Research Interests
2. Stereoselective [2+2] photocyloaddition
Controlling the regio- and stereoselectivities during the photocyclodimerization of alkenes is one of key subjects in synthetic organic photochemistry. We were interested in a reported [2+2]photocycloaddition reaction of trans-styrylpyridines, in which a syn head-to-tail (HT) dimer is obtained as the major product only in an acidic solution. However, this remarkable effect of the acid on the product distribution still remains unexplained. We found that the pyridinium-p interaction between substrates plays an essential role in the selective formation of the syn-HT dimer 5 during the photolysis of trans-4-styrylpyridines 4 in acidic media (Scheme 3).
This observation prompted us to investigate the utility of the cation-pi interaction in the solid-state [2+2] photodimerization. We found that the cation-pi interaction serves as a powerful tool to arrange 4-azachalcone hydrochlorides 6 in a head-to-tail fashion, the photolysis of which resulted in a syn head-to-tail dimer 7 with excellent stereoselectivities and quantitative yields (Scheme 4).
1. S. Yamada and C.Kawamura, “[4+4] Photodimerization of Azaanthracenes in Both Solution and Solid Phase Controlled by Cation-pai Interactions”, Org. Lett., 2012, 14, 1572-1575
2. S. Yamada, Y. Tokugawa, Y. Nojiri and E. Takamori, “Cascade reactions in crystals through cation-pi-controlled reorientation on exposure to HCl gas”, Chem. Commun., 2012, 48, 1763-1765
3. S. Yamada and Y. Nojiri, “Water-assisted assembly of (E)-arylvinylpyridine hydrochlorides: effective substrates for solid-state [2+2] photodimerization”, Chem. Commun., 2011, 47, 9143-9145
4. S. Yamada, Y. Nojiri, M. Sugawara, “[2+2]photodimerization of (Z)-4-styrylpyridine through a cation-pi interaction:formation of cis-cis-trans dimers”, Tetrahedron Lett. 2010, 51, 2533-2535
5. S. Yamada, Y. Tokugawa, “Cation-π Controlled Solid-State Photodimerization of 4-Azachalcones”, J. Am. Chem. Soc., 2009, 131, 2098-2099
6. S. Yamada, N. Uematsu, K. Yamashita, “Role of Cation-π Interactions in the Photodimerization of trans-4-Styrylpyridines”, J. Am. Chem. Soc., 2007, 129, 12100-12101
7. S. Tsuzuki, M. Mikami, S. Yamada, “Origin of Attraction, Magnitude and Directionality of Interactions in Benzene Complexes with Pyridinium Cations”, J. Am. Chem. Soc., 2007, 129, 8656-8662
8. S. Yamada, Y. Morimoto, T. Misono, "Preference of intra- and intermolecular cation-π interaction: cis-trans geometrical effects of amide bond on the interaction mode" Tetrahedron Lett., 2005, 46, 5673-5676
《NEXT》… 3. Organocatalysts with a pyridine nucleus
《PREV》… 1. Face-selective addition reactions
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2. Stereoselective [2+2] photocyloaddition
Controlling the regio- and stereoselectivities during the photocyclodimerization of alkenes is one of key subjects in synthetic organic photochemistry. We were interested in a reported [2+2]photocycloaddition reaction of trans-styrylpyridines, in which a syn head-to-tail (HT) dimer is obtained as the major product only in an acidic solution. However, this remarkable effect of the acid on the product distribution still remains unexplained. We found that the pyridinium-p interaction between substrates plays an essential role in the selective formation of the syn-HT dimer 5 during the photolysis of trans-4-styrylpyridines 4 in acidic media (Scheme 3).
This observation prompted us to investigate the utility of the cation-pi interaction in the solid-state [2+2] photodimerization. We found that the cation-pi interaction serves as a powerful tool to arrange 4-azachalcone hydrochlorides 6 in a head-to-tail fashion, the photolysis of which resulted in a syn head-to-tail dimer 7 with excellent stereoselectivities and quantitative yields (Scheme 4).
1. S. Yamada and C.Kawamura, “[4+4] Photodimerization of Azaanthracenes in Both Solution and Solid Phase Controlled by Cation-pai Interactions”, Org. Lett., 2012, 14, 1572-1575
2. S. Yamada, Y. Tokugawa, Y. Nojiri and E. Takamori, “Cascade reactions in crystals through cation-pi-controlled reorientation on exposure to HCl gas”, Chem. Commun., 2012, 48, 1763-1765
3. S. Yamada and Y. Nojiri, “Water-assisted assembly of (E)-arylvinylpyridine hydrochlorides: effective substrates for solid-state [2+2] photodimerization”, Chem. Commun., 2011, 47, 9143-9145
4. S. Yamada, Y. Nojiri, M. Sugawara, “[2+2]photodimerization of (Z)-4-styrylpyridine through a cation-pi interaction:formation of cis-cis-trans dimers”, Tetrahedron Lett. 2010, 51, 2533-2535
5. S. Yamada, Y. Tokugawa, “Cation-π Controlled Solid-State Photodimerization of 4-Azachalcones”, J. Am. Chem. Soc., 2009, 131, 2098-2099
6. S. Yamada, N. Uematsu, K. Yamashita, “Role of Cation-π Interactions in the Photodimerization of trans-4-Styrylpyridines”, J. Am. Chem. Soc., 2007, 129, 12100-12101
7. S. Tsuzuki, M. Mikami, S. Yamada, “Origin of Attraction, Magnitude and Directionality of Interactions in Benzene Complexes with Pyridinium Cations”, J. Am. Chem. Soc., 2007, 129, 8656-8662
8. S. Yamada, Y. Morimoto, T. Misono, "Preference of intra- and intermolecular cation-π interaction: cis-trans geometrical effects of amide bond on the interaction mode" Tetrahedron Lett., 2005, 46, 5673-5676
《NEXT》… 3. Organocatalysts with a pyridine nucleus
《PREV》… 1. Face-selective addition reactions
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