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Robinson, R. J. Chem. Soc. 1909, 2167. Gabriel, S.
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43, 1283. For the use of the Burgess reagent for this
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Oikawa, Y.; Yoshida, T.; Mohri, K.; Yonemitsu, O.
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971.
Hydrazinolysis of 12 (R=Phth), Scheme 3, gave 14,
which was coupled to 1513 to give 16 (77% from 12).
Protection of the indole 16 as the carbamate derivative
17 followed by dehydration with the Burgess reagent
gave 18 (71%). Hydrogenolysis of the benzyl ether
followed by treatment with trifluoroacetic acid resulted
in the aminophenol 19 (77% from 18).14 The overall
sequence provides a convenient route to the GCDEF
fragment (right-hand side) of diazonamide in multi-
gram quantities, and avoids the dehydrogenation
methodology used to introduce the 3-carbonyl group
that requires 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ).15
Further examples of the Vilsmeier procedure for the
synthesis of 3-(2-N-phthaloylacyl)indole derivatives are
listed in Table 1. Interestingly, 2-phenyl indole 24 gave
25 and the remarkably stable enamine derivative 26.
The enamine 26 was converted into 25 (87%) by treat-
ment with 2 M HCl in THF heated at reflux (2 h).
Acknowledgements
The National Institutes of Health (CA 50512), Robert
A. Welch Foundation, Merck Research Laboratories
and Novartis are thanked for their support of this
research.
References
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1
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