Iron tricarbonyl complexes acylation

Chiral diene—iron tricarbonyl complexes were acylated using aluminum chloride to give acylated diene—iron complexes with high enantiomeric purity (>96% ee). For example, /ra/ j -piperjdene—iron tricarbonyl reacted with acyl haUdes under Friedel-Crafts conditions to give l-acyl-l,3-pentadiene—iron tricarbonyl complex without any racemization. These complexes can be converted to a variety of enantiomericaHy pure tertiary alcohols (180). 

Azepines do not undergo electrophilic substitution reactions and introduction of substituents at the 3-or 4-position is a difficult problem. Acylation at C-3 can be achieved via the iron tricarbonyl complex as shown in Scheme 22.42 The N-ethoxycarbonyl group of the acylated product can be removed with methoxide methanol and the resulting 1H compound can then be methylated. 

Gibson nde Thomas, and Tustin have reported the formation of a number of iron carbonyl complexes of a,/J-unsaturated acyl silanes226. Propenoyl trimethylsilane did not give a stable complex, but the iron tricarbonyl complexes of cinnamoyl silanes were very stable. 

Although few examples of acylations of 1,3-butadienes have been described, Friedel-Crafts acylations of diene complexes, in particular iron tricarbonyl derivatives, can give synthetically useful yields. In acylations of iron tricarbonyl complexes with the Perrier reagent from acetyl chloride and aluminum chloride, acylation occurs only at unsubstituted terminal carbons (Scheme 18). ° The primary product is... 

Other hypochlorites, and in particular tert-butyl hypochlorite [114], have also been used. For example, the latter reagent was apphed in the oxidation of a (cy-clobutadiencarboxaldehyde) iron tricarbonyl complex (9), which afforded ester 10 in 90% yield [Eq. (5)]. No oxidation of the metal center occurred. The reaction path involves the aldehyde oxidation by tert-butyl hypochlorite leading to the corresponding acyl chloride, which is then converted into the methyl ester by reaction with... 

The tetra-cA-cycIononatetracne 241 is unstable and easily rearranges at 23 °C (t /2 50 min) to the isomeric d.v-8,9-dihydroindcne 242 (equation 77)89. It is interesting, however, that the iron(III) tricarbonyl complex of tetraene 241 is stable for many days at room temperature and isomerizes to the Fe-complex of 242 only upon heating in octane at 101 °C89. The principle of stabilization of the reactive multiple bonds with metal carbonyl complexes is well-known in modem organic synthesis (e.g. see the acylation of enynes90). 

The iron tricarbonyl unit has been described as a protecting group for a 1,3-diene, as in the acetylation of the complex of myrcene at low temperature (Scheme 20). The usual combinations of a,p- and p,"y-un-saturated ketones were formed. At higher temperatures, some acylation at the terminus of the diene complex was also observed. In an interesting extension, reaction of the complex with oxalyl chloride resulted in cyclization of the acid chloride initially formed by reaction at the alkene. ... 

Iron carbonyl complexes are obtained by irradiation of iron pentacarbonyl with vinylcyclopropanes. The principal modes of reaction are (i) metal insertion into a strained bond with hydrogen migration to give diene-Fe(CO)3 complexes, (ii) metal carbonyl insertion to give a n-allyl-complexed acyl iron tricarbonyl, and (iii) cycloinsertion of CO across the homodiene to give a cyclohexenone. Similar types of... 

This has an interesting consequence with the -q -cyclohexadienyl complex 10.1 (Scheme 10.12). As acylation is initially on iron, the iron and the acetyl group are cis in the -intermediate 10J9. The proton that is lost must be cis to iron (perhaps via transfer to iron in a reverse of the acylation sequence). The more acidic proton, Hb, a- to the newly installed acetyl group is trans to iron and, therefore, not available. The proton lost, therefore, is Ha on the other side resulting in net movement of the diene system to give diene complex 10.40. Better yields are obtained with the more electron rich monotriphenylphosphine complex 10.41 (L = PPhs), than the tricarbonyl complex (L = CO). ... 

The electron-donating properties of the diene-iron tricabronyl group is also indicated by the fact that phenylbutadiene-iron tricarbonyl (XVI) can be acylated with CH3COCI and SnCl4 under mild conditions to give the corresponding para-substituted complex 32). 

Diels-Alder reactions, 4, 842 flash vapour phase pyrolysis, 4, 846 reactions with 6-dimethylaminofuKenov, 4, 844 reactions with JV,n-diphenylnitrone, 4, 841 reactions with mesitonitrile oxide, 4, 841 structure, 4, 715, 725 synthesis, 4, 725, 767-769, 930 theoretical methods, 4, 3 tricarbonyl iron complexes, 4, 847 dipole moments, 4, 716 n-directing effect, 4, 44 2,5-disubstituted synthesis, 4, 116-117 from l,3-dithiolylium-4-olates, 6, 826 electrocyclization, 4, 748-750 electron bombardment, 4, 739 electronic deformation, 4, 722-723 electronic structure, 4, 715 electrophilic substitution, 4, 43, 44, 717-719, 751 directing effects, 4, 752-753 fluorescence spectra, 4, 735-736 fluorinated derivatives, 4, 679 H NMR, 4, 731 Friedel-Crafts acylation, 4, 777 with fused six-membered heterocyclic rings, 4, 973-1036 fused small rings structure, 4, 720-721 gas phase UV spectrum, 4, 734 H NMR, 4, 7, 728-731, 939 solvent effects, 4, 730 substituent constants, 4, 731 halo... 

Cyclopropanation reactions of nonheteroatom-stabilized carbenes have also been developed. The most versatile are the cationic iron carbenes that cyclopropanate alkenes with high stereospecificity under very mild reaction conditions. The cyclopropanation reagents are available from a number of iron complexes, for example, (9-alkylation of cyclopentadienyl dicarbonyliron alkyl or acyl complexes using Meerwein salts affords cationic Fischer carbenes. Cationic iron carbene intermediates can also be prepared by reaction of CpFe(CO)2 with aldehydes followed by treatment with TMS-chloride. Chiral intermolecular cyclopropanation using a chiral iron carbene having a complexed chromium tricarbonyl unit is observed (Scheme 61). 

Treatment of tricyclo[3.2.0.0 ]hept-3-ene (13) with iron carbonyls leads to a primary complex 14, which undergoes thermal rearrangement and carbonylation to 4-(tricarbonyl)ferrate-tracyclo[4.2.1.0 .0 ]nonan-5-one (15). Photochemical conversion of the primary complex 14 gives 8-(tricarbonyl)ferra-2,3-f/-tricyclo[4.2.0.0 ]oct-2-ene (17) (in equilibrium with its acyl complex 16). This system after carbonylation undergoes rearrangement to 2-(tricarbonyl)ferra-6,7-f/-tricyclo[3.2.2.0 ]non-6-en-4-one (18), which upon decomplexation gives tricyclo-[3.2.1.0 ]oct-3-en-6-one (19). Several other products (not containing cyclopropane subunits) are obtained under modified conditions. ... 

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