Novel Carbazole-Based N-Heterocyclic Carbene Ligands to Access Synthetically Relevant Stilbenes in Pd-Catalyzed Coupling Processes

A series of new carbazole-based N-heterocyclic carbene (NHC) ligands have been synthesized in a simple and facile synthetic route and subsequently used in a Pd/carbazole-based NHC catalytic system, which was found to be effective in catalyzing Heck reactions to provide substituted stilbene derivatives in good yields. Several bioactive stilbenes, including pterostilbene, pinosylvin, trimethoxy resveratrol, and resveratrol, were synthesized in good yields, and a 10 mmol scale-up was also performed for trimethoxy resveratrol. The synthetic application was also extended by performing a double-tandem chemoselective Heck reaction followed by Miyaura borylation in a one-pot procedure to give single-step access to synthetically useful stilbenyl boronate esters. Similarly, a unique triple-tandem protocol of a chemoselective Heck reaction/Miyaura borylation/Suzuki-Miyaura coupling reaction sequence was performed for the one-pot modification of biologically relevant molecules.

Crystal structure of 1-butyl-3-{2-[(indan-5-yl)amino]-2-oxoeth-yl}-1H-imidazol-3-ium chloride

In the cation of the title mol-ecular salt, C18H24N3O+·Cl-, an intra-molecular C-H⋯O hydrogen bond stabilizes the almost coplanar orientation of the aromatic ring of the indane unit and the amide plane. In the crystal, the packing is dominated by inter-molecular C-H⋯Cl hydrogen-bonding inter-actions that result in the formation of slab-like structures propagating along [010]. The slabs are linked by weak C-H⋯O inter-actions, forming layers lying parallel to (100). The methyl-ene carbon atom of the indanyl substituent is disordered over two positions with a refined occupancy ratio of 0.84 (2):0.16 (2). The crystal studied was refined as a twin with matrix [1 0 0.9, 0 0, 0 0 ]; the resulting BASF value is 0.30.