Iron, allyl complex

Although there are some reactions that use complex 76 stoichiometrically [50-58], it was not until 1979 that Roustan et al. developed the first catalytic application of complex 76-Na (Scheme 16) [59, 60]. In his publication, he could show that catalytic amounts of complex 76-Na react with an allylic chloride or acetate to form an allyl-iron-complex, which, in a second step, is substituted with a malonate to yield 77. Most importantly, they observed a preference for the ipso-substitution-product 77a, that is, the new C-Nu-bond was formed preferentially at the carbon atom that was substituted with the leaving group before. 

A recently described method for insertion of a carbon monoxide molecule into the monoepoxide of a conjugated diene gives /3-lactones in high yield. This is achieved by reaction of iron pentacarbonyl with the starting vinyloxirane to give the 7r-allyl iron complex (66), which on oxidation with cerium(IV) ammonium nitrate gives the /3-lactone. In some cases, y-Iactone products can also be obtained from this reaction (8lJCS(Pi)270). 

Complementary to the conjugate substitution reaction in which the nucleophile is transferred directly from the tetraalkyl ferrate to the allylic ligand, preformed low-valent Fe complexes can form reactive allyl-iron complexes via an SN2 -type mechanism (path C, Equations (7.8) and (7.9), Scheme 7.16], These complexes react with incoming nucleophiles and electrophiles in a substitution reaction. Depending on the nature ofthe iron complex employed in the reaction, either o- or Jt-allyl complexes are generated. 

There exist only a few scattered reports of ( -allyl)iron complexes lacking a cyclopentadienyl (see... 

The NMR spectroscopy of ( -allyl)iron complexes reveals a consistency across the various types of complexes. The relative shielding of the protons on the allyl unit is invariably Hanti > > H2 (soo Table 1). The coupling constants... 

A slight variation of the [3-I-2] cycloaddition approach <1977ICA(25)165> has also been employed for the diastereoselective synthesis of the corresponding anti- and ry -iron-substituted 1,2-dithiolane 1-oxides 243 from 237, as a source of electrophilic disulfur monoxide, and 7] -allyl iron complex 242 (Scheme 39). The method was also tested with cyclopentadienyl iron dicarbonyl crotonyl complex 244 when four diastereomers 245-248 were generated in modest yields (35%) <19980M5534>. 

In contrast to the analogous Ni and Co complexes Tp MCl that react with allyl magnesium bromide during the formation of Tp MCj/ -CsHs), Tp TeCl gives under the same reaction conditions the tetrahedral 14-electron j/ -allyl iron complex Tp Fe(fj -CH2CH = CH2). ... 

Bia.2 b,3i -pjjg synthesis of Routiennocin employed iron tricarbonyl chemistry for the synthesis of the spiroketal unit. In this sequence the allylic epoxide 39 is converted to a mixture of allyl iron complexes 40 and 41 which is not separated but carbonylated together to give lactone 42 as a 9 1 (a 3 3"y) mixture (Scheme 4.14) this mixture is subsequently reduced to the saturated lactone 43. ... 

Photoexcitation of cyclopentadienylirondicarbonyl (Fp) allyl complexes normally leads to cleavage of the Fe-GO bond. Upon irradiation of a related phosphine-chelated iron-allyl complex, the known (77 -allyl)iron complex was... 

Oxidation of tricarbonyl(trimethylenemethane)iron complexes 25 containing an olefinic side chain, with Me3NO in boiling benzene, affords dibridged dicarbonyl (bis-7r-allyl)iron complexes. 

Cyclization of an (T -trimethylenemethane)iron complex with a double bond of a diene in an appropriate distance leads to bis(T -allyl)iron complexes (Scheme 4—100), which are presumably also intermediates in the reactions presented in Scheme 4—99. ... 

In the absence of a carbonyl compound, the electroreduction leads to the formation of hexadiene, thus implying the formation of a Jt-allyl iron complex formed by addition of Fe on allyl acetate. Certainly, this is the Jt-allyl iron complex that reacts with carbonyl compounds leading to homoallylic alcohols. 

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