Pd(ii)-catalyzed β- and γ-C-(sp3)–H dienylation with allenyl acetates

Abstract

Recent years have seen the emergence of transition metal catalyzed C–H activation as a powerful synthetic tool in organic chemistry. Allenes have fascinated synthetic chemists due to their unique reactivity. While directing group assisted functionalization of C(sp²)–H bonds with allenes is well documented in the literature, their coupling with more challenging aliphatic C(sp³)–H bonds remains elusive. In this regard, we hereby report a Pd(II) catalyzed 8-aminoquinoline directed aliphatic C(sp³)–H dienylation protocol using allenyl acetates. A variety of carboxylic acids including fatty acids and amino acids were efficiently functionalized at β and γ-positions to afford diversely functionalized 1,3-dienes. Preliminary mechanistic studies revealed the crucial role of the base in the success of the transformation. The reaction proceeds via regioselective 2,3-migratory insertion of the allene with the alkylpalladium(II) species followed by β-acetoxy elimination.