Yajun Ma et al.
FULL PAPERS
pound 4c was obtained as a viscous oil after purification by
column chromatography on silica gel eluting with ethyl ace-
tate/petroleum ether (1:20); yield: 64%. The crude product
(R)-5c-1 was purified by column chromatography on silica
gel eluting with methanol, followed by recrystallization from
methanol to afford the pure form as a pale yellow solid;
yield: 51% over three steps.
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1,3-Bis{(R)-5-phenyl-6,8-dihydro-5H-[1,4]oxazino
ACHTUNGTRENNUNG
[1,2,4]triazol-2-ium-2-yl}benzene
dihexafluorophosphate
[(R)-5c-2]: This compound was prepared by the same proce-
dure as described above for (S)-5a-2. Starting material was
(R)-5c-1. Compound (R)-5c-2 was obtained as a pale yellow
solid.; yield: quantitative.
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General Procedure for the Asymmetric Benzoin
Condensation
A flame-dried Schlenk tube with a magnetic stirring bar was
charged with the triazolium salt (S)-5a-1 (0.01 mmol) and
dry THF (1.0 mL) at room temperature, followed by addi-
tion of
a THF solution of t-BuOK (0.2M, 100 mL,
0.02 mmol). After the mixture was stirred for 10 min, the
aromatic aldehyde (1.0 mmol) was added. The reaction mix-
ture was then stirred at the same temperature for 20 h,
poured into water, and extracted twice with dichlorome-
thane. The combined organic layers were evaporated and
the resulting residue was purified by column chromatogra-
phy on silica gel eluting with ethyl acetate/petroleum ether
to provide the aromatic acyloin.
The reported yields of asymmetric benzoin reactions are
isolated yields and are the averages of at least three runs.
1
The benzoin reaction products are known and their H and
13C NMR spectra agreed with those in the literature cited.
Enantiomeric excesses were determined by HPLC (LabTech
600 series) with Chiracel OD-H or OJ columns. The (S)-
configurations were assigned by comparison with optical ro-
tation values in the literature.[6,21–22]
[9] Metallophosphites as umpolung catalysts for the enan-
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Acknowledgements
This work was supported by grants from the National Natu-
ral Science Foundation of China (Nos. 20572074 and
20772086), the Program for New Century Excellent Talents
in University (NCET-04–0881), and the Outstanding Young
Scientist Award of Sichuan Province. We also thank the
Centre of Testing and Analysis, Sichuan University for NMR
and X-ray measurements.
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