PALLADIUM-CATALYZED CROSS-COUPLING OF VINYL IODIDES WITH ORGANOSTANNANES: SYNTHESIS OF UNSYMMETRICAL DIVINYL KETONES.

Article abstract of DOI:10.1021/ja00333a054

The palladium-catalyzed cross-coupling reaction of vinyl iodides with trimethyl- or tributylvinylstannanes in the presence of carbon monoxide gives unsymmetrical divinyl ketones in good yields. The reaction conditions are neutral and mild enough (40-50 degree C, 15-50 psig carbon monoxide) that other functional groups in either coupling partner can be brought unaltered into the coupled product. The E geometry in both partners is retained in the coupling product, and the Z geometry in the vinyltin reagent is maintained during the coupling reaction, but the coupled product undergoes slow Z to E isomerization under the usual reaction conditions. Isomerization of the divinyl ketone in the reaction medium is slowed in the dark. The reaction rate is especially sensitive to substituents on the vinyltin reagent, probably as a result of steric hindrance in the transmetalation step of the catalytic cycle.