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

• Published in: European journal of organic chemistry 2014-03, Vol.2014 (7), p.1461-1476
• Main Authors: Řehová, Lucie, Císařová, Ivana, Jahn, Ullrich
• Format: Article
• Language: English
• Subjects: Acidity; Alkylation; Deprotonation; Lithiation; Sulfones; Transmetalation
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201301553

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. An unusual lithiation selectivity and subsequent transfer of the metal upon warming was observed for various branched alkyl phenyl sulfones. This divergent reactivity was used to prepare substituted aryl sulfones as well as olefins by application of the Julia reaction.