Page 880 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

864 10.2.5.2. Dienes Simple dienes react readily with good dienophiles in D-A reactions.
Functionalized dienes are also important in organic synthesis. One example that illus-
CHAPTER 10 trates the versatility of such reagents is 1-methoxy-3-trimethylsiloxy-1,3-butadiene
Concerted Pericyclic (Danishefsky’s diene). 82 Its D-A adducts are trimethylsilyl enol ethers that can be
Reactions
readily hydrolyzed to ketones. The ß-methoxy group is often eliminated during
hydrolysis, leading to an enone.

OTMS TMSO
+
heat H ,H O O
+ CCH O CH 3 2
CH O CH 2 benzene CH 3
3
CH O
CH 3 CH O
OCH 3 72%
Unstable dienes can be generated in situ in the presence of a dienophile. Among
the most useful examples of this type of diene are the quinodimethanes. 83 These
compounds are especially reactive as dienes because the cycloaddition reestablishes a
benzenoid ring and results in aromatic stabilization (see p. 858).
CH 2 X
+ X
CH 2
quinodimethane

There are several possible routes to quinodimethanes, including pyrolysis of benzocyc-
lobutenes. 84
heat CH 2

CH 2
The reaction is accelerated by ERG substituents, particularly trialkylsiloxy groups, on
85
the cyclobutene ring. Quinodimethanes have been especially useful in intramolecular
Diels-Alder reactions, as is illustrated in Section 10.2.7.
Another group of dienes with extraordinarily high reactivity is made up of the
derivatives of benzo[c]furan (isobenzofuran). 86 Here again, the high reactivity can be
traced to the gain of aromatic stabilization in the adduct.
Ph
Ph
100° C
O + O
Ph Ph 69%
Ref. 87
82
S. Danishefsky and T. Kitahara, J. Am. Chem. Soc., 96, 7807 (1974).
83 W. Oppolzer, Angew. Chem. Int. Ed. Engl., 16, 10 (1977); T. Kametani and K. Fukumoto, Heterocycles,
3, 29 (1975); J. J. McCullogh, Acc. Chem. Res., 13, 270 (1980); W. Oppolzer, Synthesis, 793 (1978);
J. L. Charlton and M. M. Alauddin, Tetrahedron, 43, 2873 (1987); H. N. C. Wong, K.-L. Lau, and K.
F. Tam, Top. Curr. Chem., 133, 85 (1986); P. Y. Michellys, H.Pellissier, and M. Santelli, Org. Prep.
Proc. Int., 28, 545 (1996); J. L. Segura and N. Martin, Chem. Rev., 99, 3199 (1999).
84
M. P. Cava and M. J. Mitchell, Cyclobutadiene and Related Compounds, Academic Press, New York,
1967, Chap. 6; I. L. Klundt, Chem. Rev., 70, 471 (1970); R. P. Thummel, Acc. Chem. Res., 13,70
(1980); G. Mehta and S. Kotha, Tetrahedron, 57, 625 (2001); A. K. Sadana, R. K. Saini, and W. E.
Billups, Chem. Rev., 103, 1539 (2003).
85 J. G. Allen, M. F. Hentemann, and S. J. Danishefsky, J. Am. Chem. Soc., 122, 571 (2000).
86 M. J. Haddadin, Heterocycles, 9, 865 (1978); W. Friedrichsen, Adv. Heterocycl. Chem., 26, 135 (1980).
87
G. Wittig and T. F. Burger, Liebigs Ann. Chem., 632, 85 (1960).