8852
T. Kawasaki et al. / Tetrahedron Letters 44 (2003) 8849–8852
4. (a) Jiang, B.; Smallheer, J. M.; Amaral-Ly, C.; Wuonola,
11. For example, when 11c was heated with KOH in reflux-
ing methanol, dehydrohamacanthin B 18 was obtained in
90% yield through elimination of toluene sulfinic acid
followed by isomerization.
M. A. J. Org. Chem. 1994, 59, 6823–6827; (b) Whitlock,
C. R.; Cava, M. P. Tetrahedron Lett. 1994, 35, 371–374;
(c) Miyake, F. Y.; Yakushijin, K.; Horne, D. A. Org.
Lett. 2000, 2, 3185–3187.
5. (a) Kawasaki, T.; Enoki, H.; Matsumura, K.; Ohyama,
M.; Inagawa, M.; Sakamoto, M. Org. Lett. 2000, 2,
3027–3029; (b) Kawasaki, T.; Ohno, K.; Enoki, H.;
Umemoto, Y.; Sakamoto, M. Tetrahedron Lett. 2002, 43,
4245–4248.
6. (a) Kramer, U.; Guggisberg, A.; Hesse, M.; Schmid, H.
Angew. Chem., Int. Ed. Engl. 1977, 16, 861–862; (b)
Wasserman, H. H.; Matsuyama, H.; Robinson, R. P.
Tetrahedron 2002, 58, 7177–7190; (c) Banik, B. K.; Sama-
jdar, S.; Banik, I. Tetrahedron Lett. 2003, 44, 1699–1701;
(d) Dinsmore, A.; Doyle, P. M.; Hitchcock, P. B.; Young,
D. W. Tetrahedron Lett. 2000, 41, 10153–10158; (e)
Papadopoulos, K.; Young, D. W. Tetrahedron Lett. 2002,
43, 3951–3955; (f) Langlois, N. Org. Lett. 2002, 4, 185–
187; (g) Dinsmore, C.; Zartman, C. B. J. Tetrahedron
Lett. 2000, 41, 6309–6312; (h) Beshore, D. C.; Dinsmore,
C. J. Org. Lett. 2002, 4, 1201–1204.
7. Since some attempts to react O-monotosylate of 5 with
NaN3 were unsuccessful to result in a complex mixture,
protection of the indole nitrogen using an electron-with-
drawing group in the substitution reaction was required.
8. Da Settimo, A.; Saettone, M. F.; Nannipieri, E.; Barili, P.
Gazz. Chim. Ital. 1967, 97, 1304–1316.
12. Hamacanthin A (1a): mp 289°C (acetone–hexane) [lit.
yellow powder1a and mp 275°C3a]. IR (KBr) w: 1669,
1
1586, 1445 cm−1. H NMR (300 MHz, DMSO-d6) l: 4.05
(1H, dd, J=16.2, 8.2 Hz), 4.13 (1H, dd, J=16.2, 5.0 Hz),
4.98 (1H, ddd, J=8.2, 5.0, 2.0 Hz), 7.14 (1H, dd, J=8.4,
1.8 Hz), 7.20 (1H, dd, J=8.6, 1.8 Hz), 7.31 (1H, d, J=2.4
Hz), 7.56 (1H, d, J=1.8 Hz), 7.62 (1H, d, J=1.8 Hz),
7.66 (1H, d, J=8.4 Hz), 8.29 (1H, d, J=8.6 Hz), 8.41
(1H, d, J=2.8 Hz), 8.79 (1H, br), 11.16 (1H, br), 11.59
(1H, br). HRMS (EI): Calcd for C20H14Br2N4O:
483.9534; Found: 483.9529.
Hamacanthin B (1b): mp 167–169°C (diethyl ether–hex-
ane) [lit.1a,3b yellow powder]. IR (KBr) w: 1672, 1580,
1
1447 cm−1. H NMR (300 MHz, DMSO-d6) l: 3.46 (1H,
ddd, J=12.4, 9.5, 1.9 Hz), 3.61 (1H, dt, J=12.4, 4.8 Hz),
5.25 (1H, dd, J=9.5, 4.8 Hz), 7.12 (1H, dd, J=8.4, 1.5
Hz), 7.17 (1H, dd, J=8.6, 1.5 Hz), 7.27 (1H, d, J=2.4
Hz), 7.58 (1H, d, J=1.7 Hz), 7.62 (1H, d, J=1.7 Hz),
7.65 (1H, d, J=8.6 Hz), 8.29 (1H, d, J=8.4 Hz), 8.41
(1H, d, J=2.6 Hz), 8.51 (1H, br), 11.14 (1H, br), 11.63
(1H, br). HRMS (EI): Calcd for C20H14Br2N4O:
483.9534; Found: 483.9540.
9. General experimental procedure:
A solution of 2-
oxoethanamide 10 (1 mmol) in CH2Cl2–HCO2H (1: 1, 75
mL) was kept at room temperature for 4.5 h. The
resulted mixture was concentrated under reduced pres-
sure to give a residue, which was dissolved in 1,2-
dichloroethane (55 mL) and the pH was adjusted to 4
with HCO2H. After heating at 80°C for 1 h, the mixture
was concentrated under reduced pressure to yield a
residue, which was purified by column chromatography
on a silica-gel with hexane–ethyl acetate as an eluent to
afford 11 and 12.
13. Although intramolecular transamidations are well known
as ring-transformation of either lactam6a–c or cyclic
imide,6d–f to our knowledge, no intramolecular transami-
dation of acyclic amide to another acyclic amide followed
by cyclization to lactam has been recognized other than
Dinsmore’s report6g–h and the pathway described in this
report.
10. After complete removal of HCO2H, the reaction under
neutral conditions required prolonged heating (5 h) to
give 11a and 12a in 55 and 26% yields, respectively.