Comparative Substituent Effects of Tosyloxy, Benzyloxy, and Phosphoryloxy Substituents in Carbocation Formation. Acid-Catalized Hydration of Vinyl Tosylates, Benzoates, and 1,1-Ditosylates

Article abstract of DOI:10.1021/jo00281a036

Kinetc results for theacid-catalized hydration of alkenyl esters CH2=C(OX)R (X = Bz, Ts) and literature data for X = Ac and PO3Et2 are analyzed by the excess acidity method, and it is concluded that all the substrates react by the Ad_E2 mechanism of rate-limiting proton transfer to the double bond.Average substituent parameters ?_p⁺ derived for the groups OBz, OAc, and OPO3Et2 of -0.18, -0.16, and -0.20, respectively, are similar and indicate these groups are modestly effective electron donors, while the average values of 0.08 for the OTs group indicates this to be a net electron withdrawing group.Hydrolysis of t-BuCH=C(OTs)2 requires much stronger acid; it has k_H+/k_D+ = 5.75 and a low slope of the rate versus acidity plot that is interpreted in terms of rate-limiting protonation of a substrate whose basic oxygens interact strongly with the acid solvent.