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Experimental Evidence Supporting a Cu III Intermediate in Cross‐Coupling Reactions of Allylic Esters with Diallylcuprate Species
Author(s) -
Karlström A. Sofia E.,
Bäckvall JanE.
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010504)7:9<1981::aid-chem1981>3.0.co;2-c
Subject(s) - allylic rearrangement , chemistry , magnesium , coupling reaction , stoichiometry , reagent , dilution , coupling (piping) , copper , medicinal chemistry , yield (engineering) , olefin fiber , catalysis , polymer chemistry , organic chemistry , materials science , physics , thermodynamics , metallurgy
The reaction between an allylic ester and a magnesium diallylcuprate, or an allylic Grignard reagent in combination with a catalytic amount of a copper salt, has been studied. These reactions yield a mixture of homo‐ and cross‐coupled 1,5‐diene products. The product ratios obtained are close to those expected for a reaction proceeding via a triallylcopper( III ) intermediate consisting of three equivalent allyl groups bound to copper. When the reaction is performed with a stoichiometric amount of a preformed diallylcuprate, a homo‐coupling/cross‐coupling ratio larger than that predicted for a Cu III intermediate is observed. However, on dilution this ratio decreases and becomes close to the predicted ratio. The deviation from the predicted homo‐coupling/cross‐coupling ratio was accounted for by an olefin‐induced homo‐coupling, as demonstrated in control experiments. The possibility of the allylic ligands to coordinate to the metal center in a η 3 or η 1 fashion provides an opportunity for the stabilization of the intermediate Cu III species.