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제123회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Origin of high reactivity and enhanced endo/exo selectivity in water-accelerated Diels-Alder reactions

2019년 2월 14일 14시 30분 04초
PHYS.P-202 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
4월 19일 (금요일) 11:00~12:30
Physical Chemistry
저자 및
Yevhen Horbatenko, Cheol Ho Choi1,*
Chemistry Department, Kyungpook National University, Korea
1Department of Chemistry, Kyungpook National University, Korea
The Diels-Alder reaction is a very powerful method widely used in organic synthesis since it allows one to form two C–C bonds in one step. Some Diels-Alder reactions that were believed for a long time to be almost insensitive to solvent choice are accelerated in water as well as their endo/exo selectivity is enhanced [1]. Previous theoretical calculations made an attempt to elucidate this high reactivity in terms of hydrogen bond formation between solvent molecules and a polarized transition state (TS). However, an explanation regarding enhanced endo/exo selectivity is still missing. Here, ab initio static calculations as well as molecular dynamics simulations were performed for the Diels-Alder reaction between C5H6 (cyclopentadiene) and two dienophiles, i.e., CH2=CHCN and CH2=CHCHO to clarify the origin of the high reactivity and to understand the reason for the enhanced endo/exo selectivity in water. The simulations were done in polar H2O solvent and in less polar CH2Cl2. As shown, solvent molecules cause charge polarization of TS, in particular, the polarization of the –CN and –CHO groups. H2O gives rise to stronger effect in comparison with CH2Cl2. The TS structure is not rigid as thought before, but flexible with a wide distribution of one out of two forming C–C bonds. Moreover, a bifurcation point that may affect endo/exo selectivity was found to lie earlier than the TS point on the free energy surface. Also, a particular orientation of the dienophiles with respect to the diene was found in a reactant region. This is attributed to dipole-dipole interactions. These and other results are further discussed. [1]. D. C. Rideout, R. Breslow J. Am. Chem. Soc. 1980, 102, 7816.