Mechanisms of Kobayashi eliminations for the generation of highly strained arynes, cyclic cumulenes, and anti-Bredt olefins

First disclosed in 1983, the Kobayashi method for generating transient strained intermediates from 1,2-silyltriflate precursors has become an indispensable tool in organic synthesis. More than 1300 Kobayashi precursors to strained intermediates have been reported to date, leading to the use of these precursors in more than 17 000 strained intermediate trapping reactions. Surprisingly, the mechanism of the Kobayashi elimination to form strained intermediates has been studied only for the formation of benzyne. We report computational studies that determine the timing of Si-C and C-O cleavage, as well as the thermodynamics of strained intermediate formation. The calculated pathway for generating anti-Bredt olefins from Kobayashi precursors differs compared to the mechanism for strained intermediate generation of other species, with a particular dependence on the Si-C-C-O dihedral angle. These studies establish the mechanisms of Kobayashi eliminations and enable the rational design of new strained intermediate precursors for future use in synthesis.