LETTER
Catalyst for the Selective Transesterification of b-Keto Esters
417
Table 2 Transesterification of b-Keto Esters with Thiols, Amines, Diols and Amino Alcohols Catalysed by 1a
Entry
1
b-Keto ester
Alcohol
Time (h)
10
Product
Yield (%)b
78
O
O
O
O
O
SH
Me
Me
S
OEt
OEt
Me
O
O
O
NH2
2
16
87
Me
NH
O
O
O
O
O
O
O
O
O
O
3
4
5
14
13
12
74
90
67
OH OH
SH OH
Me
Me
Me
O
OH
Me
O
OEt
OEt
OEt
O
Me
O
SH
OH
OH NH2
Me
NH
a All the products were characterised by their spectroscopic data (IR, 1H NMR).
b Yields refer to the pure isolated products.
shown in Table 2, the hydroxy group of mercapto alcohol
reacted preferentially over thiol affording the correspond-
ing product in good yield. The selective mono-transester-
ification of diol was achieved using the present catalyst to
afford the corresponding mono-esterified product in high
yield. In case of amino alcohol (Table 2, entry 5), the
corresponding transamidation product was obtained in
good yield as the amino group is more nucleophilic than
the hydroxy one.
References and Notes
(1) (a) Fujita, T.; Tanaka, M.; Norimine, Y.; Suemune, H. J.
Org. Chem. 1997, 62, 3824. (b) Shapiro, G.; Marzi, M. J.
Org. Chem. 1997, 62, 7096.
(2) (a) Rehberg, C. E.; Fisher, C. H. J. Am. Chem. Soc. 1944, 66,
1203. (b) Rehberg, C. E.; Faucette, W. A.; Fisher, C. H. J.
Am. Chem. Soc. 1944, 66, 1723. (c) Rehberg, C. E. Org.
Synth., Coll. Vol. 3; Wiley: New York, 1955, 146.
(d) Haken, J. K. J. Appl. Chem. 1963, 13, 168.
(3) (a) Yazawa, H.; Tanaka, K.; Kariyone, K. Tetrahedron Lett.
1974, 3995. (b) Blossey, E. C.; Turner, L. M.; Neckersw, D.
C. Tetrahedron Lett. 1973, 1823.
The reaction is general as a wide range of b-keto esters
and alcohols participated successfully in the transesterifi-
cation process. It is important to note that boronic acids,
RB(OH)2, are usually crystalline solids, stable to air and
moisture. The evidence that exists indicates that the
boronic acids are of relatively low toxicity [benzene-
boronic acid:20 LD50 oral, rat = 740 mg/kg] and environ-
mental impact. Furthermore, small amount of 3-
nitrobenzeneboronic acid was found to be effective for
catalysing the selective transesterification of b-keto es-
ters. Thus it is evident that the present method represents
a novel and environmentally benign approach, which not
only preserves the simplicity but consistently provides
good to high yields of the corresponding transesterified
products.21
(4) Taber, D. F.; Amedio, J. C. Jr.; Patel, Y. K. J. Org. Chem.
1985, 50, 3618.
(5) (a) Taft, R. W. Jr.; Newman, M. S.; Verhoek, F. H. J. Am.
Chem. Soc. 1950, 72, 4511. (b) Billman, J. H.; Smith, W. T.
Jr.; Rendall, J. L. J. Am. Chem. Soc. 1947, 69, 2058.
(6) (a) Osipow, L.; Snell, F. D.; Finchler, A. J. Am. Oil Chem.
Soc. 1957, 34, 185. (b) Komori, S.; Okahara, M.; Okamoto,
K. J. Am. Oil Chem. Soc. 1960, 37, 468.
(7) Witzeman, J. S.; Nottingham, W. D. J. Org. Chem. 1991, 56,
1713.
(8) (a) Otera, J.; Yano, T.; Kawabata, A.; Hitoshi, N.
Tetrahedron Lett. 1986, 27, 2383. (b) Otera, J.; Danoh, N.;
Nozaki, H. J. Org. Chem. 1991, 56, 5307.
(9) Chavan, S. P.; Zubaidha, P. K.; Dantale, S. W.; Keshvaraja,
A.; Ramaswamy, A. V.; Ravindranathan, T. Tetrahedron
Lett. 1996, 37, 233.
In conclusion, we have demonstrated that the novel 3-ni-
trobenzeneboronic acid effectively catalysed the selective
transesterification of b-keto esters in an environmentally
acceptable process. In view of the applications of b-keto
esters in various areas, we believe that the present method
will certainly find widespread use in organic synthesis.
(10) (a) Balaji, B. S.; Sasidharan, M.; Kumar, R.; Chanda, M.
Chem. Commun. 1996, 707. (b) Balaji, B. S.; Chanda, M.
Tetrahedron 1998, 54, 13237.
(11) Ponde, D. E.; Deshpande, V. H.; Bulbule, V. J.; Sudalai, A.;
Gajare, A. S. J. Org. Chem. 1998, 63, 1058.
(12) Pais, G. C. G.; Keshavaraja, A.; Saravanan, K.; Kumar, P. J.
Chem. Res., Synop. 1996, 426.
(13) (a) Carrol, M. J. J. Chem. Soc. 1940, 704. (b) Kimel, W.;
Cope, A. C. J. Am. Chem. Soc. 1943, 65, 1992.
(14) Tale, R. H.; Patil, K. M. Tetrahedron Lett. 2002, 43, 9715.
(15) Tale, R. H.; Patil, K. M.; Dapurkar, S. E. Tetrahedron Lett.
2002, 43, 3427.
Acknowledgment
Authors are grateful to University Grant Commission (UGC), New
Delhi, India for financial support.
Synlett 2006, No. 3, 415–418 © Thieme Stuttgart · New York