Reaction of Thiolate, Sulfite, and Cyanide Ions with Cyclic Aryl Thiolsulfinates: Dibenzo-1,2-dithiin and Naphtho-1,2-dithiole 1-Oxides

Article abstract of DOI:10.1021/jo00138a001

The behavior of cyclic thiolsulfinates 5 and 6 (dibenzo-1,2-dithiin 1-oxide and naphtho<1,8-cd>-1,2-dithiole 1-oxide> upon treatment with either sulfite, cyanide, or t-BuS(1-) ions has been examined and compared with the behavior of the corresponding thiolsulfonates 1 and 2 (dibenzo-1,2-dithiin and naphtho<1,8-cd>-1,2-dithiole 1,1-dioxides).Very marked differences are observed.Whereas thiolsulfonates 1 and 2 are converted essentially quantitatively to ring-open substitution products (3 and 4) upon treatment with excess sulfite, cyanide, or t-BuS(1-), with thiolsulfinates 5 and 6 the equilibrium constants for opening of the sulfur-containing ring are so much smaller that only in the case of 5 and t-BuS(1-) is the equilibrium constant large enough that a significant fraction of the thiolsulfinate is converted to ring-opened product (7 or 8) at equilibrium.Kinetic studies of the rates of nucleophile-catalyzed racemization of optically active 5 and 6 show that the major factor responsible for the dramatic difference in the magnitude of the equilibrium constants is not a decrease in the rate constant for opening of the ring by the nucleophile but rather a huge increase in the rate constant for the reverse of the ring-opening reaction, which in the case of the thiolsulfinates involves displacement of the nucleophile from SNu by a sulfenate group, whereas for the thiolsulfonates it is a sulfinate group that performs the same displacement.In the 5-t-BuS(1-) system the rate constant for the displacement by the sulfenate is 30000 times faster than the rate constant for the corresponding displacement in the 1-t-BuS(1-) system involving the sulfinate; this provides thefirst quantitative measure of just how much more reactive a sulfenate ion is as a nucleophile than the corresponding sulfinate.Other aspects of the kinetics of the reactions of 5 and 6 with these nucleophiles provide additional information on the behavior of 7 and 8 and their conjugate acids and thereby furnish new insight into the chemistry and reactivity and of arenesulfenates and arenesulfenic acids.