Iron Carbonyl-Promoted Isomerization of Olefin Esters to Their α,β-Unsaturated Esters:  Methyl Oleate and Other Examples

Abstract

Ultraviolet photolysis of stoichiometric amounts of methyl oleate and Fe(CO)(5) in hexanes solvent at 0 degrees C gives Fe(CO)(3)(eta(4)-alpha,beta-ester) in which the alpha,beta-unsaturated ester isomer of methyl oleate is stabilized by eta(4)-oxadiene pi coordination of the olefin and ester carbonyl groups to the Fe(CO)(3) unit. Treatment of the Fe(CO)(3)(eta(4)-alpha,beta-ester) with pyridine or CO liberates the free alpha,beta-ester, methyl octadec-trans-2-enoate, in 70% yield. The Fe(CO)(3) unit both catalyzes the olefin isomerization and stabilizes the alpha,beta-unsaturated ester, which results in the formation of the alpha,beta-ester in a yield far above that (3.5%) observed for simple catalyzed methyl oleate isomerization. The much smaller olefin esters, methyl 3-butenoate and ethyl 4-methyl-4-pentenoate, are isomerized under the same conditions to their alpha,beta-unsaturated esters in 94 and 90% yields, respectively. The effects of reaction conditions on the yield, the use of Fe(CO)(3)(cis-cyclooctene)(2) as a nonphotolytic catalyst, and the mechanism of this useful synthetic process are discussed.

Combined 1 H NMR and DFT study of the solvent effects on the iron pentacarbonyl-catalyzed photo-assisted isomerization of allyl alcohol

“…Ultimately, these findings show that the efficiency of a widely used IPC‐catalyzed isomerization reaction is solvent dependent. This study concerned one of the many possible IPC‐catalyzed isomerization reactions that may be studied …”

“…Iron pentacarbonyl (IPC) has been widely used in conjunction with ultraviolet (UV) light to catalyze a number of alkene isomerization reactions . The exact mechanisms for these reactions have been studied through computational, static, and ultrafast experimental techniques .…”

Base-Metal-Catalyzed Olefin Isomerization Reactions

“…Regarding the isomerization of alkenyl esters, Fe(CO) 5 was found to be active in the isomerization of methyl oleate to yield methyl trans-crotonate (Scheme 15). 34 Other iron carbonyl complexes, such as Fe 2 (CO) 9 35 and Fe 3 (CO) 12 , 36 are also suitable catalysts for the transposition of unsaturated esters.…”

Homogeneous catalysis for the conversion of biomass and biomass-derived platform chemicals

“…In addition to the rhodium, iridium and palladium isomerisation catalysts mentioned above, Fe(CO) 5 was also found to be an active isomerisation catalyst. 108,116 Similarly, silver was utilised for lactone formation. 117 Also, the use of [Pd(μ-Br)tBu 3 P] 2 leads to isomerisation and can be combined with a metathesis catalyst to create specific unsaturated product distributions.…”