Photochemical Steps in Synthetic Planning

One of the most typical photochemical reactions, C=C double bond isomerization, may have a synthetic value. Thus, the highly oxygenated cembrane 17-deoxyprovidencin 20 has been built by joining two separately prepared building blocks and further elaboration of the macrocycle 21 via a Z-selective ring closing metathesis. The Z C=C bond isomerizes by irradiation with Pyrex-filtered light that 

A number of excellent textbooks of organic photochemistry are available, and the reader is directed to these to acquire an appropriate introduction to the field of organic chemistry (for example, see [18]). Presentations of the synthetic aspects of organic photochemistry are likewise available in books and reviews [19-21], arranged according to the chemical function reacting or to the type (mechanism) of the reaction involved. 

1 Ciana, C.L. and Bochet, C. (2007) Clean and easy photochemistry. Chimia, 61, 650-654. 

3 (a) Pfoertner, K.H. (1990) Photochemistry in industrial synthesis. Journal of Photochemistry and Photobiology, A Chemistry, 51, 81-86 (b) Braun, A.M. (1997) New potentials for photochemical technology. Speciality Chemicals, 17,21-22, 24-25 (c) Pape, M. (1975) Industrial applications of photochemistry. Pure and Applied Chemistry, 41, 535-558  

4 Morrison, H. and Malski, R. (1974) Changes in ultraviolet transmission of Coming Code 9700 glass tubing. Photochemistry and Photobiology, 19, 85. 

5 Cirkva, V., Vlkova, L., Relich, S., and Hajek, M. (2006) Preparation of the electrodeless discharge lamps for photochemical 

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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. 

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. 

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. 

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