X-ray structures and anionotropic rearrangements of di-tert-butyl-substituted thiiranium and thiirenium ions. A structure-reactivity relationship

The X-ray structures of c-2,t-3-di-tert-butyl-r-1-methylthiiranium 8 BF4-, t-2,t-3-di-tert-butyl-r-1-methylthiiranium ion 10 BF4-, and 2,3-di-tert-but yl-1-methylthiirenium 11 BF4- have been determined. The Delta G(298)double dagger values for the rearrangements from the cis and the trans tert-butyl groups of 8 SbCl6- to thietanium ion (two intramolecular S(N)2 displacement s) and for the rearrangement of 11 SbCl6- to thietium ion tan intramolecula r S(N)2-Vin displacement) are linearly correlated with the strengths of the C-S breaking bonds, suggesting that the two mechanisms are, in the absence of steric hindrance, uniquely governed by the nucleofugality of the sulfon ium leaving group.