Enone derivatives haloenones

D.ii,a. Pd-Catalyzed ct-Arylation and a-Alkenylation of Acetal-Protected Enone Derivatives (Protocol I). The reaction of 2-bromo-2-cyclohexenone and 2-iodo-2-cyclohexenone with bis[( )-l-hexenyl]zinc in the presence of 5 mol % of a Pd-PPhj complex in THF at 25 °C gives 2-[( )-l-hexenyl]-2-cyclohexenone in 0% and 31% yield, respectively. In sharp contrast, the corresponding reaction of 3-bromo-2-cyclohexenone provides 3-[( )-l-hexenyl]-2-cyclohexenone in 75% yield, with the balance of the starting bromoenone still remaining unreacted. The sluggish nature of -substitution and the greater instability of a-haloenones are clearly indicated in the competitive experiment summarized in Scheme 18. ... 

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