Palladium(0)–Lithium Iodide Cocatalyzed Asymmetric Hydroalkylation of Conjugated Enynes with Pronucleophiles Leading to 1,3-Disubstituted Allenes

Abstract

Axially chiral 1,3-disubstituted allenes were synthesized via hydroalkylation of alkyl- or aryl-substituted conjugated enynes (readily prepared via a Sonogashira reaction) with pronucleophiles such as dimethyl malonate under the cocatalysis of DTBM-SEGPHOS-ligated palladium and lithium iodide. Although the palladium catalyst ligated with (<i>S</i>)-DTBM-SEGPHOS prefers the formation of (<i>R</i>)-1,3-disubstituted allenes, lithium iodide recovers and increases the intrinsic selectivity producing (<i>S</i>)-allenes by promoting the isomerization of the <i>exo</i>-alkylidene-π-allylpalladium intermediate prior to the nucleophilic substitution step.