J. S. Yadav et al. / Tetrahedron Letters 50 (2009) 6631–6634
6633
Table 2
Effect of leaving group on rate of reaction and diastereoselectivity
Entry
Substrate (1)
Producta (2)
Time (h)
24
Yieldb (%)
80
Ratioc (%)
O
O
OH
OAc
OMe
OEt
O
BnO
BnO
BnO
a
82:18
88:12
97:3
BnO
O
O
O
O
O
BnO
BnO
BnO
b
c
19
22
15
10
83
85
92
95
BnO
O
BnO
BnO
BnO
BnO
O
BnO
BnO
BnO
d
e
99:1
BnO
O
BnO
BnO
BnO
99:1
BnO
a
b
c
All products were characterized by 1H, 13C NMR, IR and mass spectroscopy.
Yield refers to pure products after chromatography.
Ratio was determined by HPLC.
to various cyclic acetals and trialkylsilyl nucleophiles (Table 1).12
The reactions were sluggish with cyclic acetals derived from either
xylose or ribose. The reactions were clean and high yielding merely
with 2-deoxycyclic acetals. In case of 3-alkoxy acatals, the nucleo-
phile adds to the same face as the alkoxy substituent at C-3. These
results led us to hypothesize that the alkoxy group at C-3 controls
the approach of the nucleophile onto the same face of the
oxocarbenium ion.11 This method is compatible with acid labile
protective groups such as TBS ethers (Table 1, entries d and e). This
method was also effective for the azidation and cyanation of ace-
tals with trimethylsilyl azide and trimethylsilyl cyanide, respec-
tively, under identical conditions (Table 1, entries c, m and n).
Eventually, we have studied the leaving ability of various function-
alities such as OH, ethers and esters and the results are presented
in Table 2. Of these, isopropyl acetal was found be more effective in
terms of conversion and reaction rate (Table 2, entry e).
6. (a) Smith, D. M.; Tran, M. B.; Woerpel, K. A. J. Am. Chem. Soc. 2003, 125, 14149–
14152; (b) Larsen, C. H.; Ridgway, B. H.; Shaw, J. T.; Woerpel, K. A. J. Am. Chem.
Soc. 1999, 121, 12208–12209.
7. Larsen, C. H.; Ridgway, B. H.; Shaw, J. T.; Smith, D. M.; Woerpel, K. A. J. Am.
Chem. Soc. 2005, 127, 10879–10884.
8. Bur, S. K.; Martin, S. F. Org. Lett. 2000, 2, 3445–3447.
9. (a) Togo, H.; Iida, S. Synlett 2006, 2159–2175; (b) Lin, X.-F.; Cui, S.-L.; Wang, Y.-
G. Tetrahedron Lett. 2006, 47, 4509–4512; (c) Chen, W.-Y.; Lu, J. Synlett 2005,
1337–1339; (d) Royer, L.; De, S. K.; Gibbs, R. A. Tetrahedron Lett. 2005, 46, 4595–
4597; (e) Banik, B. K.; Fernandez, M.; Alvarez, C. Tetrahedron Lett. 2005, 46,
2479–2482; (f) Wang, S.-Y. Synlett 2004, 2642–2643; (g) Ko, S.; Sastry, M. N. V.;
Lin, C.; Yao, C.-F. Tetrahedron Lett. 2005, 46, 5771–5774.
10. (a) Yadav, J. S.; Reddy, B. V. S.; Hashim, S. R. J. Chem. Soc., Perkin Trans. 1 2000,
3082–3084; (b) Yadav, J. S.; Reddy, B. V. S.; Premalatha, K.; Swamy, T.
Tetrahedron Lett. 2005, 46, 2687–2690; (c) Yadav, J. S.; Reddy, B. V. S.; Sabitha,
G.; Reddy, G. S. K. K. Synthesis 2000, 1532–1534; (d) Yadav, J. S.; Reddy, B. V. S.;
Rao, C. V.; Chand, P. K.; Prasad, A. R. Synlett 2001, 1638–1640; (e) Yadav, J. S.;
Reddy, B. V. S.; Reddy, M. S.; Prasad, A. R. Tetrahedron Lett. 2002, 43, 9703–
9706.
11. (a) Schmitt, A.; Reissig, H.-U. Synlett 1990, 40; (b) Larsen, C. H.; Ridgway, B. H.;
Shaw, J. T.; Woerpel, K. A. J. Am. Chem. Soc. 1999, 121, 12208; (c) Schmitt, A.;
Reibig, H.-U. Eur. J. Org. Chem. 2000, 3893.
In conclusion, we have described a novel protocol for the substi-
tution of five-membered cyclic acetals with allyltrimethylsilane
using 5 mol % of molecular iodine as a catalyst. Enhanced diastere-
oselectivity, high conversions, mild reaction conditions and opera-
tional simplicity are the noteworthy features of this methodology.
12. General procedure:
A solution of lactol ether (100 mg, 0.31 mmol) and
allyltrimethylsilane (0.15 mL, 0.94 mmol) in 2 mL CH2Cl2 was cooled to
ꢀ78 °C. Then a freshly prepared 1.0 M solution of I2 (5 mol %) in CH2Cl2 was
added dropwise (0.015 mL, 0.015 mmol), and the solution was allowed to stir
at ꢀ78 °C for 1 h and slowly brought to room temperature. After complete
conversion as indicated by TLC, the reaction was quenched with water (10 mL)
and the reaction mixture was extracted with dichloromethane (3 ꢂ 10 mL).
The combined extracts were washed with a 15% solution of aqueous sodium
thiosulfate, dried over anhydrous Na2SO4 concentrated in vacuo. The resulting
crude residue was purified by column chromatography to afford allyl
Acknowledgement
A.S.R. and CH.S.R., thank CSIR, New Delhi, for the award of
fellowships.
derivative as
characterized by LC–MS: using Eclipse XDB C18 column. Column size:
150 ꢂ 4.6 mm with 5 m particle size. Eluent: CH3CN/H2O (65/35) with flow
a colourless liquid with >99% stereoselectivity, which was
l
rate 1.0 mL/min at 25 °C (kmax = 210 nm). Spectral data for the selected
products: Compound 3j (Table 1): Viscous liquid, ½a D20
ꢃ
ꢀ5.0 (c 1.5, CHCl3); IR
References and notes
(KBr):
m
2930, 2856, 1454, 1104, 887, 735, 697 cmꢀ1 1H NMR (300 MHz,
;
CDCl3): d 7.19–7.32 (m, 5H), 4.73 (s, 1H), 4.68 (s, 1H), 4.46 (s, 2H), 4.16 (q, 1H,
J = 6.8 Hz), 3.76–3.84 (m, 1H), 3.42 (t, 2H, J = 6.8 Hz), 2.00–2.32 (m, 3H), 1.74 (s,
3H), 1.67–1.72 (m, 2H), 1.54–1.66 (m, 2H), 1.23–1.48 (m, 8H), 0.89 (d, 3H,
J = 6.8 Hz); 13C NMR (75 MHz, CDCl3): d 143.2, 138.6, 128.2, 127.5, 127.4, 111.9,
81.0, 75.1, 72.8, 70.4, 44.9, 39.8, 35.7, 30.3, 29.6, 26.5, 26.1, 22.9, 14.0; HRMS
(ESI) m/z calcd for C22H34O2 [M+Na]+ 353.2456, found: 353.2444. Compound
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Hosomi, A. Acc. Chem. Res. 1988, 21, 200–206; (c) Langkopf, E.; Schinzer, D.
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3k (Table 1): Viscous liquid, ½a D20
ꢃ
ꢀ19 (c 1.5, CHCl3); IR (KBr):
m 2930, 2854,
1450, 1360, 1100, 993, 910, 730, 690 cmꢀ1
;
1H NMR (300 MHz, CDCl3): d 7.23–
7.32 (m, 5H), 5.65–5.88 (m, 1H), 4.96–5.10 (m, 2H), 4.46 (s, 2H), 3.83–3.98 (m,
1H), 3.43 (t, 2H, J = 6.6 Hz), 3.19–3.31 (m, 1H), 2.03–2.40 (m, 3H), 1.22–1.84 (m,
5. Postema, M. H. D. C-Glycoside Synthesis; CRC Press: Boca Raton, FL, 1995.