A. D. Dilman et al. / Tetrahedron Letters 45 (2004) 3741–3744
3743
10. General procedure: Under an argon atmosphere to solid
chlorotris(pentafluorophenyl)silane9 (6.7 mmol) were suc-
cessively added dichloroethane (6.4 mL), triethylamine
(1.25 mL, 9.0 mmol), and the carbonyl compound
(6.4 mmol). The mixture was heated under reflux for the
time indicated in Table 1, concentrated under vacuum,
diluted with 20 mL of dry hexane, filtered under argon,
and the solid residue washed with 5 mL of hexane. The
combined hexane solution was concentrated, and the
residue was fractionally distilled.
(C6F5)3
Si
O
O
(C6F5)3
Si
a
b
R
O
O
(C6F5)3
Si
R
O
O
OSi(C6F5)3
R
Scheme 1. Possible mechanisms of the aldol reaction.
1
1a: H NMR (CDCl3), d: 1.89 (s, 3H, Me), 4.05 (s, 1H),
In summary, enol ethers with new silyl fragments have
been prepared. The presence of three electron-with-
drawing pentafluorophenyl substituents imparts Lewis
acidity to these species that is reflected in their reactivity
toward aldehydes. Our further investigations will be
aimed at understanding the exact mechanism of the
observed aldol reaction, as well as at elaboration of the
chemistry of other tris(pentafluorophenyl)silyl deriva-
tives.
4.20 (s, 1H) (CsH2). 13C, d: 21.2 (Me), 93.6 (CH2), 104.5 (t,
1
2JC–F ¼ 27:4, Ci-C6F5), 137.5 (dm, JC–F ¼ 255, CF), 144.1
(dm, 1JC–F ¼ 259, CF), 149.2 (dm, 1JC–F ¼ 244, CF), 153.8
(CO). 19F, d: ꢀ161.3 (m, meta), ꢀ147.9 (tt, JF–F ¼ 6:8,
18.1, para), ꢀ128.5 (d, JF–F ¼ 18:1, ortho). 29Si, INEPT
from H, d: ꢀ37.44. Anal. Calcd for C21H5F15OSi: C,
43.02; H, 0.86. Found: C, 42.95; H, 0.92.
1
1b: H NMR (CDCl3), d: 4.61 (d, 1H, J ¼ 2:8), 5.14 (d,
1H, J ¼ 2:8) (CH2), 7.37–7.46 (m, 3H), 7.67–7.77 (m, 2H)
2
(Ph). 13C, d: 93.4 (CH2), 104.7 (t, JC–F ¼ 26:9, Ci-C6F5),
125.4, 128.2 (o-, m-CHPh), 128.6 (p-CHPh), 135.8 (Ci-Ph),
138.0 (dm, 1JC–F ¼ 255, CF), 144.7 (dm, 1JC–F ¼ 259, CF),
1
149.7 (dm, JC–F ¼ 246, CF), 154.9 (CO). 19F, d: ꢀ161.3
Acknowledgements
(m, meta), ꢀ147.8 (tt, JF–F ¼ 4:5, 20.4, para), ꢀ128.0 (d,
JF–F ¼ 20:4, ortho). 29Si, INEPT from H, d: ꢀ34.40. The
compound was contaminated with 5% of ((C6F5)3Si)2O,
which is only visible in the 19F spectra (ꢀ161.0, meta;
ꢀ146.7, para, ꢀ127.9 ortho).
This work was performed at the Scientific educational
center for young chemists and supported by the Minis-
try of Science (project MK-2352.2003.03), Russian
Foundation for Basic Research (project # 00-15-97359),
and INTAS (project # 2003-55-1185). We also thank
Prof. S. L. Ioffe for start-up funding and Prof. Yu. I.
Baukov and Dr. V. M. Danilenko for helpful discus-
sions.
1c: 1H NMR (CDCl3), d: 1.82–1.96 (m, 2H), 2.18–2.29 (m,
2H), 2.31–2.41 (m, 2H) (CH2)3, 4.66 (br s, 1H, CH). 13C, d:
2
21.3, 28.5, 32.5 (CH2)3, 104.6 (t, JC–F ¼ 27:4, Ci-C6F5),
1
105.7 (CH@), 137.7 (dm, JC–F ¼ 255, CF), 144.4 (dm,
1
1JC–F ¼ 259, CF), 149.5 (dm, JC–F ¼ 248, CF), 152.3
(CO). 19F, d: ꢀ161.1 (m, meta), ꢀ147.7 (t, JF–F ¼ 20:0,
para), ꢀ128.4 (d, JF–F ¼ 20:0, ortho). Anal. Calcd for
C23H7F15OSi: C, 45.11; H, 1.15. Found: C, 44.88; H, 1.11.
1d: 1H NMR (CDCl3), d: 1.43–1.56 (m, 2H), 1.61–1.75 (m,
2H), 1.90–2.01 (m, 2H), 2.05–2.17 (m, 2H) (CH2)4, 4.90 (t,
1H, J ¼ 3:9, CH), 13C, d: 21.9, 22.9, 23.7, 28.8 (CH2)4,
References and notes
2
1. (a) Fleming, I.; Barbero, A.; Walter, D. Chem. Rev. 1997,
97, 2063; (b) Weber, W. P. Silicon Reagents for Organic
Synthesis; Springer: New York, 1983; (c) Brownbridge, P.
Synthesis 1983, 85; (d) Poirier, J.-M. Org. Prep. Proced.
Int. 1988, 20, 317.
€
2. Burfeindt, J.; Patz, M.; Muller, M.; Mayr, H. J. Am.
Chem. Soc. 1998, 120, 3629.
3. Mukaiyama, T. Org. React. 1982, 28, 203.
4. (a) Noyori, R.; Nishida, I.; Sakata, J. J. Am. Chem. Soc.
1983, 105, 1598; (b) Chuit, C.; Corriu, R. J. P.; Reye, C.
J. Organomet. Chem. 1988, 358, 57.
5. Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem.
Rev. 1993, 93, 1371.
6. (a) Myers, A. G.; Kephart, S. E.; Chen, H. J. Am. Chem.
Soc. 1992, 114, 7922; (b) Denmark, S. E.; Griedel, B. D.;
Coe, D. M.; Schnute, M. E. J. Am. Chem. Soc. 1994, 116,
7026; (c) Franz, A. K.; Woerpel, K. A. Acc. Chem. Res.
2000, 33, 813.
7. (a) Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T.
J. Am. Chem. Soc. 1996, 118, 7404; (b) Denmark, S. E.;
Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432; (c)
Kobayashi, S.; Nishio, K. Tetrahedron Lett. 1993, 34, 3453.
8. The pentafluorophenyl group is frequently used to modify
properties of boron Lewis acids. For example, see:
Ishihara, K.; Yamamoto, H. Eur. J. Org. Chem. 1999, 527.
9. Chlorotris(pentafluorophenyl)silane was obtained accord-
ing to a literature procedure: Frohn, H.-J.; Lewin, A.;
Bardin, V. V. J. Organomet. Chem. 1998, 568, 233.
105.1 (t, JC–F ¼ 28:3, Ci-C6F5), 106.8 (CH@), 137.7 (dm,
1
1JC–F ¼ 255, CF), 144.2 (dm, JC–F ¼ 259, CF), 149.3
1
(CO), 149.7 (dm, JC–F ¼ 247, CF). 19F, d: ꢀ161.7 (m,
meta), ꢀ148.4 (tt, JF–F ¼ 4:5, 20.0, para), ꢀ128.4 (d,
JF–F ¼ 20:0, ortho). 29Si, INEPT from H, d: ꢀ37.93. The
compound contained 10% of ((C6F5)3Si)2O along with ca.
7% of other unidentified impurities.
1e: 1H NMR (CDCl3), d: 1.59 (s, 3H, Me), 1.69 (s, 3H,
Me), 6.12 (s, 1H, CH). 13C, d: 14.7, 18.8 (CMe2), 104.5 (t,
2JC–F ¼ 28:4, Ci-C6F5), 118.8 (CMe2), 120.1 (CH), 137.9
(dm, 1JC–F ¼ 254, CF), 144.7 (dm, 1JC–F ¼ 260, CF), 149.5
1
(dm, JC–F ¼ 247, CF). 19F, d: ꢀ161.3 (m, meta), ꢀ147.8
(tt, JF–F ¼ 4:5, 20.4, para), ꢀ128.6 (d, JF–F ¼ 20:4, ortho).
29Si, INEPT from H, d: ꢀ34.42. Anal. Calcd for
C22H7F15OSi: C, 44.01; H, 1.18. Found: C, 44.15; H, 1.03.
11. Crystallographic data for 1a: Crystals of C21H5F15OSi at
120 K
are
monoclinic,
space
ꢀ
group
C2/c,
ꢀ
ꢀ
3
a ¼ 18:6179ð16Þ A, b ¼ 11:5282ð9Þ A, c ¼ 20:9796ð18Þ A,
V ¼ 4158:4ð6Þ A , Z ¼ 8, M ¼ 586:34, dcalc ¼ 1:873 g cmꢀ3
,
ꢀ
lðMoKaÞ ¼ 2:62 cmꢀ1, F ð000Þ ¼ 2304; 23474 reflections
were collected; 5980 reflections were unique. R1 ¼ 0:0497
was calculated for 3256 observed reflections with
I > 2rðIÞ. Crystallographic data (excluding structure fac-
tors) have been deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC 229201) and are available
free of charge at CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44(0)-1223-336033 or e-mail: deposit@