9094
L. Moisan et al. / Tetrahedron Letters 47 (2006) 9093–9094
O
OH
N
O
O
THF/tBuOK
(95%)
BTI
CF3CH2OH
(60%)
O
N
O
N
O
N
O
2
4
5
2
Scheme 2.
O
O
N
O
O
N
HO
N
O
N
O
O
PTSA/Toluene
(80%)
4a
4b
4c
N
O
Scheme 4.
O
2
6
H
HO
O
our key product leads to the ring expansion of the lower
ring, the use of a base (e.g., potassium tert-butoxide)
induces the rearrangement of the upper carbocycle.
The latter process involves the formation of a cyclo-
propane intermediate, which readily undergoes frag-
mentation. The reactions described herein should be of
a synthetic utility in the construction of complex
carbocycles.
H
N
N
O
6a
O
6b
Scheme 3.
upon acidic treatment (e.g., catalytic PTSA in refluxing
toluene), 2 underwent a facile rearrangement leading to
the dibenzoazepinone derivative 68 in an 80% yield
(Scheme 3). This transformation probably involves the
protonation of ketone (6a) followed by the 1,2-shift of
the spiro carbon–carbon bond. The resulting carbocat-
ion 6b is then trapped by the aromatization of the upper
ring. The same type of dienone to phenol rearrangement
has already been observed and commented on by others
when working with related systems.9
References and notes
1. Saxton, J. E. In The Alkaloids; Cordell, G. A., Ed.;
Academic Press: New York, 1998; Vol. 51, Chapter 1.
2. For recent examples, see: Ishikawa, H.; Elliott, G. I.;
Velcicky, J.; Choi, Y.; Boger, D. L. J. Am. Chem. Soc.
2006, 128, 10596–10612; Elliott, G. I.; Fuchs, J. R.; Blagg,
B. S. J.; Ishikawa, H.; Tao, H.; Yuan, Z.-Q.; Boger, D. L.
J. Am. Chem. Soc. 2006, 128, 10589–10595; Marino, J. P.;
Rubio, M. B.; Cao, G.; de Dios, A. J. Am. Chem. Soc.
2002, 124, 13398–13399.
3. For a recent synthesis of Buchi’s ketone, see: Heureux, N.;
¨
Interestingly, under basic conditions (e.g., 1 equiv of
t-BuOK in THF at room temperature) a completely dif-
ferent behaviour was observed as, this time, the upper
ring underwent rearrangement (Scheme 4). Upon addi-
tion of potassium tert-butanolate, the colour of the reac-
tion mixture immediately turned to yellow as a result of
the formation of the highly conjugated system 4. This
transformation can be rationalized through the forma-
tion of a cyclopropane intermediate 4b resulting from
the conjugate addition of anion 4a on the dienone sys-
tem. Cyclopropane 4b then undergoes fragmentation
to give the rearranged product 4c. The latter spontane-
ously evolves to cycloheptaquinolinedione derivative 4
by conjugation of the double bond with the enone sys-
tem. Compound 410 is obtained in a 95% yield. To the
best of our knowledge, this base mediated 2,5-dienone
rearrangement has never been observed.
´
Woulters, J.; Marko, I. E. Org. Lett. 2005, 7, 5245–5248.
4. Buchi, G.; Matsumoto, K. E.; Nishimura, H. J. Am.
¨
Chem. Soc. 1971, 93, 3299–3301.
´
5. Moisan, L.; Thuery, P.; Nicolas, M.; Doris, E.; Rousseau,
B. Angew. Chem., Int. Ed. 2006, 45, 5334–5336.
6. 1H NMR of 2 (CDCl3, 300 MHz): d 2.77 (s, 2H), 3.44 (s,
3H), 6.34 (d, J = 10.5 Hz, 2H), 6.94 (d, J = 10.5 Hz, 2H),
7.04–7.11 (m, 3H), 7.32 (m, 1H).
7. Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2002, 102, 2523–
2584.
8. 1H NMR of 6 (CDCl3, 300 MHz): d 3.27 (s, 3H), 3.34 (d,
J = 12.9 Hz, 1H), 3.86 (d, J = 12.9 Hz, 1H), 6.92 (d,
J = 8.5 Hz, 1H), 7.13 (m, 1H), 7.23–7.33 (m, 3H), 7.40
(dd, J = 8.5 Hz, J = 1.9 Hz, 1H), 7.53 (d, J = 7.3 Hz, 1H).
9. Fenton, S. W.; Arnold, R. T.; Fritz, H. E. J. Am. Chem.
Soc. 1955, 77, 5983–5986; Taylor, E. C.; Andrade, J. G.;
Rall, G. J. H.; McKillop, A. J. Am. Chem. Soc. 1980, 102,
6513–6519.
10. 1H NMR of 4 (CDCl3, 300 MHz): d 2.76 (m, 2H), 3.25 (m,
2H), 3.75 (s, 3H), 6.33 (d, J = 12.8 Hz, 1H), 7.28 (dd,
J = 8.5 Hz, J = 7.3 Hz, 1H), 7.39 (d, J = 8.5 Hz, 1H), 7.61
(d, J = 8.5 Hz, 1H), 7.80 (d, J = 12.8 Hz, 1H), 7.92 (d,
J = 8.5 Hz, 1H).
In summary, we report here the rearrangement of a spiro-
cyclohexa[2,5]diene-1,40-quinolinedione under either
basic or acidic conditions. While acidic treatment of