Double Gold Activation of 1‐Ethynyl‐2‐(Phenylethynyl)Benzene Toward 5‐exo‐dig and 6‐endo‐dig Cyclization Reactions

Abstract

In this work, a detailed characterization was carried out of the ring-closure mechanism of EPB (1-ethynyl-2-(phenylethynyl)benzene) toward the 5-exo-dig and 6-endo-dig cyclization reactions, catalyzed by two Au-N-heterocyclic carbene (NHC) moieties. It was found that the 5-exo-dig cyclization takes place with a slightly lower activation barrier and larger exothermicity compared to that of the 6-endo-dig cyclization, in agreement with the available experimental data. A phenomenological partition (structural and electronic) for rate constants computed using transition-state theory and the reaction force analysis was used to shed light into the nature of the activation rate constant. It was found that rate constants are influenced by a strong structural component, which is larger for the 5-exo-dig cyclization due to the strain to form the five-membered ring. On the other hand, the gold activation mechanism is evidenced by a σ- and π-coordination of the Au-NHC moieties to the EPB substrate. It was found that differences in the σ-coordination arise on the reaction path for the 5-exo-dig and 6-endo-dig cyclizations. Thus, in the 6-endo-dig cyclization the σ gold-EPB interaction is weakened as a consequence of the formation of the cationic aryl intermediate, while for the 5-exo-dig cyclization this interaction was found to be favored. Furthermore, although minor changes in the Au-EPB coordination occur on the reaction path, these bonds are formally established in the TS vicinity. Results support the concerted nature of the dual gold activation mechanism.

Decomposition of the electronic activity in competing [5,6] and [6,6] cycloaddition reactions between C60 and cyclopentadiene

“…This fact has a preponderant influence on the difference observed in the activation energies: the more extensive electronic reordering in the activation process, the larger activation energy is found. This general pattern has been reported previously [82].…”

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

“…Also, because of the less weakened AuÀ C bond after reaching the transition state for 5-endo-digcyclization compared to the competitive 6-endo-dig path, the reaction proceeds by the former cyclization mode. [277] The regioselective formation of gem-diaurated dibenzopentalene intermediate was utilized to generate fluorescent tags for Förster resonance energy transfer (FRET) analysis using appropriate Au-NHC complexes. [276] By taking advantage of the dual activation gold catalysis concept, various condensed carbocyclic compounds can be prepared from various substituted substrates.…”

“…and electronic flux aligned with the experimental results and support the 5‐ endo ‐ dig cyclization. Also, because of the less weakened Au−C bond after reaching the transition state for 5‐ endo ‐ dig cyclization compared to the competitive 6‐ endo ‐ dig path, the reaction proceeds by the former cyclization mode [277] . The regioselective formation of gem ‐diaurated dibenzopentalene intermediate was utilized to generate fluorescent tags for Förster resonance energy transfer (FRET) analysis using appropriate Au‐NHC complexes [276] …”

Cyclic Compounds Incorporating Two or Four Alkyne Units in Close Proximity – Theory and Experiments

“…Very recently a non‐radical counterpart of the transannular ring closure of 2b was published . The goal of these investigations was achieved through Au I catalysis,, for which a dramatic acceleration was predicted by calculations , . Scheme summarizes the Au I ‐catalyzed transannular ring closure of 4,4,9,9‐tetramethoxycarbonyl‐cyclodeca‐1,6‐diyne ( 2b ) in the presence of p ‐xylene, mesitylene, or tert ‐butyl benzene to yield 21 – 24 .…”