101168-74-5Relevant articles and documents
Influence of Conformation and Proton-Transfer Dynamics in the Dibenzyl σ-Complex on Regioselectivity in Gattermann-Koch Formylation via Intracomplex Reaction
Tanaka, Mutsuo,Fujiwara, Masahiro,Xu, Qiang,Ando, Hisanori,Raeker, Todd J.
, p. 4408 - 4412 (2007/10/03)
The Gattermann-Koch formylations of diphenyl, diphenylmethane, dibenzyl, and 1,3-diphenyl- propane were studied in HF-SbF5, -TaF5, -BF3, -NbF5, and CF3SO3H-SbF5. While usual high para regioselectivity was obtained for diphenyl, diphenylmethane, and 1,3-diphenylpropane, unprecedented ortho regioselectivity was observed for dibenzyl which increased with decreasing the SbF5/dibenzyl molar ratio and with strength of Lewis acids used in HF. A sandwich-like complex for monoprotonated dibenzyl resulting in ortho regioselectivity via the intracomplex reaction was suggested; therefore, the conformations of protonated diphenylmethane, dibenzyl, and 1,3- diphenylpropane and their proton-transfer dynamics were probed by semiempirical calculation (PM3). The calculation predicted that ortho monoprotonation was slightly preferable for dibenzyl, and remarkable preference of dibenzyl over other aromatic compounds was observed in ortho- ortho intramolecular inter-ring proton transfer via a fan-shaped complex rather than a sandwich- like complex. The experimental and theoretical data for dibenzyl are compatible with the intracomplex reaction, whereby CO is protonated by the ortho σ-complex undergoing rapid inter- ring proton transfer to generate formyl cation in the vicinity of the ortho position leading to ortho regioselectivity.
