Intermolecular Photochemical Hydrogen Abstraction: Synthetic Applications in Relation to Carbon–Carbon Bond Formation

Authored by: Niall W.A. Geraghty , Mary Treasa Lohan

CRC Handbook of Organic Photochemistry and Photobiology

Print publication date:  March  2012
Online publication date:  March  2012

Print ISBN: 9781439899335
eBook ISBN: 9781466561250
Adobe ISBN:

10.1201/b12252-20

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Abstract

The formation of carbon–carbon bonds is the key process in the synthesis of the vast majority of organic molecules, and, understandably, an enormous range of methods for carrying it out is currently available. As a result of developments in synthetic methodology over the last 20–30 years, many of these now involve C-radicals [1]. Although such methods are synthetically very valuable, their use is problematic as the generation of the C-radicals generally involves the use of tin compounds, peroxides, or azo compounds, all of which are undesirable in terms of clean/green chemistry and of the concept of sustainability in general. This chapter explores the synthetic utility of photochemical intermolecular H-abstraction as an alternative method of generating C-radicals for use in C–C bond formation (Scheme 19.1). This process is one of a number of related photochemical processes that tend to be grouped together under the general heading of “photocatalytic methods.” The synthetic potential of these methods has been recognized in a recent comprehensive review [2], although they have been largely ignored in an otherwise thorough description of the role of C–H transformations in organic synthesis [3]. The particular focus of this chapter is on systems in which C-radical formation involves intermolecular H-atom abstraction from a C–H bond; intramolecular H-abstraction processes are only considered when they are relevant to a discussion of related intermolecular reactions. Photoreactions that involve a single electron transfer (SET) have also been excluded; details of such processes, which include the generation of α-aminoalkyl radicals, are available elsewhere [2]. Photochemical C-radical forming reactions involving peroxides, tin compounds, or γ-radiation make up a third group that are not dealt with in this chapter.

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