G. Bartoli et al. / Tetrahedron Letters 43 (2002) 6331–6333
6333
Prolonged reaction times and higher temperatures are
required when acetylation can occur only at the steri-
cally hindered ortho-position (Table 3, entry 2).
CAUTION: Lithium perchlorate and oxidizable materi-
als could lead to devastating explosions and must be
handled with care. While we have never experienced
any problem even when reactivating it by heating, we
urge users to protect themselves and to take appropri-
Higher temperatures are obviously required when the
substrate is deactivated with respect to anisole (Table 3,
entries 4, 5, 6, 8, and 9). Again steric interactions can
account for the formation of two acetylated derivatives
in the reactions of meta-substituted anisoles (Table 3,
entries 3, 5, and 6). In all cases yields are almost
quantitative, with the exception of xylenes, but it was
8
ate safety measures.
Acknowledgements
Work carried out in the framework of the National
Project ‘Stereoselezione in Sintesi Organica. Metodolo-
gie e Applicazioni’ supported by MURST, Rome, and
by the University of Bologna, and in the framework of
2
a
reported that these compounds suffer from decompo-
sition phenomena when kept at high temperatures for
long times.
‘
Progetto di Finanziamento Pluriennale, Ateneo di
Bologna 2001–2002’.
The present method appears to be competitive and in
some cases superior to recently reported catalytic proce-
dures, in which LiClO is used as additive in quantities
4
References
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in solvent free conditions, an increasingly important
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4
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2
2
4
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(
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LiClO were dried in vacuo (0.1 Torr) at 140°C for 2 h.
4
After cooling, the anhydride (1.05 equiv.) was added to
LiClO4 and the mixture was heated at the desired
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temperature until LiClO was dissolved. Then the sub-
4
strate (1 equiv.) was added dropwise and the reaction
was monitored by GLC. After the reaction was com-
plete, it was cooled and CH Cl was added. The precip-
6
2
2
itated LiClO4 was recovered by centrifugation and
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7. Detected by GLC analysis.
8. Schumacher, J. C.; Perchlorates—Their Properties, Manu-
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3
4
was recovered by simple removal of the solvent and
purified by column chromatography when necessary.