Diastereoselective synthesis of (E)-alkenes and (E)-1,omega -dienes starting from diastereoisomeric mixtures of 1-bromo-1-alkenes. New syntheses of monounsaturated or bridged ring-ketal naturally occurring substances

The PdCl2 (dppf)-catalyzed cross-coupling reaction between diastereoisomeric mixtures of 1-bromo-1-alkenes which contain n equiv. of (E)-stereoisomers and n equiv. of Grignard reagents allows to obtain (E)-alkenes or (E)-1-ω-dienes having 95.5–99% stereoisopmeric purity in satisfactory yields. Such compounds are useful precursors to several naturally occuring substances