ORGANIC
LETTERS
2
001
Vol. 3, No. 15
375-2377
LiCB Me : A Catalyst for Pericyclic
Rearrangements
11
12
2
†
†
‡
‡
Stefan Moss, Benjamin T. King, Armin de Meijere, Sergei I. Kozhushkov,
§
,†
Philip E. Eaton, and Josef Michl*
Department of Chemistry and Biochemistry, UniVersity of Colorado,
Boulder, Colorado 80309, Institut f u¨ r Organische Chemie, UniVersit a¨ t G o¨ ttingen,
Tammannstrasse 2, D-37077 G o¨ ttingen, Germany, and Department of Chemistry,
UniVersity of Chicago, 5735 S. Ellis AVenue, Chicago, Illinois 60637
Received May 28, 2001
ABSTRACT
+
-
Benzene and 1,2-dichloroethane solutions of the Li salt of the weakly coordinating anion CB11Me12 catalyze the rearrangement of cubane
to cuneane, quadricyclane to norbornadiene, basketene to Nenitzescu’s hydrocarbon, and diademane to triquinacene. The Claisen rearrangement
of phenyl allyl ether is also strongly accelerated.
-
The lithium cation has been long recognized as an effective
catalyst for pericyclic reactions. The catalysis of Diels-Alder
the parent CB11
H
12 anion are easily prepared on large scale
10
in two steps from NaBH
permethylation is facile and nearly quantitative.
CB11Me12 salts of Li and other cations, including chiral
ones, therefore promise to be practical catalysts.
The CB11Me12 anion11 is weakly coordinating and very
lipophilic; this remarkable property can be further enhanced
by the introduction of longer alkyl chains. The lithium salt
can be easily prepared and dried by heating to 180 °C under
reduced pressure. Under benchtop conditions, a saturated
4
, BF
3
, and CHCl
3
,
and its
1
1,12
reactions by solutions of LiClO
4
in Et
2
O has received the
The
1
-6
-
+
most attention,
but the explosive nature of this reaction
medium has been a concern. Lithium salts of many other
anions have been used successfully as Lewis acid catalysts,
including very weakly interacting ones, such as LiCo-
-
7
8
9
13
(B
9
C
2
H
11
)
2
, LiB(Arf)
4
, and LiAl[(OC)Ph(CF
3
)
2
]
4
. We now
14
report remarkably high rates of rearrangements in solutions
of LiCB11Me12 in benzene and 1,2-dichloroethane. Salts of
(
300 g/L, 1.1 M) solution of LiCB11Me12 in benzene is
†
University of Colorado.
Universit a¨ t G o¨ ttingen.
University of Chicago.
‡
(10) Franken, A.; King, B. T.; Rudolph, J.; Rao, P.; Michl, J. Collect.
§
Czech. Chem. Commun., in press.
(11) King, B. T.; Janou sˇ ek, Z.; Gr u¨ ner, B.; Trammell, M.; Noll, B. C.;
Michl J. J. Am. Chem. Soc. 1996, 118, 3313.
(
1) Braun, R.; Sauer, J. Chem. Ber. 1986, 119, 1269.
(2) Grieco, P. A.; Nunes, J. J.; Gaul, M. D. J. Am. Chem. Soc. 1990,
1
12, 4595.
3) Grieco, P. A. In Organic Chemistry: Its Language and its State of
the Art; Kisak u¨ rek, M. V., Ed.; VCH: New York, 1993; p 133.
(12) King, B. T.; Zharov, I.; Clayton, J. R.; Michl, J., submitted for
publication.
(
(13) Zharov, I. Ph.D. Dissertation, University of Colorado, 2000.
(14) By partitioning a solution of CsCB11Me12 in a 70/30 Et2O/acetone
mixture (10 g/L) against an aqueous solution of LiCl (15%). Quantitative
conversion and yield are obtained upon 3 × 3 countercurrent extraction:
three separate volumes of the organic phase (A, B, and C) are partitioned
in five steps against three separate volumes of the aqueous phase (1, 2, 3):
(i) C, B, A/1, 2, 3; (ii) C, B/1; A/2; 3; (iii) C/1, B/2, A/3; (iv) 1, C/2, B/3,
A.; (v) 1, 2, C/3, B, A, where only the volumes joined by a slash are
partitioned. The combined product-containing ether phases are evaporated
to dryness, and the product is then dissolved in fresh, dry 70/30 Et2O/
acetone, leaving the insoluble salts behind.
(
(
(
4) Flohr, A.; Waldmann, H. J. Prakt. Chem. 1995, 337, 609.
5) Kumar, A. Chem. ReV. 2001, 101, 1.
6) Saito, S. In Lewis Acids in Organic Synthesis; Yamamoto, H., Ed.;
Wiley-VCH: Weinheim, Germany, 2000; Vol. 1, p 9.
7) Grieco, P. A.; DuBay, W. J.; Todd, L. J. Tetrahedron Lett. 1996, 37,
707.
8) Fujiki, K.; Ikeda, S.; Kobayashi, H.; Mori, A.; Nagira, A.; Nie, J.;
Sonoda, T.; Yagupolskii, Y. Chem. Lett. 2000, 62.
9) Barbarich, T. J.; Handy, S. T.; Miller, S. M.; Anderson, O. P.; Grieco,
P. A.; Strauss, S. H. Organometallics 1996 15, 3776.
(
8
(
(
1
0.1021/ol0161864 CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/28/2001