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CO2 Elimination from Vinylene Carbonate Radical Anions and Charge Reversal in C2H2O Reactions Involving the Radical Anion and Cation of Oxirene.

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The Mn-0-Mn bond angle (120.7') is considerably
smaller than that measured for (amorphous?) Mn207
fiims.[61However, it is possible that the two findings are
not in contradiction. In the crystal, the small angle leads to
the intramolecular formation of a nido-octahedral arrangement for the bridging and the four terminal 0 atoms (cf.
Fig. 2b), which is augmented to form an octahedron by a
further 0 atom from a n adjacent molecule.
This indicates that the Mn,O, molecules are packed in a
way to yield a close-packed arrangement of all 0 atoms.
Indeed, the Mn,O, structure can be described in terms of
an fcc lattice of the 0 atoms; the actual positions of the 0
atoms deviate, on the average, by 2 4 f 5 pm (contraction of
the neighboring tetrahedral voids occupied by Mn) from
the ideal lattice positions. The formation of a close-packed
structure explains the unusual increase in the density of
Mn,O, upon crystallization.
Comparison of the crystal structures of Mn207,Tc207,
and Re20, reveals interesting similarities and differences:
In T C , O ~ , ( 'discrete
M2O7 molecules with tetrahedrally
surrounded M atoms also occur, but the M-0-M angle is
180". The molar volume of Tc207(86.5 cm3 mol-') is considerably larger than that of M n 2 0 7 (79cm3 mol-'). In
contrast, for the three-dimensional network of Re207,1''1
with tetrahedrally and octahedrally surrounded Re atoms,
a molar volume of 78 cm3 mol-' is found, which is close to
that of Mn207. This comparison shows that Tc20, occupies a special position in the series of compounds, indicating, for example, that transformations under pressure
might take place.
C 0 2 Elimination from Vinylene Carbonate Radical
Anions and Charge Reversal in C,H,O
Reactions Involving the Radical Anion and Cation
of Oxirene?**
By Ben L. M . van Baar, Nikolaus Heinrich,
Worfram Koch, Ron Postma, Johan K . Terlouw, and
Helmut Schwarz*
Vinylene carbonate 1 reacts with low-energy electrons in
the gas phase to give, via elimination of COz, a metastable
radical anion C 2 H 2 0 0 Q ,which loses an electron to form
C2H20."' It has not been possible so far to elucidate the
structures of the intermediate radical anions or of the neutral molecules of empirical formula C 2 H 2 0 (2a-5a and
2b-5b, respectively). This is not surprising in view of the
confusing chemistry of this small specie^.[^,^]
We report here on gas-phase experiments, supplemented
by extensive ab initio MO calculations, that show that
- c02
Experimental Procedure
K M n 0 4 (ca. 50 mg) was treated with HzS04 (+20% SO,). After a short period of time, M n 2 0 7 separated out as a dark, oily ring around the reaction
mixture and was sucked into a carefully cleaned capillary (0.2-mm 0.20-mm
continuous column of liquid). The (open) capillary was cooled immediately
with liquid N2 in order to prevent interruptions of the column of material by
the formation of O 2 bubbles, and it was then mounted at - 10°C on a fourcircle diffractometer. Suitable crystals, which were nearly aligned along [OOI]
in the direction of the axis of the tube, were obtained in a temperature gradient of - 10/ 20°C [7] and improved by variation of the temperature between ca. 0 and 5"C, continuously monitoring via X-ray diffraction.
Received: October 30, 1986;
revised: November 12, 1986 [Z 1974 IE]
German version: Angew. Chem. 99 (1987) 160
[I] H. Aschoff, Ann. Phys. Chem. Ser. 2 111 (1860) 217, 224.
[2] 0. Glemser, H. Schroder, Z. Anorg. Allg. Chem. 271 (1953) 293.
[3] A. Simon, F. Feher, Z. Elektrochem. Angew. Phys. Chem. 38 (1932)
[4] B. Krebs, Z. Anorg. Allg. Chem. 380 (1971) 146.
[5] M. Tromel, Acra Crysiallogr. Seer. 8 3 9 (1983) 664; the bond lengthbond strength relationship was derived from structure data, which were
not corrected for errors in the distance (bond shortening) due to vibrations of the atoms. The corresponding, uncorrected distances in M n 2 0 7
are d(Mn-0)= 176.2(3), 157.5(3), and 2 x 158.8(3) pm for the MnO, tetrahedra.
[6] W. Levason, J. S . Ogden, J . W. Turff, J. Chem. Soc. Dalion Trans. 1983,
[7] A. Simon, H.-J. Deiseroth, E. Westerbeck, B. Hillenkotter, Z. Anorg.
Allg. Chem. 423 (1976) 203.
[8] Space group P2,/c (No. 14); Z = 8 , a=679.56(4), b=1668.68(16),
c=945.39(29) pm, p= 100.20( 1)' (from modified Guinier-diffractograms
191 at -30°C); 3325 reflections, 2310 with F , , 2 3 0 ( F 0 ) (CAD4 diffractometer, -30°C); structure solved by direct methods in Pc, refinement
in P 2 , / c (SHELXTL); R,,,,,=0.043, R,=0.039, R's0.065. Further details of the crystal structure investigation may be obtained from the
Fachinformationszentrurn Energie, Physik, Mathematik grnbH, D-75 14
Eggenstein-Leopoldshafen2 (FRG), o n quoting the depository number
CSD-52 169, the names of the authors, and the journal citation.
[9] A. Simon, J. Appl. Crystallogr. 3 (1970) 1 I ; ibid. 4 (1971) 138.
[lo] B. Krebs, Z. Anorg. Allg. Chem. 380 (1971) 146.
[l I] B. Krebs, A. Miiller, H. H. Beyer, Inorg. Chem. 8 (1969) 436.
[I21 R. X. Fischer, J. Appl. Crysrallogr. 18 (1985) 258.
0 VCH Verlagsgesellschaji mbH. 0-6940 Weinheim, 1987
..-c Yo
[*] Prof. Dr. H. Schwarz, N. Heinrich, Dr. W. Koch
Institut fur Organische Chemie der Technischen Universitat
Strasse des 17. Juni 135, D-I000 Berlin 12
B. L. M. van Baar, R. Postma, Dr. J. K. Terlouw
Laboratory for Analytical Chemistry, Utrecht University
Croesestraat 77 A, NL-3522 A D Utrecht (Netherlands)
This work was supported by the Fonds der Chemischen Industrie, the
Deutsche Forschungsgemeinschaft, and the Gesellschaft von Freunden
der Technischen Universitat Berlin.
0570-0833/87/0202-0140 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 26 (1987) No. 2
elimination of C 0 2 from l a oresults in the formation of
3a, the radical anion of the ketocarbene 3b. Spontaneous
loss of an electron from the metastable 3a affords the ketene 5b. Charge reversal[41via collision-induced 2-electron
loss from 3a results mainly in formation of the ketocarbene radical cation 3c. Depending on its internal energy, it
undergoes decomposition o r isomerization to the longsought and theoretically predicted['] oxirene radical cation
Electron attachment to 1 in a ZAB-2F mass spectrometer results in loss of C 0 2 and formation of C2H,00Q ions,
which were mass-selected by employing tandem mass
spectrometry (MSMS).16] The collisional activation (CA)"]
spectra were then recorded. The CA spectrum of C 2 H 2 0 a e
formed by spontaneous loss of an electron from C2H20"",
followed by collisional reionization mass spectrometry,l8]is
identical in all respects with the C A spectrum of 5c produced from 5b.I9' This indicates that spontaneous electron
loss from C z H 2 0 0 Qleads to 5b. However, the following
experiment and a b initio results (described below) strongly suggest that C 2 H 2 0 0 0is not present as 5a but rather as
3a. If charge reversal is allowed to take place in a collision
experiment of the C 2 H 2 0 0 0 ions (vertical removal of two
electrons), the C A spectrum shown in Figure 1 is obtained.
This spectrum cannot be simulated by a linear combination of the C A spectra of 5c and 4c. In contrast, more detailed comparison with the C A spectra of these ions['] indicates that only a few percent of 4c and 5c are formed upon
generation of "reactive" C 2 H 2 0 0 0 ions from C 2 H 2 0 a e .
On the basis of the spectrum, therefore, the intermediacy
of at least one, previously unknown, C 2 H 2 0 0 e species is
suggested. We propose formation of 3c, the radical cation
of ketocarbene 3b, the most important ionic fragmentation
products of which are the ion at m/z 29 (HCOe), produced
by loss of C H , and that at m/z 26 (C2HYe), produced by
deoxygenation. m / z 41 corresponds presumably to the ion
H-C=C=O, which can also arise directly from 3c.
According to a b initio calculations,[513c is not stable.
The radical cation undergoes decomposition (see preced-
Fig. I. CA spectrum of C2H2Oo0ions generated by charge reversal from
ing paragraph) o r isomerizes to 2c (via ring closure) and 4c
or 5c (via H migration). The reaction 3c-4c is unlikely
for energetic reasons.[51 The spontaneous process 3c 5c
should, on account of the large enthalpy of formation of
3c,"I yield highly excited 5c, which, in turn, should decompose spontaneously into C O and CH:@. Indeed, we
believe that the signal at m / z 14 (Fig. 1) may originate
from the reaction 3c-+5c+CHFe + CO. However, what is
the explanation for the observation that the vertical removal of two electrons from 3a does not only lead to fragments but also to a stable ion at m/z 42 (C2H200@),
has a lifetime t >
s? The only possible explanation is
that the radical cation 3c, generated with only a small
amount of excess energy, undergoes isomerization to 2c,
the radical cation of oxirene 2b. 2c is theoretically predicted"] to reside in a sufficiently deep potential well so
that fragmentation processes are not favored.
Fig. 2. Schematic potential hypersurface for species of empirical formula C2H2000 (-)
and C 2 H 2 0(-----). The calculations were
carried out at the MP3/6-311+ +G(d,p)//6-31 +G(d) level. p= reaction coordinate; A, B = transition states; relative energies in
Angew. Chem. Int. Ed. Engl. 26 (1987) No. 2
0 VCH Verlugsgesellschufl mbH. 0-6940 Weinheim. 1987
Let us return to the initially posed question as to the
structure of the CzHzOoo ions. Supplementing and supporting the results of the experiments, a b initio calculations (performed at the MP3/6-311+ +G(d,p)//63 1 + G(d) level) yielded the following results:""] 3a (and
several of its conformers), like the bent form of 5a,["I exist
in potential minima (Fig. 2). 3a is about 27.5 kcal/mol less
stable than 5a ; the barrier for the isomerization 3a- 5a is
30.6 kcal/mol. Positive electron affinities are predicted for
both species. The experimental observation that electron
loss nonetheless occurs from 3a must be due to the fact
that 3a is generated with excess energy upon electron attachment to vinylene carbonate 1. If this amount of energy
is large enough to overcome a barrier of about 30 kcal/mol
(or less, if tunnel effects play a role), then the reaction
3a B- 5a"c A results necessarily in electron loss to form
ketene 5 b ; the latter is identified in the experiment.
The radical anion of oxirene, 2a, plays no role in the
chemistry of the C2H20"' species. 2a, which is about
100 kcal/mol less stable than 3a, corresponds, moreover,
to a saddle point of second order (two imaginary frequencies).
Received: November 4, 1986:
revised: November 25, 1986 [Z 1980 IE]
German version: Angew. Chem. 99 (1987) 153
[ I ] R. N. Compton, P. W. Reinhardt, H. C. Schweinler, Int. J. Mass Spectrom. Ion Phys. 49 (1983) 113.
[2] Further discussions of C2H20 and, in particular, of oxirene: a ) G.
Maier, H. P. Reisenauer, T. Sayraq, Chem. Ber. 115 (1982) 2192; b) W. J.
Bouma, R. H. Nobes, L. Radom, C. E. Woodward, J. Org. Chem. 47
(1982) 1869: c) E. G. Lewars, Chem. Rev. 83 (1983) 519.
131 To the best of our knowledge, neither theoretical nor other experimental
results are available for the C2H2Oo0 species.
141 J. L. Holmes, Org. Mass Specrrom. 20 (1985) 169.
[5] W. J. Bouma, P. M. W. Gill, L. Radom, Org. Mass Spectrom. 19 (1984)
[6] F. W. McLafferty (Ed.): Tandem Mass Spectrometry, Wiley, New York
[7j Review: K. Levsen, H. Schwarz, Mass Spectrom. Reu. 2 (1983) 77.
181 Selected references: a) P. 0. Danis, D. Wesdemiotis, F. W. McLafferty,
J. Am. Chem. Soc. 10s (1983) 7454: b) P. C . Burgers, J. L. Holmes, A. A.
Mommers, J . K. Terlouw, Chem. Phys. Lett. 102 (1983) 1.
[9] The CA spectra of 4c and 5c are found in B. van Baar, T. Weiske, J. K.
Terlouw, H. Schwarz, Angew. Chem. 98 (1986) 275; Angew. Chem. Int.
Ed. Engl. 25 (1986) 282.
[lo] The notation MP3/6-311+ +G(d,p)//6-31 +G(d) means that the calculation of individual points for the geometries optimized at a 6-31 +G(d)
level [ I l a j was carried out with the 6-311 + +G(d,p) basis set [Ilc],
which is more than sufficient for anions. The effects of electron correlation were taken into consideration by perturbation calculations (according to Mdler-Plesset [lld,e]) up to third order (MP3). The extended
(+) basis sets are described in [llfl. Minima and maxima were unequivocally located by an analysis of the force-constant matrix. Complete
data for geometries and energies of the structures reported here (and
their conformers) are available on request.
[I I ] a) P. C . Hariharan, J. A. Pople, 7'heor. Chim. Acta 28 (1973) 213; b) J.
Chandrasekhar, J. G. Andrade, P. von R. Schleyer, J. Am. Chem. Soc.
103 (1981) 5609, 5612: E. R. Davidson, D. Feller, Chem. Reu. 86 (1986)
681: R. H. Nobes, D. Poppinger, W.-K. Li, L. Radom in E. Buncel, T.
Durst (Eds.): Comprehensive Carbanion Chemistry. Part C, Elsevier, Amsterdam 1987: c) R. Krishnan, J . S. Binkley, R. Seeger, J. A. Pople, J.
Chem. Phys. 72 (1980) 650: d) C. Meller, M. S. Plesset, Phys. Reu 46
(1934) 618: e) R. Krishnan, M. J. Frisch, J. A. Pople, J. Chem. Phys. 72
(1980) 4244: f) T. Clark, J. Chandrasekhar, G. W. Spitmagel, P. von R.
Schleyer, J. Comput. Chem. 4 (1983) 294.
[I21 The fact that ketene has a negative electron affinity [Prof. E. lllenberger
(Berlin), Prof. N. M. M. Nibbering (Amsterdam), private communication] does not contradict the a b initio results. Vertical electron attachment to Sb yields the transition state A, corresponding to the topomerization of 5a. I n the process A - 5 a crossing with the hypersurface of the
neutral C 2 H 2 0 molecule (broken line in Fig. 2) occurs: this results in
spontaneous electron loss with re-formation of 5b.
0 V C H Yerlagsgeseil.$chaffmbH. 0-6940 Weinheim, 1987
Stereoselective Alkylation of Aromatic Compounds
with Threonine Trifluoromethanesulfonates""
By Franz Effenberger* and Thomas Weber
Dedicated to Professor Rudolf Gompper
on the occasion of his 60th birthday
Alkyl trifluoromethanesulfonates (alkyl triflates) have
only been used in special cases for the alkylation of aromatic compounds."] We have now succeeded in synthesizing the N-protected triflates of ( S ) - and (R)-serine methyl
ester as well as the N-protected triflates 1 of all diastereomeric threonine methyl esters in very good yields and
with complete retention of configuration. This was accomplished by treating the N-phthaloyl-protected amino acid
esters with trifluoromethanesulfonic anhydride in the presence of pyridine. With the triflates of the serine and
threonine esters, it was possible to alkylate benzene and
benzene derivatives to obtain phenylalanine and B-methylphenylalanine esters 2, respectively.
These reactions proceed with retention of configuration
at C-2 of the amino acid ester under all conditions employed. Of particular interest but difficult to predict was
the stereochemistry at C-3 of the B-methylphenylalanine
esters 2. The FriedelLCrafts alkylation of aromatic compounds with optically active alkylating agents usually proceeds with extensive racemization.'2' However, Suga et al.,
in particular, have shown that alkylation with optically active compounds can also be carried out without significant
racemization if special structural properties are fulfilled.[']
In general, these alkylations occur with inversion of confi-
10 h/80 OC
> H3C\ ;cy
+ by- products
H3C\ z",
Pht :
Table I Changes in configuration upon alkylation of benzene with the diastereomericthreonine derivatives l to give the phenylalanine derivatives 2 [a].
97: 3
98: 2
40 : 60
40 : 60
[a] 3R in 1 and 3 s in 2 correspond to the same configuration at C-3
[*] Prof. Dr. F. Effenberger, DipLChem. T. Weber
Institut fur Organische Chemie der Universitat
Pfaffenwaldring 55, D-7000 Stuttgart 80 (FRG)
[**I Electrophilic Aromatic Substitution, Pan 32. This work was supported
by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. T. W. thanks the Fonds der Chemischen Industrie for a
doctoral fellowship.-Part
31: F. Effenberger, F. Reisinger, K. H.
Schonwalder, P. Bauerle, J. J. Stezowski, K. H. Jogun, K. Schollkopf, W.
D. Stohrer, J. Am. Chem. press.
0570-0833/87/0202-0142 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 26 (1987) No. 2
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reaction, reversal, involving, carbonates, radical, cation, vinylene, elimination, oxirene, anion, co2, c2h2o, charge
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