Iron complexes, with dienes

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). 

Cleavage of acylated diene-iron complexes with LiAlH4 is illustrated by the following reports of Nes-meyanov and Anisimov (Scheme 12).28,29... 

Antimony—metal complexes, characteristics, 2, 34 Anti-proliferation drugs, for parasites, 12, 458 159 Anti-tumor effects, Ti(IV) complexes, 4, 662 (—)-Antofine, via ring-closing diene metathesis, 11, 222 (t-)-Aphanomol 1, via [5+2]-cycloadditions, 10, 613-614 Apical ligands, iron complexes with, 6, 313 Aqua ligands... 

Reactions of the corresponding ketones have been much less studied, but alkylation reactions appear to be highly antiselective relative to the metal. Some alkylations resulting in the isomerization of the diene geometry have been observed. For example, reaction of (85) with methyl magnesium bromide gives (86) but reaction with methyl lithium affords (87) (Scheme 137). Related reductions of dienone iron complexes with sodium borohydride are also highly antiselective. 

Recent developments include asymmetric polyene cyclisations but also include new ways to initiate cyclisations. Iron tricarbonyl stabilises pentadienyl cations and its complexes with dienes are chiral. Addition of the achiral lithium derivative 268 to the chiral complex 269 gives the polyene precursor 270 that cyclises with Lewis acid to give a single diastereoisomer of the bicyclic compound43 271. 

A variety of other macrocycles have been used in the synthesis of iron and other transition element compounds. The structures of some of these are presented in Figure 20. The abbreviations presented herein are used in the following discussion. Although iron complexes with several of these ligands have been prepared and characterized, only those of the cyclic diene 1,7-CT will be considered here (41). The several... 

Lactones from dienes. Several 1,3-dienes have been converted into lactones by monoepoxidation and conversion to iron complexes with Fe(CO)j with insertion of CO. The lactone is obtained on oxidation with CAN. ... 

Scheme 4-65. Reaction of cyclic allyl(carbene)iron complexes with C-nucleophiles to afford substituted 1,3-dienes.

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. ... 

The mechanism of this reaction involves hydroxide attack at a carbonyl ligand with concomitant cleavage of the lactone moiety to give an allyliron complex with a hydroxy group in a-position. The latter is eliminated after rotation to an antiperiplanar position in respect to the iron complex moiety. This results in formation of the (diene)iron complex with inversed configuration at Cl (Scheme 4-109). ... 

Even though the electron density of the diene system in tricarbonyl(T -diene)iron complexes is reduced due to 7t-donation to the iron center, reactions with various electrophiles are still possible. Thus, Friedel-Crafts alkylation of (diene)iron complexes with alkoxychloromethanes gives selectively cis- or tra s-(alkoxypenta-2,4-diene)iron complexes depending on the work-up conditions (Scheme 4—110). ... 

The most used reaction with respect to electrophilic substitution at (diene)iron complexes is the acylation. (Dienone)iron complexes are obtained by reaction of acyclic tricarbonyl(Ti -l,3-diene)iron complexes with carboxylic acid chlorides in the presence of aluminum trichloride in high yields (Scheme 4-11 i).P65-271]... 

Scheme 4-118. Reaction of (ri" -diene)iron complexes with carbon...

Scheme 4-122. Cyclization of (ri -diene)iron complexes with olefins.

The dynamic diastereoselectivity during the [6+2] ene spirocyclization of a mixture of two enantiopure diastereoisomeric allylamide-tethered tricarbonyl(T -cyclohexa-l,3-diene)iron complexes leads to only two diastereoisomeric spirolactams out of four possible isomers. A double cyclization of tricarbonyl(T) -cyclohexa-l,3-diene)iron complexes with pendent conjugated dienes gives rise to tricyclic (diene)iron complexes. Four new stereogenic carbon centers are formed in the course of this reaction to give a single diastereoisomer (Scheme 4-124). ° ° ... 

Scheme 4-124. Double cyclization of (ri -cyclohexadiene)iron complexes with pendent conjugated dienes.

Tricarbonyl(ri -cyclohexa-l,3-diene)iron complexes are intermediates in the reaction of tricarbonyI(T -cyclohexadienylium)iron complexes with substituted anilines in the presence of air (Scheme 4-131). Under these conditions, concomitant oxidative cyclization of the intermediate aniline-functionalized (ri -cyclohexa-l,3-diene)iron complexes occurs to give tricarbonyliron-complexed dihydrocarbazoles. The latter are... 

Scheme 4-135. Catalytic enantioselective alkylation of (Ti -diene)iron complexes with dialkylzinc reagents.

A variety of carbonyl reactions can be performed with aldehyde groups adjacent to (diene)iron complexes. This includes cyanohydrin formation as part of a synthesis employing sequential stereoselective introduction of nucleophiles to (diene)iron complexes with concomitant elongation of the carbon chain (see also Scheme 4-155). 370,371,374,375] reactions of aldehydes adjacent to (diene)iron complexes with methyl ketones have been reported. Diastereoselective intramolecular Mannich reaction of a... 

Formation of cationic T -dienyliron complexes by proton addition to (Ti -diene)iron complexes with an additional conjugated double bond can also be applied to acyclic systems. Monocyclization and polycyclization reactions proceed by nucleophilic addition of pendent double bonds to the complexes. " - " ... 

Using an acetoxy function as leaving group a to the (t -diene)iron complex, this reaction has been employed for the synthesis of the C7-C24 segment of macrolactin 1-Ethoxy-substituted T) -cyclohexadienyliumiron complexes can also be obtained by alkylation of (Ti -cyclohexadienone)iron complexes with triethyloxonium cations (Scheme 4-162). Another general approach to ri -dienyliumiron complexes proceeds via protonation of a noncomplexed double bond in [(l-4-Ti)-l,3,5-triene]iron complexes (Scheme 4-163). - ... 

An alternative approach to alkene extended cyclohexadienyliumiron complexes is the reaction of (a-keto-cyclohexa-l,3-diene)iron complexes with a nucleophile obtained by hydroalumination of methyl propiolate, subsequent ligand exchange with triphenyl-phosphane, and removal of the hydroxy group with hexafluorophosphoric acid (Scheme 4-171). Organocuprates add to these compounds at the terminus of the noncomplexed double bond.f "" ... 

Intermediate Ti -dienyliumiron complexes which are formed by reaction of (Ti -a-hydroxy-l,3-diene)iron complexes with boron trifluoride etherate can also be trapped by olefins. An intramolecular variation with tethered olefins leads to a stereospecific cyclization. The resulting cyclohexyl cations can be stabilized by addition of nucleophiles... 

Tricarbonyliron complexes of 1,2-diazepines do not show the rapid isomerization found in their azepine counterparts (Scheme 22) the iron forms a diene complex with the C=C double bonds in the 4- and 6-positions. The chemistry of the 1,2-diazepine complexes is similar to that of the azepine complexes (Section 5.18.2.1) (81ACR348). 

ALKYLATION OF DIMEDONE WITH A TRICARBONYL(DIENE)IRON COMPLEX TRlCARBONYL[2-[(2,3,4,5-t))-4-METHOXY 2,4 CYCLOHEXADUEN-l-YLJ-5,5-DIMETHYL-l,3-CYCLOHEXANEDIONE]IRON... 

Syntheses of heterocycles, among them carbazole alkaloids, with participation of tricarbonyl(Ti -diene)iron complexes 99CSR151. 

Scheme 26 1,4-Hydroboration of 1,3-diene derivatives with pinacolborane catalyzed by an iron complex...

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