Coumarins photochemical addition

Since photochemical reactions in inclusion compounds have been described in one chapter of the previous book [1], enantioselective (3-lactam formation reactions are summarized in this present chapter as a typical application of the inclusion technique for enantioselective photosynthesis. In addition, as a representative enantioselective single-crystal-to-single-crystal photoreaction, the photodimerization reactions of coumarin and thiocoumarin in their inclusion compound with a chiral host are also described. Furthermore, a host-catalyzed photodimerization reaction of chalcone and 2-pyridone in the solid state is also added to this chapter as a unique example of the application of inclusion techniques to selective photoreaction. 

Coumarin groups are commonly incorporated into photoactive polymers because of their favorable photochemical characteristics and the ease of integration into the polymer matrix. The addition of the appropriate coumarin moiety into the monomers themselves or as an additive in the polymerization process can result in the polymeric product possessing beneficial visible and ultraviolet light absorption properties. 

Haywood, D.J., Hunt, R.G., Potter, C.J., and Reid, S.T. (1977) Photochemical transformations. Part 10. Photocydo-addition reactions of 4-hydroxy-coumarin with cycloalkenes. Journal... 

The unsaturated 6-lactone (84) undergoes intramolecular photochemical (2 + 2)-cycloaddition to give (85)." The scope of the process has been evaluated and the 5-lactones (86-88) all behave similarly, affording the products shown in Scheme 2. The lactones (86) and (87) both cyclise in the two possible modes. Intramolecular cycloaddition reactions within polymethyldia-minebis(4-methyl-7-coumarinyl)oxyacetamides have been described. Zhu and Wu have reported that a biscoumarin system linked by a phenanthroline unit does not undergo photodimerisation. Instead, intramolecular addition of a coumarin unit to the phenanthroline occurs. 

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