Photoaddition solid state

The cis-syn thymine dimer from DNA is believed to be formed from intra-strand dimerization of adjacent thymine residues. Photoaddition of two unsaturated molecules in the solid state can arise only if they are initially located in proximity in the crystal lattice [545, 546]. The formation of interstrand dimers would require gross distortion of the helical structure of DNA in order for the bases to approach the limiting distance (c. 4 A.) Hence, such dimers would be formed in only very small amount. However, the composition of the photoproducts may differ under varying experimental conditions [547-550]. 

Very recently, MacGillivray et al. succeeded in the supramolecular construction of molecular ladders in the solid state using a linear template approach [48]. They designed the cocrystals 1,3-benzenediol (resorcinol) or a derivative with an all-trans-bis(4-pyridyl)butadiene or hexatriene, in which two resorcinol molecules preorganize two polyene molecules through two hydrogen bond interactions, for [2-1-2] photoaddition (Scheme 5). In this design, two polyenes would... 

Topics of relevance to the content of this chapter which have been reviewed during the year include photoactive [2]rotaxanes and [2]catenanes, photochemical synthesis of macrocycles, phototransformations of phthalimido amino acids, photoaddition reactions of amines with aryl alkenes and arenes, photoreactions between arenenitriles and benzylic donors, photostability of drugs, polycyclic heterocycles from aryl- and heteroaryl-2-propenoic acids, photoreactions of pyrroles, photoamination reactions in heterocyclic synthesis, switching of chirality by light, photochromic diarylethenes for molecular photoionics and solid state bimolecular photoreactions. 

Solvent-free conditions were found to be useful for inducing a synthetically useful photoreaction of the cinnamide derivatives of some catecholamines. This reaction is the first example of solid-state [2 -F 2] photoaddition of an alkene to the benzene ring and is exemplified in Scheme 2.24 by the photodimerization of 2V-[( )-3,4-methylenedioxycinnamoyl]dopamine [( )-43] to afford the tricyclic product 44 exclusively. By contrast, photolysis in solution (methanol) resulted in E Z isomerization in all cases. 

The photobiological activity of the psoralens is related, at least in part, to the ability of these coumarins to undergo [ 2 + 2] photocycloaddition to pyrimidine bases in DNA. The two cis-syn adducts (101) and (102) have now been obtained by irradiation of 2 -deoxycytidine in the presence of 3-carbethoxypsoralen, whereas reversible [ 2 + 2] dimerisation of the coumarin nucleus is preferred on solid state irradiation of the 8-alkoxypsoralen derivative (103). ° [ 2 +, 2] Photoadditions of 7-aminocoumarins... 

The substances for which this phenomenon has been observed are invariably polycyclic aromatic hydrocarbon structures. No exciplex formation has been reported in the literature to involve drug molecules, but this remains a possibility in concentrated solution or perhaps in solid-state mixtures. The consequences of exciplex formation are a radiative or nonradiative return to the ground state without chemical change, or electron transfer leading to chemical reaction of the drug, the quencher, or both. Many photoaddition processes are postulated to proceed via exciplex formation with the quencher molecule becoming chemically bound. 

Contrary to previous reports, acridizinium bromide yields all four isomeric [4+4]photodimerisation products both in solution and in the solid state. 2-Cyano-6,6-dimethyl-2-cyclohexenone undergoes photoaddition to 2,3-dimethyl-2-butene to give tricyclic[c,d]fused isoxazole (146) in 92% yield, possibly involving the triplet biradical (144) and the nitrene (145). With 2-methyI-2-butene and 2-methylpropene, isoxazoles (147) and (148) respectively are formed, though products from competitive formation of triplet biradical (149) are also found.The crystalline 1 2 adducts of 1,2,4,5-tetracyanobenzene with benzyl cyanide yield the coupling product (150) on irradiation this involves electron and proton transfer, radical coupling and tautomerisation steps. In solution (150) is not formed. 

The formation of highly reactive intermediates from the photolysis of aromatic azides favor their use for surface modification and the preparation of substrates for solid phase reactions. Thus, azide photochemistry has been exploited for facile modification of graphitic surfaces and N-5-azidonitrobenzoyloysuccinimide undergoes photoaddition in a solid state reaction. A review on the covalent functionalization of graphene includes examples via photogenerated nitrenes. ... 

The photochemistry of aromatic compounds is classified into the same categories adopted in the previous reviews in the series. The photoisomerization of arylalkenes, photoaddition and cycloaddition to aromatic rings, photosubstitution, photorearrangement reactions have less appeared in the period (2010-2011) considered. On the other hand, the photo-chromism including photoisomerization of azobenzenes and intramolecular photocyclization and cycloreversion of 1,2-diarylethenes, and the photodimerization have been widely developed. Supramolecular Photochemistry as a series of Molecular and Supramolecular Photochemistry was edited by Ramamurthy and Inoue in the period. In addition, it should be noteworthy that so many photochemical reactions in solid and/or crystalline states have appeared and developed. 

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