aThe reaction was performed at room temperature for 12-24 h. The concentration of 5 in CH2Cl2 was 1.0 M.
bFor the structure of diols 5, see below.
cDetermined by 1H NMR analysis of the crude mixture.
As a result, the reaction with (PhCO)2O catalyzed by Ph-NMI
or Ph-IBT acylated the primary hydroxy group of 1,n-diols (n ≥
3) with a high synthetically useful selectivity. In an actual
synthesis, isolation of the desired 6 from diester 8 by column
chromatography will be easier than from 7 because of the
difference of their polarity. The minimum generation of 7 in
Ph-NMI- or Ph-IBT-catalyzed reactions was a characteristic of
the method, which might be attained by the reasonably fast
reaction rate of conversion of 7 to 8 (Scheme 2). For instance,
We thank the Ministry of Education, Culture, Sports, Science
and Technology (MEXT) for financial support.
References and notes
1. Greene, T. W.; Wuts, P. G. M. Protective groups in organic
synthesis, 4th Ed, John Wiley & Sons, New York, 2007.
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Tetrahedron 2002, 58, 1369.
using
a slightly excess amount of (PhCO)2O in the
Ph-NMI-catalyzed reactions, 6b, 6g, and 6h were obtained in
good isolated yields from diols 5b, 5g, and 5h, respectively, by
column chromatography (Scheme 3). In the 20 mmol scale
reaction of 5b, the desired 6b was isolated in a good yield.
6. (a) Clarke, P. A. Tetrahedron Lett. 2002, 43, 4761. (b) Clarke, P.
A.; Holton, R. A.; Kayaleh, N. E. Tetrahedron Lett. 2000, 41,
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Scheme 2. Formation pathway of 6, 7 and 8.
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Scheme 3. Examples of actual synthesis.
22. General Procedure for Selective Primary Acylation of Diols.
To a mixture of diol 5 (1.0 mmol) and Ph-IBT (12.5 mg, 0.05
mmol, 5 mol%) in solvent (0.5 or 1.0 mL) was added
(i-PrCO)2O or (PhCO)2O (1.0 or 1.1 mmol) at room temperature.
The resulting mixture was stirred at ambient temperature. After
checking the reaction progress by TLC analysis, saturated
aqueous NH4Cl was added and the mixture was extracted with
ether, washed with brine, dried over MgSO4 and concentrated.
The crude residue was chromatographed on silica gel to separate
the corresponding mono-ester 6.
In
N-methyl-2-phenylimidazole
2-phenylimidazo[2,1-b]benzothiazoles
summary,
we
demonstrated
(Ph-NMI)
(Ph-IBT)
that
and
catalyzed
selective acylation of primary alcohols using acid anhydrides. In
particular, the Ph-NMI- or Ph-IBT-catalyzed reaction, using
(PhCO)2O as an acylating agent, acylated a primary hydroxy
group of 1,n-diols (n ≥ 3) with a high synthetically useful
selectivity.22
Acknowledgments