Abstract / Description of output
H-2-Labelled and O-18-labelled cyclopentenyl esters (+/-)-4 and (+/-)-5 are used as probes for memory effects in Pd-catalysed allylic alkylation. H-2-Labelled alkylation product 6 arising from stereospecific Pd-catalysed reaction of (+/-)-4 was analysed by a novel C-13 NMR method involving H-2-isotope shifts and paramagnetic diastereotopic shifts. When catalysts bearing the Trost modular ligand (R,R)-3 were employed, variable memory effects were observed with the slower reacting chirality mismatched (R)-4 substrate-catalyst pairing. The memory effect is dependent on nucleofuge steric bulk and not pK(a). Attack by [LiCH(CO2CH3)(2)] occurs with reversed site selectivity but (R)-4 remains the mismatched substrate. Mismatched ionisation leading to a Pd-pi-allyl in which (R,R)-3 acts as a monophosphine ligand may explain the memory effect.
Original language | English |
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Pages (from-to) | 2539-2549 |
Number of pages | 11 |
Journal | Chemistry - A European Journal |
Volume | 4 |
Issue number | 12 |
Publication status | Published - Dec 1998 |
Keywords / Materials (for Non-textual outputs)
- allyl complexes
- asymmetric catalysis
- isotopic labeling
- P ligands
- palladium
- SYN-ANTI DICHOTOMY
- ASYMMETRIC CATALYSIS
- (PI-ALLYL)PALLADIUM COMPLEXES
- ENANTIOSELECTIVE CATALYSIS
- NUCLEOPHILIC-SUBSTITUTION
- HOMOGENEOUS CATALYSIS
- PALLADIUM COMPLEXES
- CHIRAL LIGANDS
- MECHANISM
- SELECTIVITY