Rearrangement of Allylic Imidates to Allylic Amides
J . Org. Chem., Vol. 62, No. 5, 1997 1455
1.55-1.46 (m, 1H); 13C NMR (125 MHz, CD3CN) δ 137.1, 135.6,
127.7, 127.5, 122.9, 122.5, 71.37, 67.0, 66.3, 63.7, 59.0, 49.1,
22.8, 21.2. Anal. Calcd for C14H20N2Cl2Pd: C, 42.72; H, 5.12;
N, 7.12. Found: C, 42.73; H, 5.09; N, 7.03. An X-ray quality
crystal was grown by slow evaporation of a MeCN solution.
Meth od B. A solution of diamine 16 (62.7 mg, 0.290 mmol)
and EtOH (1 mL) was added to a red-brown suspension of Na2-
PdCl4 (82.5 mg, 0.280 mmol) and EtOH (1 mL), producing a
yellow suspension. After rapidly stirring for 3 h, the solid was
collected, dissolved in CH2Cl2, filtered through Celite, and
concentrated again, and the residue was dissolved in CH2Cl2/
hexanes (1:2, 12 mL) and slowly concentrated. Bright yellow
crystals of 17 were collected and found to be the 0.5CH2Cl2
solvate. 1H NMR analysis indicated that this sample was a
10:1 mixture of diastereomeric complexes. Anal. Calcd for
C14H20N2Cl2Pd‚0.5CH2Cl2: C, 39.94; H, 4.85; N, 6.42. Found:
C, 39.84; H, 4.86; N, 6.36.
Di-µ-ch lor o-bis[(S)-2-(isoin dolin ylm eth yl)-N-m eth ylpyr -
r olid in e]d ip a lla d iu m (II) Bis(tetr a flu or obor a te) (18). A
solution of 17 (51.4 mg, 0.131 mmol) and CH2Cl2 (6 mL) was
added to AgBF4 (98%, 260 mg, 0.131 mmol). The resulting
suspension was stirred vigorously overnight, filtered through
Celite, and then concentrated. The resulting solid was dis-
solved in CH2Cl2 (5 mL), filtered, and again concentrated. After
drying under vacuum an orange powder was obtained (58.5
mg, 100%).34,35 An X-ray quality crystal was obtained from
CH2Cl2/Et2O by vapor diffusion. 1H NMR (500 MHz, CD2Cl2)36
δ 2.8 (s, Me), 2.5 (s, Me). MS (LSIMS) m/z 803.0760 (M,
803.0741 calcd for C28H40N4BCl2F4Pd2) Anal. Calcd for
C14H20N2BClF4Pd: C, 37.79; H, 4.53; N, 6.30. Found: C, 37.76;
H, 4.68; N, 6.27.
N-(1-Eth en ylbu tyl)-N-[4-tr iflu or om eth yl)p h en yl]ben z-
a m id e (30). A Typ ica l Ca ta lytic P r oced u r e. A solution
of 29 (138 mg, 0.397 mmol), 18 (18 mg, 0.020 mmol), and CD2-
Cl2 (0.6 mL) was heated at 40 °C for 48 h, concentrated, and
chromatographed on silica gel (4% EtOAc-hexanes) to yield
30 (95 mg, 69%) as a colorless oil: 1H NMR (300 MHz, CDCl3)
δ 7.48 (d, J ) 8.3 Hz, 2 H), 7.29-7.16 (m, 7 H), 5.91 (ddd, J )
17.2, 10.2, 7.2 Hz, 1 H), 5.3-5.2 (m, 1 H), 5.30 (d, J ) 18.4, 1
H), 5.25 (d, J ) 11.4, 1 H), 1.79-1.58 (m, 2 H), 1.46 (sextet, J
) 7.3 Hz, 2 H), 0.97 (t, J ) 7.3 Hz, 3H); 13C NMR (75 MHz,
CDCl3) δ 170.5, 144.5, 137.1, 136.3, 129.9, 129.6, 129.1, 128.7,
128.3, 127.9, 125.7, 117.9, 60.1, 34.2, 19.7, 13.9; IR (CDCl3)
1663 cm-1; [R]25 -37.2 (c 0.5, CH2Cl2); 55% ee (Chiracel AS).
D
Anal. Calcd for C20H20F3NO: C, 69.15; H, 5.80; N, 4.03.
Found: C, 68.90; H, 5.76; N, 4.05.
Deter m in a tion of th e En a n tiom er ic Excess of 30. The
enantiomeric purity of 30 was determined by either of two
methods. Benzamide 30 was treated with O3/NaBH4 in MeOH
to provide amide 40 and/or ester 41. The enantiomers of these
derivatives were separated on a Chiracel OD HPLC column
(3% i-PrOH/hexanes, 0.9 mL/min, UV detection). Alterna-
tively, the enantiomeric excess of 30 could be determined
directly on a Chiracel AS HPLC column (4% i-PrOH/hexanes,
1.0 mL/min, UV detection).
(E)-2-Hexen yl N-[4-(Tr iflu or om eth yl)p h en yl]ben zim i-
d a te (29). Benzoyl chloride (0.62 mL, 4.4 mmol) was added
dropwise to a solution of 4-trifluoromethylaniline (0.50 mL,
4.0 mmol), Et3N (1.0 mL, 7.2 mmol), and CH2Cl2 (5 mL) at 0
°C, and the resulting mixture was stirred for 2 h. Saturated
aqueous NaHCO3 (50 mL) and CH2Cl2 (50 mL) were added,
and the mixture was stirred vigorously. The organic layer was
separated, and the aqueous layer was washed with CH2Cl2 (4
× 50 mL). The combined organic extracts were dried over Na2-
SO4 and concentrated to yield a crude sample of amide 32 (1.1
g, 100%) as a colorless solid: 1H NMR (500 MHz, CD3NO2) δ
8.74 (br s, 1H, NH), 7.94 (m, 4H), 7.70 (d, J ) 8.4 Hz, 2H),
7.62 (m, 1H), 7.54 (m, 2H); MS (EI) m/z 265.0719 (MH,
265.0714 calcd for C14H10F3NO).
A portion of this crude amide (0.790 g, 2.98 mmol) was
combined with PCl5 (0.620 g, 2.98 mmol) and heated at 85 °C
for 1 h. Volatile materials were then removed under vacuum
yielding N-[4-(trifluoromethyl)phenyl]benzimidoyl chloride (0.843
g, 100%) as an off-white solid that was >95% pure by 1H NMR
analysis: 1H NMR (300 MHz, CDCl3) δ 8.19 (d, J ) 7.7 Hz,
2H), 7.69 (d, J ) 8.1 Hz, 2H), 7.54 (m, 3H), 7.10 (d, J ) 8.2
Hz, 2H).
Following the procedure described for the preparation of 8,
(E)-2-hexen-1-ol (280 µL, 2.4 mmol), N-[4-(Trifluoromethyl)-
phenyl]benzimidoyl chloride (0.68 g, 2.4 mmol), and NaH (0.11
g, 57% dispersion in oil, 2.6 mmol) yielded, after silica gel
chromatography (column packed with 200:1 hexanes-Et3N
and eluted with 4:1 hexanes-CH2Cl2), allylic imidate 29 (0.629
g, 76%) as a colorless oil: 1H NMR (300 MHz, CDCl3) δ 7.42
(d, J ) 8.4 Hz, 2 H), 7.36-7.21 (m, 5 H), 6.78 (d, J ) 8.2 Hz,
2 H), 5.93-5.72 (m, 2 H), 4.81 (d, J ) 6.1 Hz, 2 H), 2.09 (q, J
) 7.2 Hz, 2 H), 1.45 (sextet, J ) 7.4 Hz, 2 H), 0.93 (t, J ) 7.3
Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 159.0, 151.8, 136.0,
130.8, 130.2, 129.3, 128.1, 126.1, 124.4, 121.7, 67.7, 34.5, 22.2,
13.7; IR (CDCl3) 1679 cm-1. Anal. Calcd for C20H20F3NO: C,
69.15; H, 5.80; N, 4.03. Found: C, 69.25.90; H, 5.77; N, 4.05.
(R)-2-[N-[4-(Tr iflu or om et h yl)p h en yl]a m in o]-1-p en t yl
ter t-Bu tyl Eth er (38). A mixture of (R)-norvaline (2.0 g, 17
mmol), LiAlH4
(1.0 g, 26 mmol), and THF (25 mL) was heated
at reflux overnight to produce norvalinol (1.5 g, 86%) after
bulb-to-bulb distillation (75 °C, 0.5 mmHg).29 Isobutylene (5
mL) was condensed into a reaction vessel at -78 °C, and a
solution of norvalinol (0.562 g, 5.45 mmol) and CH2Cl2 (10 mL)
was added followed by dropwise addition of 0.3 mL of concen-
trated H2SO4. The reaction vessel was sealed, the -78 °C bath
was removed, and the suspension was stirred vigorously
overnight. Excess isobutylene was vented and NaOH (3 N)
was added until the mixture was pH g10. This suspension
was extracted with Et2O (3 × 15 mL), and the organic layers
were dried (K2CO3), filtered, concentrated, and the residue
bulb-to-bulb distilled (100 °C, 3 mmHg) to afford ether 37 (416
mg, 63%) as a clear colorless liquid that was ∼85% pure by
1H NMR (diagnostic 9H singlet at δ 1.2).
Following the procedure of Buchwald,30 ether 37 (50 mg,
0.31 mmol) was coupled with 4-(trifluoromethyl)bromobenzene
(44 µL, 0.35 mmol) to yield, after silica gel chromatography
(hexanes then 1% EtOAc-hexanes), 38 in an unoptimized yield
of 38% (36 mg):
1H NMR (500 MHz, CDCl3) δ 7.36 (d, J ) 8.4
Hz, 2H), 6.61 (d, J ) 8.8 Hz, 2H), 4.25 (br d, J ) 7.6 Hz, 1H,
NH), 3.47 (m, 1H), 3.40 (m, 2H), 1.64 (m, 1H), 1.42 (m, 3H),
1.16 (s, 9H), 0.93 (t, J ) 7.2 Hz, 3H); 13C NMR (125 MHz, CD2-
3
1
Cl2) δ 150.7, 126.4 (q, J C,F ) 3.9 Hz), 125.2 (q, J C,F ) 271
2
Hz), 117.4 (q, J C,F ) 32.9 Hz), 111.9, 72.6, 62.7, 52.6, 34.0,
27.1, 19.3, 13.8; IR (film) 3425, 1617 cm-1; MS (CI) m/z
303.1810 (M, 303.1810 calcd for C16H24F3NO).
P r ep a r a tion of N-[4-(Tr iflu or om eth yl)p h en yl]n or va li-
n ol (39) fr om 30. A solution of benzamide 30 (21 mg, 0.060
mmol, [R]25 -37.2, 55% ee) and MeOH (5 mL) at -78 °C was
D
treated with O3 until the blue color persisted. Excess NaBH4
was added, and the -78 °C bath was removed. The resulting
suspension was stirred at rt under a flow of N2 until the solvent
had been removed. MeOH (5 mL), H2O (10 mL), HCl (1 N, 2
mL), and CH2Cl2 (10 mL) were added, and the resulting
mixture was stirred vigorously for 20 min. The organic layer
was separated, and the aqueous layer was extracted with CH2-
Cl2 (2 × 10 mL). The combined organic layers were dried (Na2-
SO4), concentrated, and purified by silica gel chromatography
(4:1 hexanes-EtOAc and then 2:1 hexanes-EtOAc) to yield
(34) LSIMS analysis of this compound in 3-nitrobenzyl alcohol
produced ions of the dimer less one tetrafluoroborate ions, ions of the
dimer less two tetrafluoroborate ions, and ions of the dimer less two
tetrafluoroborate ions plus one fluorine. These ions exhibited the
expected isotope pattern. This pattern of fragment ions from complexes
having fluorine-containing anions has been observed previously.35
(35) Arana, C. R.; Abruna, H. D. Inorg. Chem. 1993, 32, 194.
(36) NMR spectra of this material are broad and complex; repre-
sentative examples are provided in the Supporting Information.