Palladium catalyzed cross-coupling reaction of functional organozinc reagents with (2E,4E)- and (2E,4Z)-5-bromopenta-2,4-dienals:: Easy access to functional conjugated dienic aldehydes

Functional zinc reagents can be applied to palladium catalyzed cross-coupling reaction with (2E,4E)- and (2E,4Z)-5-bromopenta-2,4-dienal. The corresponding functional dienic aldehydes were obtained in goods yields. From the (2E,4E) isomer, the (2E,4E) dienals were isolated as single isomer according to a total stereoselective reaction. But, from the (2E,4Z) isomer the coupling reaction has lead to a mixture of (2E,4E) and (2E,4Z) isomers. A mechanism for the loss of stereoselectivity in the last case is proposed.