Palladium-Catalyzed Efficient Enantioselective Synthesis of Chiral Allenes: Steric and Electronic Effects of Ligands

Asymmetric synthesis of chiral allenes starting from prochiral substrates under mild reaction conditions promoted by Pd-SYNPHOS catalyst is reported. This protocol provides an efficient access to various enantioenriched aryl- and alkyl- substituted allenes, which are versatile building blocks of high utility to both organic and medicinal chemists, in excellent isolated yields (up to 96%) and high enatiomeric ratio values (up to 95:5). In addition, a comparative study using several C-2-symmetric atropisomeric diphosphine ligands revealed the overwhelming impact of the steric and electronic properties of the ligands for the catalytic efficiency of this process.