyzed, <i>N</i>-sulfonyl ketimine-directed C–H cleavage under aerobic conditions. Further synthetic transformations of the olefinic products led to interesting heterocyclic molecules

Selective C–C Bond Cleavage of Methylene-Linked Lignin Models and Kraft Lignin

Biorefinery and paper pulping lignins, referred hereto as technical lignins, contain condensed C–C interunit linkages. These robust C–C linkages with higher bond dissociation energies are difficult to disrupt under hydrogenolysis conditions, which are generally used for cleaving C–O bonds of native lignin in biomass or model C–O linked compounds. Thus, selective interunit C–C cleavage to release aromatic monomers for high-value applications is a challenge. We report an effective catalytic system to cleave such C–C bonds selectively under mild conditions. A representative methylene-linked C–C model dimer achieves 88% yield of mainly two aromatic monomers within 1.5 h at a reasonably low temperature (250 °C) using a commercial CoS₂ catalyst. Aromatic monomers convert to nonaromatic products upon the reaction for a prolonged time. The interunit C–C bond of the dimer become unreactive to cleavage upon dehydroxylation of aromatic rings, while the methoxyl group has little effect on the cleavage. β-1 and 5-5 C–C linked model dimers formed demethoxylated hydroxyl dimers as the major products. Depolymerization of a purified kraft lignin fraction yields five aromatic monomers and lower-molecular-weight soluble products. This study opens up the possibility of valorization of technical lignins using inexpensive catalysts

Enantioselective [4 + 1] Annulation Reactions of α‑Substituted Ammonium Ylides To Construct Spirocyclic Oxindoles

Ammonium ylides have a long history in organic synthesis, but their application in asymmetric catalysis is still underdeveloped in regard to both substrate scope and reaction pathways compared with phosphorus and sulfur ylides. Here a previously unreported asymmetric [4 + 1] annulation reaction of 3-bromooxindoles and electron-deficient 1-azadienes has been developed through ammonium ylide catalysis of a newly designed 2′-methyl α-isocupreine (α-MeIC), efficiently delivering spirocyclic oxindole compounds incorporating a dihydropyrrole motif in excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this work represents the first example of asymmetric catalysis of ammonium ylides bearing α-substitutions, and the catalytic [4 + 1] annulation pathway of ammonium ylides is also unprecedented. Moreover, ¹H NMR, mass spectroscopy, and computational calculation studies were conducted, and the catalytic cycle and a tentative explanation of the enantioselective mechanism have been successfully elucidated

Enantioselective [4 + 1] Annulation Reactions of α‑Substituted Ammonium Ylides To Construct Spirocyclic Oxindoles

Ammonium ylides have a long history in organic synthesis, but their application in asymmetric catalysis is still underdeveloped in regard to both substrate scope and reaction pathways compared with phosphorus and sulfur ylides. Here a previously unreported asymmetric [4 + 1] annulation reaction of 3-bromooxindoles and electron-deficient 1-azadienes has been developed through ammonium ylide catalysis of a newly designed 2′-methyl α-isocupreine (α-MeIC), efficiently delivering spirocyclic oxindole compounds incorporating a dihydropyrrole motif in excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this work represents the first example of asymmetric catalysis of ammonium ylides bearing α-substitutions, and the catalytic [4 + 1] annulation pathway of ammonium ylides is also unprecedented. Moreover, ¹H NMR, mass spectroscopy, and computational calculation studies were conducted, and the catalytic cycle and a tentative explanation of the enantioselective mechanism have been successfully elucidated

Redox-Neutral Palladium-Catalyzed C–H Functionalization To Form Isoindolinones with Carboxylic Acids or Anhydrides as Readily Available Starting Materials

An operationally simple, Pd-catalyzed C–H functionalization is described for the synthesis of important and useful isoindolinones from readily available carboxamides and carboxylic acids or anhydrides. The reactions proceed efficiently with a broad range of substrates under redox-neutral reaction conditions and tolerate a diversity of functional groups. The mechanistic investigation suggests that the reactions involve C–H activation, nucleophilic addition, β-O elimination, and dehydration steps

Spirocyclic Sultam and Heterobiaryl Synthesis through Rh-Catalyzed Cross-Dehydrogenative Coupling of <i>N</i>‑Sulfonyl Ketimines and Thiophenes or Furans

A useful approach is developed for the synthesis of various structurally interesting spirocyclic sultams and heterobiaryls using a cross-dehydrogenative coupling strategy that features high atom and step economy. This method employs [Cp*RhCl₂]₂ as a catalyst and <i>N</i>-sulfonylimine, a weak coordinating group, as an efficient directing group to assist C–H activation. A number of the coupled products were converted into interesting molecules through further synthetic transformations