Coping with substituent effects in divinylcyclopropyl diazene rearrangements

Tetrahedron Letters

Volumn 44, Issue 10, 2003, Pages 2109-2112

  Carroll, Georgia Law ^a   Harrison, Roy ^a   Gerken, James B ^a   Little, R Daniel ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKENE DERIVATIVE; CYCLOPROPANE DERIVATIVE; ESTER DERIVATIVE; KETONE DERIVATIVE;

ARTICLE; CONFORMATION; COPE REARRANGEMENT; CRYSTAL STRUCTURE; CYCLIZATION; DIASTEREOISOMER; REACTION ANALYSIS; SUBSTITUTION REACTION;

EID: 0037416841     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(03)00165-5     Document Type: Article

References (14)

1. Carroll G.L., Little R.D. Tetrahedron Lett. 39:1998;1893.
2. Adam W., Finzel R. J. Am. Chem. Soc. 114:(12):1992;4563-4568.
3. Paul G.C., Gajewski J.J., Kestyn P.A., Khorasanizadeh S., Lahti P.M. J. Org. Chem. 62:1997;7189-7191.
4. Paul G.C., Gajewski J.J. J. Org. Chem. 61:(4):1996;1399-1404.
5. Overberger C.G., Chi M.S., Pucci D.G., Barry J.A. Tetrahedron Lett. 45:(13):1972;4565-4568.
6. Piers, E. In Comprehensive Organic Synthesis; Paquette, L. A., Ed.; Pergamon: Oxford, 1991; Vol. 5, Chapter 8.2, pp. 971-998 and references cited therein.
7. Transition state calculations were conducted on both the syn and anti diazenyl ester and ketone at the following levels of theory: AM1, 6-31G*, B3LYP/6-31G*, MP2/6-31G*, and MP2. Spartan-2 software was used. The energy of the starting structure and transition state structure was determined in each instance, for rearrangement occurring either syn or anti to the diazene bridge. In each case, migration syn to the bridge proved of lower energy. Similarly, each method showed a lower barrier for migration of the ketone. Frequency checks were conducted at the 6-31G* level. Detail concerning the calculations will be reported in a full paper.
8. A possible origin of the conformational preferences is apparent from an examination of the calculated charge density surfaces for the diazenyl ester and ketone. The ketone surface clearly suggests the possibility of an attractive dipolar interaction between the electron-rich diazene linkage and the electron-poor ketone carbonyl carbon, while ester 1d is presumably conformationally mismatched in order to minimize repulsive interactions between the electron-rich diazene and the two electronegative oxygens of the ester and the electron-rich diazene linkage. The rearrangement of 1e was actually predicted prior to synthesis, and was later confirmed by experiment. Although caution is required when using ground state assessments of this nature, the fact that 11 is actually formed from 1e-syn represents either an extremely fortuitous choice of substrates for investigation, or a particularly attractive use of computational techniques.
9. Berson J.A., Duncan C.D., O'Connell G.C., Platz M.S. J. Am. Chem. Soc. 98:1976;2358-2360.
10. Little R.D., Billera C.F. Tetrahedron Lett. 29:(45):1988;5711-5714.
11. Billera C.F., Phillipp C., Little R.D. J. Org. Chem. 59:1994;2270-2272.
12. Cope rearrangements of cis-divinylcyclopropanes may occur at temperatures below 0°C, and readily at room temperature for E-substituted olefins such as A. The elevated temperatures required to induce rearrangement for the Z-substituted alkene B is attributed to the existence of transition state energy-raising steric interactions between the substituents and the cyclopropane. See: Baldwin, J. E.; Ullenius, C. J. Am. Chem. Soc. 1974, 96, 1542-1547; Schneider, M. P.; Rau, A. J. Am. Chem. Soc. 1979, 101, 4426-4427. Each of the diazenes shown in Table 1 are geminally substituted at one alkene terminus and either mono or disubstituted at the other end of the diene. Consequently Cope rearrangements were not expected to occur, and did not for 1a-d.
13. Cope rearrangements of cis-divinylcyclopropanes may occur at temperatures below 0°C, and readily at room temperature for E-substituted olefins such as A. The elevated temperatures required to induce rearrangement for the Z-substituted alkene B is attributed to the existence of transition state energy-raising steric interactions between the substituents and the cyclopropane. See: Baldwin, J. E.; Ullenius, C. J. Am. Chem. Soc. 1974, 96, 1542-1547; Schneider, M. P.; Rau, A. J. Am. Chem. Soc. 1979, 101, 4426-4427. Each of the diazenes shown in Table 1 are geminally substituted at one alkene terminus and either mono or disubstituted at the other end of the diene. Consequently Cope rearrangements were not expected to occur, and did not for 1a-d.
14. For a similar 1,4-diyl cleavage and discussion of stereoelectronics, see: Berson J.A., Olin S.S. J. Am. Chem. Soc. 91:1969;777-778.