New Synthetic Routes to β‐Olefinic Triphenylphosphonium Salts via (Diolefin)tricarbonyliron Complexes

Abstract

SummaryThe regio-and stereospecific preparation of 8-olefinic triphenylphosphonium calts. starting froim (dio1efin)tricarbonyliron compounds is described. The latter are converted by various routes into either [(allylderivatives. The allylic cations, when reacted with P (C6H5)3. yield uncomplexed (2-en-1-y1)triphenylphosphonium salts in good yields, while treatment of the dienyl cations with P (C6H5), leads to the quantitative formation of (2,4-diene-1-y1)triphenylphosphonium ions still coordinated to the Fe (CO),-moiety. A method of oxidative decomplexation is described, by which the free phosphonium salts can be obtained.All new compounds were characterized by 13C-NMR spectra and also, where necessary, by 'H-NMR decoupling experiments to confirm the stereochemical assignments. Many of the new phosphonium salts, potentially useful as Wittig reagents for natural product syntheses, are difficult to obtain by conventional unequivocal routes.

New Synthetic Routes to β‐Olefinic Trialkoxyphosphonium Salts and Phosphonates: Organometallic Variants of the Michaelis‐Arbuzov Reaction

“…Metal-coordinated phosphites can also undergo the Michaelis-Arhuzov reaction, leading to metal-coordinated phosphonates. These reactions occur under much milder conditions, following the general ionic mechanism described above in the presence of a halide complex l b had, therefore, undergone a ligand substitution by excess P(OEt),, an expected reaction, as it is also observed with other Lewis bases [7]. As the counterion in our case was the non-nucleophilic BF;, the free trialkoxyphosphonium salt was quite stable in the absence of P(OEt),.…”

“…The phosphonate 8e on the other hand, seems to undergo mainly decomposition on treatment with base. A similar base-catalyzed (Z/E)-isomerization had previously been described by us with the corresponding triphenylphosphonium salts [7] [21] and appears to be an essential feature of metal-coordinated P compounds of this type. "C-and "P-NMR data are summarized in Table 3.…”

“…Reaction of this intermediate cation 4a, which we prepared from [(butadiene)Fe(CO),] and CH,COCl/AICl, and which is normally converted by inorganic or organic bases into [(dienone)Fe(CO),] compounds [17], with P(OEt), led to the free ((2)-5-oxo-2-hexen-l-yl)phosphonate 4d in 78 % yield (Scheme 5). A similar reaction with Ph,P under the same conditions as described before [7] allows the isolation of the corresponding triphenylphosphonium salt 4f in 90 % yield. The initial s-cis-conformation of [(butadiene)Fe(CO),] is again retained throughout the reaction sequence and induces the formation of a (Z)-configurated phosphonium salt or phosphonate.…”

“…We had previously developed methods for decomplexation of metal-coordinated phosphonium ions [7]. When allylic complexes such as [(allyl)Fe(CO),]+ were used as starting materials, free P,y-unsaturated phosphonium salts are directly obtained in high yields, which are difficult to prepare by conventional routes…”

“…Of particular interest has been the addition of phosphorus nucleophiles like Ph,P to metal-coordinated olefinic ligands [5], and a number of unsaturated phosphonium salts have been isolated in this manner. We had previously developed methods for decomplexation of metal-coordinated phosphonium ions [7]. When allylic complexes such as [(allyl)Fe(CO),]+ were used as starting materials, free P,y-unsaturated phosphonium salts are directly obtained in high yields, which are difficult to prepare by conventional routes times superior in reactivity and selectivity.…”