[2,3]‐Thia‐Wittig Rearrangements of α‐Lithiated Sulfides Via De‐aromatized Cyclohexadiene Intermediates Proceed with Inversion of Configuration at the Carbanionic Center

The n BuLi‐induced tin/lithium exchange reactions of the di‐astereomeric γ‐[(methoxyethoxy)methoxy]‐]α‐(tributylstannyl) sulfides anti ‐ and syn ‐8 delivered the α‐(lithioalkyl) benzyl sulfides anti ‐ and syn ‐ 11 , respectively. Within 1 h at ‐78°C, these species underwent [2,3]‐thia‐Wittig rearrangements in THF via the de‐aromatized cyclohexadiene intermediates syn ‐ and anti ‐ 12 . Tautomerization and protonation yielded 81:19 (85%) and 19:81 mixtures (96%) of the ortho ‐functionalized toluenes syn ‐ and anti ‐ 13 . Probably, both Wittig rearrangements proceeded with 100% inversion of configuration at the carbanionic stereocenter, and the overall loss of stereoselectivity is due to an epimerization anti ‐ 11 ⇌ syn ‐ 11 of the lithio sulfide intermediates at a rate which is 3.3 times slower than the rearrangement.