(Dihydropyridine)iron tricarbonyl complexes

(N-Carboalkoxy-1,2-dihydropyridine)iron tricarbonyl complexes have been isolated by treatment of either N-carboalkoxy-1,2 or -1,4-dihydropyridines with diiron ennecarbonyl. The organic ligand was liberated from these complexes by use of trimethylamine oxide.     

The vibrational spectrum of (trimethylenemethane)iron tricarbonyl

A vibrational assignment for the trimethylenemethane molecule, in [C(CH₂)₃]Fe(CO)₃, has been proposed for the first time. CC₃ stretches were found at 1348 (E) and 918 cm⁻¹ (A₁), with skeletal deformations at 802 cm⁻¹ (A₁, out-of-plane), and 471 cm⁻¹ (E, in plane). The Fe(CO)₃ vibrations were closely similar to those in analogous complexes.     

New tricarbonyl(amido-substituted-1,3-diene)iron complexes

X-substituded benzamides (X = H; 2-OH; 4-MeO; 3-MeO; 3,5-(MeO)₂; 4-Cl and 2,4-Cl₂) have been shown to add reversibly to the dienyl rings of the organometallic compounds [(dienyl)Fe(CO)₃]BF₄ (dienyl = C₆H₇, 2-MeOC₆H₆ or C₇H₉) to give the corresponding cationic tricarbonyl(substituted-diene)iron complexes.     

Haptotropic rearrangement of tricarbonyl(2-acyloxytropone)iron

Respective two isomeric iron tricarbonyl complexes of 2-acetoxy- and 2-benzoyloxytropones were synthesized. These complexes rearranged to equilibrium mixtures of diastereomeric isomers, respectively, by 1,3-haptotropic rearrangement of iron tricarbonyl group but not by acyl migration and successive 1,2-haptotropic rearrangement, the mechanism having been clarified by the reaction of optically active complexes.     

Synthetic studies relating to acetylergosterol-(tricarbonyl)iron

Acetylergosterol(tricarbonyl)iron has been prepared in good yield using benzylideneacetone(tricarbonyl)iron. The steroidal complex may be hydroborated or subject to osmolysis, to yield potential vitamin D precursors.     

Stereochemical leakage mechanisms for tricarbonyl(dienyl)iron cations

ψ-Endo to ψ-exo leakage during solvolysis of a ψ-endo-dienol—Fe(CO)₃ dinitrobenzoate ester does not proceed via a syn, syn-cis-dienyl—Fe(CO)₃ cation. The most probable leakage mechanism involves non-stereospecific ionization of the dinitrobenzoate ester. syn,syn-cis-Dienyl—Fe(CO)₃ cations are formed from ψ-exo-dienol—Fe(CO)₃ complex during chromatography on grade I neutral alumina.     

Reaction of tricarbonyl(dienal)iron complexes with B-allyldiisopinocampheylborane

Addition of allyldiisopinocampheylborane to racemic (dienal)iron complexes, followed by oxidation, affords diastereomeric (1,4,6-trien-3-ol)iron complexes with moderate to low enantioselectivity. The high enantioselectivity typically observed for this allylborane reagent is attenuated by steric interaction between the Fe(CO)₃ group and the chiral isopinocampheyl groups. Further diminution of the enantioselectivity is observed for dienal complexes in which one rotomer predominates.     

Linkage isomerism in 5-exo thiocyanate and isothiocyanate substituted tricarbonyl(η-cyclohexa-1,3-diene)iron and tricarbonyl(η-cyclohepta-1,3-diene)iron

Nucleophilic addition to the tricarbonyl(η-cyclohexadienyl)iron cation and the tricarbonyl(η-cycloheptadienyl)iron cation by the thiocyanate ion forms initially the 5-exo-isothiocyanate (NCS) isomers, C₆H₇NCSFe(CO)₃ and C₇H₉NCSFe(CO)₃, both of which isomerise to the corresponding 5-exo thiocyanate isomers C₆H₇SCNFe(CO)₃ and C₇H₉SCNFe(CO)₃ on exposure to air.     

The electrophilic acetylation of tricarbonyl(cyclohexa-1,3-diene)iron

Friedel—Crafts acetylation of the title compound yielded as the major reaction product a $\text{4}\text{1}$ mixture of the 5-exo- and 5-endo-acetyl complexes. The major component of the mixture was shown to be the exo isomer by comparison with an authentic sample, synthesised stereospecifically.     

Diastereoselective spiroketalization: stereocontrol using an iron(0) tricarbonyl diene complex

It has been demonstrated that an element of planar chirality can influence the formation of an adjacent spiroketal stereocenter. Appropriately functionalized enantiomerically pure 1- and 2-sulfinyl 1,3-dien-5-ones and their corresponding iron(0) tricarbonyl complexes (7, 17) have been prepared, and the derived spiroketals (8, 18) are made in good to excellent diastereoselectivity. A preliminary exploration of the combined effects of planar and central chirality upon the diastereoselectivity revealed matched and mismatched combinations (14).     

Diene(tricarbonyl)iron complexes linked to spirooxazolones for the synthesis of cyclopropyldihydroxyphenylalanine

Complexed cyclopropyl-3,4-dihydroxyphenylalanine (∇ DOPA) were synthesized by diazomethane cyclopropanation of the appropriate diene(tricarbonyl)iron complexes linked to azlactones. Opening of the oxazolone ring by treatment with MeOH and DMAP gave the corresponding methyl esters. Introduction of the Boc group, cleavage of the carbamate with hydrazine provided Boc-protected cyclopropylogs of dl-dihydroxyphenylalanine.     

Fluxional behavior of methyl-substituted tricarbonyl(tropone)iron complexes and their different reactivity

The compositions of regioisomeric mixtures of tricarbonyliron complexes of 2-methyltropone (1a,b), 3-methyltropone (2a,b) and 2,6-dimethyltropone (3a,b) are studied and compared with the results of ab initio computations. The structures, frontier orbitals, and population analysis are evaluated by means of density functional theory. The thermodynamic and kinetic parameters of regioisomerizations are determined using dynamic ¹H NMR technique. The influence of methyl-substituent(s) on the equilibrium ratio of regioisomers resulting from the haptotropic rearrangement is discussed. Significant differences in the reactivity of C-protonized methyl- and dimethyl-substituted tricarbonyl(tropone)iron complexes 4–6 in nucleophilic additions and corresponding O-trimethylsilylated complexes 7–9 in [3+2] cycloadditions are explained in terms of electronic and steric effects of the methyl group(s). Various hydroazulenone cycloadducts of tricarbonyl(η⁴-2,6-dimethyltropone)iron 3a,b have been prepared by stereoselective [3+2] cycloaddition with Fp-reagents 12–14 and characterized. Formerly proposed mechanism of [3+2] cycloaddition was approved.     

Synthesis and reactivity of tricarbonyl(1-methoxycarbonyl-5-phenylpentadienyl)iron(1+) cation

Tricarbonyl(1-methoxycarbonyl-5-phenylpentadienyl)iron(1+) hexafluorophosphate (7) was prepared in two steps from tricarbonyl(methyl 6-oxo-2,4-hexadienoate)iron. While addition of carbon and heteroatom nucleophiles to 7 generally occurs at the phenyl-substituted dienyl carbon to afford (2,4-dienoate)iron products, the addition of phthalimide proceeded at C2 to afford a (pentenediyl)iron product (18). Complex 18 was structurally characterized by X-ray diffraction analysis.     

HPLC optical resolution of tricarbonyl(2,3-dihydrotropone)iron and its absolute configuration

Optical resolution of (±)-tricarbonyl(2,3-dihydrotropone)iron was carried out, and the absolute configuration was determined by X-ray diffraction and CD spectroscopic studies.     

Synthetic studies with iron carbonyl complexes. Versatile synthesis of olefinic side-chains to a tricarbonyl(cyclohexadiene)iron(0) ring

Tricarbonyl(cyclohexadiene)iron(0) complexes bearing olefinic side-chains at the 2- or the 5-position have been prepared by a versatile route. Terminal olefins are isomerised to internal isomers. The presence of a methoxy substituent at the 2-position prevents isomerisation of the coordinated diene into conjugation with the olefin, so locking the side-chain at the 5-exo-position.