LETTER
Scheme 2
A Facile and Selective Cleavage of Prenyl Esters
139
(7) Imamoto, T. Lanthanides in Organic Synthesis; Academic
Press: New York, 1994.
(8) (a) Cappa, A.; Marcantoni, E.; Torregiani, E.; Bartoli, G.;
Bellucci, M. C.; Bosco, M.; Sambri, L. J. Org. Chem. 1999,
64, 5696. (b) Marcantoni, E.; Nobili, F.; Bartoli, G.; Bosco,
M.; Sambri, L.; Torregiani, E. J. Org. Chem. 1997, 62,
4183. (c) Di Dea, M.; Marcantoni, E.; Torregiani, E.;
Bartoli, G.; Bellucci, M. C.; Bosco, M.; Sambri, L. J. Org.
Chem. 2000, 65, 2830. (d) Yadav, J. S.; Reddy, B. V. S.
Synlett 2000, 1275. (e) Yadav, J. S.; Reddy, B. V. S.; Reddy,
M. S.; Sabitha, G. Synlett 2001, 1134.
In summary, this paper describes a mild and efficient
method for the selective deprotection of prenyl esters to
their parent carboxylic acids using CeCl3 7 H2O-NaI un-
der neutral conditions thereby leaving acid- and base-la-
bile protecting groups intact. The high levels
chemoselectivity in this process combined with a simple
operation, high yields and ready availability of reagents at
low cost will find a wider use of the prenyl ester in organic
synthesis.
(9) Experimental Procedure: A mixture of 3-methylbut-2-
enoate (5 mmol) CeCl3 7 H2O (5 mmol) and NaI (5 mmol)
in acetonitrile (15 mL) was stirred at reflux temperature for
a specified time as required to complete the reaction (Table).
After complete conversion, as indicated by TLC, the
reaction mixture was diluted with water (15 mL) and
extracted with ethyl acetate (2 20 mL). The combined
organic layers were dried over anhyd Na2SO4, concentrated
in vacuo and purified by column chromatography on silica
gel (Merck, 100–200 mesh, EtOAc–hexane, 2:8) to afford
pure acid. Spectral data for the compounds 1e: Liquid, 1H
NMR (CDCl3): = 0.87 (d, 3 H, J = 6.8 Hz), 0.98 (d, 3 H,
J = 6.8 Hz), 1.73 (s, 3 H), 1.78 (s, 3 H), 2.10–2.21 (m, 1 H),
4.28 (dd, 1 H, J = 5.5, 10.3 Hz), 4.60 (d, 2 H, J = 7.0 Hz),
5.10 (s, 2 H), 5.20 (brs, NH), 5.35 (m, 1 H), 7.28–7.40 (m, 5
H). MS (EI): m/z = 319 [M+]. IR (KBr): 3347, 2965, 1723,
1511, 1220, 988, 722 cm–1. 2e: Solid, [ ]D20 +6.3 (c 4,
Acknowledgement
BVS, CVR and PKC thanks CSIR, New Delhi for the award of fel-
lowships.
References
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CHCl3), Aldrich: [ ]D20 (c 4, CHCl3). 1H NMR (CDCl3):
=
0.85 (d, 3 H, J = 7.0 Hz), 0.99 (d, 3 H, J = 7.0 Hz), 2.10–2.23
(m, 1 H), 4.20 (m, 1 H), 5.08 (s, 2 H), 5.80 (brs, NH), 7.25–
7.40 (m, 5 H). MS (EI): m/z = 251 [M+]. IR (KBr): 3339,
3037, 1695, 1531, 1229, 978, 729 cm–1. 1f: Liquid, 1H NMR
(CDCl3): = 1.40 (d, 3 H, J = 6.8 Hz), 1.78 (s, 3 H), 1.80 (s,
3 H), 4.38 (m, 1 H), 4.60 (d, 2 H, J = 7.0 Hz), 5.10 (s, 2 H),
5.37 (m, 1 H), 5.45 (brs, NH), 7.37–7.40 (m, 5 H). MS (EI):
m/z = 291 [M+]. IR (KBr): 3342, 3035, 2965, 1724, 1525,
1453, 1209, 1065, 917, 735 cm–1. 2f: Solid, [ ]D20 –13.9 (c 2,
HOAc), Aldrich: [ ]D23 –14.2 (c 2, HOAc). 1H NMR
(DMSO-d6): = 1.48 (d, 3 H, J = 7.0 Hz), 4.40 (m, 1 H), 5.18
(s, 2 H), 5.27 (brs, NH), 7.28–7.40 (m, 5 H), 8.15 (brs, OH).
MS (EI): m/z = 223 [M+]. IR (KBr): 3333, 3036, 1695,
1536, 1458, 1252, 1075, 1027, 914, 739 cm–1.
(10) IICT Commun. No: 01/x/09
Synlett 2002, No. 1, 137–139 ISSN 0936-5214 © Thieme Stuttgart · New York