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 metal-coordination 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 enantiose lective, Pd-catalyzed allylic alkylation reactions with acyclic and cyclic methyl carbonates 28-30 as substrates under various reaction conditions (Sc hemes 8 and 9). Using sodium phenyl sulfinate as a nucleophile, the reactiv ity of the catalysts formed with the new ligands and suitable palladium pre cursors was found satisfactory (> 90%); however, the ee values were in all cases poor (<4%). Slightly better results were obtained using anions of dim ethyl malonate as nucleophiles, but, also in these cases, the ee values nev er exceeded 17% (Table). P-31-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.