Notes
J . Org. Chem., Vol. 64, No. 20, 1999 7641
(contaminated with less than 10% of 4-nitrophenol) was filtered
through a short pad of silica gel to afford the desired triflated
compound.
conclusion that the charge stabilization effect of the
intermediate should be less favored in 3 than in 1, which
is indeed in accord with the higher reactivity of 1 as a
trifluoro methanesulfonyl transfer agent. On the other
hand, charge analysis of 2,4-dinitrophenyl triflate (4)
reveals that the positive charge on the sulfur atom is still
greater than that on the carbon atom. However, the
polarity index is decreased (P ) lS/lC ) 8.6 for 4) and the
pz orbital coefficient of C-1 carbon is greater than that
of sulfur. It is known that SNAr (C-O bond scission)
reactions have especially high Hammett F values (+4 to
+5) and, consequently, are very sensitive to electronic
effect.25 The presence of the second strong electron-
withdrawing nitro group on the aromatic ring thus
switched the attack of nucleophile on carbon atom, and
the SNAr pathway became predominant in the reaction
of 4 with phenol (Table 1, entry d).
4-ter t-Bu tylp h en yl tr ifla te 6: colorless oil;29 1H NMR (200
MHz, CDCl3) δ 1.66 (s, 9H), 7.22 (d, J ) 8.6 Hz, 2H), 7.49 (d, J
) 8.6 Hz, 2H). Anal. Calcd for C11H13F3O3S: C, 46.81; H, 4.64.
Found: C, 46.93; H, 4.62.
4-Iod op h en yl tr ifla te 9: colorless oil;30 1H NMR (200 MHz,
CDCl3) δ 7.04 (d, J ) 8.9 Hz, 2H), 7.79 (d, J ) 8.9 Hz, 2H); EIMS
(m/z) 372 (M•+).
5-F or m yl-2-m eth oxyp h en yl tr ifla te 11: colorless oil;31 IR
(CHCl3) ν 1701, 1609, 1518, 1427, 1286 cm-1; 1H NMR (250 MHz,
CDCl3) δ 4.03 (s, 3H), 7.19 (d, J ) 8.6 Hz, 1H), 7.77 (d, J ) 1.9
Hz, 1H), 7.90 (dd, J ) 1.9, 8.6 Hz, 1H), 9.90 (s, 1H); CIMS (m/z)
285 (M + H)+.
2-Na p h th yl tr ifla te 13: mp 30-31 °C (lit.6b mp ) 31-32 °C);
1
IR (CHCl3) ν 1631, 1600, 1513, 1463, 1425 cm-1; H NMR (250
MHz, CDCl3) δ 7.38 (dd, J ) 2.5, 9.0 Hz, 1H), 7.56-7.60 (m,
2H), 7.76 (d, J ) 2.5 Hz, 1H), 7.86-7.91 (m, 2H), 7.93 (d, J )
9.0 Hz, 1H); CIMS (m/z) 277 (M + H)+.
In conclusion, we have shown that 4-nitrophenyl
triflate (1) as well as 4-nitrophenyl nonaflate 2 are
excellent perfluoroalkanesufonyl transfer agents. The
crystalline reagents 1 and 2 are not hygroscopic and
appear to be indefinitely stable. From the viewpoint of
atom economy,26 compound 1 is superior to N-phenyltri-
flimide6 and N-(2-pyridyl)triflimide7 where one of the two
trifluoromethanesulfonyl groups was wasted.
2-Tr iflu or om eth an esu lfon yloxy-6-m eth ylpyr idin e 15: mp
164-165 °C; IR (CHCl3) ν 1675, 1613, 1569, 1425 cm-1; 1H NMR
(250 MHz, CDCl3) δ 2.57 (s, 3H), 6.99 (d, J ) 7.8 Hz, 1H), 7.23
(d, J ) 7.8 Hz, 1H), 7.77 (t, J ) 7.8 Hz, 1H); CIMS (m/z) 242 (M
+ H)+.
Tr iflu or om eth a n esu lfon ic a cid 4-(3-h yd r oxy-p r op en yl)-
p h en yl ester 17: IR (CHCl3) ν 3613, 3445, 3030, 2931, 2875,
1504, 1427, 1258 cm-1 1H NMR (250 MHz, acetone-d6) δ 4.02
;
(t, J ) 5.5 Hz, 1H, OH), 4.27 (dt, J ) 1.7, 5.5 Hz, 2H), 6.51 (dt,
J ) 4.9, 16.0 Hz, 1H), 6.70 (dt, J ) 1.7, 16.0 Hz, 1H), 7.40 (d, J
) 8.9 Hz, 2H), 7.63 (d, J ) 8.9 Hz, 2H); 13C NMR (acetone-d6) δ
62.5, 117.2 (q, J ) 317.8 Hz), 122.1, 127.4, 128.6, 133.5, 138.8,
149.1; EIMS (m/z) 282 (M•+).
Exp er im en ta l Section
General procedures and methods for characterization are
described elewhere.27 Melting points are uncorrected.
L-Tr iflu or om eth a n esu lfon ic a cid 4-[1-(2,2-d im eth ylp r o-
p ion yla m in o)-2-h yd r oxyeth yl]p h en yl ester 19: mp 73-74
°C; [R]D ) -40° (c 0.1, CHCl3); IR (CHCl3) ν 1656, 1500, 1425
4-Nitr op h en yl Tr ifla te 1. To a cooled (-10 °C) solution of
4-nitrophenol (1.38 g, 9.92 mmol) and Et3N (4.17 mL, 29.73
mmol) in CH2Cl2 (20 mL) was added triflic anhydride (2.5 mL,
14.87 mmol). After being stirred at -10 °C for 20 min, the
reaction mixture was diluted with CH2Cl2 (20 mL), and the
organic phase was washed with aqueous NaHCO3 solution,
water, and brine successively. Purification of the crude reaction
mixture by flash chromatography (SiO2, eluent: EtOAc/heptane
1/5) afforded product 1 (2.5 g, 93.0%) as a white solid: mp 52-
53 °C (lit.5 mp 52-53 °C); IR (CHCl3) ν 1623, 1539, 1490, 1434,
cm-1 1H NMR (250 MHz, acetone-d6) δ 1.20 (s, 9H), 3.82 (m,
;
2H), 4.19 (t, J ) 5.8 Hz, 1H, OH), 5.05 (m, 1H), 7.18 (m, 1H,
NH), 7.39 (d, J ) 8.6 Hz, 2H), 7.58 (d, J ) 8.6 Hz, 2H); 13C NMR
(acetone-d6) δ 27.8, 39.2, 55.6, 65.6, 118.5 (q, J ) 318.0 Hz),
121.8, 129.9, 143.7, 149.3, 178.1; EIMS (m/z) 351 (M - H2O)+.
L-Tr iflu or om et h a n esu lfon ic a cid 4-(2-ter t-b u t oxyca r -
bon yla m in o-3-h yd r oxyp r op yl)p h en yl ester 21: mp 94-95
°C; [R]D ) +21° (c 0.3, CHCl3); IR (CHCl3) ν 1708, 1497, 1427,
1349 cm-1 1H NMR (250 MHz, CDCl3) δ 7.49 (d, J ) 9.3 Hz,
;
1
1370 cm-1; H NMR (250 MHz, acetone-d6) δ 1.33 (s, 9H), 2.82
2H), 8.38 (d, J ) 9.3 Hz, 2H); 13C NMR (CDCl3) δ 118.8 (q, J )
318.2 Hz), 122.6, 126.1, 147.1, 153.2; CIMS (m/z) 272 (M + H)+.
Anal. Calcd for C7H4F3NO5S: C, 31.00; H, 1.49; N, 5.17. Found:
C, 31.27; H, 1.72; N, 5.01.
(dd, J ) 8.5, 13.6 Hz, 1H), 3.03 (dd, J ) 5.6, 13.6 Hz, 1H), 3.49-
3.60 (m, 2H), 3.83 (m, 1H), 3.97 (t, J ) 5.5 Hz, 1H, OH), 5.85 (d,
J ) 7.9 Hz, 1H, NH), 7.35 (d, J ) 8.7 Hz, 2H), 7.46 (d, J ) 8.7
Hz, 2H); 13C NMR (acetone-d6) δ 28.3, 37.2, 54.5, 64.1, 78.5, 118;5
(q, J ) 318.0 Hz), 121.6, 132.0, 141.2, 148.8, 156.1; EIMS (m/z)
368 (M• - CH2OH)+, 343 (M - C4H8)+, 326 (M - OtBu)+.
Bia r yl eth er 7: mp 107-108 °C (lit.32 mp 108.5-110 °C); IR
(CHCl3) ν 1613, 1594, 1544, 1506, 1481 cm-1; 1H NMR (200 MHz,
CDCl3) δ 1.36 (s, 9H), 7.05 (d, J ) 9.2 Hz, 1H), 7.07 (d, J ) 8.7
Hz, 2H), 7.49 (d, J ) 8.7 Hz, 2H), 8.31 (dd, J ) 2.6, 9.2 Hz, 1H),
8.85 (d, J ) 2.6 Hz, 1H); 13C NMR (CDCl3) δ 32.0, 35.3, 118.9,
120.7, 122.7, 128.2, 129.3, 139.9, 142.0, 150.5, 151.6, 157.0; EIMS
(m/z) 317 (M + H)+.
2-Nitr op h en yl Tr ifla te 3. Following the same procedure,
compound 218 was obtained in 80% yield as pale yellow oil: 1H
NMR (200 MHz, CDCl3) δ 7.48 (br d, J ) 8.0 Hz, 1H), 7.60 (br
t, J ) 8.0 Hz, 1H), 7.77 (dt, J ) 1.6, 8.0 Hz, 1H), 8.19 (dd, J )
+
1.6, 8.0 Hz, 1H); CIMS m/z 272 (M + H)
.
2,4-Nitr op h en yl Tr ifla te 4. Following the same procedure,
compound 3 was obtained in 80% yield as a yellow solid: mp
51-52 °C (lit.28 mp 50-51 °C); 1H NMR (250 MHz, CDCl3) δ
7.75 (d, J ) 9.0 Hz, 1H), 8.65 (d, J ) 2.7, 9.0 Hz, 1H), 9.04 (d,
J ) 2.7 Hz, 1H); 13C NMR (CDCl3) δ 118.6 (q, J ) 318.4 Hz),
122.6, 125.8, 129.8, 145.3, 146.7; CIMS (m/z) 317 (M + H).
Typ ica l Exp er im en ta l P r oced u r e Usin g 1 a s Tr iflu or o-
m eth a n esu lfon yl Tr a n sfer Rea gen t. To a solution of phenol
(1.0 mmol) in DMF (10 mL) were added 4-nitrophenyltriflate
(1.0 mmol) and K2CO3 (2.0 mmol) at room temperature. The
reaction solution became yellow due to the generation of 4-ni-
trophenol. At the end of the reaction (followed by TLC), the
yellow solution was diluted with H2O (10 mL) and extracted with
EtOAc. The combined organic phases were washed with 1 N
NaOH and brine, dried (Na2SO4), and evaporated. The residue
4-Nitr op h en yl Non a fla te 2. A solution of 4-nitrophenol (1.39
g, 10 mmol), triethylamine (2.08 mL, 15.0 mmol), and nonafluo-
robutanesulfonic fluoride (2.20 mL, 12.0 mmol) in CH2Cl2 was
stirred at room temperature for 12 h. The reaction mixture was
then diluted with water and was basified with aqueous NaHCO3
solution and extracted with CH2Cl2. The combined organic
extracts were washed with water and brine, dried (Na2SO4), and
evaporated to dryness. Purification by flash chromatography
(SiO2, Et2O/heptane ) 1/20) gave product 2 (3.80 g, 90%) as a
white solid: mp 70 °C; IR (CHCl3) ν 1620, 1591, 1535, 1487,
(29) Larhed, M.; Andersson, C. M.; Hallberg, A. Tetrahedron 1994,
50, 285-304.
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