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Structure of a УY-ConjugatedФ Dilithium Salt of an -Keto Dianion 1 3-Dilithiodibenzyl Ketone-(Me2NCH2CH2NMe2)2.

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ferred locations of the Li atoms are the same. The main
differences between 1 and the X-ray result can be attributed to the presence of the coordinating tetramethylenediamine (TMEDA) molecules in the experimental structure16].The lower lithium coordination in 1 is reflected by
the shorter Li-0 and Li-a-C distances (0.1 and 0.4
spectively). In addition, the C - 0 bond in 1 is 0.07 A
longer than that in the X-ray structure of 1,3-dilithiobenzyl
The experimentally observed structures of mono-enolate
anions correspond to dimers and tetramers without Li-C
interaction^^^^."^. In contrast, 1,3-lithium bridging between
C and 0 atoms is found to be structure- and reactivity-determining in a,a'-keto dianions['I.
Received: March 21, 1984;
revised: May 24, 1984 [Z 768 IE]
German version: Angew. Chem. 96 (1984) 622
[1] C. R. Hauser, T. M. Harris, J. Am. Chern. Soc. 79 (1957) 6342; 81 (1959)
1154; J. S. Hubbard, T. M. Harris, ibid. 102 (1980) 21 10. J. P. Bays, J. Org.
Chem. 43 (1978) 38.
[21 D. Wilhelm, T. Clark, P. v. R. Schleyer, J. Chem. Soc. Perkin Trans. 2
1984, 915.
[31 J. S. Binkley, J. A. Pople, W. J. Hehre, J. Am. Chem. Soc. 102 (1980) 939;
The Gaussian 82 Program, Release A: J. S. Binkley, M. J. Frisch, K.
Raghavachari, D. J. DeFrees, H. B. Schlegel, R. A. Whiteside, E. Fluder,
R. Seeger, J. A. Pople, Carnegie-Mellon University, Pittsburgh 1983, adapted by Dr. A. Sawaryn for CDC-Computers, was employed.
[4] a) T. J. Lynch, M. Newcomb, D. E. Bergbreiter, M. B. Hall, J. Org. Chern.
45 (1980) 5005; b) A. J. Kos, T. Clark, J. Chandrasekhar, P. von R.
Schleyer, paper presented at the Arbeitstag fur Theoretische Chemie,
Mariapfarr, Austria 1984.
[5] See e.g., J. J. Brooks, W. E. Rhine, G. D. Stucky, J. Am. Chem. SOC.94
(1972) 7346; W. E. Rhine, J. Davis, G . Stucky, ibid. 97 (1975) 2079; W.
Walczak, G. Stucky, ibid. 98 (1976) 5531; S. K. Arord, R. B. Bates, W. A.
Beavers, R. S. Cutler, ibid. 97 (1975) 6271. For a review of X-ray structures of lithium compounds, see: [6].
[6] W. Setzer, P. von R. Schleyer, Adu. Organomet. Chem., in press.
[7] P. von R. Schleyer, A. J. Kos, J. Chem. Soc. Chem. Commun. 1982,448; P.
von R. Schleyer, A. J. Kos, E. Kaufmann, J. Am. Chem. Soc. 105 (1983)
7617; P. von R. Schleyer, A. J. Kos, D. Wilhelm, T. Clark, G. Boche, G .
Decker, H. Etzrodt, H. Dietrich, W. Mahdi, J. Chem. Soc. Chem. Comm.,
in press.
[S] H. Dietrich, W. Mahdi, D. Wilhelm, T. Clark, P. von R. Schleyer, Angew.
Chem. 96 (1984) 623; Angew. Chem. Int. Ed. Engl. 23 (1984) 621.
191 L. M. Jackman, B. C. Lange, Tetrahedron 33 (1977) 2737; R. Amstutz, W.
B. Schweizer, D. Seebach, J. D. Dunitz, Helu. Chim. Acta 64 (1981)
Structure of a "Y-Conjugated" Dilithium Salt of
an a,a'-Keto Dianion : 1,3-Dilithiodibenzyl Ketone(Me2NCH2CH2NMe2)2**
By Hans Dietrich*, Waruno Mahdi, Dieter Wilhelm,
Timothy Clark, and Paul von Rag& Schleyer
Although the enolates commonly used in syntheses are
usually regarded as anions, their structures are complex
and involve counterions and aggregated clusters[']. Consideration of organoalkali metal structures as they really are,
rather than as oversimplified models, is necessary to understand their reactivity and stereochemistry as well as the
selectivity of their reactions[']. We report here the first Xray structure analysis of a monomeric dilithium salt of an
[*] Prof. Dr. H. Dietrich, Dr. W. Mahdi
Fritz-Haber-Institut der Max-Planck-Gesellschaft
Faradayweg 4-6, 1 Berlin 33
Prof. Dr. P. von R. Schleyer, Dr. T. Clark, Dipl.-Chem. D. Wilhelm
Institut fur Organische Chemie der Universitat Erlangen-Niirnberg
Henkestrasse 42, D-8520 Erlangen (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
Angew. Chem. Int. Ed. Engl. 23 (1984) No. 8
a,a'-keto dianion. Both the position of the lithium counterions and the geometry of the carbodianion moiety are of
interest. The a b initio structures of the parent Y-conjugated13] system, 1,3-dilithioacetone, have been reported[4].
We compare here the experimental results on 1,3-dilithiodibenzyl ketone 1 with those obtained by M N D O calculations (Fig. 2)15];the preparation and NMR spectra of 1 and
M N D O calculations on the corresponding dianion have
already been discussed[61.
The X-ray structure of 1"' shows that the benzyl groups
adopt exo,exo orientations, in agreement with the M N D O
results on the dianion, but not with the results of N M R
measurements in tetrahydrofuran (THF), which indicate a
65% exo,endo- and 35% exo.exo-mixture[61. Both phenyl
groups are twisted ca. 20" in opposite directions out of the
plane of the central atoms; the M N D O findings indicate
21" for the dilithium salt (Fig. 2) and nearly the same value
in the dianionL6].Comparison of Figures 1 and 2 indicate
that the X-ray and M N D O structures agree very well in
their general features. As in the case of the parent system[41,
other alternatives were examined calculationally, but were
found to be less stable. With approximate C2 symmetry,
the dilithium salt is chiral, which may be significant in synthetic applications.
Fig. 1. Structure of 1,3-dilithiobenzyl ketone.(TMEDA)2 in the crystal. The
hydrogen atoms have been omitted. Important bond lengths [A]: C(8)-0
1.334(1), C(B)-C(17) 1.413(2), C(S)-C(27) 1.402(2), C(ll)-C(17) 1.424(2),
1.434(2), C(l l)-C(I2)
1.423(2), C(21)-C(22)
1.386(2), C(22)-C(23)
1.395(2), C(13)-C(14)
1.381(2), C(14)-C(IS)
1.388(2), C(24)-C(25)
1.374(2), C(25)-C(26)
1.375(2), C(16)-C(11)
C(26)-C(2 I ) 1.421(2); Li(3)-0 1.849(2), Li(4)-0 1.870(2), Li(3)-C(12)
2.469(2), Li(4)-C(22) 2.425(2), Li(3)-C( 11) 2.653(2), Li(4)-C(21), 2.505(2),
Li(3)-C(17) 2.731(2), Li(4)-C(27) 2.550(2), Li(3)-C(8) 2.150(2), Li(4)-C(8)
The C - 0 bond is lengthened due to coordination with
the two Li atoms. The C-0 distance of 1.334 A (X-ray
analysis, 117 K) is comparable to that found in aggregated
lithium enolated'] and phenolates'8,"1. The M N D O value
for 1 (1.337 A) is in good agreement with the experimentally determined value, in contrast to the shorter length calculated for the dianion (1.247 A)[61.The distances between
the carbonyl and the benzylic carbon atoms (average
1.408 A) are slightly shorter than those between the benzyl
carbon atoms and the phenyl rings (1.429 A). The lengths
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
0570/0833/84/(1808-0621$ 02.50/0
62 1
TAN 76 and refined by X-RAY 76. One of the TMEDA ligands is disordered, the populations of the two alternative conformations being 67%
and 33% at 117 K. The final R factors based on the 4121 F g > 2 0 are
R(f)=0.070, R,(F)’=0.074. Further details of the crystal structure investigation are available on request from the Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road,
Cambridge CB2 1EW (England).
[8] V. W. Bhagwat, H. Manohar, N. S. Poonia, Inory. Nucl. Chem. Lett. 16
(1980) 373.
[9] B. Cetinkaya, I. Grumriikcii, M. F. Lappert, J. L. Atwood, R. Shakir, J .
Am. Chem. SOC.102 (1980) 2086.
[lo] T. J. Lynch, M. Newcomb, D. E. Bergbreiter, M. B. Hall, J. Org. Chem.
45 (1980) 5005; T. Clark, unpublished calculations.
1,4,7,l0-TetraphenyldibenzoIa,elcyclooctene5,6,11,12-tetrone from
3,6-Diphenylphthalic Anhydride**
By Theodor Troll*, Georg W. Ollmann, and Helga Leffler
Fig. 2. Calculated (MNDO) structure of 1,3-dilithiodibenzyl ketone 1 (bond
lengths in [A]).
of these bonds in the calculated and experimental structures indicate the importance of conjugation in the dilithium compound.
The two Li atoms, each solvated by tetramethylethylenediamine (TMEDA), occupy bridging positions on opposite
sides of the a,a’-keto dianion system. In addition to the
strong coordination to oxygen (d(Li-0)= 1.86 A), each Li
atom is in close contact with four C atoms (Figs. 1 and 2).
The LiC distances determined at 117 K by X-ray crystal
structure analysis range between 2.42 and 2.73 A.
The structure of 1 can be regarded as consisting of two
fused enolate units with a common C-0 bond. The lithium enolate units then correspond to the bridged form of
acetaldehyde lithium enolate, which is indicated by ab initio calculations to be slightly less stable than the structure
with a linear C-0-Li
linkage”’]. This bridged form has
not been observed for monoenolate aggregates, but is
clearly favored for “dienolate~”[~].
Received: March 21, 1984;
revised: May 24, 1984 [Z 769 IE]
German version: Angew. Chem. 96 (1984) 623
[ I ] See, e.g. R. Amstutz, W. B. Schweizer, D. Seebach, J. D. Dunitz, Helu.
Chim. Acta 64 (1981) 2617; D. Seebach, R. Amstutz, J. D. Dunitz, ibid.
64 (1981) 2622.
[2] G. B. Trimitsis, J. M. Hinkley, R. TenBrink, A. L. Faburada, R. Anderson, M. Poli, B. Christian, G. Gustafson, J. Erdman, D. Rop, J. Org.
Chem. 48 (1983) 2957.
[3] Cf. T. Clark, D. Wilhelm, P. von R. Schleyer, Tetrahedron Lett. 23 (1982)
3547, and references cited therein.
[4] A. J. Kos, T. Clark, P. von R. Schleyer, Angew. Chem. 96 (1984) 622; Angew. Chem. Int. Ed. Engl. 23 (1984) 620.
[5] M. J. S. Dewar, W. Thiel, J. Am. Chem. SOC.99 (1977) 4899; lithium parametrization: w. Thiel, T. Clark, unpublished.
161 D. Wilhelm, T. Clark, P. von R. Schleyer, J . Chem. Sac. Perkin Trans. 2
1984, 915.
[7] Monoclinic (from ether), space group P2,/n, 2 = 4 , a=8.716(2),
V=2765 A’;p,,~,=1.092 g/
b=22.569(7),~=14.057(3) &8=91.21(3)
cm3 (117 K); MoKa radiation,/2=0.71069,&;2 ” < 8 < 2 7 ” ; 61 138 reflection profiles were averaged to a set of 6016 structure factors ( f )
(4121 > 20,2893>60). The structure was refined using X-RAY 76 starting from the room temperature structure, which was solved by MUL-
0 Verlay Chemie GmbH, 0-6940 Weinheim, 1984
Electrochemical reduction of N-phenyl- and N-methylphthalimide under aprotic conditions in the presence
of trimethylchlorosilane leads to formation of 1,3-bis(trimethylsiloxy)isoindoles[1,21.
The reaction offers an extremely facile entry to 1,3-bis donor-substituted isoindoles[31.Transfer of this reaction to phthalic anhydride affords exclusively bislactone ethers”].
In the reduction of 3,6-diphenylphthalic anhydride 1
under the same conditions, however, we obtained, in addition to 4,7-diphenyl-3-hydroxyphthalide(7% yield) and the
dimers 2 (34%, two diastereomers), the acetal 3.
Reduction of 1 at the potential E’ (El,2= - 1.32 V vs.
SCE, reversible formation of the radical anion) leads to
isolation of 3 in 13% yield; at the potential E2
-2.10 V, reversible formation of the dianion), the yield
increases to 25%. A reductive cyclization of 2 can be ruled
out, since no reduction step was found in the potential
range available. Hence, a bis donor-substituted isobenzofuran 4 has been obtained for the first time as an intermediate; previously, only 1-alkoxyisobenzofurans have been
Presumably 3 adopts the sterically more favorable configuration with anti-oxygen bridges, as in the dimeric parent
compound[51.No distinction could be made by complexation with NMR shift reagents. Potassium fluoride in ace[*] Priv.-Doz. Dr. T. Troll, Dr. G. W. Ollmann, H. Leffler
lnstitut fur Organische Chemie der Universitat
Universitatsstrasse 31, D-8400 Regensburg (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
by the Fonds der Chemischen Industrie.
0570/0833/84/0808-0622 $ 02.50/0
Anqew. Chem. Int. Ed. Engl. 23 (1984) No. 8
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salt, structure, me2nch2ch2nme2, conjugate, keto, ketone, dilithiodibenzyl, dianion, dilithium
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