Divergent Reactivity of Alkyl Aryl Sulfones with Bases: Selective Functionalization of ortho‐Aryl and α‐Alkyl Units Enabled by a Unique Carbanion Transmetalation

Abstract The electron‐accepting sulfonyl group exhibits a strong acidifying influence on neighboring α‐H atoms. The Julia and related olefinations are based on this effect. Here a surprising reversal in the metalation selectivity of branched alkyl aryl sulfones is described. Such sulfones were found to initially undergo directed ortho‐metalation with good regioselectivity, despite having a more acidic α‐H atom. The structure of the alkyl unit profoundly, but predictably, influences the regioselectivity of the attack of the base. In β‐ and γ‐branched ortho‐(alkylsulfonyl)aryllithiums a transmetalation to the α‐carbanion proceeds only upon warming. Correspondingly generated ortho‐ or α‐carbanions were then selectively applied thus permitting access to synthetically interesting compound classes.