Photodimerization inclusion complexes

Irradiation of cycloocta-2,4-dien-l-one (55) in pentane gives a racemic photodimer, anti-tricyclofSAO.O Jhexadeca- , 11 -diene-3,16-dione (60) in 10% yield along with polymeric materials 34). Efficient and enantioselective photodimerization of 58 was achieved by irradiation of the 2 1 inclusion complex 59 formed between 2 a and 5813). When a solution of 2a and an equimolar amount of 58 in ether-hexane (1 1) was kept at room temperature for 12 h, 59 was obtained as colorless needles of mp 105 to 108 °C. Irradiation of 59 in the solid state for 48 h gave (—)-60 of 78 % ee in 55 % yield. 

Tanaka K, Mochizuki E, Yasui N, Kai Y, Miyahara I, Hirotsu K, Toda F (2000) Single-crystal-to-single-crystal enantioselective [2-1-2] photodimerization of coumarin, thiocoumarin and cyclohex-2-enone in the inclusion complexes with chiral host compounds. Tetrahedron 56 6853-6865... 

Enantioselective photodimerization of coumarin (97) was accomplished in the inclusion complex (100) with 12a. For example, irradiation of the 1 1 inclusion compound of 97 with 12a gave the anti-head-to-head dimer (—)-98 of 96% ee in 96% yield [52], This photochemical reaction of 100 to the complex (101) of 98 was also found to proceed by a single-crystal to single-crystal manner. However, 1 2 inclusion compound of 11 and 97 gave the. vw-head-to-head dimer (99) upon irradiation in 75% yield [53],... 

The efficient enantioselective dimerization reaction of 97 in the inclusion complex (100) with 12a suggests that two coumarin molecules are arranged in chiral positions in 100 and their [2 + 2] photodimerization occurs by keeping the chirality in 100. The chiral arrangement of 97 was detected by CD spectral measurement of the inclusion complex in Nujol mulls. The 1 1 complex of 97 with 12a and 13a showed CD spectra with a mirror-imaged relation (Fig. 17). After photoirradiation, the CD absorptions of the complex (100) at 225, 275, 300, and 330 nm disappeared, and the new CD absorption due to the inclusion complex (101) of 98 at 240 nm appeared. The photodimerization of 97 was also followed by measurement of infrared (IR) spectra as Nujol mulls. Upon photoirradiation, the nCO absorption of 97 in 100 at 1700 cm 1 decreased gradually and finally disappeared after 4 hr, and new vCO absorption due to 98 in 101 appeared at 1740 cm-1. 

The enantioselective photodimerization of thiocoumarin (102) to optically pure (+)-a ft -head-to-head dimer (103) in the 1 1 inclusion complex of 102 with 12b was also found to proceed in a single-crystal to single-crystal manner. For example, when a mixture of thiocoumarin (102) and optically active host compound 12b in butyl ether was kept at room temperature for 12 hr, a 1 1 inclusion complex of 103 with 12b was obtained as colorless needles. Photoirradiation of a 1 1 inclusion complex in the solid state (400-W high-pressure Hg lamp, Pyrex filter, room temperature, 2 hr) gave a 2 1 complex of 12b with 103,... 

The single-crystal to single-crystal nature and the steric course of the photodimerization of thiocoumarin (102) to (+)-a t/-head-to-head dimer (103) in the inclusion complex were investigated by x-ray crystallographic analysis and x-ray powder diffraction spectroscopy [54],... 

Rao et al. observed that photoirradiation of tran.v-stilbene in crystalline y-cyclodextrin inclusion complexes yields a single isomer of. svn-tctraphenylcy-clobutane (119) [109] stereoselectively in high yield (70%). In contrast, the photodimerization of stilbene in solution is very inefficient, and no photodimer was observed even after prolonged irradiation of pure stilbene crystals. 

The steric course of the photodimerization reactions of coumarin (37a) and thiocoumarin (37b) succeeded in being controlled almost perfectly by carrying out the reaction in inclusion complexes using various host compounds. Furthermore, enantioselective dimerization reactions of 37a and 37b were found to proceed through a single-crystal to single-crystal process. 

Photodimerization of 2-pyridone (46) in the presence of the 2,2/-biphenyldi-carboxylic acid host (45) also proceeded via a catalytic process. First, irradiation of the 1 2 inclusion complex of 46 and 45 in the solid state gave the trans-anti dimer (47) in 92 % yield [27], The mechanism of this stereoselective photoreaction was investigated through X-ray analysis of this complex. In the complex, two 46 molecules are arranged in ideal positions for yielding 47 by dimerization [27], Secondly, a catalytic dimerization reaction of 46 was carried out. Photoirradiation for 20 h of a 1 4 mixture of powdered 45 and 46 under occasional mixing in the solid state gave 47 in 81 % yield. These data clearly show that molecules of... 

As a model reaction for DNA damage by photodimerization of its thymine component, which finally causes a skin cancer, photodimerization reactions of 2-pyridone derivatives are interesting. Photoirradiation of a 1 2 inclusion complex of 66 a and 66 b with the host 67 gives the corresponding rac-cis-anti dimer 68 a and 68 b, respectively [37, 38], Photoirradiations of 66 c and 66 b in their inclusion complexes with 67 and 69, respectively, gives rac-trans-anti dimer 70 c and meso-cis-syn dimer 71 b, respectively [38, 39]. X-ray analysis of these inclusion complexes showed that 2-pyridone molecules are ordered at adequate positions for the corresponding photodimerization reactions in all cases [37-39]. 

A SCSC [2+2] photodimerziation involving 7-hydroxy-4-methylcoumarin has been shown to occur in the cavity of (3-cyclodextrin, as reported by Stezowski and co-workers (Fig. 2.3.6) [53]. The SCSC reaction was facilitated by the inclusion of both reactants within a single cyclodextrin cavity. In that way, the photodimerization produced very small changes in the overall shape of the inclusion complex. In addition, water molecules of crystallization were shown to afford an environment favorable for the SCSC transformation by providing a way to relieve the strain induced by the reaction. 

The photodimerization of Af-(3,4-dimethoxycinnamoyl)-anthranilic acid (113) in aqueous solutions (see Scheme 25) was accelerated by the addition of y-CD, in agreement with the occurrence of a reaction controlled by the stoichiometry (1 2, host guest) of the inclusion complex. At high y-CD concentrations, the formation of 1 1 and 2 1 complexes inhibits the reaction [298]. 

Similarly, irradiation in the solid state of a 1 1 inclusion complex of coumarin with 241a led to the cis-anti-cis head-to-head dimer 244 as an almost pure enantiomer [187]. The selectivity observed was very sensitive to the nature of the solvent used for crystallization. Replacing a mixture of ethylacetate-hexane with toluene-hexane led to a different 1 1 complex and different photodimers. Furthermore, among the numerous inclusion complexes tested, only the preceding example using 241a as the host led to an enantioselective photodimerization of coumarin. 

Irradiation of the inclusion complexes of each isomer of stilbene in the solid state leads after prolonged photolysis to photodimerization. 

ABSTRACT. The photodimerization of 2-anthracenesulfonate in water was accelerated in the presence of 3- and y-cyclodextrins (CyDs). While four configurational isomers of the photodimer were obtained in the presence of Y-CyD with similar ratio of the yields to that in the host-free solution, only one of the isomers was obtained in the presence of 3-CyD. The results were explained by the formation of two guest-one host inclusion complex in the former case and of two guest-two host inclusion complex in the latter. No evidence of an inclusion complex with a-CyD was obtained. The inclusion effects of CyD on the photodimerization of other water-soluble anthracenes were also examined. 

The configurational isomers of the photodimer given in the presence of Y-CyD were identical with those in the absence of CyD. The relative yields of these isomers were quite similar in both cases. Nevertheless, the inclusion effect of y-CyD is clear, because the quantum yield of the photodimerization was an order of magnitude greater than that in the absence of y-CyD and because 2AS was protected from photooxydation (16). The acceleration of the photodimerization is due to the formation of a 2 1 inclusion complex, in which two 2AS molecules are in a san wich configuration. The spectrophotometric measurements gave 3 x 10 M for the equilibrium constant (K) for the equation (16) ... 

The inclusion complexes between IAS and CyDs were much less stable as compared with those of 2AS. The photodimerization of IAS in the presence of 3-CyD showed little configurational selectivity, suggesting rather loose complexation. No stable complex was formed between lAC and CyDs. 

ABSTRACT 3-Cyclodextrin was found to form a crystalline inclusion complex with coumarin. The solid-state photoreaction of the inclusion compound was studied at 25-27 C, and compared with those of coumarin and of a mixture of coumarin with the cyclodextrin. Under irradiation at a wavelength longer than 300 nm, coumarin with or without 3-cyclodextrin and in the inclusion complex converted to a photodimer, cis-head-to-head dimer in the solid state. The conversion rate of coumarin was higher than that in the mixture, and the latter was higher than that in the complex. These indicate that 3-cyclodextrin retards the photodimerization of coumarin, but does not affect the course of the reaction in the solid state. 

The photodimerization of fran -cinnamic acid 30 in the presence of CB[8] studied by Ramamurthy et al. was discussed in Section 5.4 [121]. Prior to that report, they specifically examined the templating ability of CB[8] and y-cyclodextrin for this same dimeric photocycloaddition [127]. They also studied the templating action of CB[8] on the dimeric photocycloaddition of trans-1,2-bis(n-pyridyl)-ethylene 33 and other related olefins [128]. In the absence of CB[8], photoreaction of 33 produced only the monomer hydration product 34. However, in the presence of CB[8], 1 2 host guest inclusion complexes were formed, and upon irradiation gave predominantly (90%) the photodimerization product 35. These reactions are illustrated in Fig. 3.17. Thus, in this case,... 

Macartney et al. used CB[7] to mediate and template the stereoselective [4 + 4] photodimerization of 2-aminopyridine hydrochloride 36 [129]. In the presence of CB[7], 1 2 hosbguest inclusion complexes were formed, and photolysis gave exclusively the anti-trans addition photoproduct 37. In the absence of CB[7], both the anti-trans and the s)m-trans photoproduct are formed. Furthermore, they found that the formation of the photoproduct 37 inside the CB[7] nanoreactor stabilizes it significantly, preventing rearomatizalion back to the monomer reactants, which occurs thermally at room temperature in the absence of CB[7], This system is illustrated in Fig. 3.18. 

An example of the effect of CDs on the photocycloaddition reaction is the photodimerization of water-soluble 2-anthracene sulfonate 114 (Scheme 5.37). In sole water, the cycloadducts 115,116,117, and 118 were obtained in relative percentage of 45,35,18, and 2%, respectively. The presence of a- and y-CD did not change the isomeric distribution, while the /3-CD allowed only the dimer 115 to be obtained. The results were explained by the formation of different guest/host inclusion complexes. 

Moorthy, J.N. and Venkatesan, K., Stereospecific photodimerization of coumarins in crystalline inclusion complexes. Molecular and crystal structure of 1 2 complex of (s,s)-(-)-l,6-bis(o-chlo-rophenyl)- ,6-diphenyl-hexa-2,4-diyne-l,6-diol and coumarin,/. Org. Chem., 56,6957,1991. Tanaka, K. and Toda, E, Selective photodimerizations of coumarin in crystalline inclusion compounds, /. Chem. Soc., Perkin Trans. 1, 943, 1992. 

Brett, T.J., Alxander, J.M., and Stezowski, J.J., Chemical insight from crystallographic disorder — structural studies of supramolecular photochemical systems. Part 3. The P-cyclodextrin-7-hydroxy-4-methylcoumarin inclusion complex direct observation of photodimerization by x-ray crystallography,. Chem. Soc., Perkin Trans. 2, 1105, 2000. 

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