Photochemical coumarin-derivatives

Several derivatives of (57) have been studied as phototriggers for alcohols and phenols. All of them are reactive, with varying quantum yields for the release of the alcohol component from decomposition of the carbonate moiety. The best of these was found to be (58), which releases phenol with a quantum yield of 0.067. Dore and co-workers have described the photochemical activity of the related coumarin derivative (59). Irradiation brings about release of the aldehyde or ketone unit from the side chain affording (60). 

Toda et al. reported that the topotactic and enantioselective photodimerization of coumarin and thiocoumarin takes place in single crystals without significant molecular rearrangements [49]. Molecular motion needs to be called upon to explain the photochemically activated cycloaddition reaction of 2-benzyl-5-benzylidenecyclopentanone. The dimer molecules, once formed, move smoothly in the reactant crystal to form the product crystal [50]. Harris et al. investigated the reactivity of 10-hydroxy-10,9-boroxophenanthrene in the solid state and the mechanism of the solid-state reaction was characterized by both X-ray diffraction and thermal analysis [51]. It was demonstrated that the solution chemistry of 10-hydroxy-10,9-boroxophenanthrene is different from that in the solid state, where it undergoes dimerization and dehydration to form a monohydride derivative. 

The photochemical and photobiological behaviour of coumarins is well documented. It is considered that the lowest excited triplet state plays an important role in such processes and information about the nature of the Ti state of coumarin has been derived from magnetic and spectroscopic studies (76JA3460). 

Other y-lactone containing systems that have been studied include derivatives of 3-oxabicyclo[3.1.0]hexan-2-one173 and 3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3//)-one (213), which on irradiation in methanol undergoes a trans-cis photoisomerization followed by a photochemically induced trans esterification to give the coumarin (214).174... 

The photochemical behavior of coumarin and its derivatives has been the subject of numerous investigations. Triplet-sensitized cycloaddition efficiently gives the photodimers and cross-cycloadducts with simple alkenes. A kinetic study on the photocycloaddition of coumarin 106a has been reported (89JA8653). 

The most common classes of chemicals used as FWAs are stilbenes and styrenes, triazines, benzoxazoles, coumarins, naphthalimides and covalently linked or fused combinations thereof (Scheme 2.2). DSBP, a distyrylbiphenyl derivative, is one of the most widely used FWAs in laundry detergents with an estimated worldwide production of 3000 tons per year in 1990. Its photochemical degradation by Fe(III) ions in aqueous media has been studied.52... 

Substituted coumarins, such as psoralen and a number of its derivatives, exhibit strong photobiological effects on bactria [6,7], viruses [8], and mammalian skin [9,10] in presence of light. Coumarin itself is also knovm to show interesting photochemical behavior, particularly dimerization [11-17], in polar and non-polar solvents. In polar solvents such as ethanol, the cis head-to-head dimer is formed presumably via interaction of excited singlet coumarin with its groud state, while in non-polar solvents such as benzene, trans head-to-head dimer is formed via the triplet state. No detailed study on the photolysis of coumarin, however, has been done in the solid state [11,18] nor in the inclusion state. 

It is important to point out that it is possible to carry out photochemical transformations in mild conditions in order to maintain the activity of the biological molecules or encapsulated cells. For such purposes the photo-transformation of HA is carried out in the presence of several compounds, such as cinnamic acid derivatives, coumarin, thymine, methacrylic anhydride, glycidyl methacrylate and styrene. Figure 5.10 shows how methacrylic esters undergo photopolymerization in the presence of HA to form a grafted polymer [46]. 

Photo reconfigurable polymeric materials contain some chemical stmctures such as cinnamate derivatives (V) or functionalized coumarin (VI), which are enabled via reversible photochemical dimerization [13]. 

Schenck et al. studied the photochemical reactions of the adducts of duroquinone with unsaturated compounds such as cyclic dienes, acenaphthylene, coumarin, and styrene (Scheme 12). Formation of both oxetanes and cyclobutanes was observed, depending on the substituents present in the quinone. From the theoretical and experimental investigations, p-benzoquinone reacts from its triplet mt excited state to yield exclusively oxetane adducts, while its tetramethyl or tetrachloro derivatives, duroquinone... 

Invention provides a novel photochemically dimerizable coumarin or quinoline derivative. 

---