Hassall et al.
119.0, 22.6, 18.4, 10.9. 29Si NMR: δ (CDCl3) 6.66. ESI MS (m/
z): 250.1985 (M + 1), 206.1360 (M - CH(CH3)2).
(iii) 2-tert-Butyldimethylsilylmethylpyridine (7c). Yel-
low oil (49% yield). 1H NMR: δ (CDCl3) 8.34 (1H, dd, J ) 4.9,
1.6 Hz, H6), 7.42 (1H, ddd, J ) 7.7, 7.7, 1.7 Hz, H4), 6.89 (2H,
m, H3/5), 2.28 (2H, s, CH2), 0.84 (9H, s, Si-C(CH3)3), -0.18
(6H, s, Si-CH3). 13C NMR: δ (CDCl3) 161.4, 148.6, 135.7, 122.3,
119.0, 26.3, 25.8, 16.6, -6.50. 29Si NMR: δ (CDCl3) 9.09. ESI
MS (m/z): 208.1 (M + 1).
(b) General Procedure for the Preparation of 4-Tri-
isopropylsilylmethylpyridine (8b) and 4-tert-Butyldi-
methylsilylmethylpyridine (8c). To a solution of 4-picoline
(2.0 g, 21 mmol) in ether (20 mL) was added methyl lithium
(1.4 M in ether, 15 mL, 21 mmol), and the solution was
refluxed for 30 min. The reaction was cooled to -78 °C (dry
ice/acetone) prior to the dropwise addition of the trialkylsilyl
chloride (25 mmol). The mixture was slowly warmed to room
temperature and stirred for a further 3 h. The product was
extracted with 1 M HCl (2 × 50 mL) and washed with ether
(50 mL). The aqueous layer was basified (pH ) 12) with
concentrated NaOH solution, and the product was extracted
with ether (3 × 50 mL). The combined ether layers were dried
(MgSO4), and the solvent was removed under reduced pressure
to afford the product as an oil.
FIGURE 5. Huckel charges in the pyridinium cation.
C(ipso) bond distance in 6b (1.472(2) Å) than in 5b (1.488-
(2) Å). These structural effects indicate greater contri-
butions of the resonance form 6′ to the ground-state
structure of 6b than 5′ makes to the ground-state
structure of 5b. The charge distributions on the simple
pyridinium cation from Huckel calculations shown in
Figure 515 show that there is a greater degree of charge
at the 2-position than at the 4-position.
Conclusion
Both solution phase 29Si and 13C NMR data and X-ray
crystallographic data provide evidence that C-Si hyper-
conjugation with the pyridinium cation is stronger at the
2-position than at the 4-position. This result suggests
that the electron demand of the pyridinium cation is
expected to be greater at the 2-position than at the
4-position.
(i) 4-Triisopropylsilylmethylpyridine (8b). (4.653 g,
89%). 1H NMR: δ (CDCl3) 8.27 (2H, d, J ) 4.65 Hz, H2/6),
6.96 (2H, d, J ) 4.5 Hz, H3/5), 2.13 (2H, s, CH2), 0.97 (21H,
m, Si-CH(CH3)2). 13C NMR: δ (CDCl3) 151.4, 148.7, 124.0,
19.4, 18.4, 10.8. 29Si NMR: δ (CDCl3) 6.30. ESI MS (m/z):
250.1985 (M + 1).
Experimental Section
(ii) 4-tert-Butyldimethylsilylmethylpyridine (8c). Yel-
1
low oil (63% yield). H NMR: δ (CDCl3) 8.37 (2H, d, J ) 5.8
1. X-ray Crystallography. Crystals were grown of 5b from
methanol/ether and of 6b from acetonitrile/ether. The tem-
perature was maintained at 130.0(1) using an Oxford Cryo-
stream cooling device. Intensity data were collected with a
Bruker SMART Apex CCD detector using Mo KR radiation
(graphite crystal monochromator λ ) 0.71073). Data were
reduced using the program SAINT.16
Hz, H2/6), 6.92 (2H, d, J ) 5.9 Hz, H3/5), 2.09 (2H, s, CH2),
0.90 (9H, s, C(CH3)3), -0.11 (6H, s, CH3). 13C NMR: δ (CDCl3)
150.4, 149.1, 123.6, 26.3, 22.8, 16.6, -6.8. 29Si NMR: δ (CDCl3)
8.77. ESI MS (m/z): 208.1 (M + 1).
(c) Preparation of N-Methyl-2-trimethylsilylmethylpy-
ridinium Iodide (6a‚iodide). A solution of 7a (100 mg) in
deuteriochloroform (0.5 mL) was treated with methyl iodide
The structure was solved by direct methods and difference
Fourier synthesis.
1
(1.1 equiv); after 24 h the H and13C NMR signals character-
istic of 7a had disappeared and were replaced with those of
2. Synthesis. (a) General Procedure for the Prepara-
tion of 2-Trimethylsilylmethylpyridine (7a), 2-Triiso-
propylsilylmethylpyridine (7b), and 2-tert-Butyldime-
thylsilylmethylpyridine (7c). To a solution of 2-picoline (2.0
g, 21 mmol) in ether (20 mL) was added methyl lithium (1.4
M in ether, 15 mL, 21 mmol), and the solution was refluxed
for 30 min. The reaction was cooled to -78 °C (dry ice/acetone)
prior to the dropwise addition of the respective trialkylsilyl
chloride (1.4 equiv). The mixture was slowly warmed to room
temperature and stirred for a further 3 h. The product was
extracted with 1 M HCl (2 × 50 mL) and washed with ether
(50 mL). The aqueous layer was basified (pH ) 12) with
concentrated NaOH solution, and the product was extracted
with ether (3 × 50 mL). The combined ether layers were dried
(MgSO4), and the solvent was removed under reduced pres-
sure.
(i) 2-Trimethylsilylmethylpyridine (7a). A clear oil
(1.8962 g, 42.7%) was isolated by Ku¨gelrohr distillation (60
°C, 1 mmHg). 1H NMR: δ (CDCl3) 8.42 (1H, d, J ) 4.6 Hz,
H6), 7.52 (1H, ddd, J ) 7.7, 7.7, 1.5 Hz, H4), 6.97 (2H, m, H3/
5), 2.37 (2H, s, CH2), 0.01 (9H, s, SiMe3). 13C NMR: δ (CDCl3)
161.1, 148.7, 135.7, 122.0, 119.0, 30.1, -1.8. 29Si NMR: δ
(CDCl3) 7.17. ESI MS (m/z): 166 (M + 1).
1
6a. H NMR: δ (CD3CN) 9.04 (1H, d, J ) 6.4 Hz, H6), 8.14
(1H, dd, J ) 7.9 Hz, H4), 7.60 (1H, d, J ) 8.3 Hz, H3), 7.55
(1H, dd, J ) 6.4 Hz, H5), 4.19 (3H, s, N-CH3), 2.76 (2H, s,
CH2), 1.89 (9H, SiMe3). 13C NMR: δ (CD3CN) 159.3, 145.1,
143.5, 127.6, 122.8, 46.5, 26.6, -1.53.
(d) Preparation of N-Methyl-2-triisopropylsilylmeth-
ylpyridinium Triflate (6b‚triflate). A solution of 7b (100
mg) in deutero acetonitrile (0.5 mL) was treated with neat
methyl triflate (1.05 equiv). After the NMR had been recorded,
ether was allowed to diffuse into the solution overnight to
afford colorless plates suitable for X-ray analysis, mp 117-
1
121°. H NMR: δ (CD3CN) 8.59 (1H, d, J ) 6.4 Hz, H6), 8.26
(1H, dd, J ) 7.7, 7.7 Hz, H4), 7.76 (1H, d, J ) 8.2 Hz, H3),
7.66 (1H, dd, J ) 7.0, 6.5 Hz, H5), 4.22 (3H, s, N-CH3), 2.79
(2H, s, CH2), 1.23 (3H, sept, J ) 7.25 Hz, Si-CH(CH3)2), 0.96
(18H, d, J ) 7.3 Hz, Si-CH(CH3)2). 13C NMR: δ (CD3CN)
162.1, 146.8, 145.2, 130.2, 125.5, 47.32, 20.3, 18.8, 12.5. 29Si
NMR: δ (CD3CN) 17.03.
(e) Preparation of N-Methyl-2-tert-butyldimethylsi-
lylmethylpyridinium Triflate (6c‚triflate). A solution of
6c (100 mg) in deutero acetonitrile (0.5 mL) was treated with
neat methyl triflate (1.05 equiv). 1H NMR: δ (CD3CN) 8.51
(1H, d, J ) 6.4 Hz, H6), 8.24 (1H, m, H4), 7.65 (1H, m, H3/5),
4.11 (3H, s, N-CH3), 2.77 (2H, s, CH2), 1.03 (9H, s, C(CH3)3),
0.04 (6H, s, CH3). 13C NMR: δ (CD3CN) 161.7, 146.8, 145.2,
129.5, 124.3, 47.0, 26.5, 23.1, 17.9, -5.62. 29Si NMR: δ (CD3-
CN) 18.49.
(ii) 2-Triisopropylsilylmethylpyridine (7b). Yellow oil
(69% yield). 1H NMR: δ (CDCl3) 8.39 (1H, d, J ) 4.5 Hz, H6),
7.48 (1H, dd, J ) 7.7, 7.7 Hz, H4), 7.04 (1H, d, J ) 7.9 Hz,
H3), 6.97 (1H, m, H5), 2.45 (2H, s, CH2), 1.04 (21H, m, Si-
CH(CH3)2). 13C NMR: δ (CDCl3) 161.8, 148.7, 135.5, 122.5,
(f) Preparation of N-Methyl-4-triisopropylsilylmeth-
ylpyridinium Triflate (5b‚triflate). A solution of 8b (100
mg) in deutero acetonitrile (0.5 mL) was treated with neat
methyl triflate (1.05 equiv). After the NMR had been recorded,
(15) Hudson, R. F. Angew. Chem., Int. Ed. 1973, 12, 36.
(16) Siemens 1999, SMART, SAINT, SADABS; Siemens Analytical
X-ray Instruments, Inc.: Madison, WI.
1996 J. Org. Chem., Vol. 70, No. 6, 2005