1000
the acyl palladium with potassium acetate generates the acyl palladium(II) acetate which undergoes
transmetallation with the organoborane reagent. The resultant acyl organopalladium complex then
undergoes reductive elimination to generate the ketone product.
Table 1
Reaction of benzoyl chloride with tributylborane to generate valerophenonea
Several features of this reaction make it synthetically useful. These include the fact that reactions can
be carried out at moderate temperatures in THF, unlike other transition-metal-catalyzed cross-coupling
reactions involving main group organometallics. Most importantly, the reaction is not limited to aromatic
acid chlorides, aliphatic acid chlorides also undergo the coupling reaction. The reaction is straightforward
and it appears to be generally applicable (Table 2). At present, the reaction involves the transfer of only
one of the three alkyl groups and thus is not as efficient as some of the more recent developments using
arylboron derivatives which also employ smaller quantities of the palladium reagent.9,10 A detailed study
of the scope and limitations of the synthesis is in progress.
The synthesis of 1-phenyl-1-pentanone is representative: Benzoyl chloride (1.0 mmol) is added to
Pd(PPh3)4 (0.2 mmol) and the mixture stirred at room temperature for 10 min. Potassium acetate (2
mmol) and tributylborane (1 mmol) are added to the reaction mixture which is refluxed at 65°C for 3
h. The reaction is quenched with water (10 mL) and the product extracted into ether (3×20 mL). The
combined organic extracts are washed with brine and then dried over anhydrous magnesium sulfate prior
to solvent removal under reduced pressure. The product is purified by column chromatography (silica
gel) using ethyl acetate–hexanes to yield 0.74 mmol (74%) of the desired 1-phenyl-1-pentanone.
Acknowledgements
We thank the US Department of Energy and the Robert H. Cole Foundation for support.
References
1. The Chemistry of Metal–Carbon Bond; Kumar, V. G.; Chu, C. K.; Miginiae, L.; Hartley, F. R.; Patai, S., Eds.; John Wiley &
Sons: New York, 1985; Vol. 3, p. 1.
2. Baillargeon, V. P.; Stille, J. K. J. Am. Chem. Soc. 1983, 105, 7175; ibid. 1986, 108, 452.
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Beletskya, I. P. Tetrahedron Lett. 1985, 26, 4819.
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E.; Woell, J. B.; Alper, H. Tetrahedron Lett. 1984, 25, 3791.