Remote functionalisation

Intramolecular hydrogen abstraction by a photochemically generated alkoxyl radical has been employed in remote functionalisation of non-activated carbon atoms,and the stereoisomeric a-iodo epoxides (128) are formed by irradiation of 5-hydroxy-5/3-cholest-3-ene (129) in benzene containing mercury(II) oxide and iodine. 

The reactions of bare Fe" " ions and related species in the gas phase continue to attract much interest. The remote functionalisation of 1,6-hexanediol by Fe occurs by C-H activation at C(3) and C(4).26 Functionalisation of 3-methyl-2-pentanone at C(4) is diastereoselective, probably because of the conformation of a chair-like intermediate. Reactions of Fe with anisoles and phenols have also been studied.28 Interaction of Fe with silanes gives both silene and silylene species, though the two are not interconvertible. The reactions of Fe(alkene)+ complexes with pentane were found to differ dramatically from those of bare Fe" , and C-H and C-C activation were also observed in reactions of Fe(C2H4) with oxygen. 0,31 interaction of Fe(benzyne)+ with alkyl halides led to C-X or C-C addition followed by p-elimination and loss of HX.32 The gas phase reaction of Fe(NH2)Me" with C2H4 is best explained by insertion into the Fe-C bond followed by P-elimination and loss of propene. The reaction of FeMe with 1-octyne also leads to C-C bond forming processes. 

This synthesis of 1 is noteworthy for its seminal demonstration of the utility of tandem electrophilic hydrazination-nucleophilic cyclisation9 for preparing functionalised homochiral cyclic a hydrazino acids.10 It highlights, yet again, the great utility of functionalised glyceraldehyde synthons for the installation of remote hydroxy stereocentres in natural product target molecules. 

Symmetrical diols can be made by a radical reaction. Radical reactions are rarely much use in carbon-carbon bond formation as they often give poor yields and many products. They are of course useful in some FGI reactions in things like allylie bromination and in functionalising remote carbon atoms. If you want to read more about this see Tedder, Part 2, Chapter 11 or Carruthers, Chapter 4. One useful radical reaction is the pinacol reduction ... 

The change of regioselectivity from ortho- to meta-functionalisation is a significant challenge but in recent years several approaches have been successful. In this scenario, different strategies have been employed such as the use of different metals to change the mechanism or the attachment of templates to the substrate to control the regioselectivity of the reaction by remote activation. 

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