Highly stereoselective and efficient addition of organocerium reagents to syn-beta-alkyl-beta-hydroxy-alpha-methyl ketones by way of their titanium alkoxides - Synthesis of complex 1,3-diol units with three stereodefined centres

A highly efficient and stereoselective technique for additions to syn-beta -alkyl-beta -hydroxy-alpha -methyl ketones is now available. The methodolog y is based on the conversion of the starting material into a trichlorotitan ium. alkoxide derivative, which is able to assume a stable cyclic arrangeme nt exhibiting high stereofacial discrimination towards nucleophilic alkyl t ransfer by an appropriate organometallic species. The use of Grignard reage nts has serious limitations; in fact, highly hindered and basic reagents do not work well with enolizable substrates. Organocerium compounds can obvia te these drawbacks, since side processes such as enolization or interaction with titanium(IV) are almost completely suppressed. The method permits the introduction of a large variety of carbon systems, including primary, seco ndary and tertiary alkyl chains, as well as aromatic, alkynyl and benzylic moieties, in high yields and with good stereoselectivities.