Multi‐Pathway Consequent Chemoselectivities of CpRuCl(PPh3)2/MeI‐Catalysed Norbornadiene Alkyne Cycloadditions

摘要

Chemoselectivities of five experimentally realised CpRuCl(PPh3)2/MeI‐catalysed couplings of 7‐azabenzo‐norbornadienes with selected alkynes were successfully resolved from multiple reaction pathway models. Density functional theory calculations showed the following mechanistic succession to be energetically plausible: (1) CpRuI catalyst activation; (2) formation of crucial metallacyclopentene intermediate; (3) cyclobutene product (>P2) elimination (ΔG Rel(RDS)≈11.9–17.6 kcal mol⁻¹). Alternative formation of dihydrobenzoindole products (>P1) by isomerisation to azametalla‐cyclohexene followed by subsequent CpRuI release was much less favourable (ΔG Rel(RDS)≈26.5–29.8 kcal mol⁻¹). Emergent stereoselectivities were in close agreement with experimental results for reactions >a, >b, >e. Consequent investigations employing dispersion corrections similarly support the empirical findings of >P1 dominating in reactions >c and >d through >P2→>P1 product transformations as being probable (ΔG≈25.3–30.1 kcal mol⁻¹).