This work demonstrates the highly selective metal-free catalytic reactions of a-aryl a-diazoesters with a range of (hetero)cycles and olefins using Lewis acidic boranes. The simple, mild reaction protocol employed represents an alternative to the commonly used precious metal systems and may provide future applications in the generation of biologically active compounds.

Density functional theory was used to investigate the protodeauration of organogold compounds, a process which is thought to be the final step in the gold-catalyzed nucleophilic addition to activated π bonds wherein a proton is added and the gold catalyst is regenerated. In this context, we have studied two important factors which control the effectiveness of this transformation. We find that the nature of the alkenyl group in PMe3Au­(alkenyl) affects the reaction barrier through the strength of the Au–C bond; the stronger the Au–C bond, the higher the activation energy. This, in turn, is determined by the π-accepting/donating ability of the substituents on the alkenyl group. We theoretically confirm that, for protodeauration, the reaction should be rapid when π-donating groups are present. In contrast, when π-accepting substituents are present, the intermediate gold complexes may be stable enough to be isolated experimentally. The second important factor controlling the reaction is the nature of the phosphine ligands. We theoretically confirm that electron-rich ligands such as PMe3 or PPh3 accelerate the reaction. We find that this is due to the strong electron-donating nature of these ligands, which strengthens the Au–P bond in the final product and thus provides a thermodynamic driving force for the reaction. Also, it is shown how the protodeauration is affected by the number of molecules solvating the proton. The protodeauration mechanism of some other organogold compounds such as gold–alkyl, gold–alkynyl, and gold–allyl species was investigated as well. The findings of this study can be used to design more effective systems for transformations of organogold compounds.

The donor–acceptor ability of frustrated Lewis pairs (FLPs) has led to widespread applications in organic synthesis. Single electron transfer from a donor Lewis base to an acceptor Lewis acid can generate a frustrated radical pair (FRP) depending on the substrate and energy required (thermal or photochemical) to promote an FLP into an FRP system. Herein, we report the C sp 3 –C sp cross-coupling reaction of aryl esters with terminal alkynes using the B(C 6 F 5 ) 3 /Mes 3 P FLP. Significantly, when the 1-ethynyl-4-vinylbenzene substrate was employed, the exclusive formation of C sp 3 –C sp cross-coupled products was observed. However, when 1-ethynyl-2-vinylbenzene was employed, solvent-dependent site-selective C sp 3 –C sp or C sp 3 –C sp 2 cross-coupling resulted. The nature of these reaction pathways and their selectivity has been investigated by extensive electron paramagnetic resonance (EPR) studies, kinetic studies, and density functional theory (DFT) calculations both to elucidate the mechanism of these coupling reactions and to explain the solvent-dependent site selectivity.

Herein we report a facile, mild reaction protocol to form carbon–carbon bonds in the absence of transition metal catalysts. We demonstrate the metal‐free alkenylation reactions of aryl esters with α‐diazoesters to give highly functionalized enyne products. Catalytic amounts of tris(pentafluorophenyl)borane (10–20 mol %) are employed to afford the C=C coupled products (31 examples) in good to excellent yields (36–87 %). DFT studies were used to elucidate the mechanism for this alkenylation reaction.

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