AN AUTHENTIC CASE OF INPLANE NUCLEOPHILIC VINYLIC SUBSTITUTION - THE ANIONOTROPIC REARRANGEMENT OF DI-TERT-BUTYLTHIIRENIUM IONS INTO THIETIUM IONS

S-Methyl- and S-(4-chlorophenyl)-substituted di-tert-butylthiirenium ions 7a and 7b rearrange quantitatively with first-order kinetics to thietium ions ga and 8b. The specificity of the rearrangement and the relevant secondary kinetic isotope effect observed with S-(4-chlorophenyl)thiirenium ion 7c perdeuteriated at one tert-butyl group point to an intramolecular concerted in-plane vinylic substitution (S(N)2-Vin mechanism). The comparison with the rearrangements from trans-tert-butyl in S-methylthiiranium ions 4a and 4b (occurring with intramolecular S(N)2 mechanism) gives k(S(N)2)/k(S(N)2-Vin) ratios ranging from 12 to 720.