are still strongly desired in both laboratory and industry, we
believe that this new methodology without a complicated
procedure can help problems for further improvements in
transesterification.
Financial support was partially provided by MEXT,
KAKENHI (21200033), the Yazaki Memorial Foundation
for Science and Technology. MH is grateful to the Nippon
Shokubai Award in Synthetic Organic Chemistry, Japan.
Notes and references
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Fig. 2 Catalysts in situ, ee, and the yield of the products.
Table 3 Non-epimerized transesterification
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a
b
c
2 equiv. of 9 was used. 1 mol% of 3ꢁ4 was used. Powdered MS
5 A was used in situ.
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E. Ichikawa and M. Shibasaki, Synlett, 2005, 1491(b) K. Ishihara,
A. Sakakura and M. Hatano, Synlett, 2007, 686.
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12 Price list and toxicity of catalysts are summarized in the ESIw.
13 Shibasaki et al. reported that, in their asymmetric amination,
La(NO3)3ꢁ6H2O could be a useful La(III) source in place of 1.
Their approach with La(NO3)3ꢁ6H2O was not the generation of
La(OR)m(NO3)3ꢀmin situ, but La(III)–chiral salicylic amide–H-D-
Val-Ot-Bu as an active ternary complex T. Mashiko, N. Kumagai
and M. Shibasaki, J. Am. Chem. Soc., 2009, 131, 14990.
70 1C. According to the hypothesis of the equilibrium among
the catalysts (5a–c) as shown in Fig. 2, the reactions proceeded
smoothly without a loss of optical purity or with almost intact
optical purity (96–>99% ee) when 3ꢁ4 was used in place of 3ꢁ42.
Totally, not only a-oxy-substituted esters (12b and 12h), but
also a-amino esters (12c–e), a-chloro ester (12f), and naproxen
derivative (12g) could be used in 3ꢁ42- or 3ꢁ4-catalyzed
transesterification.
In summary, we have developed highly useful and homo-
geneous acid–base combined catalysts for transesterification,
nearly neutral lanthanum(III) nitrate alkoxide, which can be
readily prepared in situ from inexpensive La(NO3)3ꢁH2O and
[PMe(octyl)3](OCO2Me). The most privilege of these active La(III)
catalysts is highly practical non-epimerized transesterification of
chiral a-substituted esters under azeotropic reflux conditions
(96–>99% ee). Since really practical catalysts for transesterification
14 Commercially available La(NO3)3ꢁnH2O are hygroscopic, and were
used after desiccation to
a
monohydrate at 170 1C
W. W. Wendlandt, Anal. Chim. Acta, 1956, 15, 435.
15 M. Fabris, V. Lucchini, M. Noe, A. Perosa and M. Selva, Chem.–
Eur. J., 2009, 15, 12273.
16 For other examples of 8, a variety of carboxylic esters, and ethyl
acetate with 1–31-alcohols are shown in the ESIw.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 9465–9467 9467