Divergent Reactivity of Alkyl Aryl Sulfones with Bases: Selective Functionalization of ortho-Aryl and alpha-Alkyl Units Enabled by a Unique Carbanion Transmetalation
Abstract
The electron-accepting sulfonyl group exhibits a strong acidifying influence on neighboring -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 -H atom.
The structure of the alkyl unit profoundly, but predictably, influences the regioselectivity of the attack of the base. In - and -branched ortho-(alkylsulfonyl)aryllithiums a transmetalation to the -carbanion proceeds only upon warming.
Correspondingly generated ortho- or -carbanions were then selectively applied thus permitting access to synthetically interesting compound classes.