Binaphthalene-templated N,S- and N,P-heterobidentate Ligands with an Oxazoline Pendant. Synthesis and Assessment in Asymmetric Catalysis

Novel chiral binaphthalene-core ligands where an oxazoline pendant is flanked by a sulfur 6, or by an atropisomeric phosphite donor 5, have been synthesized using the hydroxy binaphthyl oxazoline 7 as the common starting material. This intermediate is obtained in high e.e. by Ni-catalyzed asymmetric heterocoupling of two suitably 1,2-disubstituted naphthalene derivatives. Ligands 5 and 6 feature a stereogenic axis as the unique source of chirality. They display chelate binding towards Rh(I) centres affording cationic complexes which have been inspected for their catalytic activity in several asymmetric reactions with modest success. The Pd catalyst derived from the sulfur-containing oxazoline 6a provides up to 66% e.e. in the allylic alkylation of 1,3-diphenylallyl esters with dimethyl malonate.