Towards Asymmetric Catalysis in the Major Groove of 1,1′‐Binaphthalenes

Four new diphosphane ligands, (R)‐ 4 , (R)‐ 5 , (S)‐ 6 , and (R)‐ 7 (Schemes 3, 4, 6, and 7), featuring metalcoordination sites located in the major groove of chiral 1,1′‐binaphthalene clefts, were prepared in enantiomerically pure form. The performance of this new class of ligands was tested in enantioselective, Pd‐catalyzed allylic alkylation reactions with acyclic and cyclic methyl carbonates 28 – 30 as substrates under various reaction conditions (Schemes 8 and 9). Using sodium phenyl sulfinate as a nucleophile, the reactivity of the catalysts formed with the new ligands and suitable palladium precursors was found satisfactory (>90%); however, the ee values were in all cases poor (<4%). Slightly better results were obtained using anions of dimethyl malonate as nucleophiles, but, also in these cases, the ee values never exceeded 17% (Table). ³¹P‐NMR‐Spectroscopic investigations revealed the formation of multiple‐catalyst species in solution (Fig. 2), and molecular modeling suggested a lack of embedding of the coordinated substrate in a `chiral pocket' (Fig. 3), which probably accounts for the observed low level of enantioselectvity.