Research Interests
1. Face-selective addition reactions
Scheme 1 outlines a strategy for the stereoselective synthesis of 1,4-dihydropyridines via a cation-pi interaction: (a) Conversion of compound A containing both a pyridine and a phenyl moiety into a pyridinium salt gives rise to an attractive force between the two entities to form a cation-p complex B; (b) The selective shielding of one side of the pyridinium face by the phenyl ring enables nucleophiles to attack the complex only from the non-shielded side, which would stereoselectively give 1,4-dihydropyridine C. The addition of a ketene silyl acetal to 1 in the presence of methyl chloroformate in CH2Cl2 gave 1,4-adducts 3 as a major product in excellent stereoselectivity (Scheme 2).
X-ray analyses clarified significant geometrical differences between 1 and its salt 2 (Fig. 1). The remarkable feature in 2 is that the pyridinium and the phenyl rings lie parallel to each other and the two rings are arranged face-to-face, the distance between them being about 3.4Å. On the other hand, the pyridine and the phenyl moieties of 1 are far apart from each other. The fact that the geometry significantly depends on whether the pyridine nucleus has a cationic charge or not is unambiguous evidence that a cation-p interaction governs the conformation
of 2.
1. S. Yamada, M. Inoue, “Regio- and stereoselective addition of allylmetal reagents to a pyridinium-pi and quinolinium-pi complexes”, Org. Lett., 2007, 9, 1477-1480.
2. S. Yamada, J. Yamamoto, E. Ohta, “Enantioselective cyclopropanation reaction using a conformationally fixed pyridinium ylide through a cation-pi interaction”, Tetrahedron Lett., 2007, 48, 855-858.
3. S. Yamada, C. Morita, J. Yamamoto "Elucidation of the formation of cation-p complexes and their conformational behavior in solution by CD spectroscopy", Tetrahedron Lett., 2004, 45, 7475-7478.
4. S. Yamada and C. Morita, “Face-selective Addition to a Cation-p Complex of a Pyridinium Salt: Synthesis of Chiral 1,4-Dihydropyridines”, J. Am. Chem. Soc., 2002, 124, 8184-8185
5. S. Yamada, M. Saitoh and T. Misono, “Stereoselective Synthesis of 1,2- and 1,4-Dihydropyridines by Using Cation-pi interaction as a Conformation-Controlling Tool”, Tetrahedron Lett., 2002, 43, 5853-5857
《NEXT》… 2. Stereoselective [2+2] photocyloaddition.
3. Organocatalysts with a pyridine nucleus
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1. Face-selective addition reactions
Scheme 1 outlines a strategy for the stereoselective synthesis of 1,4-dihydropyridines via a cation-pi interaction: (a) Conversion of compound A containing both a pyridine and a phenyl moiety into a pyridinium salt gives rise to an attractive force between the two entities to form a cation-p complex B; (b) The selective shielding of one side of the pyridinium face by the phenyl ring enables nucleophiles to attack the complex only from the non-shielded side, which would stereoselectively give 1,4-dihydropyridine C. The addition of a ketene silyl acetal to 1 in the presence of methyl chloroformate in CH2Cl2 gave 1,4-adducts 3 as a major product in excellent stereoselectivity (Scheme 2).
X-ray analyses clarified significant geometrical differences between 1 and its salt 2 (Fig. 1). The remarkable feature in 2 is that the pyridinium and the phenyl rings lie parallel to each other and the two rings are arranged face-to-face, the distance between them being about 3.4Å. On the other hand, the pyridine and the phenyl moieties of 1 are far apart from each other. The fact that the geometry significantly depends on whether the pyridine nucleus has a cationic charge or not is unambiguous evidence that a cation-p interaction governs the conformation
of 2.
1. S. Yamada, M. Inoue, “Regio- and stereoselective addition of allylmetal reagents to a pyridinium-pi and quinolinium-pi complexes”, Org. Lett., 2007, 9, 1477-1480.
2. S. Yamada, J. Yamamoto, E. Ohta, “Enantioselective cyclopropanation reaction using a conformationally fixed pyridinium ylide through a cation-pi interaction”, Tetrahedron Lett., 2007, 48, 855-858.
3. S. Yamada, C. Morita, J. Yamamoto "Elucidation of the formation of cation-p complexes and their conformational behavior in solution by CD spectroscopy", Tetrahedron Lett., 2004, 45, 7475-7478.
4. S. Yamada and C. Morita, “Face-selective Addition to a Cation-p Complex of a Pyridinium Salt: Synthesis of Chiral 1,4-Dihydropyridines”, J. Am. Chem. Soc., 2002, 124, 8184-8185
5. S. Yamada, M. Saitoh and T. Misono, “Stereoselective Synthesis of 1,2- and 1,4-Dihydropyridines by Using Cation-pi interaction as a Conformation-Controlling Tool”, Tetrahedron Lett., 2002, 43, 5853-5857
《NEXT》… 2. Stereoselective [2+2] photocyloaddition.
3. Organocatalysts with a pyridine nucleus
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