Highly Regioselective Rhodium-Catalysed Hydroformylation of Unsaturated Esters: The First Practical Method for Quaternary Selective Carbonylation

Highly regioselective hydroformylation of unsaturated esters can be achieved when a highly reactive, ligand-modified, rhodium catalyst is employed near ambient temperatures (15-50 degrees C) and pressures over 30 bar. The use of 1.3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantane shows distinct advantages over other commonly applied phosphanes in terms of reaction rate, and regio- and chemoselectivim Hydroformylation of a range 1,1-di- and 1,1,2-trisubstituted unsaturated esters yields quaternary aldehydes that are forbidden products according to Keulemans Rule. The aldehydes can be reductively aminated with molecular hydrogen to give beta-amino acid esters in high yield. The overall green chemical process involves converting terminal alkynes into unusual P-amino acid esters with only water generated as an essential byproduct. This catalytic system has also been applied to the hydroformylation of simple 1,2-disubstitued unsaturated esters, which have been hydroformylated with excellent alpha-selectivity and good chemoselectivity for the first time.