Multi-Pathway Consequent Chemoselectivities of CpRuCl(PPh3)2/MeI-Catalysed Norbornadiene Alkyne Cycloadditions.
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 (ΔGRel(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 (ΔGRel(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).
Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, NO. 298, Yieryi Street, Kunming, 650092, P. R. China. weihua_mu@ynnu.edu.cn.
Wei-Hua
WH
Mu
College of Chemistry, Beijing Normal University, NO. 19, Xinjiekouwai Street, Beijing, 100875, P. R. China.
De-Cai
DC
Fang
Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, NO. 298, Yieryi Street, Kunming, 650092, P. R. China.
Shu-Ya
SY
Xia
Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, NO. 298, Yieryi Street, Kunming, 650092, P. R. China.
Rui-Jiao
RJ
Cheng
School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK. g.chass@qmul.ac.uk.
Gregory A
GA
Chass
chemoselectivity; cycloaddition; norbornadienes; reaction mechanisms; ruthenium