Effective Catalytic Asymmetric Synthesis of S-(—)-3-Methoxycarbonyl-4-(3,4-methylenedioxyphenyl)butanoic Acid. A Simple and Effective Route to Chiral Lignans

Effective catalytic asymmetric synthesis of 5-2, a key intermediate for the synthesis of chiral lignans, was described.Thus, BPPM-Rh+ in the presence of triethylamine gave 5-2 in 78% optical yield.Chiral pyrrolidinephosphine-rhodium catalysts have been proven to be practically useful for the preparation of chiral a-amino acids (83-918 optical yields)2,3), salsolidine (45%) * ) , a-hydroxy esters (78.5%) 5f6), R-(-)-pantolactone (80.5-86.7%)7'8),6-amino acids (53-55%19), u-methylsuccinic acid ( 9 4 . 2% ) 10-12) and 6methylaspartic acid (58.2%113), and also the mechanistic studies14) on these asymmetric hydrogenations suggested that the 5.y-unsaturated acid is one of the most suitable substrates for the asymmetric hydrogenations catalyzed by chiral pyrrolidinephosphine-rhodium complexes to obtain the high optical yields.