1,6-dibromohexa-1,3,5-triene - Stereocontrolled synthesis of monosubstituted and disubstituted hexatrienes by palladium-catalysed cross-coupling reactions

1,6-Dibromohexa-1,3,5-triene, previously described by us and easily obtaine d from 5-bromopenta-2,4-dienal by condensation with bromomethylene tripheny lphosphorane, is a versatile precursor for the synthesis of conjugated 1,3, 5-trienic derivatives of controlled configuration. In this paper, we descri be the stereocontrolled synthesis of E,E,Z, E,E,E and Z,E,Z isomers of alph a -bromo-omega -substituted-1,3,5-hexatrienes and 1,6-disubstituted-1,3,5-h exatrienes. The synthesis is based on palladium-catalysed single or double cross-coupling reactions between the three isomers - 1E,3E,5Z, 1E,3E,5E and 1Z,3E,5Z - of the intermediate 1,6-dibromohexa-1,3,5-triene and various or ganozinc reagents.