ja011426w_si_002.pdf (259.32 kB)
Formation of Vinyl Halides via a Ruthenium-Catalyzed Three-Component Coupling
journal contribution
posted on 2002-05-30, 00:00 authored by Barry M. Trost, Anthony B. PinkertonThe ruthenium-catalyzed three-component coupling of an alkyne, an enone, and halide ion to
form E- or Z-vinyl halides has been investigated. Through systematic optimization experiments, the conditions
effecting the olefin selectivity were examined. In general, more polar solvents such as DMF favored the
formation of the E-isomer, and less polar solvents such as acetone favored formation of the Z-isomer. The
optimized conditions for the formation of E-vinyl chlorides were found to be the use of cyclopentadienyl
ruthenium (II) cyclooctadiene chloride, stannic chloride pentahydrate as a cocatalyst, and for a chloride
source, either ammonium chloride in DMF/water mixtures or tetramethylammonium chloride in DMF. A
range of several other ruthenium (II) catalysts was also shown to be effective. A wide variety of vinyl chlorides
could be formed under these conditions. Substrates with tethered alcohols or ketones either five or six
carbons from the alkyne portion gave instead diketone or cyclohexenone products. For formation of vinyl
bromides, a catalyst system involving the use of cyclopentadienylruthenium (II) tris(acetonitrile) hexafluorophosphate with stannic bromide as a cocatalyst was found to be most effective. The use of ammonium
bromide in DMF/acetone mixtures was optimal for the synthesis of E-vinyl bromides, and the use of lithium
bromide in acetone was optimal for formation of the corresponding Z-isomer. Under either set of conditions,
a wide range of vinyl bromides could be formed. When alkynes with propargylic substituents are used,
enhanced selectivity for formation of the Z-isomer is observed. When aryl acetylenes are used as the
coupling partners, complete selectivity for the Z-isomer is obtained. A mechanism involving a cis or trans
halometalation is invoked to explain formation of the observed products. The vinyl halides have been shown
to be precursors to α-hydroxy ketones and cyclopentenones, and as coupling partners in Suzuki-type
reactions.