ORGANIC
LETTERS
2011
Vol. 13, No. 1
168-171
Synthesis of 1,4-Naphthoquinone
Methides via Acid-Catalyzed Cascade
Cyclizations of Benzannulated Enediynyl
Alcohols
Bo Wen, Jeffrey L. Petersen, and Kung K. Wang*
C. Eugene Bennett Department of Chemistry, West Virginia UniVersity, Morgantown,
West Virginia 26506-6045, United States
kung.wang@mail.wVu.edu
Received November 17, 2010
ABSTRACT
Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid at room temperature promoted a cascade sequence of cyclization
reactions, leading to 1,4-naphthoquinone methides. The transformation involved an unusual two-carbon ring expansion from the cyclic alcohols
and the construction of the p-quinone methide ring from an acyclic system along the reaction pathway.
p-Quinone methides are reactive compounds implicated in
many chemical and biological processes.1 They have also
found useful applications in a variety of areas, including
serving as cationic dyes and pH-sensitive indicators.2 For
p-benzoquinone methides without substituents on the exo-
cyclic methylene group, the molecules are often too reactive
to be isolated in pure form. On the other hand, a large number
of R,R-diarylmethylene-substituted p-benzoquinones have
been isolated.3 Similarly, the diaryl-substituted 1,4-naphtho-
quinone methides are relatively stable and can be isolated.4
Several synthetic methods for the diaryl-substituted p-
quinone methides have been developed. Most of the methods
involved the preparation of triarylmethyl precursors for
subsequent transformations.1 The use of the Wittig reactions
for condensations with p-benzoquinones5 and 1,4-naphtho-
quinones6 has also been reported. In our investigations of
the cascade cyclization reactions of benzannulated enediynyl
alcohols,7 a serendipitous discovery led to the development
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Wagner, H.-U.; Gompper, R. In The Chemistry of the Quinonoid Com-
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B.; Taljaard, J. H.; Imrie, C.; Caira, M. R. Eur. J. Org. Chem. 2005, 2607–
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M. Collect. Czech. Chem. Commun. 1982, 47, 1645–1653.
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10.1021/ol102793a 2011 American Chemical Society
Published on Web 12/03/2010