Tetrahydronaphthalene-1,4-dione and its chromiumtricarbonyl complex

Article abstract of DOI:10.2533/chimia.2007.169

The article gives a brief outline of the rediscovery of tetrahydronaphthalene-1,4-dione, a stable tautomer which has been known for over half a century but has not been applied in synthesis. Desymmetrization is readily achieved via enantioselective reduction. Synthetic potential apart, the dione and its chromiumthcarbonyl complex are of theoretical interest. Thus, whereas dihydroxynaphthalene requires quite harsh conditions and leads to a 1:1 mixture of the two tautomers, the chromiumtricarbonyl complex of dihydroxynaphthalene tautomerizes under very mild conditions to the tetrahydronaphthalene-1,4-dione complex. An earlier literature report showed that in trifluoroacetic acid, the dione tautomer is present exclusively. This has now been used to isolate multigram quantities of the compound. Schweizerische Chemische Gesellschaft.

Full text of DOI:10.2533/chimia.2007.169

LAUREATES: AWARDS AND HONORS, SCS FALL MEETING 2006
169
doi:10.2533/chimia.2007.169
CHIMIA 2007, 61, No. 4
Chimia 61 (2007) 169–171
© Schweizerische Chemische Gesellschaft
ISSN 0009–4293
Tetrahydronaphthalene-1,4-dione and its
Chromiumtricarbonyl Complex
Álvaro Enríquez García§, E. Peter Kündig*, Thierry Lomberget, Ryan Bragg, Cyril Poulard, and
Gerald Bernardinelli
§SCS Poster Prize Winner
Abstract: The article gives a brief outline of the rediscovery of tetrahydronaphthalene-1,4-dione, a stable tauto-
mer which has been known for over half a century but has not been applied in synthesis. Desymmetrization is
readily achieved via enantioselective reduction. Synthetic potential apart, the dione and its chromiumtricarbonyl
complex are of theoretical interest. Thus, whereas dihydroxynaphthalene requires quite harsh conditions and
leads to a 1:1 mixture of the two tautomers, the chromiumtricarbonyl complex of dihydroxynaphthalene tautom-
erizes under very mild conditions to the tetrahydronaphthalene-1,4-dione complex. An earlier literature report
showed that in trifluoroacetic acid, the dione tautomer is present exclusively. This has now been used to isolate
multigram quantities of the compound.
Keywords: Arene complex · Asymmetric catalysis · Chromium · Ketone-enol tautomerism · Naphthoquinone
Arenes readily form π-complexes with a of other extended aromatics) have received
We recently initiated a project aimed
variety of transition metal complex frag- much less attention, primarily as a result of at the synthesis of planar chiral naphtha-
ments and the metal-coordinated arenes the lability of the metal–arene bond in this lene complexes for applications as chirons
show a rich and varied chemistry.[1] The
class of compounds.[3] This arises from a
in synthesis, as chiral Cr(CO)3 transfer
metal adds a third dimension to the planar weaker but also far more labile metal arene agents, and, after further modification, as
aromatic compounds and the two faces of bond. Easy haptotropic slippage of the chiral ligands. The route that we chose is
6
4
an arene with different ortho- or meta-sub- naphthalene ligand (change from η to η
thedesymmetrizationofmeso-naphthalene
2
stituents are enantiotopic. Coordination of or η -coordination) facilitates arene disso- complexes. As a first successful example,
a metal to an arene thus not only alters the ciation and results in a dramatic increase Scheme 1 shows the enantioselective hy-
reactivity of ring carbons and substitu- in sensitivity towards air and Lewis basic drogenolysis of [Cr(CO)3(5,8-dibromo-
ents, but in addition also gives access to solvents or reagents.[4] The lability has
naphthalene] and its derivatization.[7]
In the context of these studies we also
arene complexes, those incorporating the thalene)], in the presence of THF, is an
6
highly stereoselective reactions. Of all been put to good use: [Cr(CO)3(η -naph-
prepared the naphthoquinone complex 1
via hydrolysis/oxidation of the bis-trifluo-
roacetate naphthalene complex, which, in
turn, was obtained using [Cr(CO)3(NH3)3]/
electrophilic Cr(CO)3 group have been efficient source of the Cr(CO)3 fragment,
most extensively studied, and their use in either as a stoichiometric reagent in syn-
6
organic synthesis and as chiral ligands is thesis of more robust [Cr(η -arene)(CO3)]
well established.[1,2] In contrast, the analo- complexes[5] or as a catalyst for diene hy-
gous complexes of naphthalenes (or those drogenation.[6]
BF3.OEt2 as Cr(CO)3 transfer agent.[8] The
purple air-stable naphthoquinone complex
LiB H 4,Pd(dba) (5%)
L* (20%), D ME ,5 C
B r
H
2
H
o
Ph
Ph
B r
L* =
B r
R
C r(C O)
C r(C O)
pS
C r(C O)
3
O
3
3
PN
O
Ph
65%, 97% ee
R=SiMe ,OH, PPh ,
3
2
*Correspondence: Prof. E. P. Kündig
University of Geneva
Ph
A r,
R'
Department of Chemistry
30 Quai Ernest Ansermet
CH-1211 Geneva
Tel.: +41 22 379 6093
Fax: + 41 22 379 3215
E-Mail: peter.kundig@chiorg.unige.ch
Scheme 1. Asymmetric catalytic hydrogenolysis to access highly enantiomerically enriched
naphthalene complexes

LAUREATES: AWARDS AND HONORS, SCS FALL MEETING 2006
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CHIMIA 2007, 61, No. 4
polarity of the solvent.[11] Tetralindione 8
has been known in the literature for many
years. Thomson isolated 8 in 10.5% yield
from a mixture with 7 following fusion,[12]
N
3(10 %)
and Pearson et al. showed that melting 7
under vacuum generates a 2:1 equilibrium
H
H
NaB H 4/ C eC l
MeOH, 0C
H
O
3
H O
N
Me
2
o
(1 h, 200 °C) with its tautomer 8.[13] The
H
OH
H
O B z
82 %
B z C l1.5 eq.
E t N1eq.
MS 4Å , C H 2C l
conversion of 1 into 2 can also be effected
3
C r(C O)
C r(C O)
3
3
in neat CF3COOH.[14] The dione 8 has also
O
2
2
(-)-4,99%ee
89 %
been obtained by hydrogenation of naph-
thoquinone with Wilkinson’s catalyst[15]
O
H O
O
and very recently by benzylic oxidation of
tetrahydronaphthalene-I-one catalyzed by
Na S O
C r(C O)
2
4
E t 2O/HO
3
o
Toluene, 50 C
2
2
1
Rh2(cap)4.[16]
OH
O
94 %
The dione is kinetically stable at RT
C r(C O)
C r(C O)
3
3
but rapidly converts to the phenolic form
5(orange)
6(red)
in the presence of base. The keto-form is
implicated in the acid-catalyzed monoal-
kylation of 7[14] but, surprisingly, to our
knowledge, no chemistry of isolated 8 has
Scheme 2. Synthetic potential of naphthoquinone complex 1
ever been reported.
1 could be reduced under Luche conditions
Tautomerization of 7 to 8 in trifluo-
50 °C, the solution changed color from
roacetic acid as reported by Laatsch,[14]
to the cis-diol 2 (Scheme 2). Desymmetri-
zation of 2 was achieved via acetyl transfer
using new readily available cinchona alka-
loid-derived chiral diamine catalysts such
orange to deep red. This could not be due
followed by addition of toluene, rapid
solvent removal and crystallization from
diisopropylether gave 8 in 72% yield.[9e]
to the well-established arene exchange
of naphthalene complexes because the
expected product, [Cr(CO)3(toluene)], is
as 3[8c]. This afforded the mono-benzoate
This can be carried out conveniently on a
yellow. The color turned out to be that of
the tautomer 6.[9]
A literature search revealed that this is
not an exclusivity of the Cr(CO)3 complex.
10 g scale.
Dihydroxynaphthalene tautomerizes
slowly in solution. A ca. 1:1 equilibrium
4 in excellent yield and enantioselectiv-
ity. Reduction of 1 with sodium dithionite
yielded cleanly the dihydroxynaphthalene
is reached after more than 20 days upon
complex 5. The synthetic potential of the
Tetrahydronaphthalene-1,4-dione (8) has
heating a sample in benzene at 120 °C in
naphthoquinone complex, of the chiral
complex 4 and the scope and limitations ble than its tautomer 1,4-dihydroxynaph-
of the new diamine acyl transfer catalyst
are presently under study.
been computed to be 10.2 kcal/mol less sta-
a sealed NMR tube. This compares to the
thalene (7).[10] However preliminary re-
sults of calculations taking into account
90% conversion of complex 5 to 6 upon
heating at 50 °C for 20 h (Scheme 3 and
Fig.). Kinetic and computational studies
Complex 5 is only slightly soluble in solvent effects show that the tautomeric
are underway to rationalize these observa-
toluene. To our surprise, upon heating to
equilibrium is strongly influenced by the
tions.
Dione 8 is an attractive starting mate-
rial for synthesis as shown by the series of
%
100
transformations in Scheme 4. This chemis-
try is currently being extended and applied
in our laboratory.
7
8
90
80
70
60
50
40
30
20
10
0
0
5
10
15
20
25
OH
O
Time (days)
C D
6
6
100
120°C
%
90
80
70
60
50
40
30
20
10
0
O
H
O
7
8
5
6
H O
O
C D
6
6
O
H
O
50°C
C r(C O)
C r(C O)
3
3
5
6
0
10
20
30
40
50
Time (hours)
Fig. Rate and equilibria in the tautomerization of 5 (at 50 ˚C) and 7 (at Scheme 3. Influence of the chromium fragment on the tautomerization of
120 ˚C) (NMR ratios)
7 and 8

LAUREATES: AWARDS AND HONORS, SCS FALL MEETING 2006
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CHIMIA 2007, 61, No. 4
Ph
Ph
O
H
O
TMSO
C N
TMSC N
2
N
B
I 5mol %
C H 2C l
Me
2
.
B H 3THF
O
O
H
Ph
H
Ph
(-) 85 %e
e
O
B
OH
O
O
N
Me
(-), 99.7 %e
e
.
B H 3THF
R
R
OH
+
1. RLi (R=Me, Ph, napht, vinyl, allyl), 2. H
OH
OH
Red-A l
HF
T
rac
OH
OH
L-Selectrid
e
T
HF
Scheme 4. Some transformations of dione 8
82, 499; b) S. Zhang, J. K. Shen, F. Ba-
solo, T. D. Ju, R. F. Lang, G. Kiss, C. D.
Acknowledgements
We thank the Swiss National Science
Foundation for financial support.
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