Ketones ferrocenyl

Arnett and Bushick (2) have determined the pKA values for the conjugate acids of ferrocenyl ketones in aqueous sulfuric acid. They have found, for example, that acetylferrocene is over 2000 times more basic than acetophenone and 85 times more basic than p-hydroxyacetophenone. These data support the concept that metallocenyl groups are strongly electron-releasing compared to the phenyl group and that they possess extraordinary ability to delocalize adjacent positive charges. 

Polyferrocenylenes (221), poly(ferrocenyl ketone) (221), poly(ferrocenyl-mercury) (199). (b) Cymantrene derivatives... 

Ferrocenyl ketones (287) and ferrocenyl aldehyde (288) readily undergo a number of classic organic transformations, such as aldol, Knoevenagel, and Wittig reactions. Conversion of (288) into the dimethylaminoacetonitrile (317)... 

If other elements of chirality are present in the molecule, the descriptors should be arranged in the order central > carbocationic > axial > planar > torsional (note that Sokolov [6] uses a different order for the descriptors). The effects caused by such other types of chirality are discussed elsewhere in some detail [41], e.g., S-cis/S-trans-isomerism in ferrocenyl ketones and alkenes, as well as the chemistry of biferrocenyl (containing a direct bond between two ferrocenes). 

If an achiral ferrocene derivative is converted to a chiral one by chiral reagents or catalysts, this may be called an asymmetric synthesis. All asymmetric syntheses of ferrocene derivatives known so far are reductions of ferrocenyl ketones or aldehydes to chiral secondary alcohols. Early attempts to reduce benzoylferrocene by the Clemmensen procedure in (5)-l-methoxy-2-methylbutane as chiral solvent led to complex mixtures of products with low enantiomeric excess [65]. With (25, 3R)-4-dimethylamino-l,2-diphenyl-3-methyl-2-butanol as chiral modifier for the LiAlH4 reducing agent, the desired alcohol was formed with 53% ee (Fig. 4-9 a) [66]. An even better chiral ligand for LiAlH4 is natural quinine, which allows enantioselective reduction of several ferrocenyl ketones with up to 80% ee [67]. Inclusion complexes of ferrocenyl ketones with cyclodextrins can be reduced by NaBH4 with up to 84% enantioselectivity (Fig. 4-9 b) [68 — 70]. 

Microorganisms like baker s yeast are able to reduce some ferrocenyl ketones enantioselectively (for a review on microorganisms and enzymes for the reduction... 

In poly(methylphenylphosphazene), [Ph(Me)P=N] 58, both the phenyl and methyl substituents are potential sites for formation of derivatives [65]. Deprotonation of ca. half of the methyl substituents on this polymer was carried out in THF at — 78 °C using n-BuLi. On treatment of the intermediate polymer anion with ferrocenyl ketones and subsequent quenching with a mild proton source, phos-phazenes 59 containing the OH functional group were prepared. The amount of substitution, determined by NMR and elemental analysis, was found to be 45 and 36%, respectively, for polymers 59a and 59b (Scheme 10-27). For these substituted polymers was 187000 and 154000, respectively, and no degradation of the parent polymer occurred. 

Other reaction substrate variations that will not be covered in this chapter include the NaBHt/TFA reductive cleavage of 1,4-epoxy-1,4-dihydronaphthalenes25 and benzylic ozonides,26 the tandem solvolysis-reduction of triarylmethyl chlorides,27 the cleavage of ferrocenyl ketone hydrazines,28 and the reduction of benzophenones to diarylmethanols ( ).29... 

S-ds/S-frans-isomerism in ferrocenyl ketones and alkenes, as well as the chemistry of biferrocenyl (containing a direct bond between two ferrocenes). 

Hydrazones. The reagent is prepared from A(,Af-dimethylhydrazine and trimethylaluminum in hot toluene (97% yield). It is useful for derivatization of unre-active ketones (e.g., ferrocenyl ketones) in refluxing toluene. The fully substituted hydrazones can undergo exchange on reaction with N2H4 in ethanol. Tropone hydra-zone, which has previously been unavailable, can be prepared by this method. 

Alkylferrocenes Ionic deoxygenation of ferrocenyl ketones with Zn(BHj)j in THF... 

Palladium-catalyzed carbonylative couplings of iodoferrocene with arylboronic acids were reported by Yang and colleagues [32]. A series of aryl ferrocenyl ketones was prepared in good yields under mild conditions (Scheme 4.16). Both strongly activated and ortho-substituted arylboronic acids gave the corresponding ketones in moderate yields. 

A similar pattern of reactivity is observed with ferrocenyl ketones. Thus acetyl ferrocene is unreactive, while only one of the ortho C-H bonds of benzoyl ferrocene undergoes Ru catalyzed anti-Markovnikov addition reaction across the C-C double bonds of 1,3 Inyltetramethyldisiloxane to yield a monomeric product. On the other hand, l,r-dibenzoylferrocene undergoes Ru catalyzed copolymerization with 1 3-... 

Aqueous suspensions of ferrocenyl ketone p-CD inclusion complexes are reduced with NaBH, [77], The presence of salting-out agents (LiCl, NaCl, KCl) increases the enantioselectivity of the reaction (Table 6.10). 

Table 6.10 Asymmetric reduction of ferrocenyl ketones using P-cyclodextrin inclusion complexes...

Scheme 6.8. Effect of pyridine on the McMurry coupling of a ferrocenyl ketone.

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