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Evidence for hindered rotation of ethyl groups around sp2sp3 bonds : N-alkyl Δ4-thiazoline-2-thiones.
Tetrahedron Lstters
EVIDENCE N-ALKYL
go. 24, pp I985 - 1988,
1975.
FOR HINDERED ROTATION A4-THIAZOLINE-2-THIONES.
R .GALLOa,
A. LIDENb.
Pergaaon F+mss. printed in Great Britain.
OF ETHYL
GROUPS AROUND
J. SANDSTR6Mb
C .ROUSSELI.
sp2-sp3
and J. METZGER’
BONDS :
.
- Facult6 des Sciences de Saint-JkrameUniversit6 d’Aix-Marseille III aI.P.S.O.1. Rue Henri-Poincar6 - 13.397 - Marseille (Gdex 4) - France. b Division of Organic Chemistry - 1, Chemical Center - University of Lund - P.0.B.740. S-220 - Lund - 7, Sweden. (Received in UlI 18 April
Barriers
to rotation
1975; aooepted for publioation
I 34
of alhyl groups are of importance
1975)
to understand
1-3
. A number of cases of organic molecules 2 of alhyl groups about sp -sp3 bonds has been studied by D.N.M.R.
tions and reactivities
ture4-9,
but of alhyl groups of the type CH2R only neopentyl
We report here the dynamic the
A 4-thiaaoline-2-thione
I
a’
Ic, Models group in Ia arrangement pendicular
both conforma-
where hindered
rotation
are found in the litera-
groups have been dealt with7-?
behaviour
of neopentyl and ethyl groups in position 1 ring (I) as studied by H N.M.R.
R = t.Bu.
R4 = Me,
R5=H;
Ib. R = R3 = Me,
R4 = t.Bu
R = Me,
R4 = t.Bu.
R5=H;
Id. R = R4= Me.
R3 = H.
3 of
;
7-9 group indicate that this 10 shall have a nearly perpendicular arrangement , though in general a parallel 10.11 is assumed for the bensylic groups with at least one a-proton . The peras well as the known behaviour
arrangement
nous on slow rotation.
implies
diastereotopic
In agreement
of the neopentyl
methylene
with this the neopentyl
protons.
which become
methylene
protons
anisochro*
give one
1986
Ilo.24
Figure
1
_:::_
- ._.~ Figure
2
No. 24
1987
strongly (figure passage
broadened 1).
signal above t 25°C
The barrier
(AG’=
13.8
and an AB spectrum
kcal/mol)
is mainly
of the t-butyl group past the 4-methyl group, 12, 13 . The barrier to passage of a t-butyl
is 15.3
, which reflects
kcal/mo19
due to the strain created
which is the smaller
substituents series
below this temperature
group past a methyl
the angle differences
in five-
on the
of the flanking in the benzene
and six-membered
rings. The conformation gement smaller
(formula
II),
since the ethyl CH3 will be more
group.
2-CS
of the ethyl group in Ib and Ic may be closer
Also
in this conformation
repelled
the methylene
to the parallel
by the 4-t.Bu protons
arran-
than by the
are diastereotopic,
21
and the ethyl N.M.R. rature to an ABX3 resonance
resonance spectrum
at - 61°C
changes
from a sharp triplet
at lower temperatures
changes the methylene
(figure
resonance
and quartet
2). Irradiation
to an AB spectrum.
at ambient tempeof the ethyl CH3 The coalescence
temperature is the same, - 13°C , with and without decoupling, and the barrier t (AC = 12.1 kcal/mol) is probably mainly due to the compression caused by the passage of the ethyl past the CS group. passage
However,
some contribution
of the ethyl CH2 past the I-t.Bu,
as evidenced
probably
also comes
by the buttressing
from the
effect of the 5-CH3
group (Table). TABLE
Compound
AzB
196
t25
13.8
121
-16
12.1
IC
111
-34
11.2
Id
140b
-122
6.9
The large
toluene-c18at 100 MHz
In toluene-d$freon
Id shows a qualitatively
because AuAB
protons with respect
kcal/mol
Ib
b Compounds
AC:=
Ia
“In
temperature
T “C
Ha
of the smaller value for
similar
behaviour
as Ib, though at much lower
4-substituent.
Ia indicates
to the strongly
at 100 MHz
rather
deshielding
different
CS group.
positions
of the methylene
The somewhat
smaller
shifts
for
Ib
and
Ic
are in agreement
CH2 proton more
removed
with the proposed
conformation
from the CS group than in Ia.
II, with the low-field
The large
the rate processes
to be studied over a wide range of temperatures,
bandshape
are in progress.
analysis
To our knowledge, rotation
this constitubes the first 2 of ethyl groups around sp -sp3 bonds.
We are grateful Swedish National
to
C.N.R.S.
Science
de France
Research
council
observation
(A.T.P.
shifts values and complete
by D.N.M.R.
Internationale
for financial
allow
of hindered
9111) and to the
support.
REFERENCES 1.
G.
BINSCH.
Topics
in stereochemistry, Chem.
2.
H. KESSLER, 1.0.
SUTHERLAND in E. MOONEY, “Annual Reports vol. 4. Academic Press, 1971, pp 71 ff.
4.
A.
MANNSCHRECK
5.
A.
RIECKER
and L.
Int. Ed.,
ERNST,
and H. KESSLER,
SIDDALL
and W.E.
K.C. J.F.
6c.
A.
7.
D .T. DIX. G: 517 (1966).
8.
A.J.
REWERS, Tetrahedron
9.
B.
NILSSON, P. MARTINSSON, z, 3190 (1974) and earlier
Ber..
Tetrahedron
228 (1971)
and earlier
Chem.,
35.
1019 (1970).
and M.S.
NIEUWSTAD.
and J.’ SANDSTRhM. NEWMAN,
F.J.
K. OLSON and R.E. papers.
Tetrahedron
RANTWIJK
CARTER,
The dihedral angle between the N-C-R plane and the ring plane is 90”. and M.T. TRIBBLE, Tetrahedron Lett.. 3259 (1971).
11.
One
CH bond eclipses the ring plane . R. J. OUELLETTE. LEVIN and S. WILLIAMS, J. amer. them. Sot.. z,
12.
C.
ROUSSEL, submitted
A. LIDEN. M. GHANON. to J. amer . them. Sac .
13.
Nitrogen inversion since an X-Ray attached atoms
J. METZGER
Lett.,
and H.VAN
J. amer.
10.
C.
papers.
1227 (1969).
J; METZGER
KARNES
A. SINNEMA, T.,J. , 27, 3713 (1971).
Spectroscopy”.
WHITEHURST, W.B. WISE, R. MUKHERJEE. Org. Magn. Resoname,A 767 (1971).
LIDEN, C. ROUSSEL, M. CI-IANON, Tetrehedron Lett., 3629 (1974). H.A.
on N.M.R.
1%
Let?..,
J. Org.
RAMEY, D.J., LOUICK. P.W. ROSEN and R.M. MORIARTY,
FRAENKEL,
219 (1970).
Ghem.
STEWART.
6b.
&
97 (1968).
3.
6a. TH.
Angew.
A
B.K. SINHA, 7145 (1970).
BEKKUM
them.
Sot.,
N. L. ALLINGER J. STOLFO.
and J. STANDSTRCM,
cannot be responsible for the observed temperature dependence, crystallographic investigation shows that the ring and directly lie in one plane (G. PEPE. to be published).
EVIDENCE N-ALKYL
go. 24, pp I985 - 1988,
1975.
FOR HINDERED ROTATION A4-THIAZOLINE-2-THIONES.
R .GALLOa,
A. LIDENb.
Pergaaon F+mss. printed in Great Britain.
OF ETHYL
GROUPS AROUND
J. SANDSTR6Mb
C .ROUSSELI.
sp2-sp3
and J. METZGER’
BONDS :
.
- Facult6 des Sciences de Saint-JkrameUniversit6 d’Aix-Marseille III aI.P.S.O.1. Rue Henri-Poincar6 - 13.397 - Marseille (Gdex 4) - France. b Division of Organic Chemistry - 1, Chemical Center - University of Lund - P.0.B.740. S-220 - Lund - 7, Sweden. (Received in UlI 18 April
Barriers
to rotation
1975; aooepted for publioation
I 34
of alhyl groups are of importance
1975)
to understand
1-3
. A number of cases of organic molecules 2 of alhyl groups about sp -sp3 bonds has been studied by D.N.M.R.
tions and reactivities
ture4-9,
but of alhyl groups of the type CH2R only neopentyl
We report here the dynamic the
A 4-thiaaoline-2-thione
I
a’
Ic, Models group in Ia arrangement pendicular
both conforma-
where hindered
rotation
are found in the litera-
groups have been dealt with7-?
behaviour
of neopentyl and ethyl groups in position 1 ring (I) as studied by H N.M.R.
R = t.Bu.
R4 = Me,
R5=H;
Ib. R = R3 = Me,
R4 = t.Bu
R = Me,
R4 = t.Bu.
R5=H;
Id. R = R4= Me.
R3 = H.
3 of
;
7-9 group indicate that this 10 shall have a nearly perpendicular arrangement , though in general a parallel 10.11 is assumed for the bensylic groups with at least one a-proton . The peras well as the known behaviour
arrangement
nous on slow rotation.
implies
diastereotopic
In agreement
of the neopentyl
methylene
with this the neopentyl
protons.
which become
methylene
protons
anisochro*
give one
1986
Ilo.24
Figure
1
_:::_
- ._.~ Figure
2
No. 24
1987
strongly (figure passage
broadened 1).
signal above t 25°C
The barrier
(AG’=
13.8
and an AB spectrum
kcal/mol)
is mainly
of the t-butyl group past the 4-methyl group, 12, 13 . The barrier to passage of a t-butyl
is 15.3
, which reflects
kcal/mo19
due to the strain created
which is the smaller
substituents series
below this temperature
group past a methyl
the angle differences
in five-
on the
of the flanking in the benzene
and six-membered
rings. The conformation gement smaller
(formula
II),
since the ethyl CH3 will be more
group.
2-CS
of the ethyl group in Ib and Ic may be closer
Also
in this conformation
repelled
the methylene
to the parallel
by the 4-t.Bu protons
arran-
than by the
are diastereotopic,
21
and the ethyl N.M.R. rature to an ABX3 resonance
resonance spectrum
at - 61°C
changes
from a sharp triplet
at lower temperatures
changes the methylene
(figure
resonance
and quartet
2). Irradiation
to an AB spectrum.
at ambient tempeof the ethyl CH3 The coalescence
temperature is the same, - 13°C , with and without decoupling, and the barrier t (AC = 12.1 kcal/mol) is probably mainly due to the compression caused by the passage of the ethyl past the CS group. passage
However,
some contribution
of the ethyl CH2 past the I-t.Bu,
as evidenced
probably
also comes
by the buttressing
from the
effect of the 5-CH3
group (Table). TABLE
Compound
AzB
196
t25
13.8
121
-16
12.1
IC
111
-34
11.2
Id
140b
-122
6.9
The large
toluene-c18at 100 MHz
In toluene-d$freon
Id shows a qualitatively
because AuAB
protons with respect
kcal/mol
Ib
b Compounds
AC:=
Ia
“In
temperature
T “C
Ha
of the smaller value for
similar
behaviour
as Ib, though at much lower
4-substituent.
Ia indicates
to the strongly
at 100 MHz
rather
deshielding
different
CS group.
positions
of the methylene
The somewhat
smaller
shifts
for
Ib
and
Ic
are in agreement
CH2 proton more
removed
with the proposed
conformation
from the CS group than in Ia.
II, with the low-field
The large
the rate processes
to be studied over a wide range of temperatures,
bandshape
are in progress.
analysis
To our knowledge, rotation
this constitubes the first 2 of ethyl groups around sp -sp3 bonds.
We are grateful Swedish National
to
C.N.R.S.
Science
de France
Research
council
observation
(A.T.P.
shifts values and complete
by D.N.M.R.
Internationale
for financial
allow
of hindered
9111) and to the
support.
REFERENCES 1.
G.
BINSCH.
Topics
in stereochemistry, Chem.
2.
H. KESSLER, 1.0.
SUTHERLAND in E. MOONEY, “Annual Reports vol. 4. Academic Press, 1971, pp 71 ff.
4.
A.
MANNSCHRECK
5.
A.
RIECKER
and L.
Int. Ed.,
ERNST,
and H. KESSLER,
SIDDALL
and W.E.
K.C. J.F.
6c.
A.
7.
D .T. DIX. G: 517 (1966).
8.
A.J.
REWERS, Tetrahedron
9.
B.
NILSSON, P. MARTINSSON, z, 3190 (1974) and earlier
Ber..
Tetrahedron
228 (1971)
and earlier
Chem.,
35.
1019 (1970).
and M.S.
NIEUWSTAD.
and J.’ SANDSTRhM. NEWMAN,
F.J.
K. OLSON and R.E. papers.
Tetrahedron
RANTWIJK
CARTER,
The dihedral angle between the N-C-R plane and the ring plane is 90”. and M.T. TRIBBLE, Tetrahedron Lett.. 3259 (1971).
11.
One
CH bond eclipses the ring plane . R. J. OUELLETTE. LEVIN and S. WILLIAMS, J. amer. them. Sot.. z,
12.
C.
ROUSSEL, submitted
A. LIDEN. M. GHANON. to J. amer . them. Sac .
13.
Nitrogen inversion since an X-Ray attached atoms
J. METZGER
Lett.,
and H.VAN
J. amer.
10.
C.
papers.
1227 (1969).
J; METZGER
KARNES
A. SINNEMA, T.,J. , 27, 3713 (1971).
Spectroscopy”.
WHITEHURST, W.B. WISE, R. MUKHERJEE. Org. Magn. Resoname,A 767 (1971).
LIDEN, C. ROUSSEL, M. CI-IANON, Tetrehedron Lett., 3629 (1974). H.A.
on N.M.R.
1%
Let?..,
J. Org.
RAMEY, D.J., LOUICK. P.W. ROSEN and R.M. MORIARTY,
FRAENKEL,
219 (1970).
Ghem.
STEWART.
6b.
&
97 (1968).
3.
6a. TH.
Angew.
A
B.K. SINHA, 7145 (1970).
BEKKUM
them.
Sot.,
N. L. ALLINGER J. STOLFO.
and J. STANDSTRCM,
cannot be responsible for the observed temperature dependence, crystallographic investigation shows that the ring and directly lie in one plane (G. PEPE. to be published).