Reactions of nitrogen containing aromatic anions with chlorocarbene

A Novel Method of Self-Cross-Linking of Syringaldehyde with Activated Methoxy Groups via Cross-Coupling for Lignin-Based Wood Adhesives

As steric hindrance, methoxy groups are limiting the valorization of hardwood lignin. This paper reports a novel method of self-cross-linking of the syringaldehyde with activated methoxy groups (-OCH3) via cross-coupling reaction to obtain thermosetting polymers for lignin-based wood adhesives. The methoxy groups of syringaldehyde have been activated via cross-coupling reaction by substituting Ar-OCH3 with Ar-CH2-SiMe3, and dichloromethane, leading to cross-linking via methylene bridges to build a thermosetting polymer. FTIR spectra showed a decrease in the intensity of a -CH3 and -OH group, owing to the substitution of the methoxy group. 13C NMR spectra also supported these results with the -SiMe3 signal that disappeared after the cross-linking reaction. Furthermore, cross-linking between the activated methoxy groups was confirmed with a strong exothermic peak at 130 °C, resulting in an increase in the adhesion strength as hot-pressing temperature increased from 160 to 180 °C. These results suggest that the cross-linking between the activated methoxy groups of syringaldehyde is an important understanding of valorizing hardwood lignin via building thermosetting polymers for lignin-based adhesives.

One-Carbon Ring Expansion of Indoles and Pyrroles: A Straightforward Access to 3-Fluorinated Quinolines and Pyridines

3-Fluorinated quinolines and pyridines are prevalent pharmacophores, yet their synthesis is often challenging. Herein, we demonstrate that dibromofluoromethane as bromofluorocarbene source enables the one-carbon ring expansion of readily available indoles and pyrroles to structurally diverse 3-fluorinated quinolines and pyridines. This straightforward protocol requires only a short reaction time of ten minutes and can be performed under air atmosphere. Preliminary investigations reveal that this strategy can also be applied to the synthesis of other valuable azines by using different 1,1-dibromoalkanes as bromocarbene sources.

Preparation and Utility of N-Alkynyl Azoles in Synthesis

Heteroatom-substituted alkynes have attracted a significant amount of interest in the synthetic community due to the polarized nature of these alkynes and their utility in a wide range of reactions. One specific class of heteroatom-substituted alkynes combines this utility with the presence of an azole moiety. These N-alkynyl azoles have been known for nearly 50 years, but recently there has been a tremendous increase in the number of reports detailing the synthesis and utility of this class of compound. While much of the chemistry of N-alkynyl azoles mirrors that of the more extensively studied N-alkynyl amides (ynamides), there are notable exceptions. In addition, as azoles are extremely common in natural products and pharmaceuticals, these N-alkynyl azoles have high potential for accessing biologically important compounds. In this review, the literature reports of N-alkynyl azole synthesis, reactions, and uses have been assembled. Collectively, these reports demonstrate the growth in this area and the promise of exploiting N-alkynyl azoles in synthesis.

Transition-Metal-Free, Atom- and Step-Economic Synthesis of Aminoketopyrrolizines from Benzylamine, Acylethynylpyrroles, and Acylacetylenes

A concise, atom-economic strategy for the synthesis of pyrrolizines with amino and keto substituents has been developed. It includes the following key steps: (i) the base-catalyzed (K₃PO₄/DMSO) addition of a benzylamine to 2-acylethynylpyrroles and (ii) noncatalyzed addition of enaminones obtained to the triple bond of acylacetylenes followed by intramolecular cyclization of the intermediate pentadiendiones thus formed to the target 1-(benzylamino)-2-acyl-3-methylenoacylpyrrolizines.