S. Silva et al. / Tetrahedron Letters 49 (2008) 5583–5586
5585
from acetol according to the literature,9a and the recently
introduced -xylo-based OXT 11 was synthesized through a regio-
controlled sequence starting from
-glucose.14
Neumann, W. L. Org. Lett. 2003, 5, 4349–4352; (i) Alphonse, F. A.; Suzenet, F.;
Keromnes, A.; Lebret, B.; Guillaumet, G. Org. Lett. 2003, 5, 803–805; (j)
Oumouch, S.; Bourotte, M.; Schmitt, M.; Bourguignon, J.-J. Synthesis 2005, 25–
D
D
27; (k) Mehta, V. P.; Sharma, A.; Van der Eycken, E. Org. Lett. 2008, 10, 1147–
The OXT 10 was reacted with two coupling reagents,
p-methoxyphenyl boronic acid and 2-tributylstannylthiophene
1150.
5.
(a) Alphonse, F. A.; Suzenet, F.; Keromnes, A.; Lebret, B.; Guillaumet, G. Synlett
2002, 447–450; (b) Aguilar-Aguilar, A.; Liebeskind, L. S.; Pena-Cabrera, E. J. Org.
(Table 2), by which a fair 59% yield of the corresponding 2-substi-
Chem. 2007, 72, 8539–8542.
tuted oxazoles 12 and 13 was obtained. On the other hand, the
carbohydrate-based OXT 11 was reacted with four different boro-
nic acids (entries 3–6) to produce oxazoles in good (15, 16) to
excellent (14) yields. In the case of p-iodophenylboronic acid,
however, the outcome was more disappointing with a mediocre
6. (a) Prokopcova, H.; Kappe, C. O. J. Org. Chem. 2007, 72, 4440–4448; (b)
Prokopcova, H.; Kappe, C. O. Adv. Synth. Catal. 2007, 349, 448–452.
7.
Silva, S.; Sylla, B.; Suzenet, F.; Tatibouët, A.; Rollin, P.; Rauter, A. P. Org. Lett.
008, 10, 853–856.
2
1
5
8. (a) Velazquez, F.; Olivo, H. Curr. Org. Chem. 2002, 6, 1–38; (b) Jalce, G.; Seck, M.;
Franck, X.; Hocquemiller, R.; Figadere, B. J. Org. Chem. 2004, 69, 3240–3241; (c)
Robiette, R.; Cheboub-Benchaba, K.; Peeters, D.; Marchand-Brynaert, J. J. Org.
Chem. 2003, 68, 9809–9812; (d) Diaz Perez, V. M.; Garcia Moreno, M. I.; Ortiz
Mellet, C.; Fuentes, J.; Diaz Arribas, J. C.; Canada, F. X.; Garcia Fernandez, J. M. J.
Org. Chem. 2000, 65, 138–143; (e) Crimmins, M. T.; Shamszad, M. Org. Lett.
3
8% yield of derivative 17, and no clear reason for this drop of
the yield could be made out. Finally, both tributylstannyl reagents
tested afforded good yields (86% and 72%, respectively) of oxazoles
2007, 9, 149–152.
1
8 and 19.
9.
Some recent papers: (a) Leconte, N.; Silva, S.; Tatibouët, A.; Rauter, A. P.; Rollin,
P. Synlett 2006, 301–305; (b) Gonzalez-Romero, C.; Martinez-Palou, R.;
Jimenez-Vazquez, H. A.; Fuentes, A.; Jimenez, F.; Tamariz, J. Heterocycles
2007, 71, 305–322; (c) Onyango, E. O.; Tsurumoto, J.; Imai, N.; Takahashi, K.;
Ishihara, J.; Hatakeyama, S. Angew. Chem., Int. Ed. 2007, 46, 6703–6705.
In the case of OXTs, the direct cross-coupling procedure appears
to be more favourable than the two-step procedure previously
1
6,17
used on OZTs.
Indeed, all coupling reactions involving the
S-benzyl derivatives of compounds 10 and 11 proved sluggish
10. (a) Leconte, N.; Pellegatti, L.; Tatibouët, A.; Suzenet, F.; Rollin, P.; Guillaumet, G.
and ineffective: no Suzuki-type coupling was detected with
2
in thermal conditions, the S-benzyl derivative of 11 only reacted
partially (43% yield recovery of the starting material after 3 days)
to produce a 37% yield of oxazole 14.
This preliminary report about direct Suzuki and Stille cross-
couplings on cyclic thionocarbamates has shown interesting
reactivity features associated with such small heterocycles. When
submitted to modified Stille or Suzuki coupling protocols, the
non-aromatic OZTs have shown better results when a two-step
procedure involving a S-benzylated intermediate is used rather
than a microwave-assisted direct coupling; yet both approaches
could compete in the Stille coupling case. In sharp contrast, the
aromatic OXTs afford far better results when the direct coupling
protocol is applied. In summary, this is a first step towards expand-
ing to Pd-catalyzed cross-coupling reactions to the reactivity study
Synthesis 2007, 857–864.
Girniene, J.; Tatibouët, A.; Sackus, A.; Yang, J.; Holman, G. D.; Rollin, P.
Carbohydr. Res. 2003, 338, 711–719.
-benzylsulfanyl-4-methyloxazole (prepared from 10),9a whereas
11.
1
1
1
1
2. Tardy, S.; Lobo Vicente, J.; Tatibouët, A. Dujardin, G.; Rollin, P. Synthesis, in
press.
3. Silva, S.; Simão, A. C.; Tatibouët, A.; Rollin, P.; Rauter, A. P. Tetrahedron Lett.
2008, 49, 682–686.
4. Silva, S.; Tatibouët, A.; Ortiz-Mellet, C.; Rollin, P.; Rauter, A. P., unpublished
results.
5. Typical protocol for
a
thermal Suzuki coupling: The spiro-OZT
.24 mmol) in DMF (3 mL) was cooled to 0 °C and reacted with NaH (60%,
0 mg, 0.27 mmol) for 5 min. Then benzyl bromide (0.042 mL, 0.30 mmol) was
2 (0.08 g,
0
1
added and the mixture was allowed to return to room temperature. After 4 h, a
large excess of water was added and the solution extracted with EtOAc
(
4 ꢁ 25 mL). The collected organic phases were washed with water and brine,
then dried over MgSO and evaporated. The resulting crude was purified by
4
chromatography (PE–AcOEt, 4:1) to afford the S-benzyl derivative (0.098 g,
0.232 mmol) in 96% yield. The benzylated molecule together with CuMeSal
(
(
6
2.2 equiv) and the boronic acid (2.2 equiv) was diluted under Ar, in THF
5 mL), then Pd(Ph P) (0.05 equiv) was added. The solution was heated at
0 °C for 20 h, then suspended with a satd Na CO solution and extracted with
AcOEt (4 ꢁ 25 mL). The collected organic phases were washed with water and
brine, then dried over MgSO After evaporation, the residue was
chromatographed over silica gel (EP–AcOEt 7:3) to produce the coupling
product 5 (83 mg, 0.205 mmol) in 88% yield. Mp 124–125 °C; [ ꢂ112
) d 1.35, 1.39, 1.50, 1.54 (4s, 12H,
), 3.84 (s, 3H, OMe), 3.92 (d, 1H, H6b, J6b–6a = 12.9); 3.93 (d, 1H, H7a
7a–7b = 13.1), 3.98 (d, 1H, H1a, J1a–1b = 9.7), 4.10 (d, 1H, H1b, J1b–1a = 9.7z), 4.22
d, 1H, H7b, J7b–7a = 13.1), 4.30 (dd, 1H, H6b, J6b–6a = 12.9, J6b–5 = 3.1), 4.44 (m,
1H, H ), 4.58 (d, 1H, H , J4–5 = 7.3), 6.90 (d, 2H, Ph-H, J = 8.8), 7.86 (d, 2H, Ph-H).
C NMR (62.89 MHz) d 24.7, 25.8, 26.0, 26.4 (4CH ), 55.5 (OMe), 59.4 (C-7),
2.9 (C-6), 72.6 (C-1), 73.1 (C-5), 75.2 (C-4), 84.6 (C-3), 105.1 (C-2),
09.9 (CMe ), 111.4 (CMe ), 113.8, 119.8, 130.0, 162.8 (C-8). MS (IS): m/z
3
4
2
3
of cyclic thionocarbamates, which have been a long-term research
theme in our laboratory.18
4
.
a]
D
1
Acknowledgments
(c = 1.16, CHCl
CH
3 3
). H NMR (250 MHz, CDCl
4
J
(
3
,
We are grateful to the ANR and the CNRS for financial support
and to the FCT for a fellowship (S.S.). We would also like to thank
the Universidade de Lisboa, the Université d’Orléans and the PES-
SOA program for multiform support.
5
4
1
3
3
6
1
4
4
2
2
+
+
06.0 [M+H] . ESI-HRMS calcd for
06.1863.
21 7
C H28NO [M+H] : 406.1860, found:
References and notes
1
6. Typical protocol for a direct Suzuki coupling: In a microwave vial tube, a solution
of OXT 11 (100 mg) in THF (5 mL) with a stirring bar was prepared under
1
.
(a) Desimoni, G.; Faita, G.; Jorgensen, K. A. Chem. Rev. 2006, 106, 3561–3651;
b) McManus, H. A.; Guiry, P. J. Chem. Rev. 2004, 104, 4151–4202; (c) Yeh, V. S.
argon. Following the order, CuTc (2.2 equiv), p-MeOPhB(OH)
2
(2.2 equiv) and
(
(Ph P) Pd (0.05 equiv) were added under argon. The tube was sealed and
3
4
C. Tetrahedron 2004, 60, 11995–12042.
(a) Balasubramanian, M. In Palladium in Heterocyclic Chemistry, Li, J. J.; Gribble,
G. W. Eds.; Tetrahedron Organic Chemistry Series, 2007; Vol. 26, pp 379–406;
subjected to microwave irradiation at 100 °C with stirring for 60 min. The
reaction vessel was allowed to cool to rt, the solvent was evaporated in vacuo
and the residue was purified by column chromatography on silica gel (AcOEt/
2
.
(
3
b) Young, G. L.; Smith, S. A.; Taylor, R. J. K. Tetrahedron Lett. 2004, 45, 3797–
801; (c) Reeder, M. R.; Gleaves, H. E.; Hoover, S. A.; Imbordino, R. J.; Pangborn,
J. J. Org. Process Res. Dev. 2003, 7, 696–699; (d) Schaus, J. V.; Panek, J. S. Org. Lett.
000, 2, 469–471; (e) Krebs, O.; Taylor, R. J. K. Org. Lett. 2005, 7, 1063–1066; (f)
PE) to afford the oxazole 14 (118 mg, 86% yield) as a yellowish solid, mp 113–
1
114 °C; [
a
]
D
ꢂ34 (c = 1, MeOH). H NMR (250 MHz, CDCl
3
) d 1.36 and 1.56 (2s,
0
0
6H, iPrd), 3.84 (s, 3H, OMe), 4.41 (s, 1H, H-3 ), 4.69 (d, 1H, J
(br s, 1H, OH), 5.18 (d, 1H, J
1
0
–2
0
= 3.6, H-2 ), 4.75
0
0
2
3
0
–4
0
= 2.1, H-4 ), 6.08 (d, 1H, H-1 ), 6.95 (d, 2H,
13
Langille, N. F.; Dakin, L. A.; Panek, J. S. Org. Lett. 2002, 4, 2485–2488; (g) Su, Q.;
Dakin, L. A.; Panek, J. S. J. Org. Chem. 2007, 72, 2–24.
(a) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174–238; (b)
Derridj, F.; Djebbar, S.; Benali-Baitich, O.; Doucet, H. J. Organomet. Chem. 2008,
6
1
J = 8.8, ortho-H-ArOMe), 7.77 (s, 1H, H-5), 7.94 (d, 2H, meta-H-ArOMe).
C
*
0
3 3
NMR (62.89 MHz) d 26.2 and 26.9 (2 CH ), 55.5 (OCH ), 73.5 (C-4 ), 76.9 (C-
0
0
0
3
.
.
3 ), 85.1 (C-2 ), 105.2 (C-1 ), 111.9 (CIV-iPrd), 114.4 (CH orthoArOMe), 119.4,
128.5 (meta-CH–ArOMe), 129.5, 136.6 (C-4), 137.6 (C-5 a), 161.9 (C-2). ESI-
+
93, 135–144; (c) Bellina, F.; Cauteruccio, S.; Rossi, R. Eur. J. Org. Chem. 2006,
379–1382; (d) Flegeau, E. F.; Popkin, M. E.; Greaney, M. F. J. Org. Chem. 2008,
3, 3303–3306.
HRMS calcd for C17
H20NO
6
[M+H] : 334.1291, found: 334.1286.
17. Typical protocol for a direct Stille coupling: In a microwave vial tube, a solution of
OXT 11 (0.100 g) in THF (5 mL) with a stirring bar was prepared under argon.
7
4
(a) Liebeskind, L. S.; Srogl, J. J. Am. Chem. Soc. 2000, 122, 11260–11261; (b) Yu,
Y.; Liebeskind, L. S. J. Org. Chem. 2004, 69, 3554–3557; (c) Yang, H.; Li, H.;
Wittenberg, R.; Egi, M.; Huang, W.; Liebeskind, L. S. J. Am. Chem. Soc. 2007, 129,
Following the order, CuBrꢀMe
2
S (2.2 equiv), 2-tributylstannylthiophene
(2.2 equiv) and (Ph P) Pd (0.05 equiv) were added under argon. The tube
3
4
was sealed and subjected to microwave irradiation at 100 °C with stirring for
60 min. The reaction vessel was allowed to cool to rt, the solvent was
evaporated in vacuo and the residue was purified by column chromatography
1
132–1140; (d) Leconte, N.; Keromnes-Wuillaume, A.; Suzenet, F.; Guillaumet,
G. Synlett 2007, 204–210; (e) Liebeskind, L. S.; Srogl, J. Org. Lett. 2002, 4, 979–
9
9
81; (f) Kusturin, C. L.; Liebeskind, L. S.; Neumann, W. L. Org. Lett. 2002, 4, 983–
85; (g) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2001, 3, 91–93; (h)
on silica gel (AcOEt/PE) to afford the oxazole 18 (103 mg, 86% yield), [
a
]
D
ꢂ29
(c = 1, MeOH). 1H NMR (250 MHz, CDCl
) d 1.36 and 1.56 (2s, 6H, iPrd), 4.25 (d,
3
0
0
Kusturin, C.; Liebeskind, L. S.; Rahman, H.; Sample, K.; Schweitzer, B.; Srogl, J.;
1H, JOH-3
0
= 1.8, OH), 4.43 (s, 1H, H-3 ), 4.69 (d, 1H, J
1
0
–2
0
= 3.6, H-2 ), 5.19 (d, 1H,