A new route to 2,2′,3,3′-tetrasubstituted binaphthyls

Article abstract of DOI:10.1016/j.tetlet.2009.03.008

Based on an ortho-lithiation protocol of 2,2′-dibromo-1,1′-binaphthyl four tetrasubstituted binaphthyls, 2,2′-dibromo-3,3′-diiodo-, 3,3′-dibromo-2,2′-diiodo-, 2,2′,3,3′-tetrabromo-, and 2,2′,3,3′-tetraiodo-1,1′-binaphthyls have been prepared in excellent

Full text of DOI:10.1016/j.tetlet.2009.03.008

Tetrahedron Letters 50 (2009) 2425–2429
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Tetrahedron Letters
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A new route to 2,20,3,30-tetrasubstituted binaphthyls
a
b
Michael Widhalm a, , Christian Aichinger , Kurt Mereiter
*
a Institute for Organic Chemistry, University of Vienna, Währinger Strasse 38, A-1090 Vienna, Austria
b Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/164SC, A-1060 Vienna, Austria
a r t i c l e i n f o
a b s t r a c t
Based on an ortho-lithiation protocol of 2,20-dibromo-1,10-binaphthyl four tetrasubstituted binaphthyls,
2,20-dibromo-3,30-diiodo-, 3,30-dibromo-2,20-diiodo-, 2,20,3,30-tetrabromo-, and 2,20,3,30-tetraiodo-1,10-
binaphthyls have been prepared in excellent yield which in turn proved to be versatile key intermediates
in the synthesis of various 2,20,3,30-tetrasubstituted 1,10-binaphthyl derivatives.
Ó 2009 Elsevier Ltd. All rights reserved.
Article history:
Received 17 January 2009
Revised 28 February 2009
Accepted 4 March 2009
Available online 9 March 2009
Keywords:
ortho-Lithiation
ipso-Substitution
Suzuki–Miyaura coupling
The inherently chiral 1,10-binaphthyl fragment is probably the
best known atropisomeric unit and a motif frequently found in
those auxiliaries and ligands which are not derived from the chi-
ral pool (Fig. 1).1 Since their broad range of applicability often
with excellent asymmetric induction in numerous asymmetric
transformations has been discovered, methods for economic and
selective access were desired and numerous strategies have been
worked out.2
The introduction of at least one substituent in position 2 is
obligatory to sufficiently hinder biaryl rotation and to enable con-
figurative stability at room temperature.3 Typically symmetrically
or unsymmetrically 2,20-disubstituted binaphthyls have been syn-
thesized with potential of forming substrate-reagent complexes or
chelates with transition metals. In the majority of cases their syn-
thesis is based on three chiral key intermediates 1–3, easily resolv-
able into enantiomers which are subsequently transformed into
the desired derivatives.4 Alternatively, enantioselective or diaste-
reoselective oxidative coupling or cross-coupling protocols of achi-
ral or chirally modified precursors using substoichiometric (chiral)
copper, palladium, and nickel complexes, respectively have been
performed.5 Moreover, optical resolution procedures for the final
products have been reported (Scheme 1).6,2
tion of binaphthyls with 2,20-substituents other than OR, since this
requires either (a) a stereoconservative exchange of two OR, both
di-ortho substituted; which may be difficult from steric reasons
and reduced racemization barrier of intermediates,8 (b) the use
of other ortho-directing groups,9 (c) a diastereoselective binaph-
thyl coupling of suitable substituted naphthalene precursors or
(d) an optical resolution step of the final product.10
Examples for the first route have been published by Maruoka’s
group to obtain tetrasubstituted binaphthyls with carbon substitu-
ents in pos. 2, 20, 3, and 30 from binaphthol (7–10 steps, 50–65%
overall yield).11 Similar compounds were also accessible via an
ortho-magnesation of 1,10-binaphthyl-2,20-dicarboxylic acid diiso-
propylester as the key step (5 steps, 74% overall yield)12 and
ortho-lithiation of the free diacid followed by bromination with
2,4,4,6-tetrabromo-2,5-hexadien-1-on.13,14 To the best of our
knowledge no attempt has been made to find routes to 2,20,3,30-
substituted binaphthyls via ortho-metallation of 2,20-dibromo-
1,10-binaphthyl 4 although various bromoarenes have been fre-
quently ortho-metallated with lithium dialkylamides.15
Further substituents have been introduced in pos. 3 and 30 when
either extended chiral environment or improved conformative sta-
bility through a buttressing effect was desired. Since ortho-metal-
lation of O-protected binaphthol derivatives is readily performed,
2,20-OR-3,300-X substituted binaphthyls are accessible in excellent
yield from binaphthol in few steps.7 More difficult is the prepara-
* Corresponding author. Tel.: +43 1 4277 52111; fax: +43 1 4277 9521.
E-mail address: m.widhalm@univie.ac.at (M. Widhalm).
Scheme 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.008

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M. Widhalm et al. / Tetrahedron Letters 50 (2009) 2425–2429
Scheme 2. 2,20,3,30-Tetrahalo-1,10-binaphthyls. Reagents and conditions: (a) LiTMP/ClSiMe3, ꢀ78 °C?rt (81%); (b) NBS, acetonitrile, rt (quant.); (c) n-BuLi/THF/ꢀ78/ꢀ40/
ꢀ78 °C, ICH2CH2I (94%); (d) ICl, DCM, ꢀ40 °C (93%); (e) ICl, DCM, ꢀ40 °C (92%); (f) NBS, acetonitrile, rt (85%).
Scheme 3. 2,20,3,30-Tetrasubstituted binaphthyl derivatives accessible from 9. Reagents and conditions: (a) n-BuLi/THF/ꢀ78/ꢀ40/ꢀ78 °C, PhSSPh (73%); (b) n-BuLi/THF/ꢀ78/
ꢀ40/ꢀ78 °C, CO2(s), CH2N2, MeOH (75%); (c) n-BuLi/THF/ꢀ78/ꢀ40/ꢀ78 °C, DMF (74%); (d) PhB(OH)2, Pd(PPh3)4, toluene, reflux (92%); (e) n-BuLi/THF/ꢀ78/ꢀ40/ꢀ78 °C,
ICH2CH2I (87%); (f) n-BuLi/THF/ꢀ78/ꢀ40/ꢀ78 °C, Ph2PCl (89%); (g) 2-MeO–C6H4–B(OH)2, Pd(PPh3)4, toluene, reflux (75%); (h) 2-furyl-B(OH)2 or 2-thienyl-B(OH)2,
respectively, Pd(PPh3)4, DME, 120 °C (MW) (12% and 61%, respectively).
Such binaphthyl precursors with two pairs of independently
transformable substituents in pos. 2 and 20 as well as in 3 and 30
would offer improved synthetic flexibility particularly in the field
of ligand design for asymmetric catalysis. In classical biaryl ligands
or auxiliaries bearing exclusively 2,20 substituents, these are
responsible for both, kinetic stability of the chelate and catalytic
activity as a consequence of electron density and orbital geome-
tries, but also for the chirality transfer from the chiral backbone

M. Widhalm et al. / Tetrahedron Letters 50 (2009) 2425–2429
2427
(usually through a propeller-shaped arrangement of phenyl rings).
Ligands with additional substituents in pos. 3,30 should better
match these twofold requirements. While alkyl or aryl groups of
proper size and shape in pos. 3 and 30 will influence the coordina-
tion mode of substrate, donor groups in pos. 2 and 20 can be rather
optimized for stability of the (chelate) complex. Further benefits of
this concept could be a buttressing effect increasing the racemiza-
tion barrier in 2,20-dilithio intermediates and facilitating a stereo-
conservative transformation.
Treatment of 4 with excess of Li-2,2,6,6-tetramethylpiperidid
(LiTMP) at ꢀ78 °C and in situ trapping with trimethylchlorosi-
lane16 afforded 6 in 81% yield which could be further converted
to 7 under standard conditions (n-BuLi, ꢀ78 °C, ICH2CH2I). From
each of these intermediates two tetra-halo binaphthyls, 5 and 9
from 6, as well as 8 and 10 from 7 could be synthesized as outlined
in Scheme 2. While for a Me3Si?I exchange17 a standard protocol
was applied the corresponding Me3Si?Br transformation was best
performed with NBS in acetonitrile (Scheme 2).18
Scheme 4. 2,20,3,30-Tetrasubstituted binaphthyl derivatives with cyano and ethy-
nyl substituents from 8, 9, and 10. Reagents and conditions: (a) Zn(CN)2, Pd2(dba)3,
dppf, DMF, 110 °C, 5 h (67%); (b) Zn(CN)2, Pd2(dba)3, dppf, DMF, 110 °C, 20 h (74%);
(c) PhC„CZnCl, Pd(PPh3)4, THF, reflux, 1 h (85%); (d) PhC„CZnCl, THF, reflux, 1 h
(7%).
To demonstrate the versatility of tetrahalogenids as synthetic
key intermediates some subsequent transformations were per-
formed as outlined in Schemes 3 and 4. The Suzuki–Miyaura cou-
pling19 of 9 with phenyl boronic acid afforded selectively 14
while arylation with 2-bromoanisole yielded a mixture of three
interconverting rotamers of 17 in fair yield (coalescence of OMe
groups in 1H NMR, 400 MHz at ca. 315 K). No coupling products
18 and 19 were isolated with 2-bromo-furane and 2-bromo-thio-
phene boronic acid under similar conditions. Only when applying
more harsh conditions (microwave heating, 120 °C, 3 days) 18
and 19 were formed in low yield (12% and 61%, respectively). Sub-
sequent bromide-lithio exchange in 9 and treatment with PhSSPh,
CO2, DMF, and ICH2CH2I led to 11, 12 (isolated as methylester), 13,
and 15, respectively.
Palladium-catalyzed cyanation (Scheme 4) gave the dicyano
compound 20 while enforcing conditions furnished 2,20,3,30-
tetracyano-1,10-binaphthyl 21 albeit in moderate yield. More
straightforward was the reaction from tetraiodide 8 (74% of 21).
Regioisomers 9 and 10 were also found to be suitable substrates
for a site selective Sonogashira coupling with phenylacetylene to
give 22 and 23 although in very different yields (85% vs 7%)
reflecting the steric congestion in 23. An attempted introduction
of diphenylphosphino groups into 14 failed (n-BuLi, ꢀ78 °C,
ClPPh2). As the only isolable product the yellow tetraarylphospho-
nium salt 16 was obtained (89%) as a crystalline compound with
intensive green-yellow fluorescence. Its solid-state structure was
determined.
Scheme 5. Reagents and conditions: (a) LiTMP/B(i-PrO)3, ꢀ78 °C?rt (90%); (b)
H2O2, MeOH, rt (76%); (c) 2-bromopyridine, Pd(PPh3)4, DME, 110 °C (MW) (43%).
Figure 1. Atropisomeric 1,10-binaphthyls.
Figure 2. Molecular structure of 5 in solid state. Left: ORTEP representation of a molecule with 50% displacement ellipsoids. Right: Superposition of an R-configured molecule
and a S-configured molecule in space filling representation was encountered statistically in solid state due to the partial orientation disorder of the naphthyl moieties; Br red,
C grey, H white; a related situation was encountered with the 2,20-dibromo-3,30-dicyano-compound 20, see text.

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M. Widhalm et al. / Tetrahedron Letters 50 (2009) 2425–2429
Another key intermediate was diboronic acid 24 that was sim-
crystallizes in the monoclinic space group P21/n, the binaphthyl
moiety exhibits a naphthyl–naphthyl angle of 89.79(5)° and an
intramolecular BrꢁꢁꢁBr distance of 3.973(1) Å, by 0.3 Å larger than
two van der Waals radii of Br (Fig. 3).
ilarly synthesized as 6 from 4 (71% yield, Scheme 5). Oxidation of
24 with H2O2 furnished diphenol 25 (76%), Suzuki–Miyaura cou-
pling with 2-bromopyridine yielded 26 in moderate yield (43%).
Crystallographic investigations: Simple 1,10-binaphthyl deriva-
tives other than those based on 2,20-dihydroxy-1,10-binaphthyl
have been explored scarcely by crystallography. Therefore it was
considered rewarding to study some representatives of the new
compound library by X-ray crystal structure determinations. The
selection of compounds for this purpose was in part dictated by
crystallization behavior. Thus, the key compound 14 resisted all ef-
forts to obtain crystals of sufficient size. Finally following com-
pounds were studied: 5, 20, 11, 22, and the phosphonium salt
16. Crystallographic details are reported in the Supplementary
data. The 2,20,3,30-tetrabromo-compound 5 crystallized from DMF
as a solvate of monoclinic symmetry, space group P21/n, with the
1,10-binaphthyl moiety in general position (Fig. 2) showing normal
bond lengths and angles and a naphthyl–naphthyl angle of 88.1(1)°
(defined as interplanar angle between the least-squares planes of
the two naphthyl moieties). Interestingly, the structure determina-
tion revealed the presence of significant disorder by which the Br
atoms and the terminal benzenes of the naphthyl groups inter-
changed positions for about 10% of all molecules (1st naphthyl
13%, 2nd naphthyl 7% orientation reversal). As shown in Figure
ure 2, the two Br atoms of each naphthyl moiety have a similar
space requirement as the terminal benzene ring at the opposite
side. In the lack of strongly directing intermolecular forces such
as hydrogen bonds, the crystal lattice of 5 is partly tolerant and
can take up a certain amount of S-configured molecules in sites de-
signed for R-configured molecules and vice versa.20
The phosphonium bromide 16, which crystallized as the mono-
clinic solvate 16ꢁ2CHCl3, deviates most significantly in geometry
from all previous compounds (Fig. 4). Because of the bridging phos-
phorus the naphthyl–naphthyl angle is low, 42.0(1)°, and both
naphthyl moieties are very distinctly bent and twisted in order
to achieve an acceptable peri-hydrogen contact (H9ꢁꢁꢁH19 =
2.32 Å). Therefore, the torsion angle C2–C1–C11–C12 = 24.0(4)°
differs considerably from the naphthyl-naphthyl interplanar angle.
Because of a sterical congestion between the four phenyl substitu-
ents of 16 the bond angles around phosphorus deviate distinctly
from those of an ideal tetrahedron (C–P–C angles from 94.1° to
118.8°), but the molecule of 16 approaches a non-crystallographic
C2-symmetry quite well.
This conclusion is supported by the observation that also 2,20-
dibromo-3,30-dicyano-compound 20, which crystallized without
solvent in a lattice of monoclinic symmetry, space group C2/c (dif-
ferent from 5), showed the same kind of R/S-tolerance, albeit at a
lower level: only 8.8% of one naphthyl moiety is in reverse orienta-
tion, whereas the second naphthyl moiety is practically ordered
(misorientation < 2%). This situation changes of course as soon as
substituents in the 2,20- and/or 3,30-positions of the binaphthyl
core become large enough to inhibit false naphthyl orientation,
as is the case with the phenylsulfanyl-phenyl compound 11 or
the bromo phenylethinyl compound 22 (Fig. 3). In compound 11,
Figure 4. Molecular structure of 16ꢁ2CHCl3 in the solid state showing 50%
displacement ellipsoids. Bromide and CHCl3 omitted for clarity. Selected bond
distances and angles (Å, °): P1–C1 1.797(2), P1–C11 1.794(2), P1–C33 1.793(3), P1–
C39 1.791(2); C2–P1–C12 94.1(1), P1–C2–C1 107.6(2), P1–C12–C11 107.9(2), C2–
C1–C11 113.4(2), C12–C11–C1 112.6(2), C2–P1–C33 107.9(1), C2–P1–C39 118.8(1),
C12–P1–C33 117.6(1), C12–P1–C39 106.0(1), C33–P1–C39 111.7(1).
ꢀ
which crystallizes in the triclinic space group P1, the molecule
adopts a conformation that is nearly C2-symmetric and shows a
naphthyl–naphthyl angle of 73.89(2)°. In compound 22, which
Figure 3. Molecular structure of 11 (left) and 22 (right) in the solid state showing 50% displacement ellipsoids.

M. Widhalm et al. / Tetrahedron Letters 50 (2009) 2425–2429
2429
Cammidge, A. N.; Crépy, K. V. L. Tetrahedron 2004, 60, 4377–4386; (k) Genov,
M.; Fuentes, B.; Espinet, P.; Pelaz, B. Tetrahedron: Asymmetry 2006, 17, 2593–
2595.
In summary we developed a short and high yielding path to four
2,20,3,30-tetrahalo-1,10-binaphthyls and demonstrated their use as
flexible precursors for regioselective access to various tetrasubsti-
tuted binaphthyl derivatives.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.03.008.
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20. Note: While all compounds of the present study were racemates, this
observation has a consequence for enantiomerically enriched material, which
cannot be expected to be efficiently purified from the subordinate enantiomer
by fractional crystallization because of the partial tolerance against molecules
of the antipode.