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Retention of configuration at SP2 carbon in bimolecular nucleophilic displacement of halide ion from hydrazonyl halides
TetrahedronLetters No. 5, pp 395 - 396, 1976.
RETENTION
OF CONFIGURATION DISPLACEMENT
AT SP' CARBON
OF HALIDE
Department,
Rinted in Greet Britain.
IN BIMOLECULAR
ION FROM HYDRAZONYL
M.T. McCormack Chemistry
Perguon Rces.
NUCLEOPHILIC
HALIDES
and A.F. Hegarty*
University
College,
Cork,
Ireland
(Bccrircdin UIC5 Deeember 1975; accepted for publiartier22 Detembor 1975) Stereoselective carbon in vinyl One example
nucleophilic
systems proceed
substitution
generally
of a stereospecific
with retention
bimolecular
an imino carbon has been reported
nucleophilic
by Johnson, Nally
at spz hybridised of configurat.lon.' displacement
ion as nucleophile,
converted
to methyl-(Z)-0-methylbenzhydroximate
This result cannot be general,
chloride
with inversion
however,
wa$:
of confiigur-
since we now report a bl-
C=NIN/Me
Ar
R
\
at
usir;g
and Weidiy;'
(El-0-methylbenzoh$&oximoyl
methoxide ation.
reactions
Ar
3
Me
2,4-(NOz)?CsHs
a
t-Bu
b
Ph
2,4-(NO21 :
C
Ph
p-NOsCsHr
d
Ph
Ph
Me0 \ C = NAN:Ar
-+.Meo'C R'
R'
= N
Me 'N' \Ar
molecular
nucleophilic
proceeds with retention Hydrazonyl 2
substitution
at the carbcn-nitrogen
halides may exist in two geometrically
We have found that the halide or treatment
exclusively unequivocally
(Z)-isomers confirmed
which
of configuration.
(X = Cl or Br), which do not rapidly
hydrazone
double bond
interconvert
formed either
of the hydrazides (2).
on bromination
with phosphorous
This is consistent
in one instance
isomerlc
at ambient
of the corresponding pentachloride
with nrnr evidence'
(la, X = Br) by x-ray /v
analysis.
395
forms &or temperatures.3
are
and was
crystallographic
No. 5
396
When treated with methoxide is bimolecular)
the
(Z)-methyl hydrazonates arises that the observed controlled However,
ion (under conditions
(2) isomers J
but merely
2 uncontaminated formation
represents
where
the reaction
(X = Cl or Br) gave exclusively by the isomers
of the (Z) isomers
formation
4.
is-not kinetically
of the more stable product.
this does not appear to be the case since at elevated
undergoes
thermal
isomerisation
(Table) generally
to ,4+and the ratios
favour the E isomer
ation of the starting
4.
of 2 to2
Methoxide
temperature 3 N at equilibrium
ion catalysed
isomeris-
halide ,& or of the hydrazonate 2 was also: investigated
and shown to be insignificant
under the reaction
conditions.
Z/E ISOMER RATIOS AT EQUILIBRIUM
TABLE:
the
The possibility
IN CHLORCBENZENE
Hydrazonates:
3a:4a
3b:4b
3c:4c
3d: 4d
Isomer Ratios:
80:20
22:78
43:57
20280
H
Cl
-HCl . /
C=N R/
Meo\~~
=NyR1
R'
R SCHEME It is difficult
related hydroxamoyl stereochemical
course.
the imino nitrogen proton
transfer)
transition undergo
to rationalise and hydrazonyl
state
A possible
(Scheme);
displacements
in the
should take such a different
factor might be the greater basicity
This would
in2.
to the nitrogen
anti-elimination
why bimolecular systems
promote hydrogen
bonding
lone pair by the solvent
the tetrahedral
of HCl without
intermediate
of
(and thus
at this site in the then formed could
further C-N bond rotation
or nitrogen
inversion. REFERENCES 1.
G. Mcdena, Ace. Chem. Res., 4, 73 (1971); T.C. Clarke, B.H. Kelsey and R.G. Bergman, J. Amer. Chem.=Soc., 94, 3626 (1972); R.H. Summerville and P.v.R. Schleyer, ibid., 94, 3629 (1972).
2.
J.E. Johnson, (1973).
E.A. Nally
and C. Weidig, J.
Amer.
Chem.
3,' C.G. McCarty in "The Chemistry of the Carbon-Nitrogen Patai, Ed., Wiley, New York, N.Y. 1970. 4.
Sot.,
95,
2051
Doub:!e Bond", S.
The configurational assignments were based on the positions of the chemical shifts of the N-Me protons in >, 2 and 4 and the O-methyl protons in_3 and A (see: G.R. Newkome and W.S. Bhacca, J. Org. Chem., 36, 1719 (1971); J.E. Johnson, J.R. Springfield, J.S. Hwang, L.J. Hayes, W.Cf Cunningham and D.L. McClaugherty, J. Org. C&m,, 36, 284 (1971).
RETENTION
OF CONFIGURATION DISPLACEMENT
AT SP' CARBON
OF HALIDE
Department,
Rinted in Greet Britain.
IN BIMOLECULAR
ION FROM HYDRAZONYL
M.T. McCormack Chemistry
Perguon Rces.
NUCLEOPHILIC
HALIDES
and A.F. Hegarty*
University
College,
Cork,
Ireland
(Bccrircdin UIC5 Deeember 1975; accepted for publiartier22 Detembor 1975) Stereoselective carbon in vinyl One example
nucleophilic
systems proceed
substitution
generally
of a stereospecific
with retention
bimolecular
an imino carbon has been reported
nucleophilic
by Johnson, Nally
at spz hybridised of configurat.lon.' displacement
ion as nucleophile,
converted
to methyl-(Z)-0-methylbenzhydroximate
This result cannot be general,
chloride
with inversion
however,
wa$:
of confiigur-
since we now report a bl-
C=NIN/Me
Ar
R
\
at
usir;g
and Weidiy;'
(El-0-methylbenzoh$&oximoyl
methoxide ation.
reactions
Ar
3
Me
2,4-(NOz)?CsHs
a
t-Bu
b
Ph
2,4-(NO21 :
C
Ph
p-NOsCsHr
d
Ph
Ph
Me0 \ C = NAN:Ar
-+.Meo'C R'
R'
= N
Me 'N' \Ar
molecular
nucleophilic
proceeds with retention Hydrazonyl 2
substitution
at the carbcn-nitrogen
halides may exist in two geometrically
We have found that the halide or treatment
exclusively unequivocally
(Z)-isomers confirmed
which
of configuration.
(X = Cl or Br), which do not rapidly
hydrazone
double bond
interconvert
formed either
of the hydrazides (2).
on bromination
with phosphorous
This is consistent
in one instance
isomerlc
at ambient
of the corresponding pentachloride
with nrnr evidence'
(la, X = Br) by x-ray /v
analysis.
395
forms &or temperatures.3
are
and was
crystallographic
No. 5
396
When treated with methoxide is bimolecular)
the
(Z)-methyl hydrazonates arises that the observed controlled However,
ion (under conditions
(2) isomers J
but merely
2 uncontaminated formation
represents
where
the reaction
(X = Cl or Br) gave exclusively by the isomers
of the (Z) isomers
formation
4.
is-not kinetically
of the more stable product.
this does not appear to be the case since at elevated
undergoes
thermal
isomerisation
(Table) generally
to ,4+and the ratios
favour the E isomer
ation of the starting
4.
of 2 to2
Methoxide
temperature 3 N at equilibrium
ion catalysed
isomeris-
halide ,& or of the hydrazonate 2 was also: investigated
and shown to be insignificant
under the reaction
conditions.
Z/E ISOMER RATIOS AT EQUILIBRIUM
TABLE:
the
The possibility
IN CHLORCBENZENE
Hydrazonates:
3a:4a
3b:4b
3c:4c
3d: 4d
Isomer Ratios:
80:20
22:78
43:57
20280
H
Cl
-HCl . /
C=N R/
Meo\~~
=NyR1
R'
R SCHEME It is difficult
related hydroxamoyl stereochemical
course.
the imino nitrogen proton
transfer)
transition undergo
to rationalise and hydrazonyl
state
A possible
(Scheme);
displacements
in the
should take such a different
factor might be the greater basicity
This would
in2.
to the nitrogen
anti-elimination
why bimolecular systems
promote hydrogen
bonding
lone pair by the solvent
the tetrahedral
of HCl without
intermediate
of
(and thus
at this site in the then formed could
further C-N bond rotation
or nitrogen
inversion. REFERENCES 1.
G. Mcdena, Ace. Chem. Res., 4, 73 (1971); T.C. Clarke, B.H. Kelsey and R.G. Bergman, J. Amer. Chem.=Soc., 94, 3626 (1972); R.H. Summerville and P.v.R. Schleyer, ibid., 94, 3629 (1972).
2.
J.E. Johnson, (1973).
E.A. Nally
and C. Weidig, J.
Amer.
Chem.
3,' C.G. McCarty in "The Chemistry of the Carbon-Nitrogen Patai, Ed., Wiley, New York, N.Y. 1970. 4.
Sot.,
95,
2051
Doub:!e Bond", S.
The configurational assignments were based on the positions of the chemical shifts of the N-Me protons in >, 2 and 4 and the O-methyl protons in_3 and A (see: G.R. Newkome and W.S. Bhacca, J. Org. Chem., 36, 1719 (1971); J.E. Johnson, J.R. Springfield, J.S. Hwang, L.J. Hayes, W.Cf Cunningham and D.L. McClaugherty, J. Org. C&m,, 36, 284 (1971).