Remote hydrogen abstraction

Scaiano, J.C., McGimpsey, W.C., Leigh, W.J., Jakobs, S., "Kinetic and Spectroscopic Study of a Ketyl-Phenoxy Biradical Produced by Remote Hydrogen Abstraction , J. Org. Chem., 1987, 52, 4540. 

Hasegawa, T., Horikoshi, Y., Iwata, S., and Yoshioka, M. (1991) Photocyclization of fl-oxoesters limiting factors for remote hydrogen abstraction through a mediumsized cyclic transition state. Journal of the Chemical Society, Chemical Communications, 1617-1618. 

Abad, S., Bosca, F., Domingo, L.R., Gil, S., Pischel, U., and Miranda, M.A. (2007) Triplet reactivity and regio-/stereo-selectivity in the macrocydization of diastereomeric ketoprofen-quencher conjugates via remote hydrogen abstractions. Journal of the American Chemical Society, 129, 7407—7420. 

There is only one limitation of general scope, namely the possibility for more remote hydrogen abstraction, especially from carbons next to strong electron donors, and for competing intramolecular Paterno-Buchi reaction with appropriately located double bonds. Chapters 3 and 4 cover these processes and may provide the information necessary to determine the likelihood of such reactions competing with y-hydrogen abstraction in a particular compound. 

Due to the low rate constants for y-hydrogen abstraction ( 1% of those for analogous phenyl ketone triplets), more remote hydrogen abstractions and cycloadditions to remote double bonds commonly compete and sometimes are the only reactions of pyruvates. 

Several different elegant studies have been concerned with the availability of remote hydrogens for intramolecular abstraction by a triplet benzoyl group. Breslow and Winnik first reported remote hydrogen abstraction from para-substituted benzophenones 79). Winnik has shown that the accessibility of... 

Hu, S. K., Neckers, D. C., Photochemical Reactions of Alkoxy containing Alkyl Phenyl glyoxylates Remote Hydrogen Abstraction, J. Chem. Soc., Perkin Tram. 2 1997, 1751 1754. 

In summary, ketones react preferentially with y-CH bonds. Reducing their reactivity can allow more remote hydrogen abstractions to compete, but the only way to eliminate y-hydrogen abstraction is to ehminate y-hydrogens. This constraint does not apply to similar hydrogen abstraction reactions of thioketones and N-alkyHmides. ... 

T -Hydrogen Abstraction Very Remote Hydrogen Abstraction Hydrogen Abstraction Followed by Biradical Rearrangements... 

Some (co-dialkylamino)alkyl benzoylacetate esters undergo remote hydrogen abstraction probably initiated by electron transfer to form 1,8, 1,9, or 1,10 biradicals and their azalactone cyclization products. Contrary to most other such reactions, a hydrogen gets transferred from an internal methylene next to nitrogen to produce aminolactones. 

Hasegawa, X, Xakashima, K., Aoyama, H., and Yoshioka, M., Photochemical reactions of 4-oxo carboxylic esters remote hydrogen abstraction and cis-trans isomerization. Bull. Chem. Soc. Jpn., 65, 3498,1992. 

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