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Indications of Cesium in a Higher Oxidation State.

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values['81 (Fig. 1) shows that acceptor substituents retard
the ring closure to 3 and therefore the formation of 4. In the
absence of nucleophiles-for example, in chloroform solution-the allenyl azides polymerize. In the presence of tributyl(hexadecy1)phosphonium azide"'] in chloroform, 2d is
transformed into 2f, which rapidly rearranges to 7 (maximum proportion of 2f, 30 %).
\
-1.oj
I
0.0
"
"
I
"
'
.
0.5
I
1.o
6*Fig. 1. Plot of log(k/k,) versus Taft o*values for the reaction 2 + 4 in CD,OD
k, = k(2b) = 9 . 3 4 ~ O - ' S - ~ k(2c)
,
=
at 29°C; k(2a) = 2.81 x lO"sC',
2 . 5 3 x I O ~ ' s ~ ' , a n d k ( 2 d ) =1 . 1 3 ~ l O - ~ s ~ ' g i v =
e@
-0.87.
*
Our results confirm that allenyl azides are better stabilized
by acceptor substituents than by sterically demandingIZbl
alkyl substituents which act as donors. The title compounds
are of interest as potential precursors of the still unknown
methylene azirines.IZb.
Received: August 16, 1989 [Z 3503 IE]
German version: Angew. Chem. 101 (1989) 1710
CAS Registry numbers:
la, 14989-89-0,l b , 105643-77-4;Ic, 118724-01-9;Id, 119720-88-6;l e , 11872398-1 ; If, 91686-83-8; t a , 88596-79-6; 2b, 123625036; 2c, 123625-04-7; 2d,
123625-05-8;2e, 123625-06-9;Zf, 91686-85-0;3b, 123625-13-8;4a, 123625-092; 4b, 123625-10-5; 4c, 123625-11-6; 4d, 123625-12-7; 5, 123625-07-0; 6,
123625-08-1; 7,91686-86-1; TsOCH,C E CCH,, 56563-37-2.
[l] G . Smolinsky, C. A. Pryde in S . Patai (Ed.): The Chemistry ofthe Azido
Group, Wiley-Interscience, London 1971, pp. 555-585; G . L'abbk,
A. Hassner. Angew. Chem. 83 (1971) 103-109; Angew. Chem. in[. Ed.
Engl. 10 (1971) 9X-104; A. Hassner in E. F. V. Scriven (Ed.): Arides and
Nirrenes, Academic Press, Orlando (USA) 1984, pp. 35-94; E. F. V.
Scriven, K. Turnbull, Chem. Rev. 88 (1988) 297-368.
[2] a) V. J. Shiner, Jr., J. S. Humphrey, Jr., J. Am. Chem. Soc. 89 (1967) 622630; b) G. L'abbe, M. Mahy, M. Bollyn, G. Germaiu, G. Scheefer, BUN.
Soc. Chim. Belg. 92 (1983) 881 -891; G. L'abbe, ibrd. 93 (1984) 579-592,
c) A. Hassner, J. Keogh, J. Org. Chem. 51 (1986) 2767-2770.
[3] The 'H NMR signals mentioned in [2a] are not due, as suggested by the
authors, to l-azido-3-methyl-1,2-butadiene,but to 4-(l-azido-lmethylethyl)-1H-1,2,3-triazole; cf. 151.
[4] If the azide group and the allenyl system are separated by one carbon atom,
an isolable compound is obtained: K. Banert, Angew. Chem. 97 (1985)
231-232; Angew. Chem. Int. Ed. Engl. 24 (1985) 216-217.
[5] K. Banert, Chem. Ber. 122 (1989) 911 -918.
[6] Investigations of the reaction of triazafulvenes with nucleophiles (e.g.,
methanol): E. M. Burgess, J. P. Sanchez, J. Org. Chem. 38(1973) 176-178;
ihid. 39 (1974) 940-948.
1676
[7] K. Banert, Chem. Ber. I22 (1989), 1963-1967.
[El K. Banert, Chem. Ber. 122 (1989) 1175-1178.
[9] Caution should he exercised duringisolation of propargyl azides: a) M. G.
Baldwin, K. E. Johnson, J. A. Lovinger, C. 0. Parker, J. Polym. Sci. Part
B 5 (1967) 803-806; b) J. Almlof, G. 0 . Braathen, P. Klaeboe, C. J.
Nielsen, H. Priebe, S. H. Schei, J. Mol. Struct. 160 (1987) 1-26.
[lo] Azide 1b can be prepared from the tosylate [ l l ] of 2-butyn-1-01and sodium azide in aqueous methanol in 78% yield: see also C. J. Nielsen, H.
Priebe, R. Salzer, J. Mol. Struct. 162 (1987) 41 -56.
[11] A. Marszak-Fleury. Bull. Soc. Chim. Fr. 1958, 490-493.
[12] Pure I d (yield 77%) may be prepared by treatment of l e with thionyl
chloride in pyridine and ether.
[13] In [D,]methanol, slow H/D exchange of the alkyne proton further complicates the reaction 1 a + 2a + -B 4a.
[14] For formation of a tricyclic dimer from l a , see, H. Priehe, Acta Chem.
Scand. Ser. 5 3 8 (1984) 623-626.
[15] H. Priebe, Angew. Chem. 96 (1984) 728-729; Angew. Chem. Inl. Ed. Engl.
23 (1984) 736-737.
[I61 K. Banert, Chem. Ber. 120(1987) 1891-1896; Tetrahedron Lerr. 26 (1985)
5261 - 5264.
[17] All attempts to record Raman spectra have failed so far-presumably
owing to the low photostability of the title compounds.
[18] R. W.Taft, Jr., 1 Am. Chem. Soc. 75 (1953) 4231-4238.
[19] D. Landini, A. Maia, F. Montanari, J. Am. Chem. SOC.100 (1978) 27962801; Nouv. J. Chim. 3 (1979) 575-577; D. Landini. A. Maia, E Montanari, F. Rolla, .
I
Org. Chem. 48 (1983) 3774-3777; K. Banert, W. Kirmse,
J. Am. Chem. Soc. 104 (1982) 3766-3767; K. Bauert, Chem. Ber. 118
(1985) 1564-1574.
Q VCH YerlagsgeseNschafimbH, 0-6940 Weinheim, 1989
.
Indications of Cesium in a Higher Oxidation State **
By Klaus Moock and Konrad Seppelt *
The idea that alkali metals could exist in a higher oxidation state than 1 is older than the first demonstration of
noble gas compounds with oxidation states up to + 8. Earlier
reports on the preparation of KF, ,RbF, and CsF, J1, 21
however, proved to be completely false; the authors had
presumably mistaken KHF, RbClF,, and CsCIF, for these
corn pound^.[^.^^ R. Hoppe et al. estimated the enthalpy of
formation of CsF, to be about -85 kJ mol-1.15*61
Because
of the high lattice energy of CsF, the decomposition into CsF
and F, should be extremely exothermic (-445 kJ mol-I).
Although the lattice energy should remain nearly constant
on fluorination of Cs6SbF: to CsFFSbF:, all such attempts failed ~ompletely.~'~
Cocondensation of KF, RbF,
and CsF and fluorine in argon matrices affords compounds
whose IR spectra can be interpreted in terms of the presence
of FF ,I8] in complete analogy to the well known trihalides.
Thus, attempts to synthesize higher valence alkali-metal
compounds with fluorine have so far failed.
During cyclovoltammetric investigations on OTeF,-compounds r91we observed an electrochemical activity in the system Cs60TeFF/CH,CN in the extremely oxidative region at
ca. + 3 V (versus SCE). By painstakingly accurate tests we
were able to show that this oxidation, which is still irreversible at - 35 T , is dependent upon the cesium concentration but cannot be attributed to the solvent, theelectrolyte or
the anion OTeFF. Thus, K@OTeF$, RbOOTeFF, HOTeF,
and (nBu),N@OTeFF are inert in the oxidative region. The
findings are always reproducible, providing a vacuum-tight
electrochemical ceI1llol and extremely pure acetonitrile or
propionitrile are used.["] To support the assumption that
+
[*I Prof. Dr. K. Seppelt, Dr. K. Moock
Institut fur Anorganische und Analytische Chemie der Freien Universitat
Fabeckstra5e 34-36, D-1000 Berlin 33
[**I This work was supported by the Fonds der Chemischen Industrie. We
thank Dr. U . Zennerk, Universitdt Heidelberg, for recording the ESR
spectra.
o57~-0833~89j1212-1676
S 02.50JO
Angew. Chem. Int. Ed. Engl. 28 (1989) No. 12
Cs@is oxidized, we have also used cesium as CsePF: and in
the complexed forms as [Cse([18]crown-6)]PF: 1 and
[Cse(crypt.2.2.2)]PFf 2. The crown ethers/cryptands employed are obtainable in high purity, and they are "too
small" for Cse, so that a more stable complex is present after
the oxidation through ion contraction. In fact, the oxidation
takes place at a somewhat lower potential (+2.7 V in the
case of the cryptate versus 2 3.0 V in the case of Cs@PFF)
(Table 1). The decrease of ca. 0.3 V through the cryptands
+
Table 1. Electrochemical data of Cs"PF2, [Cs@([l8]crown-6)]PFP 1, and
[Cse(crypt.2.2.2)] PFF 2.
Cyclovoltammogram
(C.V.)
ED.IV1 IbI E,
T I"C1
Cs@PFF[d]
1 Idl
2 [d1
irrev.
irrev.
irrev.
2 f3.0
+3.0
+2.7
Alternating current
polarogram (ax.) [a1
Eiiz
E,iz [mvl Icl T W l
irrev.
irrev.
+2.6
-35
-35
-35
-
360
+ 20
+ 20
+ 20
[a] w = 1.3 KHz, AE = 10 mV. [b] All potentials are measured against FeCp,/
FeCpy as internal standard referred to SCE. [c] Half-widths of the curves.
[d] 0.1 mol L- ' in acetonitrile; supporting electrolyte Et,N@PFp, three-electrode system (platinum).
corresponds to a change of energy of 29 kJ mol-' and thus
has the order of magnitude of a typical chelate effect. Once
again it could be shown that the complex ligands, free or
together with K@ or Rb@, are not oxidized. In the most
favorable case of [Cse(crypt.2.2.2)]PFF 2 an oxidation could
even be detected by alternating current polarography
(Fig. 1).
I
C.V.
I
a.c.
exceed 2400 kJ mol-1.1121In the case of Css/Cs2@ this is
2046 kJ mol- I . From thermodynamic considerations and by
analogy, however, it follows that not Cs2@but at best Cs3@
should be stable. The gas reaction 2 C s 2 @ ~ C s 3+@Cs@
(856 kJ mol-') is exothermic and should not reverse, even
upon solvation, because of the same total charge. Hence, we
expect immediate further oxidation of Cs2@to Cs3@.It
would then also be understandable why ESR measurements
were unsuccessful in simultaneous electrochemical oxidations. (Cs2@with a nuclear spin 7/2 (100%) would be an
excellent ESR probe-providing a minimum concentration
of ca. lo-' mol L-' is achieved.) The isoelectronic system
Xe/XeF,, which is also irreversible, has a redox potential of
' ~ ]this respect the higher values
2.2 V in acid ~ o l u t i o n . ~In
found for C S @ / C S ~ @are
(~@
fully
) consistent with expectati~n.['~I
A major argument against the conclusions drawn from the
above findings is that an oxidation of the solvent, of the
electrolyte, or of the cryptand takes place only with Cs@
catalysis. We do not refute that such oxidations proceed as
secondary processes, but we cannot imagine a Cs@catalysis
without prior oxidation, because complex formation with
the positive center (here Cs@)usually stabilizes the complex
ligands against oxidation.
Although the isolation of a Cs3* species has still to be
reported, from the present results it would seem more feasible than was hitherto imagined. The use of cesium salts as
oxidation transfer reagents in electrochemical processes is
also conceivable.
Experimental
Electrochemical measurements: PAR 173 potentiostat, PAR 5208 lock-in-amplifier and PAR 175 programer, closed electrochemical cell [lo]. Purification of
acetonitrile as described in Ref. [ll]; preparation of OTeF, salts according to
Ref. [ 151.
[Cs@(crypt2.2.2)IPFp: 0.57 g (2.05 mmol) of CsPF, and 0.77 g (2.05 mmol) of
,IO-diazabicyclo[8.8.8]hexadried Kryptofix-2-2-2Im (4,7,13,16,21,24-hexaoxa-l
cosane) were each transferred in a glove box into separate limbs of a two-limbed
flask fitted with magnetic stirrers. 5 mL of acetonitrile were distilled under
vacuum into each limb. The two solutions were then united in the first limb of
the flask and stirred for 30 min at room temperature. After decantation of the
clear solution into the second limb of the flask the solvent was removed in a
vacuum. There remained a white crystalline solid in almost quantitative yield.
Correct elemantdl analysis. IR (Nujol): i [cm-'1 = 1296, 1259, 1234, 1170.
1102, 1074, 1065, 1051, 1018,945, 926,910, 873, 840 (v,PFf), 774, 746, 557
(v,PFF), 521, 507. Raman (solid): C [cm-'1 = 2971, 2956, 2919, 2902, 2874,
2841,2830,2807,1121,1075,837,819.745 (v, PFF), 564(vzPFF), 534,520.468
(v5PF?), 390, 333, 259, 169.
10pA 1pA
Received: April 20, 1989 [Z 3302 IE]
German version: Angew. Chem. 101 (1989) 1713
i
SCE
3
2
1
0
I
-1
-
-2
Potential I V I
Fig. 1. Cyclovoltammogram (cv) of Kryptofix-2.2.2a (A) and [Cs@(crypt.2.2.2)JPFF 2 (B), and alternating current polarogram (ac) of 2 (C).
H . Ahrens had already stated as long ago as 1956 that
oxidations by chemical methods are possible if the relevant
difference in ionization energy of the gas particle does not
Anxew. Chem. Jnt. Ed. Engl. 28 (1989) No. 12
0 VCH
[11 H. Bode, Nuturwissenschuf&n 37 (1950) 477.
[2] H. Bode, E. Klesper, Z . Anorg. Allg. Chem. 267 (1952) 97.
[3] L. B. Asprey, J. L. Margrave, M. E. Silverthorn, J. Am. Chem. Soc. 83
(1961) 2955.
[4] H. Bode, E. Klesper, Z . Anorg. A&. Chem. 313 (1961162) 161.
[5] R. Hoppe, Forrschr. Chem. Forsch. 5 (1965) 213.
161 R. Hoppe. H. Mattauch, M. Rodder, W. Dahme in H. H. Hymdn (Ed.):
Noble Gus Compounds, University of Chicago of Chicago Press 1963, S. 98.
[7] K. Seppelt, 1978, unpublished. The negative result of this experiment
merely shows that the higher valent cesium is no longer stable at the
high temperatures used. Under normal conditions the equilibrium
Cs@SbFF F, CsFySbFp should lie on the right-hand side if the average Cs-F bond energy is greater than 76 kJ mol-' (cf. average bond energy
in XeF, 136, in KrF, 51 kJ mot-').
[S] B. S. A&, L. Andrews, J. Am. Chrm. SOC.98 (1976) 1591; Inorg. Chem. 16
(1977) 2024 The reaction enthalpy F, + Fe FY has been calculated to
be -46.6 kJmol-I: R. A. Cahill, C. F. Dykstra, J. C . Martin, J. Am.
Chem. Soc. 107 (1985) 6359.
+
*
Verlugsgesellschaji mbH. 0-6940 Weinheim, 1989
+
0570-0833/89{l212-1677$02.50/0
1677
[9] K. Moock, K. Seppelt, 2. Anorg. A&. Chem. 561 (1988) 132.
[lo] G. M. Anderson, J. Iqbal, D. W. A. Sharp, J. M. Winfield, J. H. Cameron,
A. G. McLeod, J. Fluorine Chem. 24 (1984) 303; G. A. Heath, K. H.
Moock, D. W. A. Sharp, L. J. Yellowless, unpublished.
[ l l ] J. M. Winfield, .
I
Fluorine Chem. 25 (1984) 91.
[I21 H. Ahrens, J. Inorg. Nucl. Chem. 2 (1956) 290; Geochrm. Cosmorhim. Acta
2 (1952) 155; ibrd. 3 (1953) 1.
[13] B. Jaselskis, Science (Washmgron D C ) 146 (1964) 263.
[14] An accurate estimation of the redox potential Cse/Cs3@was not possible.
True, the ionization potentials and the salvation energy of&@ are known,
but Cs3' is presumably not spherical-shaped but disk-shaped with a radius
ratio of 1 :2. The solvation energy of a charged particle depends approximately on r - '. All desired redox potentials can be predicted when 60 5 T I .
ri 5 120 pm.
[15] S . H. Strauss, K . D. Abney, 0. P. Anderson, Inorg. Chem. 25 (1986) 2806;
F. Sladky, H. Kropshofer, 0. Leitzke, P. Peiger, J Inorg. Nucl. Chem.
Herbert H . Hyman Mem. Vol. 1976, 69.
The iron-complex 2 is readily accessible in four steps from
p-methoxyphenylacetic acid l.[61
Compound 2 is converted
by 0-functionalization (3) and hydride abstraction into the
complex salts 4. The spiroannelation with p-anisidine 5 leads
diastereoselectively to the spiro[l,2,3,4-tetrahydroquinoline4,1'-cyclohexaneJ derivative 6 a (Schema 1 ) . Cyclization to
OH
OH
1
2
OCH,
OCH,
I\,FelCOl,
Iron-Mediated Diastereoselective Spiroannelation
to the Spiro(l,2,3,4-tetrahydroquinoline-4,l'-cyclohexane] System and a Novel Rearrangement
to 2,3-Dihydroindole Derivatives **
By Hans-Joachim Knolker,* Rolaod Boese,
and Konrad Hartmann
The use of iron-diene complexes in the synthesis of heterocycles recently opened up a versatile entry to carbazole
derivatives."] We have now extended this concept to the
synthesis of other nitrogen-heterocycles. Cyclization, instead
of being carried out oxidatively, as hitherto, was now
achieved via nucleophilic substitution. This permitted closure of the C-C bond and the C-N bond in a one-pot reaction and thus the stereoselective synthesis of spirocycles.
The discorhabdins ['I and prianosins [31 recently isolated
from marine sources are distinguished by their high cytotoxic and antimicrobial activity. The discorhabdin D
described only recently[41also exhibits a strong antitumor
activity in vivo. A common feature of these compounds
'-cyclohexane] subis a spiro[ 1,2,3,4-tetrahydroquinoline-4,1
structure. We report here on an iron-mediated diastereoselective entry to this ring system.
The addition of nucleophiles to tricarbonyl(q5-l-aIkyl4-methoxycyclohexadienylium)iron cations enables the stereocontrolled synthesis of quaternary centers.I5' We have recently been able to show that iron-complexed cyclohexadienylium cations are very effective as mild electrophiles for
the reaction with highly substituted electron-rich and thus
oxidation-sensitive arylamines.[ll With the iron-complex
salts 4 we have now succeeded for the first time in using this
electrophilic substitution of aromatic systems for the
diastereoselective generation of quaternary carbon atoms.
Combination of this reaction with the subsequent in situ
nucleophilic substitution of the leaving group in the side
chain of 4 affords a new method for spiroannelation.
[*] Dr. H.-J. Knolker, DipLChem. K. Hartmann
[**I
Institut fur Organische Chemie der Universitat
Schneiderberg 1 B, D-3000 Hannover 1 (FRG)
Dr. R. Boese
Institut fur Anorganische Chemie der Universit5t-Gesamthochschule
Universitatsstrasse 5-7, D-4300 Essen 1 (FRG)
Transition-metal Diene Complexes in Organic Synthesis, Part 3. This work
was supported by the Volkswagen foundation and the Deutsche Forschungsgemeinschaft. We thank Dr. K Wruy, Gesellschaft fur Biotechnologische Forschung, Braunschweig-Stockheim fur the 13C and 2D-NMR
spectra and Dr. K.-H. Geiss, BASF AG, Ludwigshafen, for a supply of
pentacarbony1iron.-Part 2: [l b].
1618
0 VCH
krlagsgesellschafi mbH. 0-6940 Weinheim, 1989
4
6a
Scheme 1. DIBAH
= diisobutylaluminum
hydride, B = base
6a still takes place even with the methoxy derivative 4a. A
systematic optimization of the spiroannelation could be
achieved by varying the leaving group in the side-chain
(Table 1). In some cases (4a,c,d), owing to the stability of
Table 1. Variation of the leaving group R in the complex salt 4, and results of
the spirocyclization to 6a.
R
3, Yield
[%I
4, Yield [%]
~
CH3
CH,SO,
4-CH3(C6H,)S02
CH,CO
CF,CO
4-N02(C6H4)C0
~
4a, 69 (PF;) (61
4b, 77
4c, 27 (PF;)
4d, 74 (PF;) [6]
4e, 80
4f, 92
3a, 96 [6]
3b, 94
3c, 87
3d, 98 [6]
3e, 80
3f, 98
6a, Yield [%]
~~~~
20
53
54
68
53
80
the salt, the hexafluorophosphate had to be used. The route
via the p-nitrobenzoate derivatives 3f and 4f proved to be
the best over a11 three steps (2 3 --t 4 -+ 6 4 .
The structure of 6a follows from spectroscopic data ('H-,
I3C- and COSY-NMR spectra) and an X-ray structure analysis (Fig. l).['' The latter revealed that the aryl ring is anti to
the Fe(CO), group referred to the cyclohexadiene ring plane.
This can be explained by the stereodirecting effect of the
Fe(CO), group (anti selectivity). With the amines 5b-5e the
same diastereoselectivity is observed in the spiroannelation
as with 5a (Scheme 2, Table 2). The stereochemistry was established by comparison of the 'H- and 13C-NMR spectra of
6b-6e with those of 6a. In addition, the synthesis of 6d
clearly demonstrates that the reaction with 3,4-disubstituted
anilines is regiospecific.
0570-0833/89j1212-1678$02.50/0
--f
Angew. Chem. Int. Ed. Engl. 28 (1989) No. 12
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