Iron complexes formyls

Chiral tricarbonyl(butadienyl)iron complexes are easily accessible by resolution and show excellent diastereofacial selectivities with a variety of reagents55. The tricarbonyl(trienyl)iron complex 2 and methyl diazoacetate (copper bronze catalysis) give only two cis 7/m -isomeric cyclopropanes 5< These can be separated by column chromatography, and each diastereomer transformed into methyl traits- or 7.r-2-formyl-3.3-dimcthylcyclopropanecarboxylate (hemica-ronic aldehyde) by destructive cleavage of the diene complex auxiliary. The enantiomeric excess in these compounds is above 90%. 

Stoichiometric hydroformylation of a polyolefin iron complex was reported by loset and Roulet [8], which preferentially afforded the ewrfo-formyl isomer together with the hydrogenation product (Scheme 1.60). 

Treatment of tricarbonylh4-1-(ethoxycarbonyl)-l//-azepine]iron(0) (30) with acetic anhydride and tetrafluoroboric acid at 0 C (Method A) yields the 3-acetyl derivative 31.226 The acetyl derivative is also formed, but in lower yield, by the action of acetic anhydride and tin(IV) chloride (Method B) on complex 30. The 3-propanoyl derivative (20% mp 95-96 C) can be prepared similarly, whereas formylation to give aldehyde 32 is successful under Vilsmeier conditions. 

The reactivity of five-membered rings with one heteroatom to electrophilic reagents has been quantitatively compared. Table 1 shows that the rates of substitution for (a) formylation by phosgene and V,iV-dimethylformamide, (b) acetylation by acetic anhydride and tin(IV) chloride, and (c) trifluoroacetylation with trifluoroacetic anhydride (71AHC(13)235) are all in the sequence furan > tellurophene > selenophene > thiophene. Pyrrole is still more reactive as shown by the rate for trifluoroacetylation, by the relative rates of bromination of the 2-methoxycarbonyl derivatives (pyrrole > furan > selenophene > thiophene), and by the rate data on the reaction of the iron tricarbonyl-complexed carbocation [C6H7Fe(CO)3]+ (Scheme 5) (2-methylindole ss V-methylindole > indole > pyrrole > furan > thiophene (73CC540)). 

When various [Fe(heptafulvene)(CO)3] complexes are treated with POCI3 in DMF formylated products are produced.41 The reactivity of the iron carbonyl complex is markedly different than the reactivity of uncoordinated heptafulvenes which react with electrophiles to form the tropylium ion. 

The reaction ofimines such as 33 with ethyl diazoacetates yields complex product mixtures consisting ofaziridines and P-enamino esters. When phenyldiazomethane is used as the nucleophilic component in this iron-catalyzed reaction, aziridines such as 34 are obtained in high yield and as single diastereoisomers (Scheme 8.11) [42]. The catalyst is the same Fe(II)-complex that was applied for the preparation of a-formyl ester 23 (cf. Scheme 8.6). 

The reaction by which the complex is formed is thought to proceed via a formyl (HCO)Fe(CO)4 species, resulting from an attack of the hydride hydrogen on CO bonded to iron. 

Reaction of Complex III with acetyl chloride and aluminum chloride under typical Friedel-Crafts conditions affords acetylcyclobutadiene-iron tricarbonyl (VII) in high yields. The corresponding benzoyl derivative is similarly prepared with benzoyl chloride. Formylation with AT-methyl-formanilide and POCI3 produces cyclobutadienecarboxaldehyde-iron tricarbonyl (VIII), while chloromethylation with formaldehyde and HCl affords the chloromethyl derivative (IX). 

Chiral electrophilic cyclopropanes (63) are prepared in high enantiomeric excess starting from butadiene-iron tricarbonyl complexes (60) containing a non-complexed double bond. Reaction with diazomethane and decomposition of the resulting pyrazolines (61) in the presence of Ce" gave the corresponding chiral cyclopropanes (62). Breakdown of the dienic substituent of electrophilic cyclopropane (62) by means of ozonization resulted in the formation of formyl-substituted electrophilic cyclopropane (63) still carrying the asymmetric centre (equation 10) " . ... 

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