CATALYTIC DECARBONYLATION, HYDROACYLATION, AND RESOLUTION OF RACEMIC PENT-4-ENALS USING CHIRAL BIS(DITERTIARY-PHOSPHINE) COMPLEXES OF RHODIUM(I)

Article abstract of DOI:10.1016/0022-328X(85)87377-0

Attempts to decarbonylate racemic aldehydes catalytically using rhodium(I) complexes containing chiral di-tertiary-phosphine ligands are described.Incorporation of an alkenic moiety into the aldehyde, for subsequent probing of induced asymmetry by chiral shift reagents, leads instead to formation of optically active hydroacylated products via kinetic resolution of the precursor racemic aldehyde.For example, (RS)-2-methyl-2-phenylpent-4-enal (1a) yields, on treatment with Cl, 2-methyl-2-phenylcyclopentanone with up to 69percent e.e of the (-)-(S) optical isomer and remaining unreacted aldehyde which is possibly the enantiomerically pure (-)-(R) form.Extension of this cyclization reaction to a 3,3-disubstituted pent-4-enal similarly provides a synthesis for an optically active 3,3-disubstituted cyclopentanone.Decarbonylation by-products are also observed; those from 1a appear as E- and Z-2-phenylpent-2-ene.The cyclization of 1a is catalyzed also by Rh(chiraphos)(solvent)2⁺ but with lower e.e.