Orbital unsymmetrization affects facial selectivities of Diels-Alder dienophiles

Journal of Organic Chemistry

Volumn 61, Issue 9, 1996, Pages 3155-3166

  Okamoto, Iwao ^a   Ohwada, Tomohiko ^a   Shudo, Koichi ^a  

^a UNIVERSITY OF TOKYO   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001261487     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo9520811     Document Type: Article

References (93)

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67. Orbital pictures based on the PM3 method confirmed the orbital interactions discussed here in the combined molecules, intermediate convex dihydroanthracenes, and the whole anhydrides 1. The LUMOs of unsubstituted dihydroanthracene or hydroxydihydroanthracene have orbital distributions precisely or approximately symmetric in amplitude and phase with respect to the maleic anhydride plane, respectively. Therefore the LUMO of the aromatic moiety does not interact with the LUMO of maleic anhydride owing to the symmetry disagreement in 1a and 1b.
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70. Sustmann, R.; Trill, H. Angew. Chem., Int. Ed. Engl. 1972, 11, 838-840. Sustmann, R.; Schubert, R. Angew. Chem., Int. Ed. Engl. 1972, 11, 840-840. See also Ishida, M.; Kakita, S.; Inagaki, S. Chem. Lett. 1995, 469-470.
71. 4*) of the diene is encouraged by orbital symmetry, resulting in localization of the coefficients at the reacting C1 and C2 carbons (and finally conversion into two stable σ orbitals).
72. This orbital picture (Scheme 3 (C)) may oversimplify the orbital rehybrizidation and orbital energy changes resulting from geometrical distortion of addends. There is a difference in the trajectory of addition between the endo and exo modes. However, they can be represented in terms of second-order mixing of the s and p orbitals into the π (and π*) orbitals of the initial reactants. Therefore the primary orbital interaction, depicted in Scheme 3 (C), should still be maintained even in the vicinity of the transition state.
73. Large rate acceleration was encountered in the reverse-electron-demand Diels-Alder cycloadditions of 7-isopropylidenebenzonorbornadiene (IPBND) as compared with benzonorbornadiene (BND) (as a dienophile) in the reaction of tropone (as an electron-deficient diene) (ref 37c). As pointed out in ref 37d, the initial orbital interaction of the HOMO of IPBND (the dienophile) and the LUMO of the diene is a noninteracting one because of the orbital symmetry disagreement (i), leading to decreased reactivity of IPBND. Thus, the observed large acceleration and high exo-selectivity of IPBND may also be rationalized in terms of favorable late-developing π* back-lobe interaction of the diene (the LUMO) with the HOMO of IPBND (ii), rather than the sterically congested secondary orbital interactions proposed in ref 37c. (Matrix Presented)
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83. Frontier orbital energy changes for the synchronous Diels-Alder reaction affording cyclohexene are discussed in Townshend, R. E.; Ramunni, G.; Segal, G.; Hehre, W. J.; Salem, L. J. Am. Chem. Soc. 1976, 98, 2190-2198. Bach, R. D.; McDouall, J. J. W.; Schegel, H. B.; Wolber, G. J. J. Org. Chem. 1989, 54, 2931-2935. On the other hand, calculational studies demonstrated that borohydride addition to formaldehyde proceeds through a single-step mechanism with a nonsynchronous four-center TS with a productlike geometry, indicating an early bond-formation interaction as depicted in Scheme 3A. Eisenstein O.; Schlegel, H. B.; Kayser, M. M. J. Org. Chem. 1982, 47, 2886-2891. Bonaccorsi, R.; Palla, P.; Tomasi, J. J. Mol. Struct. (THEOCHEM) 1982, 87, 181-196.
84. Frontier orbital energy changes for the synchronous Diels-Alder reaction affording cyclohexene are discussed in Townshend, R. E.; Ramunni, G.; Segal, G.; Hehre, W. J.; Salem, L. J. Am. Chem. Soc. 1976, 98, 2190-2198. Bach, R. D.; McDouall, J. J. W.; Schegel, H. B.; Wolber, G. J. J. Org. Chem. 1989, 54, 2931-2935. On the other hand, calculational studies demonstrated that borohydride addition to formaldehyde proceeds through a single-step mechanism with a nonsynchronous four-center TS with a productlike geometry, indicating an early bond-formation interaction as depicted in Scheme 3A. Eisenstein O.; Schlegel, H. B.; Kayser, M. M. J. Org. Chem. 1982, 47, 2886-2891. Bonaccorsi, R.; Palla, P.; Tomasi, J. J. Mol. Struct. (THEOCHEM) 1982, 87, 181-196.
85. Frontier orbital energy changes for the synchronous Diels-Alder reaction affording cyclohexene are discussed in Townshend, R. E.; Ramunni, G.; Segal, G.; Hehre, W. J.; Salem, L. J. Am. Chem. Soc. 1976, 98, 2190-2198. Bach, R. D.; McDouall, J. J. W.; Schegel, H. B.; Wolber, G. J. J. Org. Chem. 1989, 54, 2931-2935. On the other hand, calculational studies demonstrated that borohydride addition to formaldehyde proceeds through a single-step mechanism with a nonsynchronous four-center TS with a productlike geometry, indicating an early bond-formation interaction as depicted in Scheme 3A. Eisenstein O.; Schlegel, H. B.; Kayser, M. M. J. Org. Chem. 1982, 47, 2886-2891. Bonaccorsi, R.; Palla, P.; Tomasi, J. J. Mol. Struct. (THEOCHEM) 1982, 87, 181-196.
86. Frontier orbital energy changes for the synchronous Diels-Alder reaction affording cyclohexene are discussed in Townshend, R. E.; Ramunni, G.; Segal, G.; Hehre, W. J.; Salem, L. J. Am. Chem. Soc. 1976, 98, 2190-2198. Bach, R. D.; McDouall, J. J. W.; Schegel, H. B.; Wolber, G. J. J. Org. Chem. 1989, 54, 2931-2935. On the other hand, calculational studies demonstrated that borohydride addition to formaldehyde proceeds through a single-step mechanism with a nonsynchronous four-center TS with a productlike geometry, indicating an early bond-formation interaction as depicted in Scheme 3A. Eisenstein O.; Schlegel, H. B.; Kayser, M. M. J. Org. Chem. 1982, 47, 2886-2891. Bonaccorsi, R.; Palla, P.; Tomasi, J. J. Mol. Struct. (THEOCHEM) 1982, 87, 181-196.
87. In order to emphasize electron density distribution of the internuclear region in addition to the phase relation of the interacting orbitals, we adopted the diagram depicted in Scheme 4a. The removal of a bonding electron from the internuclear region can be regarded as diffusion of the electron of each fragment into each antibonding region along the internuclear axis; the buildup of a bonding electron is equivalent to diffusion of the electron into each bonding region along the bond axis. Ohwada, T. J. Am. Chem. Soc. 1992, 114, 8818-8827.
88. 1 orbital of the diene (1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and cyclopentadiene) is symmetry-disfavored (F), a sort of orbital noninteraction, leading to relief of the four-electron destabilization interaction on the anti side of the substituent. However, this type of noninteraction (G) also exists on the NXHOMO of the dienophile, favoring the syn reaction. As pointed out by Inagaki et al. (Ishida, M.; Inagaki, S. J. Synth. Org. Chem. Jpn. 1994, 52, 649-657, and ref 30b, chapter 2) these two-orbital, four-electron destabilization effects are canceled out because the energy gap is inert to such destabilization. On the other hand, the two-electron case of the relevant orbital interaction motif was proposed in the rationalization of the syn preference of dibenzobicyclo[2.2.2]octatrienes 3 in electrophilic oxidative reactions (ref 12). (Matrix Presented)
89. Ishida, M.; Aoyama, T.; Kato, S. Chem. Lett. 1989, 663. Weinstein, S.; Lewin, A. H.; Panda, K. C. J. Am. Chem. Soc. 1963, 85, 2324.
90. Ishida, M.; Aoyama, T.; Kato, S. Chem. Lett. 1989, 663. Weinstein, S.; Lewin, A. H.; Panda, K. C. J. Am. Chem. Soc. 1963, 85, 2324.
91. Mulliken, R. S.; J. Chem. Phys. 1955, 23, 1833, 1841, 2338, 2343.
92. The electron-withdrawing tetrafluoro substituents, in particular at the C2 and C5 positions, can also lower the LUMO level of 1d in a through-bond manner, which should be at least partially responsible for the rate acceleration on both sides of 1d.
93. Moffett, R B. Organic Syntheses; Wiley: New York, 1963; Vol. 4, pp 238-241.