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T. Enomoto et al.
LETTER
(14) For recent examples of gold-catalyzed hydroaminations,
see: (a) Zhang, J.; Yang, C.-G.; He, C. J. Am. Chem. Soc.
2006, 128, 1798. (b) Hashmi, A. S. K.; Rudolph, M.;
Schymura, S.; Visus, J.; Frey, W. Eur. J. Org. Chem. 2006,
4905. (c) Liu, X.-Y.; Ding, P.; Huang, J.-S.; Che, C.-M. Org.
Lett. 2007, 9, 2645. (d) Ritter, S.; Hackelöer, K.; Schmalz,
H.-G. Heterocycles 2007, 74, 731. (e) See also ref 9a.
(15) (a) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka, M. Angew.
Chem. Int. Ed. 2002, 41, 4563. (b) Mizushima, E.; Hayashi,
T.; Tanaka, M. Org. Lett. 2003, 5, 3349.
(16) For examples, see: (a) Piera, J.; Krumlinde, P.; Strübing, D.;
Bäckvall, J.-E. Org. Lett. 2007, 9, 2235. (b) Watanabe, T.;
Oishi, S.; Fujii, N.; Ohno, H. Org. Lett. 2007, 9, 4821.
(c) Also see ref 12a.
(17) Similar high-field shifts have been observed often in related
systems. For example, see: Cava, M. P.; Mitchell, M. J.;
Havlicek, S. C.; Lindert, A.; Spangler, R. J. J. Org. Chem.
1970, 35, 175.
Compound 2e: colorless crystals; Rf 0.55 (hexane–EtOAc,
6:1); mp 168–169 °C. 1H NMR (500 MHz, CDCl3, TMS):
d = 7.16–7.26 (m, 4 H), 7.09 (s, 2 H), 6.94 (s, 1 H), 6.41 (s,
1 H), 4.87 (s, 2 H), 2.33 (s, 6 H), 1.06 (s, 9 H). 13C NMR (126
MHz, CDCl3): d = 153.0, 140.8, 138.7, 137.5, 132.7, 131.9,
129.3, 127.5, 127.0, 125.0, 124.9, 124.1, 114.6, 80.8, 47.5,
27.6, 21.2. IR (CHCl3): 1691 cm–1. MS (FAB): m/z = 335
[M+]. Anal. Calcd for C22H25NO2: C, 78.77; H, 7.51; N, 4.18.
Found: C, 78.66; H, 7.50; N, 4.23.
Compound 2h: white powder; Rf 0.50 (hexane–EtOAc, 1:1);
mp 115–116 °C. 1H NMR (500 MHz, CDCl3, TMS): d =
7.46 (d, J = 8.2 Hz, 2 H), 7.34 (d, J = 8.2 Hz, 2 H), 7.15–7.26
(m, 4 H), 6.42 (s, 1 H), 4.85 (s, 2 H), 4.68 (s, 2 H), 2.58 (s, 1
H), 1.06 (s, 9 H). 13C NMR (126 MHz, CDCl3): d = 152.9,
140.6, 140.2, 137.9, 132.5, 131.8, 127.5, 127.2, 126.6,
126.2, 125.0, 124.9, 115.2, 81.0, 64.7, 47.4, 27.6.
IR (CHCl3): 3606, 1693 cm–1. MS (FAB): m/z = 337 [M+].
Anal. Calcd for C21H23NO3: C, 74.75; H, 6.87; N, 4.15.
Found: C, 74.47; H, 6.87; N, 3.88.
(18) For example, see: Kitamura, M.; Hsiao, Y.; Ohta, M.;
Tsukamoto, M.; Ohta, T.; Takaya, H.; Noyori, R. J. Org.
Chem. 1994, 59, 297.
Compound 4a: colorless needles: Rf 0.38 (hexane–EtOAc,
2:1); mp 164–165 °C. 1H NMR (500 MHz, CDCl3, TMS):
d = 7.47 (d, J = 7.6 Hz, 2 H), 7.32 (dd, J1 = J2 = 7.6 Hz, 2 H),
7.21 (s, 1 H), 7.19 (t, J = 7.6 Hz, 1 H), 6.74 (s, 1 H), 6.61 (s,
1 H), 4.60 (br, 1 H), 3.97 (s, 3 H), 3.89 (s, 3 H), 3.27 (br, 1
H), 3.13 (br, 1 H), 2.66 (br, 1 H), 1.02 (s, 9 H). 13C NMR
(126 MHz, CDCl3): d = 153.3, 149.3, 147.7, 137.2, 134.0,
128.4, 128.3, 128.0, 126.8, 125.4, 117.6, 111.7, 106.4, 80.3,
56.2, 55.9, 43.0, 28.5, 27.7. IR (CHCl3): 1682 cm–1.
MS (FAB): m/z = 381 [M+]. Anal. Calcd for C23H27NO4: C,
72.42; H, 7.13; N, 3.67. Found: C, 72.38; H, 7.08; N, 3.47.
Compound 4c: colorless crystals; Rf 0.38 (hexane–EtOAc,
2:1); mp 146–147 °C. 1H NMR (500 MHz, CDCl3, TMS):
δ = 7.46 (s, 1 H), 7.36 (d, J = 7.8 Hz, 1 H), 7.24 (dd, J1 =
J2 = 7.8 Hz, 1 H), 7.18 (s, 1 H), 7.17 (d, J = 7.8 Hz, 1 H), 6.68
(s, 1 H), 6.61 (s, 1 H), 4.59 (br, 1 H), 3.96 (s, 3 H), 3.89 (s, 3
H), 3.26 (br, 1 H), 3.12 (br, 1 H), 2.66 (br, 1 H), 1.07 (s, 9 H).
13C NMR (126 MHz, CDCl3): d = 153.0, 149.5, 147.7, 139.1,
135.3, 134.2, 129.5, 128.3, 128.2, 126.7, 126.3, 125.0,
116.0, 111.7, 106.4, 80.6, 56.2, 55.9, 43.1, 28.3, 27.8.
IR (CHCl3): 1685 cm–1. MS (FAB): m/z = 415 [M+]. Anal.
Calcd for C23H26ClNO4: C, 66.42; H, 6.30; N, 3.37. Found:
C, 66.38; H, 6.32; N, 3.35.
(19) Typical Procedure for the Gold(I)-Catalyzed
Hydroamination: To a solution of 1a (309 mg, 1.00 mmol)
in DCE (2 mL) were added EtOH (231 mg, 293 mL, 5.02
mmol) and a suspension of AuCl(PPh3) (4.9 mg, 0.0099
mmol) and AgNTf2 (3.8 mg, 0.0098 mmol) in DCE (1 mL)
at r.t. After stirring for 2 h, sat. aq NaHCO3 was added and
the product was extracted with CHCl3 (3 × 10 mL). The
combined organic extracts were washed with brine, dried
over Na2SO4, filtered, and concentrated. The residue was
purified by silica gel column chromatography (hexane–
EtOAc, 25:1) to afford 2a (256 mg, 83%) as colorless
crystals: Rf 0.70 (hexane–EtOAc, 3:1); mp 105–106 °C.
1H NMR (500 MHz, CDCl3, TMS): d = 7.48 (d, J = 7.3 Hz,
2 H), 7.36 (dd, J1 = 7.1 Hz, J2 = 7.3 Hz, 2 H), 7.30 (t, J = 7.1
Hz, 1 H), 7.18–7.27 (m, 4 H), 6.42 (s, 1 H), 4.89 (s, 2 H),
1.05 (s, 9 H). 13C NMR (126 MHz, CDCl3): d = 153.0, 140.6,
139.0, 132.7, 132.0, 128.1, 127.7, 127.5, 127.2, 126.3,
125.1, 125.0, 115.2, 81.0, 47.5, 27.6. IR (CHCl3): 1693
cm–1. MS (FAB): m/z = 307 [M+]. Anal. Calcd for
C20H21NO2: C, 78.15; H, 6.89; 4.56. Found: C, 78.23; H,
7.07; N, 4.48.
Synlett 2008, No. 11, 1647–1650 © Thieme Stuttgart · New York