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7-Norbornenylidene - a potentially nonclassical carbene
Tetrahedron Letters No.14, pp. 931-934, 1971.
- A POTENTIALLY
7-NORBORNENYLIDENE Robert Wright
A.
Ulf-Helge
MOSS,
Laboratory, University
Pergamon Press.
School of New
Printed in Great Britain.
NONCLASSICAL
Dolling:
and
CARBENE
Joanne
of Chemistry, Rutgers Jersey, New Brunswick,
R. Whittle
University, The N. J., 08903
State
(Received in USA 11 February 1971; received in UK for publication 16 March 1971) 7-Norbornenylidene,
I,
is predicted
to be
a "singlet,
stabilized,
nonclass-
0 ical and
methylene", toward
anylidene,
its
the
carbenic 1 double bond.
II,
which
should
bridge No
ought
such
have
to
incline
stabilization
normal
geometry
-20
away
from
is predicted
for
and
a triplet
have
discussed
marized
in eq.
report
the
intramolecular which
[l]),
.-detailed
initial,
vertical
7-norborn-
ground
state.
1
II
I We
the
should
chemistry
of
significantly
studies
of
differ
important
the
80%
thermally-generated from
carbene
I,
+
+
(sum-
II2
Now
that
of
I.
and
we
comment
we on
[ll
\
& II
a
12%
14%
74% its
intramolecular
chemistry.
was
converted
thorough system
to
tosylhydrazone
vacuum at
0.05
was 5 15 min.
its
and
temperature
made
least
About
77OK.
Gc
a 15',
0.25",
in
stases, -
"Allied
indicated
over
Chemical
Li
drying, Torr.
15% 164
4
0
3
7-Norbornenone
at
salt
with
5 g.
of
the 0 .
yield
17 components,
min.
Company
salt
on
90/100
Injector Fellow,
mp.
156-157.5
decomp.,
of "-butyllithium
1 equiv.
was
pyrolyzed
from
CHsOH), After
in ether.
in a previously
degassed
The
approach to the rather sharp pyrolysis 0 the salt was stable for at from 179 , where
190-191 0 -0.35 /min.
a 50%
SF-96
(83%,
of
hydrocarbon
most
of which
Anakrom and
ABS
detector
1971-2.
931
product were column
mixture
trapped
at
(cl%).
We
used
50' , programmed
to
160°,
very at
was
minor
temperatures
were
120'
and
130'.
932
Gc
No.14
isolation
fied tor
was
carried
out
at
a column
products
and
their
distribution
response)
are
shown
in eq.
temperature
(% of
all
of
50'.
products,
The
major
uncorrected
identi-
for
gc
bl. +&g+(yJ+b+m
&s+Lh 0.9%
2.3%
detec-
bl
1.0%
-
6.9% V
1.6%
67% IV
III
d 1,3_Cyclohexadiene, by
comparison
samples.
of
toluene,
their
Norbornene
nmr
and
and
spectra
III'
and
were
Bicyclo[3.2.O]heptadiene-1,6, 91,
and
a "carbon
count"
of
spiro[2,4]heptadiene,
7 (m/e
gc
retention
identified
only
IV,
at
had
93 was
M+
2.4%).
V,
times by
were
with
those
retention
(m/e) 92 .s A pure
identified of
authentic
times.
(30.3%),
a base
sample
peakat
absorbed
2.0
0 equiv.
of
Ha
(nmr)
with
(10%
Pd/C,
-30
, ether),
yielding
bicyclo[3.2.O]heptane,
identical 0
a sample
Definitive
prepared
spectral -47')
spectrum
(CSa,
distinct
l-proton
and
by
hydrogenation
of bicyclo[3.2.0]heptadiene-2,6. 10 IV is based upon the 100 MHz.
identification
of
60 MHz.
resonance
signals
double
(3 vinyl,
experiments
1 doubly
allylic,
follows:
6.716,
(CSa,
2 allylic,
32').
nmr Eight
and 2 "isolated")
14
observed
were
and
are
assigned
as
d,
J=1.5,
H2;
6.4(X,
t,J-2,
HI VI
IV
4.966,
Hl;
in
H4;
2.276,
5 major 1.42,
diene,
VI.
non-allenic
(VI
H7. most
any
(The
analogous
of
at
to
observations
either are
quintet,
spacings
1.64,
difficult-to-exclude
protons
that
H3
is coupled
H2
or
Hl
consistent
(~1 with
1.62,
is consistent
The
Hz.),
further
splitting),
with
chemical of VI,
shift but
occurs
to H4 which
IV.15'16'17
and
H5
are
-6,
1.54,
IV,
but
among of H3
5.136).'
mutually
In VI,
with
9 other, consis-
for
IV.
Double 4 Hz.),
coupled
however,
m
l-53,1.51,
is not
at
and
1.536,
not
the
reasonable
-2
separalicms
H6;
is
(by
split),
major
1.61,
alternative
in bicyclo[3.2.0]heptene-1
show
(eachbranch
further
1.72,
spectrum
cyclopentadiene
proton
experiments coupled
the
"t"
with
1.916,
peaks The
crude
each
4, H5;
(individual
the
3.386,
(7 bands,
spacings
1.31), is
H3;
bicyclo[3.2.0]heptadienes).
with
These
m
octet,
1.40,
tent
is not
-1.5,
2.836,
sections
1.43,
nance
spacings
8, H8;
spacings -5,
q,
by
each
resobut it -2 Hz.
vinyl
proton
should be coupled
to at least one other vinyl proton
Allylic proton
5 can be readily analyzed
is not coupled
to H6.
(Jrs-2, J,s-5 Hz.).17
giving J,,=16, J,,=4,
A model of IV, constructed
and
J,,=8
p orbital
to maximize
H5
Hz.
overlap,
17
indicates
a dihedral
angle of 90' between H5 and H6, predicting
double resonance
experiments,
iated, consistent
J values,
and a satisfactory
computed
Addiliaml
J=O.
spectrum, with assoc16
Control pyrolyses and 0.1 Torr., experiments
support the above assignments.
experiments,
demonstrated
the stability
showed invariant
tures up to 185'. onds residence,
over lithium
product
and independence
distribution
IV could be rearranged
He stream,
toluene-p-sulfinate
to toluene
at 18-195'
of III, IV, and V. Cc
at varying
injector
tempera-
in a glass flow system at 170°, 15 setNo other products
and benzene.
could be
19
detected; Eq.
V was stable under these conditions. [3] offers an attractive
rationalization
IV could arise by fulfillment
IV and V.
via dipolar VII, which combines pylcarbinyl
cation.
features
for the formation
of products
of the carbene-Il interaction;'
of a cyclopropyl
(VII could be either a transition
perhaps
anion and a cyclopro-
state or an unstable
in-
1
The "foiled methylene" adduct, VIII, could also be a fleeting irr tennediate). a1 a direct, 1,7-vinyl shift, fatermediate. Alternatively, IV could arise y& 1
22
vored
by the calculated,
bridge
of I could afford unstable
and reduced
insertion
tronic and geometric
geometry
of I.
VI, and thence V.
and abstraction 1 features in I.
Migration Dominance
of the ethano
of IV over V(W),
(compared to II) may suggest special elec1,3Cyclohexadiene
could stem from cyclo-
by the release of Cr. This would resemble the be23 of 7-quadricyclanylidene. Reversion of I to cyclopentadienylidene and
reversion havior
distinctive
ethylene,
of I, accompanied
followed by cyclopropanation,
constitutes
an alternative
route to V,
which we will investigate. Fisch and Pierce
have recently described
reactions
of bicyclo[3.3.l]non-2-
No.14
934
which they analyzed as suggestive of a "foiled methylene"(nonclass14 It remains to be seen whether the related intramolecular chemisical carbene). 24 and now for I; is diagnostic of a nonclassical try reported for this species, en-9-ylidene,
carbene.
We are searching
for "nucleophilic"
intermolecular
chemistry
of I,
which could aid in this evaluation. Acknowledcnnents. We are grateful to the National Institutes of Health&to We thank Drs. D.Z. Demey the National Science Foundation for financial support. and D. White for 100 MHz. nmr spectra, and Prof. R. Hoffman, Dr. F. A. Bovey ani Dr. D. White (who calculated the nmr spectrum of IV) for helpful discussions. 1. 2. 3. 4. 5. 6. 7. a.
9. 10.
11. 12. 13. 14. 15. 16. 17. la. 19. 20. 21. 22. 23. 24.
REFERENCES R. Gleiter and R. Hoffmann, J. Amer. Chem. Sot., 90, 5457 (1968). R. A. Moss and J. R. Whittle, Chem. Commun., 341 n969). P. G. Gassman and P. G. Pape, J. Ora. Chem., 29 160 (1964). A satisfactory elemental analysis was obtaineh(C, H, and N). More rapid heating led to varying product yields and distributions. G. Chiurdoglu and B. Tursch, Bull. Sot. Chim. Belaes, 66, 600 (1957). P. R. Story, J. Amer Chem. Soq 83, 3347 (1961). Mass spectrometer iniet temperat&??ZOO, chamber temperature 100'. At higher IV is apparently unstable inlet temperatures (160') dimeric ions were seen. An elementalanalin air. It also polymerizes with distressing spontaneity. ysis was not obtained. W. G. Dauben and R. L. Cargill, Tetrahedron, 2, 186 (1961). Polymer deposited dur255(nm)(E>3900), 207sh (~24600). hmax (cyclohexane): A strain-induced bathochromic ing sample preparation makes E values minima. Methylenecycloshifti of -20 nm is needed to rationalize the 255 nm band. Ir (neat) showed the strongest butene itself has Amax (isooctane) 221 nm.le C=C band at 6.19~~ a "cyclobutene" band was lacking, as it is in methylenecyc1obutene.l"" H. H. Jaff& and M. Orchin, "Theory and Applications of Ultraviolet Spectroscopy", John Wiley and Sons, Inc., New York, 1962, pp. 203-4. D. E. Applequist and J. D. Roberts, J. Amer. Chem. Sot., 78, 4012 (1956). b Co., LonL. J. Bellamy, "Advances in Infrared Group Frequencies", Ethuen don, 1968, p. 29. Chemical shifts refer to centers of signals and are in ppm downfield from inSplittings and "spacings" are in Hz. Much of the abundant fine ternal TMS. structure is not detailed in this description. E. W. Garbisch, Jr., J. Amer. Chem. SW., 86, 5561 (1964). m 3451 (1965). A. A. Bothner-By and R. K. Harris, ibid.,._, L. M. Jackman and S. Sternhell, "Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry", 2nd. Ed., Pergamon Press, New York, N.Y., 1969. Further discussion will appear in a full paper. This can be taken as evidence against VI as the isolated major product; for VI and V are expected to be connected by a facile, [1,5], sigmatropic rearrangement.20 N. K. Hamer and M. Stubbs, Chem. Commun., 1013 (1970); J.M.E. Krekels, J.W. de Haan, and H. Kloosterziel, Tetrahedron Lett., 2751 (1970). I, VII, and VIII are not canonical forms of a resonance hybrid, for their atomic positions differ. R. Hoffmann, G. D. Zeiss, and This would be the "least motion" 1,7-shift: G. W. Van Dine, J. Amer. Chem. Sot., 90, 1485 (1968). P. B. Shevlin and A. P. Wolf, mahedron Lett., 3987 (1970). M. H. Fisch and H. D. Pierce, Jr., Chem. Commun., 503 (1970).
- A POTENTIALLY
7-NORBORNENYLIDENE Robert Wright
A.
Ulf-Helge
MOSS,
Laboratory, University
Pergamon Press.
School of New
Printed in Great Britain.
NONCLASSICAL
Dolling:
and
CARBENE
Joanne
of Chemistry, Rutgers Jersey, New Brunswick,
R. Whittle
University, The N. J., 08903
State
(Received in USA 11 February 1971; received in UK for publication 16 March 1971) 7-Norbornenylidene,
I,
is predicted
to be
a "singlet,
stabilized,
nonclass-
0 ical and
methylene", toward
anylidene,
its
the
carbenic 1 double bond.
II,
which
should
bridge No
ought
such
have
to
incline
stabilization
normal
geometry
-20
away
from
is predicted
for
and
a triplet
have
discussed
marized
in eq.
report
the
intramolecular which
[l]),
.-detailed
initial,
vertical
7-norborn-
ground
state.
1
II
I We
the
should
chemistry
of
significantly
studies
of
differ
important
the
80%
thermally-generated from
carbene
I,
+
+
(sum-
II2
Now
that
of
I.
and
we
comment
we on
[ll
\
& II
a
12%
14%
74% its
intramolecular
chemistry.
was
converted
thorough system
to
tosylhydrazone
vacuum at
0.05
was 5 15 min.
its
and
temperature
made
least
About
77OK.
Gc
a 15',
0.25",
in
stases, -
"Allied
indicated
over
Chemical
Li
drying, Torr.
15% 164
4
0
3
7-Norbornenone
at
salt
with
5 g.
of
the 0 .
yield
17 components,
min.
Company
salt
on
90/100
Injector Fellow,
mp.
156-157.5
decomp.,
of "-butyllithium
1 equiv.
was
pyrolyzed
from
CHsOH), After
in ether.
in a previously
degassed
The
approach to the rather sharp pyrolysis 0 the salt was stable for at from 179 , where
190-191 0 -0.35 /min.
a 50%
SF-96
(83%,
of
hydrocarbon
most
of which
Anakrom and
ABS
detector
1971-2.
931
product were column
mixture
trapped
at
(cl%).
We
used
50' , programmed
to
160°,
very at
was
minor
temperatures
were
120'
and
130'.
932
Gc
No.14
isolation
fied tor
was
carried
out
at
a column
products
and
their
distribution
response)
are
shown
in eq.
temperature
(% of
all
of
50'.
products,
The
major
uncorrected
identi-
for
gc
bl. +&g+(yJ+b+m
&s+Lh 0.9%
2.3%
detec-
bl
1.0%
-
6.9% V
1.6%
67% IV
III
d 1,3_Cyclohexadiene, by
comparison
samples.
of
toluene,
their
Norbornene
nmr
and
and
spectra
III'
and
were
Bicyclo[3.2.O]heptadiene-1,6, 91,
and
a "carbon
count"
of
spiro[2,4]heptadiene,
7 (m/e
gc
retention
identified
only
IV,
at
had
93 was
M+
2.4%).
V,
times by
were
with
those
retention
(m/e) 92 .s A pure
identified of
authentic
times.
(30.3%),
a base
sample
peakat
absorbed
2.0
0 equiv.
of
Ha
(nmr)
with
(10%
Pd/C,
-30
, ether),
yielding
bicyclo[3.2.O]heptane,
identical 0
a sample
Definitive
prepared
spectral -47')
spectrum
(CSa,
distinct
l-proton
and
by
hydrogenation
of bicyclo[3.2.0]heptadiene-2,6. 10 IV is based upon the 100 MHz.
identification
of
60 MHz.
resonance
signals
double
(3 vinyl,
experiments
1 doubly
allylic,
follows:
6.716,
(CSa,
2 allylic,
32').
nmr Eight
and 2 "isolated")
14
observed
were
and
are
assigned
as
d,
J=1.5,
H2;
6.4(X,
t,J-2,
HI VI
IV
4.966,
Hl;
in
H4;
2.276,
5 major 1.42,
diene,
VI.
non-allenic
(VI
H7. most
any
(The
analogous
of
at
to
observations
either are
quintet,
spacings
1.64,
difficult-to-exclude
protons
that
H3
is coupled
H2
or
Hl
consistent
(~1 with
1.62,
is consistent
The
Hz.),
further
splitting),
with
chemical of VI,
shift but
occurs
to H4 which
IV.15'16'17
and
H5
are
-6,
1.54,
IV,
but
among of H3
5.136).'
mutually
In VI,
with
9 other, consis-
for
IV.
Double 4 Hz.),
coupled
however,
m
l-53,1.51,
is not
at
and
1.536,
not
the
reasonable
-2
separalicms
H6;
is
(by
split),
major
1.61,
alternative
in bicyclo[3.2.0]heptene-1
show
(eachbranch
further
1.72,
spectrum
cyclopentadiene
proton
experiments coupled
the
"t"
with
1.916,
peaks The
crude
each
4, H5;
(individual
the
3.386,
(7 bands,
spacings
1.31), is
H3;
bicyclo[3.2.0]heptadienes).
with
These
m
octet,
1.40,
tent
is not
-1.5,
2.836,
sections
1.43,
nance
spacings
8, H8;
spacings -5,
q,
by
each
resobut it -2 Hz.
vinyl
proton
should be coupled
to at least one other vinyl proton
Allylic proton
5 can be readily analyzed
is not coupled
to H6.
(Jrs-2, J,s-5 Hz.).17
giving J,,=16, J,,=4,
A model of IV, constructed
and
J,,=8
p orbital
to maximize
H5
Hz.
overlap,
17
indicates
a dihedral
angle of 90' between H5 and H6, predicting
double resonance
experiments,
iated, consistent
J values,
and a satisfactory
computed
Addiliaml
J=O.
spectrum, with assoc16
Control pyrolyses and 0.1 Torr., experiments
support the above assignments.
experiments,
demonstrated
the stability
showed invariant
tures up to 185'. onds residence,
over lithium
product
and independence
distribution
IV could be rearranged
He stream,
toluene-p-sulfinate
to toluene
at 18-195'
of III, IV, and V. Cc
at varying
injector
tempera-
in a glass flow system at 170°, 15 setNo other products
and benzene.
could be
19
detected; Eq.
V was stable under these conditions. [3] offers an attractive
rationalization
IV could arise by fulfillment
IV and V.
via dipolar VII, which combines pylcarbinyl
cation.
features
for the formation
of products
of the carbene-Il interaction;'
of a cyclopropyl
(VII could be either a transition
perhaps
anion and a cyclopro-
state or an unstable
in-
1
The "foiled methylene" adduct, VIII, could also be a fleeting irr tennediate). a1 a direct, 1,7-vinyl shift, fatermediate. Alternatively, IV could arise y& 1
22
vored
by the calculated,
bridge
of I could afford unstable
and reduced
insertion
tronic and geometric
geometry
of I.
VI, and thence V.
and abstraction 1 features in I.
Migration Dominance
of the ethano
of IV over V(W),
(compared to II) may suggest special elec1,3Cyclohexadiene
could stem from cyclo-
by the release of Cr. This would resemble the be23 of 7-quadricyclanylidene. Reversion of I to cyclopentadienylidene and
reversion havior
distinctive
ethylene,
of I, accompanied
followed by cyclopropanation,
constitutes
an alternative
route to V,
which we will investigate. Fisch and Pierce
have recently described
reactions
of bicyclo[3.3.l]non-2-
No.14
934
which they analyzed as suggestive of a "foiled methylene"(nonclass14 It remains to be seen whether the related intramolecular chemisical carbene). 24 and now for I; is diagnostic of a nonclassical try reported for this species, en-9-ylidene,
carbene.
We are searching
for "nucleophilic"
intermolecular
chemistry
of I,
which could aid in this evaluation. Acknowledcnnents. We are grateful to the National Institutes of Health&to We thank Drs. D.Z. Demey the National Science Foundation for financial support. and D. White for 100 MHz. nmr spectra, and Prof. R. Hoffman, Dr. F. A. Bovey ani Dr. D. White (who calculated the nmr spectrum of IV) for helpful discussions. 1. 2. 3. 4. 5. 6. 7. a.
9. 10.
11. 12. 13. 14. 15. 16. 17. la. 19. 20. 21. 22. 23. 24.
REFERENCES R. Gleiter and R. Hoffmann, J. Amer. Chem. Sot., 90, 5457 (1968). R. A. Moss and J. R. Whittle, Chem. Commun., 341 n969). P. G. Gassman and P. G. Pape, J. Ora. Chem., 29 160 (1964). A satisfactory elemental analysis was obtaineh(C, H, and N). More rapid heating led to varying product yields and distributions. G. Chiurdoglu and B. Tursch, Bull. Sot. Chim. Belaes, 66, 600 (1957). P. R. Story, J. Amer Chem. Soq 83, 3347 (1961). Mass spectrometer iniet temperat&??ZOO, chamber temperature 100'. At higher IV is apparently unstable inlet temperatures (160') dimeric ions were seen. An elementalanalin air. It also polymerizes with distressing spontaneity. ysis was not obtained. W. G. Dauben and R. L. Cargill, Tetrahedron, 2, 186 (1961). Polymer deposited dur255(nm)(E>3900), 207sh (~24600). hmax (cyclohexane): A strain-induced bathochromic ing sample preparation makes E values minima. Methylenecycloshifti of -20 nm is needed to rationalize the 255 nm band. Ir (neat) showed the strongest butene itself has Amax (isooctane) 221 nm.le C=C band at 6.19~~ a "cyclobutene" band was lacking, as it is in methylenecyc1obutene.l"" H. H. Jaff& and M. Orchin, "Theory and Applications of Ultraviolet Spectroscopy", John Wiley and Sons, Inc., New York, 1962, pp. 203-4. D. E. Applequist and J. D. Roberts, J. Amer. Chem. Sot., 78, 4012 (1956). b Co., LonL. J. Bellamy, "Advances in Infrared Group Frequencies", Ethuen don, 1968, p. 29. Chemical shifts refer to centers of signals and are in ppm downfield from inSplittings and "spacings" are in Hz. Much of the abundant fine ternal TMS. structure is not detailed in this description. E. W. Garbisch, Jr., J. Amer. Chem. SW., 86, 5561 (1964). m 3451 (1965). A. A. Bothner-By and R. K. Harris, ibid.,._, L. M. Jackman and S. Sternhell, "Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry", 2nd. Ed., Pergamon Press, New York, N.Y., 1969. Further discussion will appear in a full paper. This can be taken as evidence against VI as the isolated major product; for VI and V are expected to be connected by a facile, [1,5], sigmatropic rearrangement.20 N. K. Hamer and M. Stubbs, Chem. Commun., 1013 (1970); J.M.E. Krekels, J.W. de Haan, and H. Kloosterziel, Tetrahedron Lett., 2751 (1970). I, VII, and VIII are not canonical forms of a resonance hybrid, for their atomic positions differ. R. Hoffmann, G. D. Zeiss, and This would be the "least motion" 1,7-shift: G. W. Van Dine, J. Amer. Chem. Sot., 90, 1485 (1968). P. B. Shevlin and A. P. Wolf, mahedron Lett., 3987 (1970). M. H. Fisch and H. D. Pierce, Jr., Chem. Commun., 503 (1970).