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Inversion of Secondary Cyclic Grignard Compounds.

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Table 1. Substituted cycloheptatrienes from 2,4,6-cycloheptatriene-l-carbonitrile
( l ) ,b. p. 78-80112
was prepared from tropylium tetrafluoroborate [a].
torr, which
CPd. [a1
R
Preparation
B.p. ("Citorr)
12)
13)
14)
(5) PI
COOCH,
COOH
COCI
CON(CH,),
CONH(CH,),CI
HCI/CH,OH
CH,OH/H,O/NaHCO,/NaOH
as in ref. [8]
from ( 4 ) and HN(CH,),
from ( 4 ) and 2 mole aziridine
87/12
76/0.005
7411
93-95/0.001
m.p. 97°C
16) [cl
[a] All compounds gave correct elemental analyses.
[b] v C 0 = 1640cm-I.
[c] v C 0 = 1650cm-I.
are shifted 0.4 ppm upfield from those of ( 5 ) and ( 6 ) ,
and a comparison of the chemical shifts of (7) and (8)
Inversion of Secondary Cyclic Grignard
Compounds[**'
By Adalbert Muercker and Reinhurt Geuss[*]
Table 2. Chemical shifts (T values i n ppm).
( 5 ) [a1
161 P I
171 [c,d]
17) [cl
18) [he]
(8)P I
1 9 4 [91
(96) [9]
7.7 (t)
7.4 (1)
6.85 [f3
rfl
6.9 (t)
7.0 (t)
4.6 (9)
4.5 (4)
5.3
5.0 (t)
4.9 [fl
4.8 [fl
4.28
7.14
3.2 -4.0
3.2 -3.9
3.4 -3.8
3.15-3.7
3.25-3.8
3.1-3.7
30
30
30
- 45
30
- 42
[a] In CCI,. [b] In CDCI,. [c] in CD,C-N. [d] >N-CH,:
6.65 (d):
-0-CH,-CH,:
8.6(1); 5.4(q).[e] >N-H:
0; >N-CH,-:
5.9(t):
-0-CH,-:
4.95 (t). [f3 T values not accurately determinable.
with those of dimethyl 2,4,6-cycloheptatriene-l,l-dicarboxylate (9u) and dimethyl norcaradiene-7,7-dicarboxylate (9b)[91show that neither the cycloheptatrienes (7u)
and (8u) nor the norcaradienes (7b) and (8b) are present.
However, these values would be expected for the
equilibria (7u)=(7b) and ( 8 u ) e ( 8 b ) , the cycloheptatriene structure having the lower free energy in each
case. The temperature dependence of the 'H-NMR
spectra of ( 7 ) and ( 8 ) is also a strong indication of
dynamic equilibria.
Received: January 14,1971 [Z 360 IE]
German version: Angew. Chem. 83,289 (1971)
[l] Part of Diplomarbeit by W B e t z , Universitat Stuttgart 1970.
[2] For a review, see G. Maier, Angew. Chem. 79,446 (1967); Angew.
Chem. internat. Edit. 6, 402 (1967). R . Hofmann, Tetrahedron Lett.
1970, 2907: H. Giinther, ihid. 1970, 5173: and further literature cited
there.
[ 3 ] M . E. VoFpin, 1. S . Akhrem, and D. N. Kursanoc, Khim. Nauka i
Prom. 2, 656 (1957); Chem. Abstr. 52,4294 (1958).
[4] C.R. Ganellin and R . Pettit, J. Chem. SOC./958, 576.
[5] W c. E. Doering and D. W Wiley, Tetrahedron 11, 183 (1960).
[6] G . D. Sargenr, N. Lowry, and S . D. Reich, J. Amer. Chem. SOC.89,
5985 (1967).
[7] H . J . Dauben j r . , personal communication to G D. Sargent, cited
in [6].
[8] M . J. S. Dewar and R . Pettit, J. Chem. SOC.1956, 2021.
[9] J . A . Berson, D. R . Hartrer, H . Klinger, and P . W Grubb, J. Org.
Chem. 33, 1669 (1968): M . Gdrlitz and H . Gunrher, Tetrahedron 25,
4467 (1969).
270
Inversion at the a-carbon atom of primary Grignard
compounds can be detected by NMR spectroscopy[".
Particular attention has been devoted to 3,3-dimethylbutyl (neohexyl) Grignard compounds (RMgX) and the
corresponding dialkyl compounds (R2Mg)[la-'I, as well
as 2-methylbutylmagnesium compounds['d1. In contrast,
inversion has not yet been observed with secondary
Grignard compounds in spite of many efforts to detect
Neither the reason for the slow (NMR time scale)
inversion process of secondary carbanion centers nor the
mechanism of inversion is known; the latter has been
considered both as a bimolecular~'"~*dJ
and as a unimolecular ionization-recombination process"'].
It was noted in NMR studies on carbanion rearrangements of cyclic homoallyl Grignard compounds[31that
the peak due to the a proton of 3-cyclohexenylmagnesium
bromide ( I ) in THF, which lies in the TMS range as
expected, is remarkably broad and unresolved at room
temperature, whereas well resolved signals exhibiting
fine structure were obtained at lower and at higher temperatures (Fig. 1). The high temperature spectrum, which
65°C
lmg
L0"C
20°C
7°C
Fig. 1. Variation of the NMR signal (60 MHz) of the
( I ) with temperature; [D,]-THF solution, 1.5 mole/l.
-8°C
CL
proton of
does not show any change above 70°C (up to 110 "C),
differed from the low temperature spectrum, which did
not change below - 10 "C. The occurrence of coalescence
at 20°C can only be explained by an inversion at the
ct carbon atom, i.e. this is the first example of a secondary
Grignard compound whose ct inversion is fast enough
to be detectable by NMR spectroscopy. We assume that
the inductive effect of the double bond between C-3 and
C-4 enhances the electrophilicity of the magnesium, thus
increasing the ease of replacement of the group in an
SE2mechanism.
[*] Priv.-Doz. Dr. A. Maercker and DipLChem. R. Geuss
Institut fur Organische Chemie der Universitat Erlangen-Nurnberg
852 Erlangen, Henkestrasse 42 (Germany)
This work was supported by the Deutsche Forscbungsgemeinschaft and the Fonds der Chemischen Industrie.
[**I
A n g e w . C h e m . internat. E d i t . J Vol. I0 (1971) 1 No. 4
The spectrum of the 3-cyclopentenyl Grignard compound
(2) also supports this concept : The CL proton gives a clear
quintet at r=10.2 (J=IO Hz) in ether and in THF.
Thus, unlike the alcohol and the bromide, there is only
one coupling constant to all four neighbors. This again
suggests rapid inversion, although conclusive proof has
not yet been obtained because the Grignard compound (2)
is precipitated below - 20 “C before the coalescence temperature has been reachedc4]. However, it is quite reasonable to suppose that the five-membered ring Grignard
compound (2) should invert more rapidly than the sixmembered ring compound ( I ) , since in the former case
the -I effect of the double bonds can act from both sides
via only two single bonds. It is therefore understandable
that the coalescence point has still not been reached at
as low a temperature as -20°C. It is unlikely that
homoallyl resonance plays a very important role in
comparison with the inductive effects, particularly since
the anion of ( 2 ) , even if (T overlapping with the TC
electrons of the double bond were permitted by the
stereochemistry, would be a “bishomoantiaromatic” system[”. In this connection it is interesting to note that
primary, open-chain homoallyl Grignard compounds d o
not invert significantly more rapidly than the corresponding saturated compounds[61.
The inversion of the cyclic compound ( I ) , like that of
primary Grignard compounds, depends on the medium[‘,6].
It is particularly noteworthy that the rate of inversion is
lowered not only on going from diethyl ether to T H F but
also on changing to more dilute solutions. This observation
makes an ionization-recombination mechanism appear
unlikely for the inversion of these Grignard compounds.
Received: January 13, 1971 [Z 359 IE]
German version: Angew. Chem. 83, 288 (1971)
[l] a) G . M . Whitesides and J.D. Roberts, J. Amer. Chem. SOC.87,
4878 (1965); b) M . Witanowski and J.D. Roberts, ibid. 88, 737 (1966);
c) G.M . Whitesides, M . Witanowski, and J.D. Roberts, ibid. 87, 2854
(1965); d) G.Fraenkel and D. 7: Dix, ibid. 88, 979 (1966).
[2] a) N . G.Krieghoffand D.O. Cowan, J. Amer. Chem. SOC.88, 1322
(1966); b) F . R . Jensen and K . L . Nakamaye, ibid. 88, 3437 (1966);
c) E . Pechhold, Dissertation, Ohio State University, Columbus 1968.
[3] A . Maercker and R . Geuss, Angew. Chem. 82, 938 (1970); Angew.
Chem. internat. Edit. 9,909 (1970).
[4] The fact that the form of the quintet signal is independent of the
temperature (-19 to +94”C), of the solvent, of the concentration,
and of the addition of magnesium bromide (also at 100 MHz), and
does not change on going to the dialkylmagnesium compound, tends
to dismiss any likelihood of an accidental equality of the cis and trans
coupling constants.
[5] R . Breslow, R . Pagni, and W N . Washburn, Tetrahedron Lett. 1970,
547.
[6] A. Maercker and K . Weber, to be published
Electrophilic Alkylation of a-Diazosulfones with
Enamines
By A . M . van Leusen, B. A . Reith, R.J. Mulder, and
J. Strating“]
The course of reaction of diazo compounds with enamines
seems to be determined mainly by the type of diazo comAngew. Chem. internat. Edit. / Vol. I0 (1971) / No. 4
pound involved. During a study of the photolysis of
a-diazosulfones“] it was found that, without irradiation,
a-diazosulfones ( I ) add to enamines. Surprisingly, the
diazo group is not involved directly in this reaction,
since the adducts are a-alkylated-a-diazosulfones( 3 ) .
The alkylated diazosulfones (3) are obtained easily in
high yields, either by reaction of (I)[’] dissolved in an
excess of (2) (neat), or by reaction of equimolar quantities
of ( I ) and (2) in acetonitrile, for 2-5 days at room
temperature in the dark. After removal of the solvent the
residue is crystallized from methanol or ether/pet. ether.
R
R’
RZ
R’
X
p-Tolyl
p-Tolyl
p-Tolyl
p-Tolyl
C(CH,),
C,H5CHz
CH,
CH,
C6H5
H
CH,
CH,
CH,
CH,
H
H
CH,
CH,
H
H
H
C6H5
H
H
0
CH2
0
Yield
0;)
0
0
0
IR (cm- ‘)
M. P
(“ C)
VNEN
YO,
103-104
82- 83.5
109-111
86- 87
91- 92
84- 85
2067
2072
2060
2100
2072
2076
1330, 1155
1335, 1157
1308,ll SO, 1120
1330, 1155
1315, 1155
1318,1120
~
89
77
50
78
88
82
[a] NMR-Data (in CDCI,) of ( 3 a ) [typical for the compounds (3)]:
6(R)=2.43(3H/s), 7.73(2 H/d), 7.33(2H/d),J=8Hz;6(R1)=0.58(3H/d);
6(R2)=1.02(3H/d), J = 6 Hz; 6(H)= 1.1-2.3(1H/m); 6(R3)=2.95
(1 H/d), J = 11 Hz; G(morpho1ino) 2.39 (4 H/m), 3.63 (4 H/m).
As far as diazo compounds are concerned, this is one of
the very few examples in which an a-hydrogen becomes
substituted by an alkyl group[31. Moreover, the reaction
can be considered as a nucleophilic addition at the C, of
an enamine. Such reactions are common for iminium
salts, but not for the unprotonated enaminesr4I.
a-Diazoketones or a-diazoesters, bearing an a-hydrogen,
react differently with enamines. Through a 1,3-dipolar
cycloaddition involving the diazo function pyrazoles are
formed eventually[51.This difference may be explained as
follows: The ability of the methine proton to act as a donor
in hydrogen bonding presumably is larger in a-diazosulfones than in a-diazoketones[61. In the case of a-diazosulfones some iminium salt character may be induced in
the enamine through a hydrogen bond as indicated in
(4)L7]. Thus, nucleophilic attack of the diazo carbon at the
[*] Dr. A.M. van Leusen, Drs. B.A. Reith, and Prof. Dr. J. Strating
Department of Organic Chemistry
Groningen University, Zernikelaan, Groningen (The Netherlands)
Dr. R. J. Mulder, present address:
Koninklijke Zwavelzuurfabrieken v/h Ketjen N. V.,
Amsterdam (The Netherlands)
27 1
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