Suprafacial and antarafacial paths for the thermal vinylcyclopropane- to-cyclopentene rearrangement of 1-ethenylbicyclo[4.1.0]heptane to bicyclo[4.3.0]non-1(9)-ene

Article abstract of DOI:10.1021/jo9824091

The gas phase thermal rearrangement of 1-ethenylbicyclo[4.1.0]heptane at 338 °C gives the expected vinylcyclopropane-to-cyclopentene product, bicyclo[4.3.0]non-1(9)-ene. The analogous rearrangement of 1.(2'-(E)-d- ethenyl)bicyclo[4.1.0]heptane takes place

Full text of DOI:10.1021/jo9824091

J . Org. Chem. 1999, 64, 3567-3571
3567
Su p r a fa cia l a n d An ta r a fa cia l P a th s for th e Th er m a l
Vin ylcyclop r op a n e-to-Cyclop en ten e Rea r r a n gem en t of
-Eth en ylbicyclo[4.1.0]h ep ta n e to Bicyclo[4.3.0]n on -1(9)-en e
1
J ohn E. Baldwin* and Richard C. Burrell
Department of Chemistry, Syracuse University, Syracuse, New York 13244
Received December 9, 1998
The gas phase thermal rearrangement of 1-ethenylbicyclo[4.1.0]heptane at 338 °C gives the expected
vinylcyclopropane-to-cyclopentene product, bicyclo[4.3.0]non-1(9)-ene. The analogous rearrangement
of 1-(2′-(E)-d-ethenyl)bicyclo[4.1.0]heptane takes place with the allylic moiety being utilized in
both suprafacial and antarafacial stereochemical ways, for both endo and exo isomers of 8-d-bicyclo-
[4.3.0]non-1(9)-ene are formed. The product ratio, defined by deuterium NMR in the presence of
Ag(fod) and Yb(fod)
antarafacial (ar + ai) reaction stereochemistry.
3
shift reagents, corresponds to (79 ( 2)% suprafacial (sr + si) and (21 ( 2)%
In tr od u ction
particular interest to the present work, the ar and ai
paths together range in relative importance from 13 to
The stereochemical aspects of vinylcyclopropane-to-
cyclopentene isomerizations gained theoretical promi-
3
7% of the four paths in the eight cases most thoroughly
1
5
-14
investigated.
Suprafacial utilization of the allylic
nence in the wake of Woodward-Hoffmann understand-
ings of sigmatropic rearrangements.2 The conversion,
a [1,3] sigmatropic carbon shift, was recognized to be
moiety is always preferred, but the antarafacial alterna-
tive is always in evidence as a substantial contributor.
In an effort to test whether extensive rotation about
C3-C4 in a hypothetical (2Z)-pentene-1,5-diyl system is
required for access to antarafacial rearrangement prod-
ucts, deuterium- and phenyl-substituted 1-ethenylbicyclo-
,3
“
(
allowed” when occurring through suprafacial, inversion
si) or antarafacial, retention (ar) paths and “forbidden”
when taking place with sr or ai stereochemistry. Product
isomers corresponding to sr or ai paths “cannot be formed
in a symmetry-allowed process.” Yet the thermochemical
characteristics of the reaction made it seem that a two-
step, nonconcerted path for the conversion of vinylcyclo-
propane to cyclopentene was not “thermodynamically
unreasonable.”3
[
4.1.0]heptanes were prepared and isomerized to the
1
5
corresponding bicyclo[4.3.0]non-1(9)-enes. The major
product isolated corresponded to migration with reten-
tion. Both sr and ar stereochemical paths contributed to
the overall isomerization. Starting with the (E)-deuterium-
labeled ethenyl group as shown, the balance was 86%
sr, 14% ar; the substrate with a (Z)-deuterium-labeled
1
5
ethenyl group gave 84% sr and 16% ar products.
Determining reaction stereochemistry for vinylcyclo-
propane-to-cyclopentene isomerizations proved difficult,
for stereochemically well-defined starting materials typi-
4
These stereochemical results imply that an antarafa-
cial outcome when migration proceeds with retention
cally showed thermal stereomutations faster than they
provided [1,3] sigmatropic shift products, and determina-
tions of rate constants for conversions of specific stere-
oisomers of a vinylcyclopropane system to specific stere-
oisomers of cyclopentene products presented nontrivial
methodological challenges. But, in time, the stereochem-
ical facts became available and they revealed, for a
variety of monocyclic, geometrically unconstrained vi-
nylcyclopropanes substituted with cyano, deuterium,
methyl, or phenyl stereochemical markers, that the
isomerization takes place through all four paths. All four
stereochemical options are kinetically competitive. Of
(
5) Andrews, G. D.; Baldwin, J . E. J . Am. Chem. Soc. 1976, 98,
6
705-6706.
(6) Barsa, E. A. The Thermal Rearrangements of Substituted
Cyclopropanes and the Stereochemistry of the Vinylcyclopropane
Rearrangement. Ph.D. Dissertation, Harvard University, 1977.
(7) Baldwin, J . E.; Ghatlia, N. D. J . Am. Chem. Soc. 1991, 113,
6273-6274.
(
8) Baldwin, J . E.; Bonacorsi, S. J . J . Am. Chem. Soc. 1993, 115,
1
0621-10627.
(
9) Baldwin, J . E.; Bonacorsi, S. J . J . Org. Chem. 1994, 59, 7401-
7409.
(10) Baldwin, J . E.; Villarica, K. A.; Freedberg, D. I.; Anet, F. A. L.
J . Am. Chem. Soc. 1994, 116, 10845-10846.
(11) Baldwin, J . E.; Villarica, K. A. J . Org. Chem. 1995, 60, 186-
(1) For a synopsis of work on this rearrangement and a listing of
190.
(12) Asuncion, L. A.; Baldwin, J . E. J . Org. Chem. 1995, 60, 5778-
5784.
(13) Asuncion, L. A.; Baldwin, J . E. J . Am. Chem. Soc. 1995, 117,
review articles, see: Baldwin, J . E. J . Comput. Chem. 1998, 19, 222-
2
31.
(
2) Woodward, R. B.; Hoffmann, R. J . Am. Chem. Soc. 1965, 87,
2
511-2513.
10672-10677.
(
3) Woodward, R. B.; Hoffmann, R. The Conservation of Orbital
(14) Baldwin, J . E.; Bonacorsi, S. J . J . Am. Chem. Soc. 1996, 118,
8258-8265.
Symmetry; Verlag Chemie: Weinheim, 1970; pp 121-122.
4) Baldwin, J . E. In The Chemistry of the Cyclopropyl Group;
Rappoport, Z., Ed.; Wiley: Chichester, 1995; Vol. 2, pp 469-494.
(
(15) Baldwin, J . E.; Bonacorsi, S. J .; Burrell, R. C. J . Org. Chem.
1998, 63, 4721-4725.
1
0.1021/jo9824091 CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/14/1999

3
568 J . Org. Chem., Vol. 64, No. 10, 1999
Baldwin and Burrell
does not require C2-C3-C4-C5 dihedral angle changes
of more than 180° in a hypothetical 3,4-tetramethylene-
bridged 2-pentene-1,5-diyl species; rather, the conforma-
tional flexibility required to present the migrating carbon
with the initially less accessible face of the allylic
component takes place through planar or nearly planar
geometries of the five carbons of the 2-pentene-1,5-diyl
structure, with C1-C5 in close proximity.
Sch em e 1
The present study was undertaken to extend these
results by progressing to a system that retained the
tetramethylene tether to restrict conformation possibili-
ties and yet did not favor any stereochemical outcome
based on product stability differences. The reaction
selected for study, the isomerization of 1-ethenylbicyclo-
Sch em e 2
[4.1.0]heptane (1) to bicyclo[4.3.0]non-1(9)-ene (2), satis-
fies these requirements.
Resu lts
Syn th eses. The unlabeled substrate 1 was prepared
according to the sequence of reactions outlined in Scheme
product E-1-d with very high stereoselectivity, as judged
by NMR spectral criteria. The same two-step reaction
sequence, starting with 1-(d-ethynyl)bicyclo[4.1.0]heptane
1
(
. Cyclohexanone and PCl
5
afford 1-chlorocyclohexene
3); the corresponding organolithium compound17 and
1
6
1
8
formaldehyde give 1-hydroxymethylcyclohexene (4).
A
(
7-d ), provided 1-d
The gas-phase thermal reactions of 1, 1-d
were run using a well-conditioned 300-mL kinetic bulb;
h at 338 °C was sufficient to achieve a 79% conversion
2
.
Simmons-Smith cyclopropanation reaction leads to
2
, and E-1-d
1
9-21
1
-hydroxymethylbicyclo[4.1.0]heptane (5).
Oxidation
2
6
2
2
of this alcohol gives an aldehyde (6) that may be
converted through a Wittig reaction to 1-ethenylbicyclo-
6
2
3
of 1 to the vinylcyclopropane-cyclopentene rearrange-
ment product 2 (70%; 89% yield) and several minor
[
4.1.0]heptane (1).24
Aldehyde 6 served as well as synthetic intermediate
2
7
products (9%). The bicyclic olefin 2, a known compound,
for 1-ethynylbicyclo[4.1.0]heptane. The aldehyde was
reacted with triphenylphosphine and CBr following
Corey and Fuchs25 to give 1-(2′,2′-dibromoethenyl)bicyclo-
4.1.0]heptane, which was dehydrobrominated with bu-
was identified through proton and carbon-13 NMR
spectroscopy.
The isomerization of 1-d to 2-d provided material
2 2
needed to test NMR methods for measuring integrated
absorption intensities for exo and endo deuteriums at C8.
4
[
tyllithium to provide alkyne 7.
2
The two diastereotopic deuteriums in 2-d , awkwardly
enough, happened to have the same chemical shift: they
2
appeared in a H NMR spectrum as a single observable
resonance! In the presence of Ag(fod) and Yb(fod)
reagents, however, the resonances were well resolved.
The combination shift reagent Ag(fod) and Yb(fod)
complexes with the most sterically accessible face of an
olefin, causing NMR resonance absorptions for allylic
protons to shift downfield, with those on the most
3
shift
2
8,29
3
The deuterium-labeled versions of vinylcyclopropane
1
1
required, 1-(2′-(E)-d-ethenyl)bicyclo[4.1.0]heptane (E-
-d ) and 1-(2′,2′-d -ethenyl)bicyclo[4.1.0]heptane (1-d ),
2
2
were made from alkyne 7 through the reactions sum-
marized in Scheme 2. Reduction of the triple bond with
DIBALH in pentane, followed by treatment of the reac-
sterically accessible face of the olefin experiencing the
more pronounced shifts.2
8,29
On the basis of this prece-
dence, the more downfield resonance observed in the
deuterium NMR spectrum of 2-d 2 was assigned to the
exo deuterium at C8, for the exo face of bicyclo[4.3.0]non-
1(9)-ene was judged to be the more accessible.
Isomerization of E-1-d for 6 h at 338 °C gave both
en d o-2-d and exo-2-d . The integrated intensities of the
two absorptions in the deuterium NMR spectrum of GC
purified product, recorded in the presence of Ag(fod) and
2
tion mixture with D O, gave the (E)-deuterio-labeled
(16) Brandsma, L.; Verkruijsse H. D. Preparative Polar Organome-
tallic Chemistry 1; Springer-Verlag: Berlin, 1987; pp 65-66.
(
17) Brandsma, L.; Verkruijsse H. D. Ibid. pp 50-52.
(18) Arnold, R. T.; Lee, W. W. J . Am. Chem. Soc. 1953, 75, 5396-
5
2
400.
(
19) Rawson, R. T.; Harrison, I. T. J . Org. Chem. 1970, 35, 2057-
058.
(
20) Prakash, G. K. S.; Fung, A. P.; Olah, G. A.; Rawdah, T. N. Proc.
Natl. Acad. Sci. U.S.A. 1987, 84, 5092-5095.
21) Harding, K. E.; Trotter, J . W.; May, L. M. J . Org. Chem. 1977,
3
Yb(fod) shift reagents, showed the more downfield signal
(from the exo-2-d isomer) to be the weaker (Figure 1):
(
4
2, 2715-2719.
(
22) Corey, E. J .; Suggs, J . W. Tetrahedron Lett. 1975, 2647-2650.
23) Wittig, G.; Schoellkopf, U. Organic Syntheses; Wiley: New York,
(26) Compare: Baldwin, J . E.; Carter, C. G. J . Am. Chem. Soc. 1982,
(
104, 1362-1368.
1
973; Collect. Vol. V, pp 751-754.
24) Gassman, P. G.; Valcho, J . J .; Proehl, G. S.; Copper, C. F. J .
Am. Chem. Soc. 1980, 102, 6519-6526.
25) Corey, E. J .; Fuchs, P. L. Tetrahedron Lett. 1972, 3769-3772.
(27) Stierman, J . T.; J ohnson, R. P. J . Am. Chem. Soc. 1985, 107,
3971-3980.
(
(28) Wenzel, T. J .; Sievers, R. E. Anal. Chem. 1981, 53, 393-399.
(29) Smith, W. B. Org. Magn. Reson. 1981, 17, 124-126.
(

Thermal Vinylcyclopropane-to-Cyclopentene Rearrangement
J . Org. Chem., Vol. 64, No. 10, 1999 3569
one corresponding to suprafacial, the other antarafacial
3
0-32
utilization of the allylic moiety ((P )-7 and (M)-7).
The conformational isomerization by way of C
s
-8 leaves
the choice between inversion or retention stereochemistry
unaltered: that option, according to theory,3
0,31
is deter-
mined earlier in the progress from the ground state to
the transition region through conformational flexibilities
involving primarily torsions about the C5-C4 axis as the
cyclopropyl C-C bond of the starting material lengthens
and cleaves.
The present results imply that this configurational
freedom remains essentially unimpaired despite the
tetramethylene tether for isomerizations that are ther-
mochemically unbiased, for isomerizations free to use
inversion as well as retention stereochemical paths.
While the respective structures (P )-9 and (M)-9 are no
F igu r e 1. Deuterium NMR spectrum recorded in the presence
of Ag(fod) and Yb(fod)
-d obtained through thermal isomerization of E-1-d over 6 h
at 338 °C.
3
shift reagents of en d o-2-d and exo-
2
the vinylcyclopropane-to-cyclopentene rearrangement oc-
curred with 78% (sr + si) and 22% (ar + ai) stereochem-
istry.
s
longer enantiomeric, and 10 is no longer of C symmetry,
access to (M)-9 and thus access to the initially remote
face of the allyl π system by way of 10 is apparently not
much encumbered by the conformational restraints im-
posed by the tetramethylene bridge.
A second isomerization over a 4.5-h period gave a
2
smaller sample of product estimated by H NMR in the
presence of the mixed shift reagents to be en d o-2-d and
exo-2-d in 81:19 proportions, an outcome essentially
identical to the 78:22 ratio observed for the product
mixture from a 6-h reaction, thus providing some assur-
ance that the stereochemical result is reproducible and
corresponds to a kinetically controlled product mixture.
These schematic structural representations prompt
consideration of other possible influences on conforma-
tional flexibility, such as steric effects associated with
substituents at C2 of the core (2Z)-pentene-1,5-diyl
structure. For instance: there is good experimental
evidence indicating that vinylcyclopropanes substituted
with tert-butyl at C1′ of the ethenyl group isomerize to
Discu ssion a n d Con clu sion s
1
-(tert-butyl)cyclopentenes with predominant suprafacial,
3
3-36
inversion stereochemistry.
Might the very high pref-
The stereochemical results obtained through the present
work may be summarized succinctly: for the isomeriza-
tion of vinylcyclopropane 1 to the corresponding cyclo-
pentene product 2 at 338 °C, deuterium labeling experi-
ments show that the isomerization modes (sr + si) and
erence for suprafacial stereochemistry be associated with
passage of the tert-butyl group past the C1- and C3-
hydrogens in transition structure C -12?
s
(ar + ai) take place in (79 ( 2):(21 ( 2) proportions. These
stereochemical results may be compared with those
reported for the isomerizations of the 7-exo-phenyl sub-
stituted analogue of 1 at 220 °C: sr/ar ) (85 ( 1):(15 (
1
5
1
). The suprafacial to antarafacial balances, with and
without contributions from pathways involving inversion
at the migrating carbon, are remarkably similar. They
also correspond reasonably with the range of observed
contributions from antarafacial paths (13-37% of all
paths) determined for isomerizations of conformationally
less constricted, substituted monocyclic vinylcyclopro-
panes.5
The most recent published theoretical models for
thermal vinylcyclopropane-to-cyclopentene rearrange-
s
ments place a C -symmetric transition structure (8)
That question might be probed computationally. Simi-
lar questions could be addressed and answered experi-
(30) Davidson, E. R.; Gajewski, J . J . J . Am. Chem. Soc. 1997, 119,
1
0543-10544.
31) Houk, K. N.; Nendel, M.; Wiest, O.; Storer, J . W. J . Am. Chem.
Soc. 1997, 119, 10545-10546.
32) Doubleday, C.; Nendel, M.; Houk, K. N.; Thweatt, D.; Page, M.
(
-14
(
Direct Dynamics Quasiclassical Trajectory Study of the Stereochem-
istry of the Vinylcyclopropane-Cyclopentene Rearrangement. J . Am.
Chem. Soc., in press.
(
33) Gajewski, J . J .; Warner, J . M. J . Am. Chem. Soc. 1984, 106,
02-803.
34) Gajewski, J . J .; Squicciarini, M. P. J . Am. Chem. Soc. 1989,
111, 6717-6728.
between and only slightly higher in energy than two
enanatiomerically related helical (Z)-2-pentene-1,5-diyl
transition structures leading to cyclopentene products,
8
(

3
570 J . Org. Chem., Vol. 64, No. 10, 1999
Baldwin and Burrell
heptane-1-methanol20,21 as a clear oil. A small sample was
mentally through syntheses and stereochemical studies
of suitable vinylcyclopropane systems. The present re-
sults for a tetramethylene-tethered reactant stress the
conformational flexibility available on paths linking
vinylcyclopropane substrate 1 to cyclopentene product 2;
other systems could well provide insights on structural
factors that could substantially influence relative prefer-
ences among alternative stereochemical outcomes.
1
further purified by preparative GC (10% SE-30, 100 °C):
H
NMR δ 3.28-3.41 (m, 2 H), 1.81-1.94 (m, 2 H), 1.55-1.78 (m,
2
9
2
1
H), 1.15-1.38 (m, 5 H), 0.78-0.88 (m, 1 H), 0.48 (dd, J )
.3, 4.5 Hz, 1 H), 0.25 (t, J ) 5.0 Hz, 1 H); 13C NMR δ 72.7,
6.4, 23.7, 22.0, 21.7, 21.3, 15.7, 15.0; MS m/z (rel intensity)
+
26 (2, M ), 108 (18), 95 (81), 79 (48), 67 (98), 55 (60), 39 (100).
Bicyclo[4.1.0]h ep ta n e-1-ca r boxa ld eh yd e (6). To a 50-
mL round-bottomed flask were added PCC22 (2.57 g, 11.9
2 2
mmol), dry CH Cl (25 mL), and bicyclo[4.1.0]heptane-1-
methanol (1.01 g, 11.9 mmol). The black reaction mixture was
stirred for 2 h at room temperature under argon and then
diluted with ether (25 mL) and filtered through Florisil. The
black tar that remained in the flask was washed with ether
Exp er im en ta l Section
Elemental analyses were done by E & R Microanalytical
1
2
13
Laboratory, Corona, NY. The H NMR, H NMR, and C NMR
spectra were recorded for CDCl solutions.
-Ch lor ocycloh exen e (3), prepared following the proce-
(
3 × 10 mL), the washings were filtered through Florisil, and
3
the Florisil was washed with ether (100 mL). The combined
1
1
6
ethereal material was dried (MgSO ), filtered, and concen-
dure of Brandsma and Verkuijsse, was distilled through a
4
trated. Column chromatography (silica gel, hexanes/ethyl
acetate 9:1) gave 0.91 g (92%) of aldehyde 6 as a clear oil. A
small sample was further purified by preparative GC (10% SE-
1
8-cm Vigreux column and had bp 32-36 °C (12 mm). A small
sample was further purified by preparative gas chromatogra-
1
phy (17% Carbowax, 45 °C): H NMR δ 5.77-5.82 (m, 1 H),
3
0, 100 °C): 1H NMR δ 8.64 (s, 1 H), 2.55-2.67 (m, 1 H), 1.82-
2
1
2
.25-2.32 (m, 2 H), 2.04-2.12 (m, 2 H), 1.68-1.78 (m, 2 H),
13
1.90 (m, 2 H), 1.28-1.61 (m, 6 H), 1.11-1.24 (m, 2 H), 0.91
.53-1.62 (m, 2 H); C NMR δ 131.9, 124.5, 33.7, 26.0, 23.7,
1.3.
(
3
1
dd, J ) 7.0, 4.8 Hz, 1 H) (compare ref 21); 13C NMR δ 202.3,
1.3, 22.8, 21.4, 21.2, 20.5, 20.2, 19.0; MS m/z (rel intensity)
Cycloh exen e-1-m eth a n ol (4). A flattened piece of lithium
2.03 g, 275 mmol) containing 0.5-1% sodium was cut directly
into a 250-mL three-necked flask containing 60 mL of dry
+
24 (10, M ), 109 (15), 95 (71), 80 (37), 67 (77), 55 (46), 39
(
(100).
1
7
1-Eth en ylbicyclo[4.1.0]h ep ta n e (1). To a stirred solution
ether. Pieces of glass from 0.5 to 1.5 cm long obtained by
breaking cautiously two Pasteur pipets with a hammer were
introduced into the flask; it was then fitted with a reflux
condenser and mechanical stirrer, and it was flushed with
argon. 1-Chlorocyclohexene (11.4 g, 98 mmol) was added and
the mixture was stirred slowly at room temperature. After 3
h, the reaction solution was heated to reflux with stirring for
an additional 2 h and then cooled to room temperature and
stirred for another 9 h. The resultant grayish suspension was
transferred to a 250-mL three-necked flask previously flushed
with argon. The broken glass pieces were washed with ether
of methyltriphenylphosphonium bromide (5.17 g, 14.5 mmol)
in THF (20 mL) under argon was added MeLi (10.4 mL, 14.47
mmol, 1.4 M) at -78 °C.23 The reaction mixture was warmed
to 0 °C and stirred for 1.5 h. The bicyclic aldehyde 6 (1.50 g,
1
2.0 mmol) in 5 mL of THF was added dropwise to the red
2
3
solution of Wittig reagent at 0 °C, and the reaction mixture
was then warmed to room temperature and stirred for 5 h. It
was quenched with water (40 mL); the organic layer was
removed, and the aqueous layer was extracted with pentane
(
3 × 30 mL). The combined organic material was washed with
water (15 mL), dried (MgSO ), filtered, and concentrated.
4
(
3 × 10 mL), and the ethereal solution was combined with the
Column chromatography (silica gel, pentane) gave 0.96 g (65%)
transferred suspension. Gaseous formaldehyde (from the de-
polymerization of 4.02 g (123 mmol) of paraformaldehyde in a
of 124 as a clear oil. A small sample was further purified by
1
1
8
preparative GC (15% SE-30, 65 °C): H NMR δ 5.48 (dd, J )
separate flask at 180-200 °C) was bubbled into the gray
mixture at 0 °C; this introduction of paraformaldehyde was
repeated to ensure complete reaction of the cyclohexenyl-
lithium. The reaction mixture was allowed to warm to room
temperature, stirred for 10 h, and then poured into 300 mL of
1
7.3, 10.6 Hz, 1 H), 4.90 (dd, J ) 17.3, 1.3 Hz, 1 H), 4.84 (dd,
J ) 10.6, 1.3 Hz, 1 H), 1.85-2.03 (m, 2 H), 1.71-1.81 (m, 1
H), 1.50-1.62 (m, 1 H), 1.11-1.48 (m, 4 H), 0.91-1.02 (m, 1
H), 0.67 (dd, J ) 9.3, 4.4 Hz, 1 H), 0.52 (dd, J ) 5.9, 4.4 Hz,
1
2
H) (compare ref 24); 13C NMR δ 148.1, 108.4, 26.0, 23.8, 21.7,
4
saturated aqueous NH Cl at 0 °C. The two-phase system was
+
1.6, 21.0, 20.3, 19.0; MS m/z (rel intensity) 122 (10, M ), 107
stirred vigorously, the ethereal layer was removed, and the
aqueous layer was extracted with ether (2 × 50 mL). The
combined organic material was washed with water (50 mL),
dried over MgSO , filtered, and concentrated. The resultant
4
oil was distilled through an 18-cm Vigreux column to give 4.82
(
16), 93 (34), 79 (100), 67 (31), 53 (22), 39 (47).
-Eth yn ylbicyclo[4.1.0]h ep ta n e (7). To a 100-mL three-
necked flask were added under argon CBr (6.04 g, 18.2 mmol),
PPh (9.56 g, 36.4 mmol), and dry CH Cl
The orange solution was then stirred for 30 min at 0 °C; the
bicyclic aldehyde 6 (1.13 g, 9.11 mmol) in CH Cl (10 mL) was
1
4
2
5
3
2
2
(25 mL) at 0 °C.
g of cyclohexene-1-methanol (37%) boiling at 84-89 °C (14-
6 mm) (lit. bp 84 °C (10 mm)). A small sample was further
1
8
1
2
2
1
added, and the reaction mixture was stirred for an additional
2 h at room temperature. It was then filtered, and the filtrate
was concentrated. The concentrate was triturated with pen-
purified by preparative GC (10% SE-30, 100 °C): H NMR δ
1
5
4
2
.68 (s, 1 H), 3.98 (s, 2 H), 1.97-2.08 (m, 4 H), 1.54-1.71 (m,
13
H), 1.34 (s, 1 H); C NMR δ 137.6, 123.1, 67.7, 25.7, 24.9,
+
tane, and PPh was removed by filtration. Several repetitions
2.6, 22.5; MS m/z (rel intensity) 112 (34, M ), 94, (20), 81
3
of this process (trituration with pentane, filtration, and
concentration) served to remove most of the PPh . Column
3
(
88), 79 (100), 67 (26), 55 (46), 39 (76).
Bicyclo[4.1.0]h eptan e-1-m eth an ol (5). To a 100-mL three-
chromatography of the final oily concentrate (silica gel, pen-
tane) gave 1.77 g (69%) of the dibromoolefin intermediate as
necked flask were added zinc powder (7.28 g, 111 mmol),
copper chloride (1.10 g, 11.2 mmol), and dry ether (50 mL).19
+
a clear oil: MS m/z (rel intensity) 278:280:282 (3:6:3, M ), 252
The flask was fitted with a reflux condenser and flushed with
argon, and the reaction mixture was heated to reflux for 1 h.
Cyclohexene-1-methanol (4.82 g, 43.0 mmol) and CH I (14.9
2 2
(
(
7), 226 (21), 212 (16), 199 (17), 171 (13), 145 (14), 119 (99), 91
100), 77 (35), 65 (34), 51 (39), 39 (74).
To 2.03 g (7.55 mmol) of the dibromide in 30 mL of dry
g, 55.7 mmol, 4.5 mL) were added to the lime green solution.
The reaction mixture was heated to reflux for 60 h, and then
the gray mixture was cooled to room temperature and filtered.
The filtrate was washed with 3 M aqueous NaOH (4 × 30 mL)
pentane under argon at -78 °C was added 1.6 M BuLi in
hexanes (11.3 mL, 18.1 mmol). The reaction mixture was
stirred at -78 °C for 1 h, allowed to warm to room tempera-
ture, and stirred for another 1 h. It was then cooled to 0 °C,
and 25 mL of water was added slowly. The organic layer was
removed, and the aqueous layer was extracted with pentane
4
and water (30 mL). The organic layer was dried over MgSO ,
filtered, and concentrated to give 4.29 g (79%) of bicyclo[4.1.0]-
(
3 × 25 mL). The combined organic material was dried
(
35) Gajewski, J . J .; Olson, L. P. J . Am. Chem. Soc. 1991, 113, 7432-
(MgSO ) and filtered, and the filtrate was concentrated to give
4
7
433.
(
36) Gajewski, J . J .; Olson, L. P.; Willcott, M. R. J . Am. Chem. Soc.
0.65 g of 1-ethynylbicyclo[4.1.0]heptane (72%) as a clear oil.
A small sample was further purified by preparative GC (15%
1
996, 118, 299-306.

Thermal Vinylcyclopropane-to-Cyclopentene Rearrangement
J . Org. Chem., Vol. 64, No. 10, 1999 3571
SE-30, 65 °C): 1H NMR δ 1.88-2.06 (m, 3 H), 1.86 (s, 1 H),
sensitive to the vapor pressure of the sample. After appropriate
stopcocks on the line were manipulated, the trap was removed
and its contents dissolved in pentane. The pentane solution
was analyzed directly by analytical GC using a 25-m Ultra 2
column, and recovered starting material and unlabeled or
deuterium-labeled bicyclo[4.3.0]non-1(9)-ene products were
isolated in pure form by preparative GC (15% SE-30, 65 °C).
Thermal reactions of 1 in base-washed sealed ampules gave
irreproducible reaction kinetics and complex product mixtures;
a substantial component in these mixtures was found to be
bicyclo[4.3.0]non-1(6)-ene,37 a structure presumably formed
through an acid-catalyzed isomerization of the primary ther-
1
.52-1.63 (m, 1 H), 1.06-1.42 (m, 5 H), 0.99 (dd, J ) 9.3, 4.4
13
Hz, 1 H), 0.54 (dd, J ) 6.3, 4.4 Hz, 1 H); C NMR δ 92.6 (C),
2.6 (CH), 29.3 (CH ), 23.0 (CH ), 20.9 (CH ), 20.9 (CH), 20.3
CH ), 19.9 (CH ), 9.7 (C); MS m/z (rel intensity) 120 (25, M ),
05 (60), 91 (100), 77 (35), 65 (22), 51 (24), 39 (52). Anal. Calcd
12: C, 89.94; H, 10.06. Found: C, 89.88; H, 10.23.
-(2′,2′-d -Eth en yl)bicyclo[4.1.0]h eptan e (1-d ). A sample
6
(
2
2
2
+
2
2
1
9
for C H
1
2
2
of the alkyne 7 (0.20 g, 1.66 mmol) dissolved in dry pentane
under argon was cooled to -78 °C, and 1.6 M BuLi in hexanes
(1.2 mL, 1.99 mmol) was added. The mixture was warmed to
room temperature and stirred for 20 min; it was then cooled
to 0 °C, and 2 mL of D O (99.9% D) was added slowly with
2
mal product, 2. Compounds 1, E-1-d , and 1-d , after careful
2
rapid stirring. The reaction mixture was transferred to a
purification by preparative GC, exhibited reproducible kinetic
separatory funnel and extracted with pentane (3 × 10 mL). A
behavior and gave primarily 2, 2-d , and 2-d , respectively,
2
when isomerized thermally in the gas phase using the well-
conditioned kinetic bulb described above.
1
second exchange was then performed; H NMR spectroscopy
showed the acetylenic proton to be substantially replaced with
deuterium. To the labeled acetylene 7-d (1.66 mmol) in 20 mL
of dry pentane at 0 °C was added DIBALH (0.59 mL, 0.47 g,
Bicyclo[4.3.0]n on -1(9)-en e (2). Ethenylbicyclo[4.1.0]-hep-
tane (1) was heated in the gas phase for 6 h at 338 °C; the
reaction mixture was transferred from the kinetic bulb,
analyzed by GC, and found to contain unreacted 1 (21%),
3
.32 mmol) in 5 mL of dry pentane through an addition funnel.
The reaction mixture was warmed to room temperature and
monitored by GC. After 2 h, the reaction flask was cooled to 0
27
bicyclo[4.3.0]non-1(9)-ene (2, 70%), and several minor prod-
°
2
C, and 5 mL of D O was added slowly. The resultant mixture
ucts (9%). The rearrangement product 2 was purified by
was allowed to warm to room temperature and was stirred
rapidly for 3 h, and then a small amount of 10% aqueous HCl
was added to dissolve the gelatinous mixture that had formed.
The contents of the flask were transferred to a separatory
funnel, and the aqueous layer was extracted with pentane (5
1
preparative GC: H NMR δ 5.23 (t, J ) 2.2 Hz, 1 H), 2.48-
2
1
1
.33 (m, 2 H), 2.29-2.22 (m, 2 H), 2.14-2.05 (m, 1 H), 1.99-
.86 (m, 2 H), 1.80-1.70 (m, 2 H), 1.40-1.27 (m, 2 H), 1.23-
13
.12 (m, 1 H), 0.94 (quartet d, J ) 12.6, 3.3 Hz, 1 H); C NMR
δ 146.4, 120.1, 45.5, 35.9, 31.1, 30.7, 28.9, 27.3, 26.2; MS m/z
×
15 mL). The combined organic material was washed with
saturated aqueous NaHCO (20 mL), dried (MgSO ), and
filtered. Concentration of the filtrate gave 140 mg (68% for
the three steps) of 1-d . A small sample was further purified
+
(
rel intensity) 122 (43, M ), 107 (10), 93 (85), 80 (97), 79 (100),
7 (16), 53 (15), 39 (36).
-d -Bicyclo[4.3.0]n on -1(9)-en e (2-d
of 1-(2′,2′-d -ethenyl)bicyclo[4.1.0]heptane (1-d
for 6 h at 338 °C. The reaction mixture contained 1-d
-d (69%) and several minor products (10%). The deuterium
NMR spectrum of the preparative GC purified 2-d showed
only a single resonance, at δ 2.25. In the presence of Ag(fod)
3
4
6
8
2
2
). A gas-phase sample
) was heated
(21%),
2
2
2
1
by preparative GC (15% SE-30, 65 °C): H NMR (olefinic
2
region) δ 5.48 (s, 1 H), 4.90 (d, J ) 17.3 Hz, 13% of 1 H).
2
2
1
-(2′-(E)-d -eth en yl)bicyclo[4.1.0]h ep ta n e (E-1-d ). To a
2
sample of the bicyclic alkyne 7 (0.10 g, 0.83 mmol) in 10 mL
of dry pentane at 0 °C was added DIBALH (0.30 mL, 0.24 g,
28,29
2
(
22 mg) and Yb(fod)
NMR δ 4.89 (s, 1 D), 4.23 (s, 1 D). The recovered starting
material 1-d isolated by preparative GC was found to be
unchanged according to H NMR criteria.
-d -Bicyclo[4.3.0]n on -1(9)-en e (2-d ) fr om 1-(2′-(E)-d -
3
(11 mg),
2
2-d showed two peaks: H
1
.67 mmol) in 5 mL of dry pentane through an addition funnel.
The reaction mixture was allowed to warm to room temper-
ature and monitored by GC. After 4 h, the flask was cooled to
2
1
0
°C and 5 mL of D
allowed to warm to room temperature and was stirred rapidly
for 3 h. A workup as described for 1-d led to 74 mg (73%) of
2
O was added slowly. The mixture was
8
eth en yl)bicyclo[4.1.0]h ep ta n e (E-1-d ). A sample of E-1-d
was heated for 6 h at 338 °C. The reaction mixture contained
E-1-d (20%), bicyclo[4.3.0]non-1(9)-ene (2-d , 72%), and several
minor products (8%). Product 2-d was purified by preparative
GC and examined by deuterium NMR in the presence of Ag-
2
E-1-d . A small sample was further purified by preparative
1
GC: H NMR (olefinic region) δ 5.48 (d, J ) 17.3 Hz, 1 H),
4
.90 (d, J ) 17.3 Hz, 1 H).
Ga s-P h a se Rea ction s. Thermal reactions of unlabeled and
(13 mg): 2H NMR δ 6.05 (s, 22% of
fod) (26 mg) and Yb(fod)
3
(
1
deuterium-labeled 1-ethenylbicyclo[4.1.0]heptanes (100-mL of
% solutions in pentane) were carried out at 338.1 °C in a 300-
D), 5.43 (s, 78% of 1 D) (Figure 1). The stereochemistry about
5
1
the vinyl group in recovered E-1-d was unchanged ( H NMR).
A second sample of E-1-d was heated for 4.5 h at 338 °C to
give a reaction mixture containing unreacted E-1-d (28%), 2-d
2
6
mL Pyrex bulb encased in an aluminum block. The bulb was
conditioned before use by pyrolyzing 50-mL samples of cyclo-
hexene at 350 °C for 24 h three times. A spherical cavity
machined in the block accommodated the flask; the aluminum
top hemisphere was halved to allow facile dismantling of the
apparatus. Eight cartridge heaters in vertical holes around
the block were connected alternately to a Variac and to a
Bailey Instruments model 253 precision temperature control-
ler. Temperature measurements were made with a calibrated
Hewlett-Packard model 2802A digital thermometer and a
platinum resistance temperature probe (Omega Engineering,
part no. OSK5045 PR-11-3-100-1/8-6-E). The aluminum block
was supported with firebrick and enclosed in a 34-cm × 34-
cm × 27-cm plywood box packed with diatomaceous earth.
Prior to each thermal reaction, the bulb was evacuated to
(
60%), and several minor products (12%). Rearrangement
2
product 2-d was purified by preparative GC: H NMR δ (in
the presence of Ag(fod) (26 mg) and Yb(fod) (13 mg)), two
3
peaks, 6.61 (s, 19% of 1 D) and 5.43 (s, 81% of 1 D). Unreacted
E-1-d was isolated by preparative GC and shown to have
1
retained stereochemical integrity at the vinyl C2′ position ( H
NMR).
Ack n ow led gm en t. We thank the National Science
Foundation for supporting this work through Grant
CHE 95-32016.
-2
less than 2.2 × 10 Torr and the stopcock was closed. Samples
were injected into the bulb through a septum with a 0.5-mL
gastight syringe. After a thermal reaction, the stopcock was
opened and the reaction mixture was pumped into a liquid
nitrogen cooled U-tube attached to the vacuum line with O-ring
seals and threaded connectors (Ace Glass No. 5027-30); this
method provided immediate recovery of the sample, whereas
longer times would have been required for transfers more
Su p p or tin g In for m a tion Ava ila ble: Copies of NMR
spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O9824091
(37) Kagayama, T.; Okabayashi, S.; Amaike, Y.; Matsukawa, Y.;
Ishii, Y.; Ogawa, M. Bull. Chem. Soc. J pn. 1982, 55, 2297-2298.