Catalytic Asymmetric Cyclocarbonylation of<i>o</i>-Isopropenylphenols:  Enantioselective Synthesis of Six-Membered Ring Lactones

Abstract

Cyclocarbonylation of o-isopropenylphenols with CO (500 psi) and H(2) (100 psi), using Pd(OAc)(2) and (+)-DIOP as the chiral catalyst, in CH(2)Cl(2) affords 3,4-dihydro-4-methylcoumarins in 60-85% yield and in up to 90% enantiomeric excess. The stereoselectivity is influenced by the structure of the chiral phosphine ligands and substrates, as well as by the reaction conditions.