Ring opening of bicyclo[n.1.0]alkanones to 2-cycloalkanone-13-diyls. why does oxyallyl diradical formation require less energy from bicyclo[3.1.0]hexan-6-ones than from bicyclo[1.1.0]butan-2-ones?

Journal of the American Chemical Society

Volumn 118, Issue 17, 1996, Pages 4159-4166

  Hrovat, David A ^a   Rauk, Arvi ^b   Sorensen, T S ^b   Powell, Helen K ^a   Borden, Weston Thatcher ^a  

^a UNIVERSITY OF WASHINGTON   (United States)

^b UNIVERSITY OF CALGARY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

BICYCLO COMPOUND;

ARTICLE; DRUG SYNTHESIS; MOLECULAR DYNAMICS; REACTION ANALYSIS; THEORY;

EID: 0029967253     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja954296y     Document Type: Article

References (21)

1. Black, C.; Lario, P.; Masters, A. P.; Sorensen, T. S.; Sun, F. Can. J. Chem 1993, 71, 1910.
2. Such species are called oxyallyls, because they are often written as zwitterions, with a negatively charged oxygen, singly bonded to C-2 of an allylic cation. However, several lines of evidence indicate that oxyallyls are probably better described as 1,3-diradicals, with a carbonyl group at C-2, than as zwrtterions.
3. (a) Osamura, Y.; Borden, W. T.; Morokuma, K. J. Am Chem. Soc. 1984, 106, 5112.
4. (b) Coolidge, M. B.; Yamashita, K.; Morokuma, K.; Borden, W. T. J. Am. Chem. Soc. 1990, 112, 1751.
5. (c) Lim, D.; Hrovat, D. A.; Borden, W. T.; Jorgensen, W. L. J. Am. Chem. Soc. 1994, 116, 3494.
6. Rauk, A.; Sorensen, T. S.; Sun, F. J. Am. Chem. Soc. 1995, 117, 4506.
7. Masters, A. P; Parvez, M.; Sorensen, T. S.; Sun, F. J. Am. Chem. Soc. 1994, 116, 2804.
8. Ichimura, A. S.; Lahti, P. M.; Matlin, A. R. J. Am. Chem. Soc. 1990, 112, 2868.
9. Powell, H. K.; Borden, W. T. J. Org. Chem. 1995, 60, 2654.
10. 2,3-Di-tert-butylcyclopropanone has also been prepared and isolated. Sorensen, T. S.; Sun, F. J. Am. Chem. Soc. 1995, 117, 5592.
11. Sorensen, T. S.; Sun, F. Can. J. Chem. 1996, 74, 79.
12. Heats of formation (from Cox, J. P.; Pilcher, G. Thermochemistry of Organic and Organometallic Compounds; Academic Press: New York, 1970) show that hydrogen addition to bicyclo[1.1.0]butane to form cyclobutane is more exothermic by 6.5 kcal/mol than hydrogen addition to bicyclo[3.1.0]hexane to form cyclohexane.
13. Hanharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
14. Frisch, M. J.; Trucks, G. W.; Head-Gordon, M., Gill, W. P. M.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, D.; Binkley, J. S.; Gonzalez, C.; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.; Steward, J. J. P.; Pople, J. A.; Gaussian, Inc.: Pittsburgh, PA, 1992.
15. Ordering information is given on any current masthead page.
16. Andersson, K.; Malmqvist, P.-Å.; Roos, B O. J. Chem. Phys. 1992, 96, 1218.
17. Andersson, K.; Blomberg, M. R. A.; Fülscher, M. P.; Kellö, V.; Lindh, R.; Malmqvist, P.-Å.; Noga, J.; Olsen, J.; Roos, B. O.; Sadlej, A. J.; Seigbahn, P. E. M.; Urban, M.; Widmark, P.-O. MOLCAS; Version 3, Universiry of Lund, Sweden, 1994.
18. This appears also to be the case at the CASPT2N/6-31G* level, since a small distortion of 4a along the vibrational coordinate with the imaginary CASSCF frequency also lowered the CASPT2N enerav.
19. Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80, 3265.
20. The size of the differential scabilization provided by the methyl groups in oxyallyl diradical 4b, relative to hydrocarbon diradical 10b, is actually greater than 6.6 kcal/mol. Presumably because of the extraordinarily long bonds between the bridgehead carbons in 1a (1.658 Å) and 1b (1.649 Å), the methyl groups in 1b stabilize it relative to bicyclo[1.1.0]-buian-2-one (1a) by more than the methyl groups in 7b stabilize it relative to bicyclo[1.1.0]butane (7a). This can be seen by calculating the energy of the isodesmic reaction, 1a + 7b → 1b + 7a, which amounts to -2.4 kcal/mol at the CASPT2N level. The CASPT2N energy of the isodesmic reaction. 4a + 10b → 4b + 10a, shows that substitution of methyl groups at C-1 and C-3 of 2-cyclobutanone-1,3-diyl (4a) and cyclobutane-1,3-diyl (10a) actually provides 9.0 kcal/mol more stabilization for the oxyallyl diradical (4b) than for the hydrocarbon diradical (10b).
21. At the Becke3LYP/6-31G* level both 6b and 6c are transition states, whereas at the CASSCF level 6b is an intermediate.