Page 926 - Advanced Organic Chemistry Part B - Reactions & Synthesis

902 Scheme 10.7. (Continued)

CHAPTER 10 B. Boronate fragmentation
Reactions Involving 9 i OSO 2 CH 3 CH 3
Carbocations, Carbenes,
and Radicals as Reactive CH 3 1) B H
Intermediates 2 6
–
2) H O , OH
CH 3 CH 3 2 2 CH 3 CH 3 70%
C. δ-Tosyloxy fragmentation
OH
10 j H O CH
1) LiNR 2 3
CH 3 CH
2) R AlH H 3
2
CH 3 25°C, 2 h 93%
H
OSO C H
2 6 5
a. J. A. Marshall and S. F. Brady, J. Org. Chem., 35, 4068 (1970).
b. J. A. Marshall, W. F. Huffman, and J. A. Ruth, J. Am. Chem. Soc., 94, 4691 (1972).
c. A. J. Birch and J. S. Hill, J. Chem. Soc., C, 419 (1966).
d. J. A. Marshall and J. H. Babler, J. Org. Chem., 34, 4186 (1969).
e. T. Yoshimitsu, M Yanagiya, and H. Nagoka, Tetrahedron Lett.., 40, 5215 (1999).
f. Y. Hirai, T. Suga, and H. Nagaoka, Tetrahedron Lett., 38, 4997 (1997).
g. D. Rennenberg, H. Pfander, and C. J. Leumann, J. Org. Chem., 65, 9069 (2000).
h. L. A. Paquette, J. Yang, and Y. O. Long, J. Am. Chem. Soc., 124, 6542 (2002).
i. J. A. Marshall and J. H. Babler, Tetrahedron Lett., 3861 (1970).
j. D. A. Clark and P. L. Fuchs, J. Am. Chem. Soc., 101, 3567 (1979).
chemistry of the reactant, which is readily available by a Diels-Alder reaction of 1-
methoxycyclohexadiene. This acid-catalyzed fragmentation is induced by protonation
of the acetyl group.

O
+
O CH
OCH 3 OCH 3 3 OH
+
O O H
CH 3
CH 3 CH 3
CH 3
O
Entry 4 involves nitrogen participation and formation of an iminium
ion that is reduced by NaBH . The reaction in Entry 5 creates an 11-
4
methylenebicyclo[4.3.1]undecen-3-one structure found in a biologically active natural
product. Note that this fragmentation creates a bridgehead double bond. Entry 6
involves construction of a portion of the taxol structure. The reaction in Entry 7 is
stereospecific, leading to the E-double bond.

OSO Ar
2
CH 3
CH 3
O O
O O – O
O

Entry 8 was used to create the central nine-membered ring system found in
the diterpene jatrophatrione. Entry 9 is an example of a boronate fragmentation (see
p. 899). Entry 10 illustrates enolate fragmentation. The reaction presumably proceeds