Submitted by Daniel L. Comins, Ali Dehghani, Christopher J. Foti, and Sajan P. Joseph
1.
Checked by Maria A. Cichy and Amos B. Smith, III.
1. Procedure
A.
N-(2-Pyridyl)triflimide (1). A
2-L, two-necked, round-bottomed flask equipped with a
mechanical stirrer (Note
1) and a
rubber septum is charged with
2-aminopyridine (19.859 g, 0.211 mol) (Note
2) and
pyridine (35.04 g, 35.88 mL, 0.443 mol) (Note
3) in
800 mL of dichloromethane (CH2Cl2) (Note
4) under an
argon atmosphere. The reaction mixture is cooled to −78°C and a solution of
triflic anhydride (125 g, 74.54 mL, 0.443 mol) (Note
5) in
150 mL of CH2Cl2 is added dropwise via a cannula over 3.5 hr with vigorous stirring. After the solution is stirred for 2 hr at −78°C, the
cooling bath is removed and stirring is continued at room temperature for 19 hr. The reaction mixture is quenched with 50 mL of cold water and the layers are separated. The aqueous layer is extracted with
CH2Cl2 (4 × 50 mL). The combined organic extracts are washed with cold aqueous
10% sodium hydroxide (1 × 150 mL), cold water (1 × 100 mL),
brine (1 × 100 mL) and dried over
magnesium sulfate. After filtration, the solvent is removed under vacuum to give
69 g of the crude product. After Kugelrohr distillation (Note
6),
61 g (
81%) of pure
N-(2-pyridyl)triflimide (bp
85–100°C/0.25 mm, mp
41–42°C) (Note
7) is obtained as a white solid.
2. Notes
1. A
magnetic stirrer can be used with a
large stirrer bar and
1.5 L of dichloromethane.
2.
2-Aminopyridine was purchased from Aldrich Chemical Company, Inc., and used without further purification.
3. Anhydrous
pyridine was purchased from Aldrich Chemical Company, Inc., and kept over 3 Å molecular sieves for two days prior to use.
4. Anhydrous
dichloromethane was purchased from Aldrich Chemical Company, Inc., and used without further purification.
5.
Triflic anhydride was purchased from Aldrich Chemical Company, Inc., and used as such.
6. Sometimes a second distillation is needed to obtain pure compound.
7. The spectral properties of
N-(2-pyridyl)triflimide are as follows: IR (nujol) cm
−1: 1590, 1570, 1460, 1220, 1215, 1120, 1040, 990, 940, 910, 880, 735, 710;
1H NMR (300 MHz, CDCl
3) δ: 7.46–7.55 (m, 2 H), 7.91–7.97 (dt, 1 H, J = 8.06, 2.2), 8.63 (dd, 1 H, J = 4.4, 1.46);
13C NMR (75 MHz, CDCl
3) δ: 112.80, 117.10, 121.39, 125.50, 125.69, 126.79, 139.71, 145.98, 150.31.
9. The spectral properties of
N-(5-chloro-2-pyridyl)triflimide are as follows: IR (nujol) cm
−1: 1570, 1460, 1230, 1215, 1125, 1010, 925, 905, 745, 730;
1H NMR (300 MHz, CDCl
3) δ: 7.42 (d, 1 H, J = 8.8), 7.90 (dd, 1 H, J = 8.8, 2.2), 8.58 (d, 1 H, J = 2.93);
13C NMR (75 MHz, CDCl
3) δ: 112.77, 117.06, 121.36, 125.66, 126.18, 135.84, 139.33, 143.82, 149.31.
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
Vinyl triflates are important intermediates, since they can be used as synthetic precursors for vinyl cations and alkylidene carbenes, and as substrates for regiospecific coupling reactions.
2 3,4 5 6 7 8 9 10 Vinyl triflates are also valuable intermediates in a mild, two-step procedure for the deoxygenation of ketones.
11 12,13 These new triflating reagents are highly reactive and easy to prepare and handle.
14 When compared with other triflating reagents, the
vinyl triflate can in most cases be made at lower temperatures, and any excess reagent and by-products can be removed by washing with cold aqueous
5% sodium hydroxide solution. The utility of the pyridine-derived triflating reagents is illustrated by the examples in the Table.
14 Recently reagent
2 has been used in the total syntheses of
(−)-porantheridine15 and
trans-decahydroquinoline alkaloid (+)-219 A.
16
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