closure to form the five membered ring (Scheme 2). The
resultant diradical would then be capped with hydrogen from
cyclohexa-1,4-diene to provide the reactive fulvene 7 which
undergoes fast transfer hydrogenation under the reaction
conditions to yield 8.13 Further evidence for the intermediacy of
(t, J 7.4 Hz, 1 H), 7.45 (t, J 7.5 Hz, 1 H), 7.55 (t, J 7.4 Hz, 1 H), 7.62 (d, J 7.4
Hz, 1 H), 7.80 (d, J 7.5 Hz, 1 H), 7.88 (m, 2 H), 7.92 (d, J 8.2 Hz, 1 H), 8.17
2
1
(d, J 7.3 Hz, 1 H); nmax(neat)/cm 3353, 3053, 2927, 1466, 1022, 909, 821,
7
60.
7
is found in the thermolysis of 2 in MeOH at 217 °C, in which
References
the methyl group of the solvent is the hydrogen source. In this
case 11-(2-hydroxyethyl)-1H-benzo[a]fluorene¶ is formed
1 (a) L. T. Scott, Pure Appl. Chem., 1996, 68, 291; (b) P. W. Rabideau and
A. Sygula, Acc. Chem. Res., 1996, 29, 235; (c) R. F. C. Brown and F. W.
Eastwood, Pure Appl. Chem., 1996, 68, 261; (d) L. W. Jenneskens, M.
Sarobe and J. W. Zwikker, Pure Appl. Chem., 1996, 68, 219.
(
26%) along with 6 (4.3%). This product is suggested to arise by
trapping of 7 with ·CH OH, followed by H abstraction from
2
MeOH. The absence of products arising from 5-exo closure in
the gas phase pyrolysis suggests that equilibration of the two
diradicals to give the more stable didehydrochrysene is rapid
under the conditions employed and/or that decomposition of the
dibenzofulvene occurs in the absence of a good hydrogen
donor.
Finally, we note that the observed conversion of phenylene 1
to the cyclopenta fused polycyclic benzenoid 5 constitutes the
first of a series of potential conversions of larger phenylenes to
semifullerenes.
2
3
U. E. Wiersum, Janssen Chim. Acta, 1992, 10, 3.
R. Diercks and K. P. C. Vollhardt, Angew. Chem., 1986, 98, 268;
Angew. Chem., Int. Ed. Engl., 1986, 25, 266.
4
B. C. Berris, G. H. Hovakeemian, Y.-H. Lai, H. Mestdagh and K. P. C.
Vollhardt, J. Am. Chem. Soc., 1985, 107, 5670.
5 R. Diercks and K. P. C. Vollhardt, J. Am. Chem. Soc., 1986, 108,
3150
6 J. W. Barton and R. B. Walker, Tetrahedron Lett., 1978, 1005.
7
W. Karcher, R. J. Fordham, J. J. Dubois, P. G. J. M. Glaude and J. A. M.
Ligthart, Spectral Atlas of Polycyclic Aromatic Compounds, Reidel,
Dordrecht, 1985.
This work was supported by the National Science Foundation
CHE-9202152). A. J. M. was a Syntex predoctoral fellow
1994–1995) and an ACS Division of Organic Chemistry
8
The synthesis of acepentalene and its tribenzo derivative have recently
been reported: R. Haag, D. Schr o¨ der, T. Zywietz, H. Jiao, H. Schwarz,
P. von R. Schleyer and A. de Meijere, Angew. Chem., 1996, 108, 1413;
Angew. Chem., Int. Ed. Engl., 1996, 35, 1317; R. Haag, B. Ohlhorst, M.
Noltemeyer, R. Fleischer, D. Stalke, A. Schuster, D. Kuck and A. de
Meijere, J. Am. Chem. Soc., 1995, 117, 10474.
(
(
Graduate Fellow (sponsored by Rohm and Haas Co.)
1995–1996).
(
9
G. Zimmermann, U. Nuechter, S. Hagen and M. Nuechter, Tetrahedron
Lett., 1994, 35, 4747; R. F. C. Brown, N. Choi, K. J. Coulston, F. W.
Eastwood, U. E. Wiersum and L. J. Jenneskens, Tetrahedron Lett.,
1994, 35, 4405.
Footnotes
*
†
E-mail: vollhard@cchem.berkeley.edu
This report describes 5 as a side product, resulting from loss of C .
2
Consistent with this finding is our observation of fluoranthene in the
pyrolysis of 1.
10 U. E. Wiersum and L. W. Jenneskens, Tetrahedron Lett., 1993, 34,
6615.
‡
Synthesized from bis[2-(trimethylsilylethynyl)phenyl]ethyne using
MeOD and K CO
GC–MS indicates that most of the diradicals formed add to cyclohex-
11 K. N. Bharucha, R. M. Marsh, R. E. Minto and R. G. Bergman, J. Am.
Chem. Soc., 1992, 114, 3120.
12 G. M. Badger, J. Chem. Soc., 1941, 535.
2
3
.
§
adiene or benzene rather than being trapped as 4 or 5, thus accounting for the
13 The rapid hydrogenation of dibenzofulvene by a radical mechanism has
been observed: T. E. Nalesnik, J. H. Freudenberger and M. Orchin,
J. Organomet. Chem., 1981, 221, 193.
low combined yield of these products (21.5%).
+
¶
11-(2-Hydroxyethyl)-1H-benzo[a]fluorene: m/z (EI-MS) 260 (M , 71%),
1
242 (49), 241 (30), 229 (16), 228 (19), 226 (15), 215 (100); H NMR (500
MHz, CDCl
3
): d 2.40 (dq, J 13.4, 6.7 Hz, 1 H), 2.69 (dtd, J 13.9, 7.1, 3.6 Hz,
1
H), 3.38 (m, 2 H), 4.55 (dd, J 7.0, 3.6 Hz, 2 H), 7.32 (t, J 7.3 Hz, 1 H), 7.40
Received in Corvallis, OR, USA, 17th April 1997; 7/02680C
1416
Chem. Commun., 1997