Axially Chiral 1,1'-Binaphthyl-2-Carboxylic Acid (BINA-Cox) as Ligands for Titanium-Catalyzed Asymmetric Hydroalkoxylation

Axially chiral, enantiopure 1,1'-binaphthyl-2-carboxylic acids (BINA-Cox) have recently been introduced as chiral ligands for transition metal catalysis. Together with equimolar, co-catalytic amounts of Ti(OiPr)₄ and water they form an in situ catalyst that performs the asymmetric catalytic hydroalkoxylation of 2-allylphenols to 2-methylcoumarans at high temperature (240 °C, microwave heating). The synthesis of reference ligand 2'-MeO-BINA-Cox (L1) has been optimized and performed at molar scale. Synthetic routes have been developed to access a variety of substituted BINA-Cox ligands (>30 examples), which have been tested for ligand effects on the reference asymmetric cyclization of 2-allylphenol. The substrate range of asymmetric catalytic hydroalkoxylation has been explored through systematic substrate structure variations to define scope and limitations of the titanium-catalyzed process. The new substrates 2-(1-vinylcycloalkyl)phenols (1j, 1k), 2-(2-vinylphenyl)propan-2-ol (1t), and 2'-vinyl-[1,1'-biphenyl]-2-ol (1u) are shown to undergo asymmetric catalytic cyclization to benzodihydrofurans and benzo[c]chromene, respectively.