Rhodium catalysed asymmetric hydroformylation with chiral diphosphite ligands

Article abstract of DOI:10.1016/S0957-4166(00)80370-5

Chiral diphosphites have been synthesised starting from 1,2:5,6-diisopropylidene-D-mannitol, L-α,α,α,α,-tetramethyla-1,3-dioxolan-4,5-dimethanol and L-diethyltertrate. The diols react in moderate to good yields with 2,2'-bisphenoxyphosphorus chloride and 4,4'6,6',-tetra-t-butyl-2,2'-bisphenoxyphosphorus chloride (32-92%) to the corresponding chiral diphosphites. The compounds all exhibit C₂ symmetry and have been used as ligands in the rhodium catalysed asymmetric hydroformylation of styrene. The catalytic activity of the diphosphites strongly depends on the bulkynes of the ligand. With a bulky ligand enantiomeric excesses up till 20% have been obtained under mild reaction conditions (25-40°C, 40 bar syngas). It was found that both enantiomeric excess and regioselectivity to the branched aldehyde strongly depend on the hydroformylation reaction conditions.