ORGANIC
LETTERS
2009
Vol. 11, No. 1
169-171
Reaction of Benzyne with
Salicylaldehydes: General Synthesis of
Xanthenes, Xanthones, and Xanthols
Kentaro Okuma,* Akiko Nojima, Nahoko Matsunaga, and Kosei Shioji
Department of Chemistry, Faculty of Science, Fukuoka UniVersity, Jonan-ku,
Fukuoka 814-0180, Japan
Received November 10, 2008
ABSTRACT
The reaction of salicylaldehydes with benzyne prepared from o-trimethylsilyphenyl triflate and CsF gave xanthenes and xanthones. When the
reaction was carried out under basic conditions, 9-hydroxyxanthenes (xanthols) were obtained in good yields.
Arynes are highly reactive intermediates that have found
numerous applications in organic synthesis.1,2 Our ongoing
interest in the exploration of reactive benzyne with thio- and
selenocarbonyl compounds for the synthesis of functionalized
S- and Se-heterocycles has led to our investigation of the
synthesis of benzothietes, benzothianes, and benzoselenates.3
Although reactions of aldehydes with benzyne to give CdO
bond insertion products (ca. 20%) were reported in the early
seventies,4 Yoshida et al. reported the formation of 9-arylx-
anthenes by a novel insertion reaction of benzyne derived
from o-trimethylsilylphenyl triflate (1) with aromatic alde-
hydes (22-70%).5 Larock and Zhao have reported the
reaction of arynes with benzoates, which afforded xanthones
and thioxanthones, and acridones (35-81%).6
The reaction of benzyne derived from benzenediazonium
carboxylate with N,N-dimethylformamide was reported by
Yaroslavsky, in which the product was only salicylaldehyde
(2a) in 32% yield.7 These interesting observations raise the
question whether salicylaldehydes will react with benzyne
to give xanthene derivatives, which constitute functionalized
molecules as dyes, natural products, and pharmaceuticals.8
Herein, we report our preliminary results on the annulation
of arynes by salicylaldehydes.
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10.1021/ol802597x CCC: $40.75
Published on Web 12/03/2008
2009 American Chemical Society