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J.-M. Vatele / Tetrahedron Letters 47 (2006) 715–718
717
Table 2. Chemoselective oxidation/olefination of primary alcohols in the presence of secondary ones
Entry
Substrate
Conditionsa
Product (isolated yield)
OH
OH
OH
COR
22
1
2
(1) 2 h, rt; (2) 1 h, rt
(1) 2 h, rt; (2) 3 h, rt
23 R = OEt (87%)
24 R = Me (69%)
OH
CO2Et
O
O
OBn
OBn
3
(1) 6 h, rt; (2) 30 min, 0 °C
HO
OMe
OBn
26 (68%)b
HO
OMe
OBn
25
OH
BnO
CO2Et
BnO
4
(1) 3 h, rt; (2) 1 h, rt
OH
28 (50%)
OH
27
a Reaction conditions: (1) BAIB (1.15 equiv), TEMPO (0.1 equiv), CH2Cl2; (2) Ph3P@CH–COR (1.3 equiv).
b E/Z ratio: 1/2.
was stirred for 150 min, cooled to 0 °C and (carboeth-
oxymethylene)triphenylphosphorane (0.423 g, 1.3 equiv)
was added. The reaction mixture was allowed to warm
to room temperature and stirred for 1 h. The solution was
poured onto a column of silica gel and eluted with a
mixture of ethyl acetate–petroleum ether (1:3) to give pure
ethyl 10-hydroxyundec-2-enoate 23 (0.184 g, 87%) as an
secondary ones (Table 2). Under the same reaction
conditions as described above, 1,8-nonanediol 22 was
transformed to the mono-(E)-unsaturated ester 23 in
a rewarding 87% yield (entry 1), thus demonstrating
the excellent chemoselectivity of our procedure. Methyl
2,3-di-O-benzyl-a-D-glucopyranoside 25 gave 26 in good
yield but with a low selectivity in favour of the Z isomer
(entry 3). In the case of 1,3-diol 27, the ester 28 was
obtained in a moderate yield due to the formation of
several minor products at the oxidation stage (entry
4).
1
oil. IR (film): 3424, 1721, 1654 cmÀ1. H NMR (CDCl3,
200 MHz): 1.16 (d, 3H, J = 6.2 Hz, Me), 1.23–1.40
(m, 15H, 5 CH2, Me), 2.03 (br s, 1H, OH), 2.18 (br q,
2H, J = 6.8 Hz, CH2–CH@CH), 3.77 (sextuplet, 1H,
J = 6.2 Hz, CHOH), 4.16 (q, 2H, J = 7.1 Hz, Me), 5.79
(dt, 1H, J = 15.64 and 1.5 Hz, CH@CH–CO2Et), 6.94 (tt,
1H, J = 15.64 and 6.9 Hz, CH@CH–CO2Et). 13C NMR:
14.3, 23.5, 25.6, 27.9, 29.1, 29.4, 32.1, 39.3, 60.1, 68.1,
121.3, 149.4, 166.8. Anal. Calcd for C13H24O3: C, 68.38;
H, 10.59; O, 21.02. Found: C, 68.27; H, 10.71; O, 21.07.
5. In the presence of (carboethoxymethylene)triphenylphos-
phorane, the ability of the BAIB/TEMPO system to act as
an oxidizing agent was inhibited (tested on compounds 1
and 16).
In conclusion, we have shown that the BAIB/TEMPO
system in combination with stabilized phosphoranes
constitutes a mild and stereoselective one-pot method
for the conversion of a variety of alcohols into their cor-
responding a,b-unsaturated esters. Our procedure has
significant advantages over the existing ones such as its
chemoselectivity (primary alcohols over secondary
ones),11,12 general applicability,13 commercially avail-
able and safer reagents.14
6. All new compounds gave satisfactory physical and ana-
lytical data.
7. Einhorn, J.; Einhorn, C.; Ratajczak, F.; Pierre, J.-L. J.
Org. Chem. 1996, 61, 7452–7454.
8. (a) Barrett, A. G. M.; Hamprecht, D.; White, A. J. P.;
Williams, D. J. J. Am. Chem. Soc. 1997, 119, 8608–8615;
(b) Barrett, A. G. M.; Hamprecht, D.; Ohkubo, M. J. Org.
Chem. 1997, 62, 9376–9378.
Acknowledgements
The author thanks Mrs. Huynh Dong Doan and
Alexandre Piou, for preliminary experiments.
9. For other examples of catalysis of the Wittig olefination
by acids, see: benzoic acid catalysis: (a) Ruchardt, C.;
¨
Panse, P.; Eichler, S. Chem. Ber. 1967, 100, 1144–1164;
Bose, A. K.; Manhas, M. S.; Ramer, R. M. J. Chem. Soc.
(C) 1969, 2728–2730; silica gel catalysis: (b) Patil, V. J.;
Ma¨vers, U. Tetrahedron Lett. 1996, 67, 1281–1284.
10. The presence of about 5–6% of compound 10 (Table 1,
entry 7) was detected by 13C NMR.
11. Swern oxidation used in this kind of one-pot process,
developed by Ireland and Norbeck (Ref. 1) or pyridinium
chlorochromate (PCC), have no selectivity on primary OH
groups over secondary ones. For PCC, see: Bressette, A.
R.; Glover, L. C. IV. Synlett 2004, 738–740.
References and notes
1. Ireland, R. E.; Norbeck, D. W. J. Org. Chem. 1985, 50,
2198–2200.
2. De Mico, A.; Margarita, R.; Parlanti, L.; Vescovi, A.;
Piancatelli, G. J. Org. Chem. 1997, 62, 6974–6977.
3. De Nooy, A. E. J.; Besemer, A. C.; Van Bekkum, H.
Synthesis 1996, 1153–1174.
4. Representative experimental procedure (Table 2, entry 1).
To
a stirred solution of 1,8-nonanediol 22 (0.15 g,
0.94 mmol) in CH2Cl2 (4 mL) were added bis(acetoxy)iodo-
benzene (0.346 g, 1.15 equiv) and 2,2,6,6-tetramethyl-
piperidinyloxy (0.015 g, 0.1 equiv). The yellow solution
12. A chemoselective one-pot protocol for the C-2 homolo-
gation of carbohydrate-derived glycols, using SO3Æpyridine
(5 equiv) as oxidant, has been very recently published.