Iron complexes, tricarbonyl cycloaddition reactions

Benzocyclobutene, when generated by oxidation of its iron tricarbonyl complex, can function as the dipolarophile in 1,3-dipolar cycloaddition reactions with arylnitrile oxides (Scheme 113).177 Unfortunately the synthetic versatility of this type of process is limited because of the unreactivity of other 1,3-dipolar species such as phenyl azide, benzonitrile N-phenylimide, and a-(p-tolyl)benzylidenamine N-oxide.177... 

The reaction of two alkynes in the presence of pentacarbonyliron affords via a [2 + 2 + 1]-cycloaddition tricarbonyl(ri4-cyclopentadienone)iron complexes (Scheme 1.6) [5, 21-23]. An initial ligand exchange of two carbon monoxide ligands by two alkynes generating a tricarbonyl[bis(ri2-alkyne)]iron complex followed by an oxidative cyclization generates an intermediate ferracyclopentadiene. Insertion of carbon monoxide and subsequent reductive elimination lead to the tricarbonyl(T 4-cyclopentadienone)iron complex. These cyclopentadienone-iron complexes are fairly stable but can be demetallated to their corresponding free ligands (see Section 1.2.2). The [2 + 2 + l]-cycloaddition requires stoichiometric amounts of iron as the final 18-electron cyclopentadienone complex is stable under the reaction conditions. 

The dimerization of thioformylketene was investigated by B3LYP and G3MP2B3 methods. The 4 + 4-pathway has the lowest energy barrier and calculations suggest that the reaction is pseudopericyclic.231 The stereospecific intramolecular 4 + 4-cycloaddition reaction between cyclohexadiene iron tricarbonyl complex and appended dienes (198) generates cyclooctadiene tricyclic adducts (199) (Scheme 56).232 The first example of an asymmetric intermolecular 4 + 4-photocycloaddition reaction in solution between 9-cyanoanthracene and chiral 2-methoxy-l-naphthamides has been reported. The frozen chirality is effectively transferred to the optically active product.233... 

Two Fe(CO)3 complexes of dimeric cyclooctatetraenes (29 and 30) are formed by irradiation of cyclooctatetraene iron tricarbonyl in the presence of free cyclooctatetraene, posing a formidable problem with respect to the mechanism of this cycloaddition reaction 244,403,407,4io). 

Cycloaddition.— Reactions of electrophilic olefins and acetylenes with tricarbonyl-iron complexes of cycloheptatriene and cyclo-octatetraene lead to 1,3-exo-products. Troponetricarbonyliron and tcne, however, have now been found to give complex (20) which results from previously unobserved 1,5-exo-cycloaddition. A dipolar intermediate (21) resulting from initial attack by the electrophile on the hydrocarbon... 

A [5+1] carbonylative cycloaddition of chromium Fischer carbene complexes having /ra j,/ra 5-dienyl substituents at the carbene carbon atom with nonacarbonyldiiron gives ri -2-alkoxycyclohexa-2,4-dienone(tricarbonyl)iron complexes and 2-alkoxyphenols (Scheme 4-13). Without the addition of the carbonyliron complex, this reaction works only for substrates that have a cw-disposition at the a,P-double bond. The ri -2-alkoxycyclohexa-2,4-dienone(tricarbonyl)iron complexes can be converted to the corresponding phenols by treatment with base or by stirring with silica gel in the presence of air. 

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Cyclobutadiene iron tricarbonyl complexes can be isolated and have been utilized in organic synthesis. Both intra- and intermolecular [2 + 2] cycloadditions of alkenes with cyclobutadiene complexes are observed upon decomplexation using CAN or TMANO (Schemes 164-165). The stereochemistry of the aUcene is retained in the product. Iron tricarbonyl diene complexes are compatible with metathesis reactions... 

The dipolar addition reaction between DMAD or dimethyl maleate and the diimine species [Fe(CNR)3(Pr N=C HCH=NPr>)] (R = Bu , CH2Ph, Cy, 2,6-xylyl etc.) occurs to give complexes of type (4) in the case of [Fe(CO)2(CNR)(Pr N=CHCH=NPri)] there is a competition between CO and CNR insertion into the metallacycle. Compounds containing fused pyrrole rings arc also formed which on heating release substituted 2-vinylpyrroles. -64 similar cycloaddition also occurs between [Fe(C0)3(Bu N=CHCR=0)] (R = Me, Ph) and DMAD. 5 Purther details of the insertion of alkynes into vinylketene iron tricarbonyl complexes have appeared thermolysis of the insertion products gives cyclopentenediones or phenols. -... 

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