Transmetallation palladium enolate preparation

Scheme 2.50 C-bound nickel and palladium enolates prepared by transmetallation.

Transmetallation of the lithium or potassium enolates is also a reliable method for the preparation of palladium and nickel enolates, as illustrated in Scheme 2.50. Clear evidence for the C-bound structure of enolates 172 and 173 thus prepared was provided by NMR spectroscopy and - for nickel enolate 172 (M = Ni, L = Cp ) - by a crystal structure analysis. The reaction of C-bound nickel and palladium enolates 172 and 173 with aldehydes is much more sluggish and much less uniform than the analogs of that of the polar main-group metals. In addition to P-hydroxyketones or esters, products resulting from a Tishchenko reaction were also observed [164b]. 

Transition Metal-Catalyzed Allylie Alkylation. Chelated amino acid ester enolates were found to be suitable nucleophiles for palladium-catalyzed allylie alkylations (eq 25). They were conveniently prepared by deprotonation of a glycine derivative with LHMDS followed by transmetallation with zinc chloride. The palladium-catalyzed allylie alkylation then takes place in the presence of allyl carbonates to produce the desired anti amino acid derivative. ... 

Transmetallation is also a highly important concept to obtain enolates of the late transition metals rhodium, palladium, and nickel, not only for their preparation and isolation, but also for their intermediate generation in catalytic cycles. When 2 equiv. of the potassium enolates 166 of acetophenone and pinacolone... 

Scheme 2.54 Preparation of 0-bound palladium ester enolate 184 by transmetallation.

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