Ring selectivity in the Na/EtOH reduction of 1-aryl-7-methoxynaphthalenes

Article abstract of DOI:10.1055/s-2005-869857

Na/EtOH reduction of 1-aryl-7-methoxynaphthalenes occurred preferentially at the A-ring when no substituents were present at the ortho-positions of the aryl group (up to 100% selectivity), to afford 1-aryl-7-methoxy-1,2,3,4- tetrahydronaphthalenes. Ortho-

Full text of DOI:10.1055/s-2005-869857

LETTER
1601
Ring Selectivity in the Na/EtOH Reduction of 1-Aryl-7-methoxynaphthalenes
N
a/EtOH Reduction of
.
1-Arylnaph
C
Departamento de Química Orgánica (C-I), Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
Fax 34(91)4973966; E-mail: carmen.carrenno@uam.es; E-mail: antonio.urbano@uam.es
Received 20 April 2005
addressed only using the carbanion-induced condensation
Abstract: Na/EtOH reduction of 1-aryl-7-methoxynaphthalenes
occurred preferentially at the A-ring when no substituents were
present at the ortho-positions of the aryl group (up to 100% selec-
tivity), to afford 1-aryl-7-methoxy-1,2,3,4-tetrahydronaphthalenes.
Ortho-substitution of the 1-aryl moiety favored B-ring reduction
(up to 85:15 selectivity) giving rise, after acidic hydrolysis of the
vinyl ether intermediate, to the corresponding 8-aryl-2-tetralones.
of differently substituted 2H-pyran-2-ones with a 1,4-cy-
clohexanedione monoketal,12 however, the synthesis of
these starting materials is not easy.
R1
R1
Key words: biaryls, chemoselectivity, steric hindrance, reductions,
sodium
R2
R3
R2
R3
8
1
7
O
MeO
2
A
B
Selective reduction of polyaromatic compounds has
received little attention despite the fact there is much
interest in a controlled access to differently substituted
hydroaromatic derivatives. The few studies published so
far deal with metal/ammonia reduction of terphenyls1 and
naphthyl or dinaphthylbenzenes.2 These studies revealed
that the ratio of central to outer ring reduction products de-
pended on the particular metal used in the case of p-ter-
phenyls, whereas m- and o-terphenyls gave only central
ring reduction. Moreover, reduction of 1- and 2-phenyl-
naphthalene never occurred at the phenyl ring.2a The con-
trolled reduction of substituted 2-methoxy naphthalene
derivatives is of great interest since the resulting vinyl
ether can be easily hydrolyzed to 2-tetralones. Such com-
pounds have been frequently used in organic synthesis
due to their high versatility and suitability as precursors of
a wide range of synthetic and natural products and their
derivatives,3 heterocycles,4 and pharmaceuticals5 showing
biological activities and other useful properties. However,
unlike their congeners the 1-tetralones, which are inex-
pensive, easily prepared, and commercially available sub-
stances, 2-tetralones are often very expensive and much
more difficult to synthesize.
O
1
2
MeO
MeO
R1
4
5
OTf
R2
R3
4
6
MeO
3
Scheme 1 Retrosynthesis to 8-aryl-2-tetralones 1.
Among the known synthetic approaches to 2-tetralones,
we decided to use the Na/EtOH reduction of 2-methoxy-
naphthalenes,13 initially described by Cornforth et al.,14
which had been successfully applied by us for the synthe-
sis of differently substituted 8-alkyl-2-tetralones.15 Birch
reductions16 of naphthalenes bearing electron-releasing
substituents at the C-1 are known to occur at the unsubsti-
tuted aromatic ring, whereas electron-withdrawing groups
at C-1 direct the reduction to the same ring.17 On the other
hand, reduction of 1-phenylnaphthalene afforded exclu-
sively the product resulting from reaction of the naphtha-
lene ring bearing the phenyl substituent, but the effect of
the presence of an alkyl- or alkoxy-substituted phenyl ring
on the reduction of 1-arylnaphthalenes is unknown. In the
present paper we report a study on the ring selectivity of
the Na/EtOH reduction of differently substituted 1-aryl-7-
methoxynaphthalenes 2 (Scheme 1) and show that the rel-
ative ratio of reduction of the A or B rings of the naphtha-
lene unit is dependent on the substitution pattern at the
aryl moiety.
The most common methods for the preparation of 2-
tetralones6 involves 1,2-transposition of the carbonyl
group of 1-tetralones,7 reduction of substituted 2-meth-
oxy-naphthalenes followed by hydrolysis,8 cyclization of
diazoketones,9 and the Friedel–Crafts reaction of aromatic
acyl chlorides with olefins.10
In connection with a program devoted to the synthesis of
polyaromatic compounds such as helicenes,11 we required
several 8-aryl-2-tetralones (1; Scheme 1) bearing differ-
ent substituents at the aryl moiety. To the best of our
knowledge, the synthesis of 8-aryl-2-tetralones has been
In order to describe a general synthesis of 1-aryl-7-meth-
oxynaphthalenes 2 we decided to apply the retrosynthesis
shown in Scheme 1. Thus, compounds 2 could be formed
by aromatization of the corresponding 4-aryl-6-methoxy-
SYNLETT 2005, No. 10, pp 1601–1605
Advanced online publication: 07.06.2005
DOI: 10.1055/s-2005-869857; Art ID: G14105ST
© Georg Thieme Verlag Stuttgart · New York
1
7
.0
6
.2
0
0
5

1602
M. C. Carreño et al.
LETTER
1,2-dihydronaphthalene derivatives 3. The introduction of Then, we turned our attention to the alternative route de-
the aryl substituent at the required position was envisaged picted in Scheme 1, the metal-catalyzed cross-coupling
by two alternative routes: addition of the corresponding reaction between enol triflate 5 and an organometallic
aryl Grignard to the a-tetralone 4, followed by dehydra- species. Among the different organometallic reagents
tion of the resulting carbinol, or metal-catalyzed cross- available, we decided to use boronic acids,19 due to the ex-
coupling reaction of the corresponding aryl organometal- cellent results achieved in their cross-coupling reactions
lic species with the enol triflate 5, also accessible from 4. with sterically hindered derivatives.20 Thus, the reaction
of enol triflate 5,21 prepared in 96% yield from a-tetralone
For the synthesis of compounds 3 (Scheme 2), we initially
4, with commercially available 2-ethylphenyl boronic
chose the route based on the addition of differently substi-
acid (7d) [Pd(PPh3)4, Ba(OH)2·8H2O, DME–H2O, 80 °C,
tuted aryl Grignard reagents 6 to a-tetralone 4.18
40 min],20 furnished dihydronaphthalene 3d in, an excel-
lent, 94% yield. Under the same experimental conditions,
the cross-coupling reactions between enol triflate 5 and
O
OTf
differently substituted aryl boronic acids 7e–h,22 bearing
one or two substituents at the ortho-positions, afforded the
corresponding dihydronaphthalenes 3e–h with good to
excellent yields (70–97%, Scheme 2).
Tf2NPh, KHMDS
MeO
MeO
THF, -78 °C, 1 h
96%
4
5
R2
The full aromatization of dihydroaromatic derivatives 3a–
h was achieved using DDQ in dichloromethane at room
temperature for 15 minutes giving rise to the correspond-
ing 1-aryl-7-methoxynaphthalenes 2a–h with excellent
yields ranging from 71–97% (Scheme 2).
R2
R1
7d–h
B(OH)2
R1
i.
MgBr
R3
R3
6a–d
Et2O, r.t.
Pd(PPh3)4, Ba(OH)2
DME/H2O, 80 °C
With 1-aryl-7-methoxynaphthalenes 2a–h in hand, we
carried out metal-mediated reductions (Scheme 3). All re-
actions were performed with an excess of sodium in etha-
nol at 100 °C until all of the starting material had been
consumed by TLC, this was followed by treatment with
35% hydrochloric acid to hydrolyze the vinyl methyl ether
initially formed from the reduction of the B-ring of com-
pounds 2a–h.
ii. 35% HCl
(70–97%) for 3d–h
(20–86%) for 3a–d
R1
R3
R2
MeO
When 1-p-tolyl-7-methoxynaphthalene 2a was submitted
to typical reduction conditions and treated with 35% hy-
drochloric acid, we obtained 1-(p-tolyl)-7-methoxy-
1,2,3,4-tetrahydronaphthalene (8a), resulting from reduc-
tion of ring-A of the naphthalene unit, as the exclusive
product, in 62% yield (Scheme 3). Compound 8a was
probably formed from reduction of 2a to the correspond-
ing 1,4-dihydroaromatic intermediate I (Scheme 3),
isomerization of the double bond to derivative II and fur-
ther reduction under the experimental conditions to give
the 1,2,3,4-tetrahydronaphthalene 8a. This result was not
unexpected since Rabideau et al.2a had shown that the
Birch reduction of 1-phenylnaphthalene afforded exclu-
sively the product resulting from the reduction of the
naphthalene ring bearing the phenyl substituent.
3a–h
DDQ, CH2Cl2
R1
a: R1 = Me, R2 = R3 = H
b: R1 = OMe, R2 = R3 = H
c: R1 = R2 = OMe, R3 = H
d: R1 = R3 = H, R2 = Et
e: R1 = R3 = H, R2 = i-Pr
f: R1 = R2 = R3 = OMe
g: R1 = R2 = OMe; R3 = Me
h: R1 = R2 = R3 = Me
r.t., 15 min
(71–97%)
R3
R2
MeO
2a–h
Scheme 2 Synthesis of 1-aryl-7-methoxynaphthalenes 2a–h.
Thus, the reaction of p-tolylmagnesium bromide 6a with
commercially available 7-methoxy-1-tetralone (4) afford-
ed the corresponding carbinol which, after treatment with
35% HCl, gave 4-(p-tolyl)-6-methoxy-1,2-dihydronaph-
thalene (3a), in 73% yield (Scheme 2). Under the same
conditions, 4-methoxyphenyl magnesium bromide (6b)
and the 2,4-dimethoxyphenyl derivative 6c furnished di-
hydronaphthalenes 3b (86%) and 3c (72%), respectively.
Nevertheless, when the reaction was carried out with 2-
ethylphenyl magnesium bromide (6d), bearing a bulky
ethyl substituent at the ortho-position, compound 3d was
formed in a poor 20% yield.
The reduction of derivative 2b, bearing a p-methoxyphe-
nyl substituent at C-1 afforded 1-(p-methoxyphenyl)-7-
methoxy-1,2,3,4-tetrahydronaphthalene (8b) again as the
exclusive product, in 71% yield, showing that the pres-
ence of a more electron-donating substituent on the phe-
nyl unit has no influence on the ring-selectivity of the
reduction process.
Reduction of compound 2c, with a 2,4-dimethoxyphenyl
substituent, gave a 30:70 mixture of b-tetralone 1c and tet-
rahydronaphthalene 8c. Compound 1c was formed from
reduction of the B-ring of 2c followed by acidic hydroly-
sis of the vinyl ether intermediate III (Scheme 3).
Synlett 2005, No. 10, 1601–1605 © Thieme Stuttgart · New York

LETTER
Na/EtOH Reduction of 1-Arylnaphthalenes
1603
With the aim of evaluating if this result was due to the case, a 75:25 mixture of derivatives 1g (60% isolated
presence of two electron-donor groups or the existence of yield) and 8g23 resulted.
a methoxy substituent at the ortho-position of the 1-aryl
Finally, the best B-ring selectivity in the reduction process
group in 2c, we performed the reduction of naphthalene
(85:15) was achieved using compound 2h, bearing two
2d, bearing a 2-ethylphenyl group at C-1. In this case, a
methyl groups at the ortho-positions, as starting material.
50:50 mixture of compounds 1d and 8d was obtained,
Under the reduction conditions followed by acidic hydro-
lysis, 8-aryl-2-tetralone 1h could be isolated pure after
flash chromatography in 54% yield.
showing that the presence of a bulky substituent at the
ortho-position enhanced the B-ring reduction of the naph-
thalene derivative. This assumption was confirmed after
reduction of compound 2e, with a 2-isopropylphenyl
group at C-1, which gave a 60:40 mixture of compounds
1e and 8e, with reduction of the B-ring of 2e the major
process. An identical result was obtained from reduction
of derivative 2f, with two methoxy groups at the ortho-po-
The relative ratio of A-ring/B-ring reduction products
achieved from 1-arylnaphthalenes 2 is not easy to ratio-
nalize from the mechanistic point of view. Taking into ac-
count that the structure of the metal-mediated reduction
product is determined by the site of protonation of the rad-
ical anion formed after the first electron transfer,24 this fa-
sitions, affording a 60:40 mixture of compounds 1f and 8f.
vored formation of the radical anion of the initial
intermediate I, (Scheme 3) which could explain the pre-
ferred ring-A reduction. Two resonance forms with the
radical at C-1 of I and the anion at C-4, or the reverse, can
be considered. In the former, an ortho-unsubstituted aryl
group could result in delocalization of the electrons, thus
favoring the reduction of the A-ring. The existence of
ortho-substituents on the aryl group could distort the pla-
narity of the system causing the destabilization of the rad-
ical intermediate and increasing the ratio of the product
resulting from B-ring reduction. If the negative charge on
the radical anion is situated at C-1 of I, the non-planar ge-
ometry caused by ortho-substitution at the aryl group
could inhibit protonation of this intermediate due to steric
influences, thus B-ring reduction would be favored.
R1
R1
Ring A
reduction
R2
R3
R2
R3
1
MeO
MeO
1
4
B
A
I
2a–h
i. Na, EtOH, 100 °C
ii. 35% HCl
Ring B
reduction
R1
R1
R2
R3
R2
R3
8
MeO
MeO
In summary, we have shown that the ring-selectivity of
the reduction of 1-aryl-7-methoxynaphthalenes can be
modulated by the substitution pattern at the 1-aryl frag-
ment. The existence of small substituents (H or OMe) at
the ortho-positions gives rise mainly to the formation of
the products resulting from reduction of the aryl substitut-
ed A-ring of the naphthalene unit affording 1-aryl-7-
methoxy-1,2,3,4-tetrahydronaphthalenes. With one or
two alkyl groups at the ortho-positions of the 1-aryl moi-
ety, reduction of the B-ring is preferred, giving rise to the
corresponding 8-aryl-2-tetralones, after acidic work-up.
The ring-selectivity of the process seems to be governed
by the ease of protonation and/or stabilization of the ini-
tially formed radical anion at C-1, both disfavored when
the co-planarity between the 1-aryl group and the dihy-
dronaphthalene ring is lost due to the presence of different
bulky substituents at the ortho-positions of the 1-aryl moi-
ety.
III
II
R1
R1
R2
R3
R2
R3
8
MeO
O
+
8a–h
1a–h
a: R1 = Me, R2 = R3 = H
100 (62)
100 (71)
70 (50)
50 (36)
40 (20)
40 (28)
25 (22)
15 (8)
a
0
0
b: R1 = OMe, R2 = R3 = H
c: R1 = R2 = OMe, R3 = H
d: R1 = R3 = H, R2 = Et
e: R1 = R3 = H, R2 = i-Pr
f: R1 = R2 = R3 = OMe
g: R1 = R2 = OMe; R3 = Me
h: R1 = R2 = R3 = Me
a
30 (29)
50 (36)
60 (45)
60 (32)
75 (60)
85 (54)
a In brackets, isolated yields of compounds 1 and 8 after flash chromatography
Na/EtOH Reduction; Typical Procedure
To a solution of the corresponding 1-aryl-7-methoxynaphthalene 2
(0.7 mmol) in EtOH (35 mL) heated at 100 °C, under argon, 6 or 7
pieces of Na of ca. 0.5 cm were added, and during the reaction time
the same amount of Na was maintained in the reaction media. The
mixture was vigorously stirred at 100 °C until all the starting mate-
rial had been consumed by TLC. The reaction was quenched with
Scheme 3 Na/EtOH reduction of 1-aryl-7-methoxynaphthalenes
2a–h.
To further increase the ratio of B-ring reduction, and as a
consequence the yield of the 8-aryl-2-tetralones, we car-
ried out the reaction with 1-arylnaphthalene 2g, with a EtOH and cooled to room temperature. When all the Na had com-
pletely disappeared, H2O was slowly added, the mixture was cooled
to 0 °C and 35% HCl was added dropwise until acid pH (1–2). After
methoxy and a methyl group at the ortho-positions. In this
Synlett 2005, No. 10, 1601–1605 © Thieme Stuttgart · New York

1604
M. C. Carreño et al.
LETTER
11, 521. (c) Wang, X.-Z.; Yao, Z.-J.; Liu, H.; Zhang, M.;
Yang, D.; George, C.; Burke, T. R. Tetrahedron 2003, 59,
6087.
extraction with CH2Cl2, washing with sodium bicarbonate, and usu-
al workup, the corresponding mixture of 1-aryl-7-methoxy-1,2,3,4-
tetrahydronaphthalenes 8 and 8-aryl-2-tetralones 1 was obtained
and separated by flash chromatography.
(5) Recent examples: (a) Youngman, M. A.; Willard, N. M.;
Dax, S. L.; McNally, J. J. Synth. Commun. 2003, 33, 2215.
(b) Gemma, S.; Butini, S.; Fattorusso, C.; Fiorini, I.; Nacci,
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Tetrahedron 2003, 59, 87.
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Lenardao, E. J. Tetrahedron 2004, 60, 8295. (b) Schner, V.
F.; Przhiyaglovskaya, N. M. Russ. Chem. Rev. 1966, 35, 523.
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2003, 558. (b) Alcock, L. J.; Mann, I.; Peach, P.; Wills, M.
Tetrahedron: Asymmetry 2002, 13, 2485. (c) Parker, M. H.;
Chen, R.; Conway, K. A.; Lee, D. H. S.; Luo, C.; Boyd, R.
E.; Nortey, S. O.; Ross, T. M.; Scorr, M. K.; Reitz, A. B.
Bioorg. Med. Chem. 2002, 10, 3565.
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Bioorg. Med. Chem. Lett. 2003, 13, 133. (d) Jha, A.;
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LaVoie, E. J. Bioorg. Med. Chem. 2003, 11, 3795.
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Deschamps, J. R.; Burke, T. R. Jr. Tetrahedron 2004, 60,
2971. (b) Gray, A. D.; Smith, T. P. J. Org. Chem. 2001, 66,
7113.
Spectral Data for 8-Aryl-2-tetralones 1c–h
Compound 1c: 1H NMR: d = 2.49 (m, 2 H), 3.12 (m, 2 H), 3.28 and
3.48 (AB system, 2 H, J = 19.6 Hz), 3.72 (s, 3 H), 3.84 (s, 3 H), 6.52
(t, 1 H, J = 2.3 Hz), 6.55 (d, 1 H, J = 2.5 Hz), 7.04 (d, 1 H, J = 8.0
Hz), 7.13 (dd, 1 H, J = 2.3 and 6.8 Hz), 7.24 (m, 2 H). 13C NMR:
d = 28.4, 38.1, 43.0, 55.3, 55.4, 98.5, 104.5, 121.9, 126.3, 126.6,
128.9, 131.4, 132.4, 136.5, 138.0, 157.4, 160.7, 211.6.
Compound 1d: 1H NMR: d = 1.02 (t, 3 H, J = 7.6 Hz), 2.35 (ddd, 2
H, J = 7.4, 7.6 and 10.2 Hz), 2.57 (t, 2 H, J = 6.7 Hz), 3.15 (t, 2 H,
J = 6.7 Hz), 3.19 and 3.33 (AB system, 2 H, J = 19.0 Hz), 7.01–7.32
(m, 7 H). 13C NMR: d = 16.1, 27.1, 29.9, 39.1, 43.7, 126.7, 127.2,
127.6, 128.8, 129.3, 129.4, 130.4, 132.3, 137.8, 140.3, 142.0, 142.7,
211.7.
Compound 1e: 1H NMR: d = 1.11 (d, 3 H, J = 6.8 Hz), 1.17 (d, 3 H,
J = 6.8 Hz), 2.61 (t, 2 H, J = 6.8 Hz), 2.65 (sept, 1 H, J = 6.8 Hz),
3.18 (t, 2 H, J = 6.8 Hz), 3.23 and 3.37 (AB system, 2 H, J = 19.6
Hz), 7.02–7.46 (m, 7 H). 13C NMR: d = 23.1, 24.6, 28.8, 29.9, 38.1,
42.9, 125.5, 125.6, 126.1, 126.6, 128.0, 128.3, 129.3, 131.4, 136.8,
138.6, 141.1, 146.5, 210.6.
Compound 1f: 1H NMR: d = 2.56 (t, 2 H, J = 6.6 Hz), 3.11 (t, 2 H,
J = 6.6 Hz), 3.32 (s, 2 H), 3.68 (s, 6 H), 3.86 (s, 3 H), 6.21 (s, 2 H),
7.11–7.30 (m, 3 H). 13C NMR: d = 28.9, 38.2, 42.7, 55.4, 55.7, 90.7,
109.9, 125.8, 126.5, 130.0, 133.1, 133.6, 136.2, 158.2, 161.0, 211.8.
Compound 1g: 1H NMR: d = 1.96 (s, 3 H), 2.60 (m, 2 H), 3.15 (t, 2
H, J = 6.4 Hz), 3.20 and 3.33 (AB system, 2 H, J = 19.9 Hz), 3.68
(s, 3 H), 3.86 (s, 3 H), 6.40 (d, 1 H, J = 2.1 Hz), 6.45 (d, 1 H, J = 2.1
Hz), 7.05 (dd, 1 H, J = 2.1 and 6.4 Hz), 7.25 (m, 2 H). 13C NMR:
d = 20.5, 28.9, 38.3, 42.3, 55.3, 55.5, 96.0, 106.4, 121.0, 126.3,
126.5, 129.0, 132.5, 136.5, 136.8, 138.1, 157.6, 159.8, 211.7.
Compound 1h: 1H NMR: d = 1.87 (s, 6 H), 2.32 (s, 3 H), 2.56 (t, 2H,
J = 6.6 Hz), 3.10–3.15 (m, 4 H), 6.92 (s, 2 H), 6.99 (d, 1 H, J = 2.0
Hz), 7.25 (m, 2 H). 13C NMR: d = 20.2, 21.0, 28.9, 38.3, 42.1,
126.4, 126.8, 127.9, 128.2, 131.3, 135.6, 136.5, 136.9, 137.0, 140.2,
210.9.
(11) (a) Carreño, M. C.; González-López, M.; Urbano, A. Chem.
Commun. 2005, 611. (b) Carreño, M. C.; García-Cerrada,
S.; Urbano, A. Chem.–Eur. J. 2003, 9, 4118–4131.
(c) Carreño, M. C.; García-Cerrada, S.; Urbano, A. Chem.
Commun. 2002, 1412. (d) Carreño, M. C.; García-Cerrada,
S.; Urbano, A. J. Am. Chem. Soc. 2001, 123, 7929.
(12) (a) Ram, V. J.; Agarwal, N.; Saxena, A. S.; Farhanullah, ;
Sharon, A.; Maulik, P. R. J. Chem. Soc., Perkin Trans. 1
2002, 1426. (b) Ram, V. J.; Agarwal, N.; Farhanullah,
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Acknowledgment
We thank Ministerio de Ciencia y Tecnología (Grant BQU2002-
03371) and Comunidad Autónoma de Madrid (Grant GR/MAT/
0152/2004) for financial support. M.G.L. wishes to thank Comuni-
dad Autónoma de Madrid for a fellowship.
(13) Soffer, M. D.; Bellis, M. P.; Gellerson, H. E.; Stewart, R. A.
Org. Synth. 1952, 32, 97.
(14) Cornforth, J. W.; Cornforth, R. H.; Robinson, R. J. Chem.
Soc. 1942, 689.
(15) (a) Carreño, M. C.; García-Cerrada, S.; Sanz-Cuesta, M. J.;
Urbano, A. Chem. Commun. 2001, 1452–1453. (b)
Carreño, M. C.; Enríquez, A.; García-Cerrada, S.; Sanz-
Cuesta, M. J.; Urbano, A. unpublished results.
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Braga, A. L.; Lenardao, E. J. Tetrahedron Lett. 2004, 45,
4077. (c) Barolo, S. M.; Lukach, A. E.; Rossi, R. A. J. Org.
Chem. 2003, 68, 2807. (d) Renaud, J. L.; Dupau, P.; Hay,
A.-E.; Guingouain, M.; Dixneuf, P. H.; Bruneau, C. Adv.
Synth. Catal. 2003, 345, 230.
(4) Recent examples: (a) Jha, A.; Beal, J. Tetrahedron Lett.
2004, 45, 8999. (b) Li, D.; Zhao, B.; Sim, S.-P.; Li, T.-K.;
Liu, A.; Liu, L. F.; LaVoie, E. J. Bioorg. Med. Chem. 2003,
(18) For examples on the additions of aryl Grignard reagents to
a-tetralones see: (a) Alcock, N. J.; Mann, I.; Peach, P.;
Wills, M. Tetrahedron: Asymmetry 2002, 13, 2485.
(b) Schneider, M. R.; Schiller, C. D. Arch. Pharm. 1990,
323, 17. (c) Laus, G.; Tourwe, D.; Van Binst, G.
Heterocycles 1984, 22, 311. (d) Adam, G.; Andrieux, J.;
Plat, M. Tetrahedron 1982, 38, 2403. (e) Bindal, R. D.;
Durani, S.; Kapil, R. S.; Anand, N. Synthesis 1982, 405.
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(19) (a) Suzuki, A. Modern Arene Chemistry; Wiley-VCH: New
York, 2002, 53. (b) Miyaura, N.; Suzuki, A. Chem. Rev.;
1995, 95, 2457. For examples of cross-coupling reactions
between enol triflates and boronic acids and derivatives see:
(c) Miyashita, K.; Sakai, T.; Imanishi, T. Org. Lett. 2003, 5,
2683. (d) Basil, L. F.; Nakano, H.; Frutos, R.; Kopach, M.;
Meyers, A. I. Synthesis 2002, 2064. (e) Pal, K. Synthesis
1995, 1485.
(20) Watanabe, T.; Miyaura, N.; Suzuki, A. Synlett 1992, 207.
(21) Scheiper, B.; Bonnekessel, M.; Krause, H.; Fürstner, A. J.
Org. Chem. 2004, 69, 3943.
(22) Boronic acids 7d–h were commercially available (7d–f and
7h) or previously described: 7g: Bringmann, G.; Goetz, R.;
Keller, P. A.; Walter, R.; Boyd, M. R.; Lang, F.; Garcia, A.;
Walsh, J. J.; Tellitu, I.; Bhaskar, K. V.; Kelly, T. R. J. Org.
Chem. 1998, 63, 1090.
(23) The 1H NMR spectrum (CDCl3) of compound 8g showed
several broad non-well resolved signals probably due to the
presence of atropisomers caused by a hindered rotation
about the aryl(sp2)-C1(sp3) single bond: Eliel, E. L.; Wilen,
S. H.; Doyle, M. P. In Basic Organic Stereochemistry;
Wiley: New York, 2001, 629; when 8g was heated in
C2D2Cl4 at 390 K the broad signals coalesced.
(24) Carey, F. A.; Sundberg, R. J. In Advanced Organic
Chemistry. Part B: Reactions and Synthesis, 4th ed.;
Kluwer: Norwell, 2000.
Synlett 2005, No. 10, 1601–1605 © Thieme Stuttgart · New York