Abstract
A series of endo-6-substituted bicyclo[2.2.1]hept-2-yl carbenes have been generated by pyrolysis of the sodium salt of the tosylhydrazone precursors. The endo-6-trimethylsilyl and endo-6-thiomethoxy substituted carbenes give 1,3-migration of these substituents to the carbene center. However groups such as methyl, CH2SiMe3, phenyl, and methoxy are ineffective 1,3-migrating groups. The facile 1,3-migration of trimethylsilyl and thiomethoxy has been rationalized in terms of stabilized transition states where the migrating group interacts effectively with the carbene vacant orbital. In the cases of endo-6-thiomethoxy and methoxy derivatives, the carbene also inserts effectively into the methyl group of the substituent. Heteroatom stabilization of the transition state for C-H insertion facilitates these processes. Certain exo-6-substituted bicyclo[2.2.1]hept-2-yl carbenes have also been generated. While the exo-6-thiomethoxy and carbomethoxy systems give exclusive 1,3-hydrogen migration, the exo-6-sulfonyl derivative gives, in addition to 1,3-hydrogen migration, an alkene product derived from 1,2-hydrogen migration. The lowered propensity for 1,3-hydrogen migration is attributed to the strong electron-withdrawing sulfonyl group, which decreases the hydridic 1,3-interaction with the carbene vacant orbital.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References and notes
H.M. Frey and A.W. Scaplehorn, J. Chem. Soc. A 968 (1966).
H.C. Brown, The Nonclassical Ion Problem Plenum Press, New York, 1977.
L. Friedman and H. Shechter, J. Am. Chem. Soc. 83, 3159 (1961).
P.K. Freeman, D.E. George, and V.N.M. Rao, J. Org. Chem. 29, 1682 (1964).
R.H. Shapiro, J.H. Duncan, and J.C. Clopton, J. Am. Chem. Soc. 89, 1442 (1967), and references therein.
R.R. Sauers and R.J. Kiesel, J. Am. Chem. Soc. 89, 4695 (1967).
J.W. Wilt and P.J. Chenier, J. Am. Chem. Soc. 90, 7366 (1968).
E.P. Kyba and C.W. Hudson, J. Am. Chem. Soc. 98, 5696 (1976).
P.K. Freeman, T.A. Hardy, J.R. Balyeat, and L.D. Wescott, Jr., J. Org. Chem. 42, 3356 (1977).
P.K. Freeman and D.M. Balls, J. Org. Chem. 32, 2354 (1967).
A. Nickon, F. Huang, R. Weglein, K. Matsuo, and H. Yagi, J. Am. Chem. Soc. 96, 5264 (1974).
P.v.R. Schleyer, J. Am. Chem. Soc. 89, 699 (1967).
X. Creary and Y.-S. Wang, Tetrahedron Lett. 30, 2493 (1989).
a) K. Lal and R.G. Salomon, J. Org. Chem. 54, 2628 (1989). See also b) P.-A. Carrupt, Vogel, Tetrahedron Lett. 23, 2563 (1982).
For a discussion of the tosylhydrazone salt pyrolysis method of diazocompound and carbene generation, see a) W.R. Bamford and T.S. Stevens, J. Chem. Soc. 4735 (1952); b) G.M. Kaufman, J.A. Smith, G.G. Vander Stouw, and H. Shecter, J. Am. Chem. Soc. 87, 935 (1965); c) X.C. Creary, Org. Synth. 64, 207 (1986).
See J.B. Lambert, G.-T. Wang, R.B. Finzel, and D.H. Teramura, J. Am. Chem. Soc. 109, 7838 (1987) and references therein. See also E.W. Colvin, Silicon in Organic Synthesis, Butterworths, London, 1981, p. 15-20.
C.J. Collins, Quart. Rev. Chem. Soc. 14, 357 (1960).
For use of the analogous Me4CoLi2 reagent, see T. Kauffman, G. Hopp, B. Laarmann, D. Stegemann, and D. Wingbermuhle, Tetrahedron Lett. 31, 511 (1990).
a) B. Capon, Q. Rev. Chem. Soc. 18, 45 (1964); b) B. Capon and S.P. McManus, Neighboring Group Participation, Plenum Press, New York, 1976.
J.H. Robson and H. Shechter, J. Am. Chem. Soc. 89, 7113 (1967).
A.P. Rothwell, R.G. Cooks, T.-V. Singh, L. De Cárdenas, and H. Morrison, Org. Mass. Spectrom. 12, 757 (1985).
W.v.E. Doering, L.H. Knox, and M. Jones, Jr., J. Org. Chem. 24, 136 (1959).
X. Creary and S. McDonald, J. Ors. Chem. 50, 474 (1985).
The structure of this product is based on spectral comparison with an authentic sample of 76 prepared by reduction of the lactone derived from endo-2-hydroxynorbornane-endo-6-carboxylic acid using a procedure analogous to that previously described. See G.R. Pettit and D.M. Piatak, J. Org. Chem. 27, 2127 (1962).
The σP value of SO2CH3 is 0.73 while that of CO2CH3 is 0.44. These values indicate that SO2CH3 is a more potent electron-withdrawing group. See J. March, Advanced Organic Chemistry, 3rd Edition, John Wiley and Sons, New York, 1985, pp. 244.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Creary, X., Wang, Y.X. Substituted 2-norbornyl carbenes. Res. Chem. Intermed. 20, 201–222 (1994). https://doi.org/10.1163/156856794X00207
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1163/156856794X00207