Photochemical synthetic planning

That the knowledge of the main classes of such reactions is more largely diffused among synthetic practitioners, so that a photochemical step comes more often into consideration when discussing a synthetic plan. 

Practitioners of organic photochemistry feel that this science has a great potential for synthesis. Indeed, nowadays many reactions are known that lead to useful transformations and have been exploited as key steps in complex synthetic plans. These achievements attract the interest of synthetic chemists. However, photochemical methods are probably less often adopted than they may be, and are still less familiar to the broad chemical community than other methods. In the present handbook it has been attempted to offer an easy approach to the use of photochemical methods in synthesis. Thus, rather than discussing the chemistry of the various chromo-phores, as usual in photochemistry books, reactions have been grouped according to the molecular transformation involved and care has been given that experimental aspects (much less elaborate with many other methods) are clearly presented. We are convinced that a more general application in nonspecialized laboratories will lead to the discovery of new applications and even new reactions. 

Abstract Photochemical reactions are generally easily carried out, at least in laboratory scale, and require no expensive apparatus. Some general reactions, e.g. the cycloaddition of enones to alkenes and various oxygenations have been extensively investigated and represent an excellent choice for preparative applications. Many other possibilities are known—and a few are presented below. This suggests that photochemical steps should be considered more often in synthetic planning. 

A brief survey of the general classes of photochemical reactions is given below. Some recent examples, in most of which a photochemical step is incorporated in a complex synthetic plan, are reported, in order to give at least a flavour of the (potential) role of photochemical synthesis. 

Interest in organic photochemistry has also developed from a different direction, as synthetic organic chemists have incorporated into their strategic planning of syntheses, reaction types that can best be accomplished photochemicafly, or in some instances can be carried out only by a photochemical method. A great many of these organic photochemical reactions have been discovered relatively recently. 

The adopted plan follows the different types of photochemical reactions [substitutions, additions, rearrangements, reduction, oxidation, photolabile protections] with the presentation of some typical synthetic examples and of some mechanistic aspects. 

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