Synthesis of C 2 ‐Symmetric Bisphosphine Ligands from Tartaric Acid, and Their Performance in the Pd‐Catalyzed Asymmetric O ‐Allylation of a Phenol

Starting from tartaric acid derived chiral diols or dicarboxylic acid dichlorides with either a 2,2‐dimethyl‐1,3‐dioxolane (Taddol) or a 2,3‐dimethoxy‐2,3‐dimethyl‐1,4‐dioxane (Tatrol) core structure, and BH 3 ‐protected ortho ‐phosphanyl phenols, a set of fourteen new C 2 ‐symmetric diphosphine ligands was synthesized. In addition, three related ligands were obtained from ortho ‐diphenylphosphino‐anilines. The fully characterized ligands were then tested in the Pd‐catalyzed enantioselective O ‐allylation of 4‐methoxyphenol using crotyl methyl carbonate as a reagent. In addition, a pseudo‐intramolecular variant of the reaction, using crotyl 4‐methoxyphenyl carbonate as a substrate, was studied. The so‐called Trost ligand was used as a reference. Although the Trost ligand (3 mol‐%) gave up to 84 % ee , one of the new ligands showed higher activity (50 % ee with 0.075 mol‐%).