Reaction of atomic and molecular carbon with cyclooctatetraene

Full text of DOI:10.1021/ja9615280

10004
J. Am. Chem. Soc. 1996, 118, 10004-10005
5
Reaction of Atomic and Molecular Carbon with
Cyclooctatetraene
Allison generated 4 from the corresponding dibromide with
butyl- or methyllithium, 2 was the sole product with evidence
strongly favoring the intermediacy of 5. The fact that 2 is
labeled in the 9-position is in agreement with our proposed
mechanism. Although there is considerable precedence for the
formation of 2 from 5, the labeling experiment demonstrates
that 5 results from an initial CdC addition by carbon rather
than initial C-H insertion to give cyclooctatetraenylmethylene,
Weitao Pan and Philip B. Shevlin*
Department of Chemistry, Auburn UniVersity
Auburn UniVersity, Alabama 36849-5310
7
, which could also produce 5 by ring expansion. Equation 1
ReceiVed May 7, 1996
6
,7
shows AM-1
calculated heats of formation of relevant
ReVised Manuscript ReceiVed August 29, 1996
intermediates confirming the expected exothermicity of each
step.
The formation of 3 in the reaction of C2 with 1 is perhaps
Speculation on the mechanism of fullerene formation has
generated considerable interest in the manner in which small
carbon fragments interact with cyclic unsaturated systems to
more interesting in that little is known concerning the reactions
1
generate the polycyclic rings which eventually become fullerenes.
of C . Although the label in 3 is found on all of the carbons,
2
In this study, we report a simple example of this reaction in
which we demonstrate that C1 and C2 react with the monocyclic
cyclooctatetraene, 1, to generate bicyclic systems.2
it is distributed in a nonstatistical manner, implying that 3 may
arise by more than one mechanism. The labeling pattern is
consistent with one mechanism which places the label in the
Cocondensation of arc generated carbon vapor with 1 at 77
K generates indene, 2, and naphthalene, 3, in a 4:1 ratio as the
9
,10 positions and another which either places it on the 1,2
positions or distributes it statistically on all carbons.
major volatile products detectable by GC/MS and 1 C NMR.
3
3
Much of the chemistry that has been observed for C2 is that
of a biradical. Thus, C2 abstracts hydrogen to give acetylene8
and adds consecutively to 2 molecules of an acyclic alkene to
give biradicals 8 and 9 which abstract hydrogen and/or
9
disproportionate (eq 2). It is the intramolecular version of this
Since these products contain one and two more carbons than 1,
it is logical to assume that they arise from the respective addition
of C1 and C2 to 1.
The use of carbon vapor enriched in 13C confirms this
assumption.4 Thus, GC/MS analysis of the products of this
13
latter reaction that we propose leads to the formation of 3 as
outlined in Scheme 1. Initial addition of C2 to 1 generates
biradical 10 which can close to cyclopropylidenecarbenes, 11a
and 11b. Intramolecular addition of conformer 11a across the
reaction reveals that the ratio of C enrichment in 3 to that in
2
is 2.2 ( 0.2. An examination of the 13C NMR spectra of the
products demonstrates that the label is introduced exclusively
at the 9-position in 2 while 3 bears 74 ( 10% of the introduced
1
3
2,10 5,7
C at the 9 and 10 positions with the remainder distributed
ring generates the interesting tetracyclo[4.4.0.0 .0 ]deca-
equally at the 1 and 2 carbons. The possibility that 3 arises by
a subsequent addition of C1 to 2 is ruled out by a control
experiment in which the reaction of 13C enriched carbon vapor
with 2 generates 3 as a minor product with the label at the
1(6),3,8-triene, 12, which can ring open to 3 labeled in the 9,
10 positions.
Although 12 is simply a valence bond tautomer of naphtha-
lene, it does not appear to have received much attention perhaps
due to its obvious excess of strain energy. In fact, we have
2
-position.
In view of the known propensity of atomic carbon to add to
10
used molecular mechanics calculations to estimate that 12 has
double bonds to generate cyclopropylidenes which ring open
1
55 kcal of strain energy as compared to 3. Although one may
2
,4b
to cumulenes,
it seems reasonable to propose that initial
question whether 12 is actually an energy minimum, AM-1 and
addition of C1 to 1 will yield bicyclo[6.1.0]nona-2,4,6-trien-9-
ylidene, 4, which ring expands to 1,2,4,6,8-cyclononapentaene,
1
1
ab initio calculations at the 6-31G* level indicate that it has
zero negative eigen vectors. An analysis of the rearrangement
of 12 to 3 reveals that it is symmetry forbidden and it may be
5
. Subsequent electrocyclic ring closure generates bicyclo[4.3.0]-
nona-2,4,6,8-tetraene, 6, which rearranges to 2 by a [1,5]
sigmatropic hydrogen shift (eq 1). In fact, when Waali and
(
3) The C atom reactor is modeled after that described by: Skell, P. S.;
Wescott, L. D., Jr.; Golstein, J. P.; Engel, R. R. J. Am. Chem. Soc. 1965,
7, 2829. Products were identified by 13C NMR spectroscopy, mass
spectrometry, and CG/MS.
4) (a) Carbon vapor enriched in 13C was generated as described earlier.4b
8
(
(
b) Emanuel, C. J.; Shevlin, P. B. J. Am. Chem. Soc. 1994, 116, 5991-2.
(
(
5) Waali, E. E.; Allison, N. T. J. Org. Chem. 1979, 44, 3266.
6) Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J.
Am. Chem. Soc. 1985, 107, 3902.
(
7) For an extensive MNDO treatment of 4 and 5 and related species
see: Kassaee, M. Z.; Nimlos, M. R.; Downie, K. E.; Waali, E. E.
Tetrahedron 1985, 41, 1579.
(
8) (a) Skell, P. S.; Harris, R. F. J. Am. Chem. Soc. 1966, 88, 5933. (b)
Skell, P. S.; Plonka, J. H. J. Am. Chem. Soc. 1970, 92, 5620. (c) Skell, P.
S.; Harris, R. F. Chem. Commun. 1970, 689.
(
9) Skell, P. S.; Jackman, L. M.; Ahmed, S.; McKee, M. L.; Shevlin, P.
(
1) Goroff, N. S. Acc. Chem. Res. 1996, 29, 77 and references cited
B. J. Am. Chem. Soc. 1989, 111, 4422.
therein.
(10) (a) Allinger, N. L.; Hindman, D.; Helmut, H. J. Am. Chem. Soc.
1977, 99, 3282. (b) The PCMODEL V 5.0 program from Serena Software,
Bloomington, IN, was used.
(2) For reviews of the chemistry of atomic carbon see: (a) Skell, P. S.;
Havel, J.; McGlinchey, M. J. Acc. Chem. Res. 1973, 6, 97. (b) MacKay, C.
In Carbenes; Moss, R. A., Jones, M., Jr., Eds.; Wiley-Interscience: New
York, 1975; Vol. II, pp l-42. (c) Shevlin, P. B. In ReactiVe Intermediates;
Abramovitch, R. A., Ed.; Plenum Press: New York, 1980; Vol. I, pp 1-36.
(11) (a) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab
Initio Molecular Orbital Theory; Wiley: New York, 1968. (b) The
SPARTAN V 4.0 program from Wavefunction, Inc., Irvine, CA, was used.
S0002-7863(96)01528-4 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 41, 1996 10005
Scheme 1
In order to rationalize the label at the 1,2 positions in 3, we
propose (Scheme 1) that 11b ring expands to carbene 15 which
subsequently undergoes electrocyclic closure and ring expansion
to generate trans-bicyclo[4.4.0]deca-2,4,7-trien-9-yne, 16, which
can rearrange to appropriately labeled 3 by two [1,5] hydrogen
shifts.
The proposed electrocyclic closure and ring expansion of 15
finds analogies in the rapid rearrangement of nonafulvenes to
1
4
methylene indenes and in the familiar cycloalkylidenecar-
15
bene-cycloalkyne rearrangement. The mechanisms in Scheme
1
thus rationalize the labeling results and have analogy in the
reactions of related hydrocarbons.
These experiments, which demonstrate that carbon is capable
of inserting itself into cyclic unsaturated carbon rings, provide
possible mechanisms for carbon cluster formation en route to
fullerenes.
that 12, like Dewar benzene,12 is trapped by symmetry into an
energy minimum. These considerations indicate that it may be
possible to observe and/or trap 12 on a low-temperature matrix.
It is interesting that 13, a dihydro analog of 12 lacking the ability
to aromatize, rearranges by a reverse Diels-Alder reaction
Acknowledgment. Support of this work through National Science
Foundation Grant CHE-9508570 is gratefully acknowledged.
JA9615280
1
3
yielding 14. In the case of 12, this pathway would lead to a
(
14) (a) Escher, A.; Neuenschwander, M. HelV. Chim. Acta 1987, 70,
cyclohexyne and provide little thermodynamaic driving force.
49. (b) Escher, A.; Neuenschwander, M. HelV. Chim. Acta 1987, 70, 1623.
(
c) Furrer, J.; B o¨ nzli, P.; Frey, A.; Neuenschwander, M. HelV. Chim. Acta
1987, 70, 862.
(
12) van Tamelen, E. E.; Pappas, S. P.; Kirk, K. L. J. Am. Chem. Soc.
971, 93, 6092.
13) Masamune, S.; Seidner, R. T.; Zenda, H.; Wiesel, M.; Nakatsuka,
N.; Bigam, G. J. Am. Chem. Soc. 1968, 90, 5286.
1
(15) (a) Erickson, K. L.; Wolinsky, J. J. Am. Chem. Soc. 1965, 87, 1142.
(b) Tseng, J.; McKee, M. L.; Shevlin, P. B. J. Am. Chem. Soc. 1987, 109,
5474.
(