Theoretical studies allylic substitution

As recently highlighted by Woodward, enantioselective Sf/2 allylic substitution reactions are mechanistically related to conjugate addition reactions . Theoretical studies carried out by Nakamura and coworkers for the conjugate addition and allylic alkylation using Gilman s cuprates revealed profound mechanistic similarities between these two processes . ... 

The 5n2 reactions of y-substituted allyl chlorides where the nucleophile is a free anion and an ion pair were studied theoretically at the HF/6-31+G level of theory.10 The calculations showed that the free ion, S N2 reaction proceeds through a transition state (7) with significant positive charge on Ca and little conjugation with the n-system. Placing substituents on Cy of the free ion reactions gave computed Hammett p values of -3.3 and -4.6 for the trans- and ds-conformation reactions, respectively. The transition states (8) for the ion pair reactions, on the other hand, have considerable positive charge on both Ca and Cy and the computed Hammett p value is +18.8. 

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