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G. W. Amarante et al. / Tetrahedron Letters 47 (2006) 8427–8431
O
O H
O
F3C
F3C
O
F3C
CO2CH3
CO2CH3
TFA
CO2CH3
1b
O
N
NO2
N
O
OH
4
OH
O
N
OH
TFA
OH
CO2CH3
CO2CH3
H+
CO2CH3
H
H
N
O
O
N
O
3b
Scheme 3. A new key intermediate 4 incorporated in the mechanism leading to 3 from BH adducts 1.
spectral data were identical to 3b produced from 1b by
TFA treatment. This experimental result constitutes
therefore evidence of the key role played by the trifluoro-
acetate BH adduct 4 into the formation of 3b, as revealed
by the ESI/MS(/MS) experiments. It is also clear that the
presence of an acid is crucial for cyclization of 4.
References and notes
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Based therefore on data from the ESI-MS(/MS) moni-
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In summary, ESI-MS(/MS) monitoring has permitted us
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Acknowledgments
We thank the following Brazilian science foundations
FAPESP and CNPq for the financial support and for
fellowships to GWA and MB.
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