close

Вход

Забыли?

вход по аккаунту

?

Geometry of the Transition State in Polar Cycloadditions.

код для вставкиСкачать
Sigiial C consists of nine lines ( U H = 1.7 gauss), which have
further structure at low power levels, the separation being
about 0.3 gauss (Fig. 2).
5G
Geometry of the Transition State in Polar
Cycloadditiondl] [**I
By Richard R . Schmidt and Rudolf Machatr*]
I
The specific cis-addition of amidomethylium ions ( / ) to
olefins 121 is a prerequisite for, but no proof of, a synchronous
process [31. Polar cycloadditions, however, may possibly
proceed in two steps, even though orbital symmetry considerations formally suggest a synchronous formation of the two
new 0 bonds. In order t o make a decision between these two
possibilities we have carried out investigations o n the geometry of the transition state.
I
81552:
Fig. 2. ESR spectrum "C", from pentaphenylphosphole with potassiu m in D M E a t 25 ' C . (High resolution.)
R'
The g-values of all three signals, measured with respect to
FrCmy's salt ( g = 2.0055) are g = 2.0027.
All three signals have been observed from each phosphole in
both D M E and T H F , in no particular sequence, although
signal C is usually the ultimate signal. We consider signal A
t o be identical t o that reported in references 11-31.
That these signals are associated with the phenyl group is
confirmed by the fact that no such signals are observed when
R I = alkyl. We consider that whichever radical is produced
initially, whether A, B, or C, this is a result of a radical polymerization of the cleaved phenyl group; this could occur via
a dehydrobenzene type of intermediate, which has already
been postulated for the reaction of benzene with alkali metal
in hexamethylphosphoric triamide 151. A high polymer is indicated by the large number of hyperfine lines. Since our
solvent drying procedure also involved the use of LiAlH4
(cf. (1-39, the reaction would seem t o be catalyzed by some
impurity derived from the use of this compound. We d o not
consider the initial radical to undergo further polymerization,
as this should change the g-values and the spin distributions.
In fact, the coupling constants of the major splittings remain
the same, and only the number of lines change (the largest
and smallest splittings are lost in Spectrum C). This could
arise from some form of rearrangement of the initial radical
t o one with a closely related structure.
The radicals are not the anions of the phospholes, as the
spectra of these show a large phosphorus doublet 161.
N o such radicals have been observed on reaction with N a or
Li, the former not cleaving the phosphole, the latter reacting
too slowly to give any observable radicals.
Received: November 29, 1969;
[Z 155 IE]
Revised: J a n u a r y 15, 1970
G e r m a n version: Angew. C h e m . 82. 325 (1970)
[ * ] Dr. C. Thomson and D. Kilcast [**I
Department of Chemistry, The University of St. Andrews,
St. Andrews, Fife (Scotland)
[**I We thank Dr. E. H . Braye (Union Carbide, Brussels) for
t h e phosphole samples and the Carnegie Trust for a maintenance grant to D.K.
[ l ] W. Kohnlein, K . W. Boddeker, and U . Scliindewolf, Angew.
Chem. 79, 318 (1967); Angew. Chem. internat. Edit. 6 , 360
(1967).
[2] K . W . Boddeker, G . Lung, and U. Schindewolf, Angew.
Chem.80,998 (1968); Angew.Chem. internat. Edit. 7,954(1968).
[3] P . Wormington and J . R . Bolton, Angew. Chem. 80, 997
(1968); Angew. Chem. internat. Edit. 7, 954 (1968); J . Kelm
and K . Mobius, ibid. 82, 45 (1970) and 9, 73 (1970).
[4] E. H. Braye, private communication.
[S] D . Dubois and C. Dodirz, Tetrahedron Letters, 1969, 2325.
161 D . Kilcast and C . Thomson, unpublished.
Angew. Chem. internat. Edit. / VoI. 9 (1970)
1 No. 4
H3
The reactions of (2) with olefins confirmed the regio- and
stereospecific cis-addition 121. Since R is chiral, the two diastereoisomeric oxazine derivatives (3) and (4)were obtained
in varying amounts f 5 l (see Table 1) as a result of asymmetric
induction 141.
Table I . Diasterromeric 2-(a-niethoxybenzy1)- 5,6- d i h y d r o - 4 H - I . 3 oxazines 13) a n d ( 4 ) synthesized from (2) a n d olefins.
I
R3
H
H
CH3
C2Hs
n-CIH,
H
H
Hb
1
R4
Ha
CH3
Ha
Ha
Ha
H
H
Ha
Yield
131
(4)
+
( %)
78
82
69
78
63
69
72
70
Ja.b
(Hz)
(3)/(4)
8.9
1.8
1.1
1.8
1.8
1.7
[a1
:1
:1
:1
:I
:1
1.4 : 1
-
9.2
8.4
8.0
-
7.9 [S]
1.6 : I
6.7 : I
[a] Determined by N M R spectroscopy.
The ratio of diastereoisomers ought t o depend upon the substituents of the olefin which are adjacent t o the chiral center
R. If the sizes of Rl and R 2 , and R3 and R 4 , are comparable
or equal, the geometry of the transition state can readily be
established. The ratio ( 3 a ) / ( 4 a )can be used as a reference in
the addition of styrene; the ratio ( 3 ) / ( 4 )in the adducts of the
styrene derivatives (b)-+(e) is influenced mainly by the
nature of R 2 and practically not by the nature of R1. In the
transition state of this reaction, therefore, R 2 is very much
nearer t o R than is RI.
This finding is consistent only with the transition state ( 5 )
previously discussed for synchronous cycloadditions 161 and
not with the typical transition state [71(6) for the primary electrophilic attack of (2)o n olefins, since the ratio R 1 - R i R 2 - R
(Rl = R 2 =: CH3) is 2.6 : 1 in the case of ( 5 ) and 1.1 : 1 in
31 1
the case of (6). The large increase in the ratio ( 3 ) / ( 4 )in the
series of cycloolefin derivatives (f)-(h) supports the cyclic
transition state ( 5 ) . This and the strong influence of the
methyl group in ( b ) provide evidence for the C-2 atom being
situated about two bond lengths distant from the asymmetric
C atom in R ; such is the case only in (5).
reaction (1) should also take place on a preparative scale in
a glow-discharge plasma. When compound (I) was fed as
vapor through a high-frequency glow discharge at reduced
pressure (zl torr), the main product formed was biphenylene (2) (see Table).
Experimental:
Yields o l biphenylene in a glow-discharge plasma; composition of reaction products formed from 9-fluorenone (in wt.-%) at various R F
energies.
A mixture of ( 2 ) (0.01 mole) and olefin (0.015 mole) in
glacial acetic acid (20ml) was treated with a solution of
conc. sulfuric acid (1.25 g) in glacial acetic acid (5 ml) (added
over a period of 5 minutes). After 4 hours the reaction mixture was added with stirring t o a mixture of 8 N NaOH
(100 ml) and chloroform (100 ml) at O°C. The chloroform
phase was separated off, dried over potash, and the compounds ( 3 ) and ( 4 ) isolated by distillation.
Received: February 10, 1970
[Z 157 BE]
German version: Angew. Chem. 82, 322 (1970)
["I
Doz. Dr. R. R. Schmidt and R. Machat
Institut fur Organische Chemie der Universitat
7 Stuttgart 1, Azenbergstrasse 14 (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft.
[ l ] Polar 1,4-Cycloaddttion, Part 8. - Part 7: R. R. Schnzidr,
Tetrahedron Letters 1969, 5279.
[2] R . R . Schmidt, Angew. Chem. $1, 576 (1969); Angew.
Chem. internat. Edit. 8, 602 (1969).
[3] This case is also considered in the other criteria used in the
mechanistic discussion of cycloadditions; cf. R. Gompper,
Angew. Chem. 81, 348 (1969); Angew. Chem. internat. Edit. 8,
312 (1969).
[4] J . Sauer, Angew. Chem. 79, 76 (1967); Angew. Chem.
internat. Edit. 6, 16 (1967).
[5] Racemization under the reaction conditions could be ruled
out by independent investigations with optically active substances; furthermore the reaction is irreversible.
[6] R. B. Woodward and R . Hoffmann, Angew. Chem. 81, 197
(1969); Angew. Chern. internat. Edit. 8, 781 (1969).
[71 G . Heubkin, 2. Chem. 9, 281 (1969).
[8] The exo-addition of (2) to norbornene can be deduced
from the NMR spectrum.
Single-Step Synthesis of Biphenylene from
9-Fluorenone in a Discharge Plasma
By Harald Suhr and Rudolf
I. Weiss I*]
Decarbonylations by electron impact are well known in mass
spectroscopy; thus, e.g., 9-fluorenone ( I ) , which is very
stable towards the action of light and heat, decomposes into
C O and a C12H8 fragment,
- p-q'
r
7+
Energy consumption
of enlitter (VA)
I 1 1
(I)
I
(2)
1
Naphthalene
I
Biphenyl
I
Polymer
1
30
41
60
90
10
8 2 5 1 7 5
93
0I
-
795205
01
01
01
01
01
-
16
08
14
80
1.8
When the vapor pressure of ( 1 ) is kept constant, the amount
of (2) in the condensed reaction mixture increases t o about
20 wt.-% on increasing the emission energy. A further
increase in energy results in decomposition of ( I ) and (2)
with formation of black, insoluble polymers.
Most of the compound ( 2 ) that is formed can be separated
from unreacted ( I ) by vacuum distillation and then purified
chromatographically. The reaction probably proceeds via
cleavage of CO from the molecular ion of ( I ) with subsequent
stabilization by electron capture (three-body collision o r wall
reaction) t o give (2).
A discharge apparatus having the oscillation coil of a pushpull LC oscillator (25-27 Hz) wound around it proved suitable for the experimentsr31. Both the chamber used for
vaporization of the fluorenone and the reaction tube were
double-walled and were thermostated at 130-131 O C by
recirculating oil. In each of the experiments, 10 g of compound ( I ) was passed through the reaction tube in a period
of 60--70 minutes; the reaction products were collected in a
cold trap at -78 "C. After gas chromatographic analysis of
the reaction products [FM 5750, 2 m, 20% silicone oil MS
710; 220°C; 3 7 m l Nz/min] the fraction distilling at temperatures up t o 120 "C (2 x 10-3 torr) was separated off for
identification and subsequent isolation of the biphenylene.
This was achieved by chromatographic separation with
petroleum ether on a n 80 cm A1203 column (Woelm, basic)
semisaturated with picric acid [41. After repeated recrystallization the biphenylene thus obtained had m.p. 110.9 t o
111.2OC. The UV spectrum agreed with that given in the
literature 151.
Received: January 7. 1970
[Z 159 IEI
German version: Angew. Chem. 82. 295 (1970)
['I Prof. Dr. H . Suhr and Dip1.-Chem. R . I. Weiss
Chemisches Institut der Universitat
74 Tubingen, Wilhelmstrasse 33 (Germany)
[ l ] J . H. Beynon, G. R . Lester, and A. E. Williams, J. physic.
Chem. 63, 1861 (1959).
[2] H. Suhr and R . I . Weiss, Z . Naturforsch. 256, 41 (1970).
[3] H . Suhr, Z. Naturforsch. 236, 1559 (1968).
[4] E. Miiller, H. Kessler, and H. Suhr, Tetrahedron Letters
1965, 423.
[S] H. Heaney, F. G . Mann, and I . T . Millar, I. chem. SOC.
(London) 1957, 3930.
- co
which has been formulated by Beynon et al. [I] as containing
a one-electron bond:
Hydrogen Bonds in a Ni-Ni System
By Klaus Jonas and Gunther Wilke [*I
Since the primary processes in mass spectroscopy and in
plasmas are very similar [21 - particularly at high electron
temperatures and low gas temperatures (cold plasmas) --
312
The NiO complex (LzNi)2Nz (L = (C6H11)3P)[11, in which
two nickel atoms are bound t o one nitrogen molecule can be
used as starting material for the preparation of hydridonickel complexes having the composition LzNiHX (where X,
for example, is CI, CH3CO0, C6H@ or CH3, C6H5)[2]. In
the following paper we report o n hydridonickel complexes,
Angew. Chem. internat. Edit.
1 Vol. 9 (1970) No. 4
Документ
Категория
Без категории
Просмотров
0
Размер файла
230 Кб
Теги
geometry, cycloadditions, state, transitional, pola
1/--страниц
Пожаловаться на содержимое документа