Rates and products of acetolysis of trans-2-arylcyclopentyl tosylates. Evidence for major control of the stereochemistry of the substitution process by neighboring aryl in the absence of rate accelerations

Inductive enhancement of aryl participation

“…The current study was designed to determine whether aryl participation can be enhanced by the placement of an electron-withdrawing substituent vicinal to the leaving benzenesulfonate. Such "inductive enhancement of participation" has been observed previously for double bond assistance in the norbornenyl system.3 Whereas exo-2-norborn-5-enyl tosylate (1) acetolyzes only 3.4 times more slowly than its saturated analogue, m,cxo-2,3-norborn-5-enyl ditosylate (2) acetolyzes 1 2 500 times more rapidly than its saturated analogue, for an overall enhancement of about 1700. A trans tosyloxy group or a cis acetoxy group has the same effect as the cis tosyloxy group in 2.…”

“…Thus the double bond in the vicinally substituted system 2 responds to the greater need for charge delocalization, with the result that homoallylic participation is much greater in 2 than in 1. /L 7-x C?OTs -X (2) Inductive enhancement of participation is complementary to the Gassman-Fentiman approach,4 by which participation is reduced through increased stabilization of the localized carbonium ion. Inductive enhancement, by contrast, increases the amount of participation by making the localized carbonium ion less stable.…”