Page 964 - Advanced Organic Chemistry Part B - Reactions & Synthesis

940 Scheme 10.13. (Continued)

CHAPTER 10 a. R. H. Shapiro, J. H. Duncan, and J. C. Clopton, J. Am. Chem. Soc., 89, 1442 (1967).
b. T. Sasaki, S. Eguchi, and T. Kiriyama, J. Am. Chem. Soc., 91, 212 (1969).
Reactions Involving c. U. R. Ghatak and S. Chakrabarty, J. Am. Chem. Soc., 94, 4756 (1972).
Carbocations, Carbenes, d. D. F. Taber and J. L. Schuchardt, J. Am. Chem. Soc., 107, 5289 (1985).
and Radicals as Reactive e. M. P. Doyle, V. Bagheri, M. M. Pearson, and J. D. Edwards, Tetrahedron Lett., 30, 7001
Intermediates (1989).
f. Z. Majerski, Z. Hamersak, and R. Sarac-Arneri, J. Org. Chem., 53, 5053 (1988).
g. L. A. Paquette, S. E. Williams, R. P. Henzel, and G. R. Allen, Jr., J. Am. Chem. Soc., 94,
7761 (1972).
h. M. P. Doyle and W. Hu, Chirality, 14, 169 (2002).

O O
Rh (O CCH ) H O
2
3 4
2
CH 2 CH(CH ) C(CH ) CCHN 2 O
2 2
2 3
Ref. 223
Allylic ethers and acetals can react with carbenoid reagents to generate oxonium ylides
that undergo [2,3]-sigmatropic shifts. 224
O
O Rh (O CCH ) Ph H – CHCPh CH 2 CH O
Ph H 2 2 3 4
CHCPh O + PhCHCHCPh
+ N 2 H CH 2
H CH 2 OCH 3
CH 3
OCH 3
10.2.6. Rearrangement Reactions
The most common rearrangement reaction of alkyl carbenes is the shift of
hydrogen, generating an alkene. This mode of stabilization predominates to the
exclusion of most intermolecular reactions of aliphatic carbenes and often competes
with intramolecular insertion reactions. For example, the carbene generated by decom-
position of the tosylhydrazone of 2-methylcyclohexanone gives mainly 1- and 3-
methylcyclohexene rather than the intramolecular insertion product.
CH 3 CH 3 CH 3
NNHSO Ar NaOCH
2
3
+ +
180˚C
38% 16% trace Ref. 225

Carbenes can also be stabilized by migration of alkyl or aryl groups. 2-Methyl-2-
phenyl-1-diazopropane provides a case in which products of both phenyl and methyl
migration, as well as intramolecular insertion, are observed.

CH 3 CH 3
60°C CH 3
PhCCHN 2 (CH 3 ) 2 C CHPh + PhC CHCH 3 + Ph
CH 3 50%
9% 41% Ref. 226
223
A. Padwa, S. F. Hornbuckle, G. E. Fryxell, and P. D. Stull, J. Org. Chem., 54, 819 (1989).
224 M. P. Doyle, V. Bagheri, and N. K. Harn, Tetrahedron Lett., 29, 5119 (1988).
225 J. W. Wilt and W. J. Wagner, J. Org. Chem., 29, 2788 (1964).
226
H. Philip and J. Keating, Tetrahedron Lett., 523 (1961).