Polar-π and cation-π stabilizing interactions between constrained cofacial aromatic rings favoring the more sterically hindered diastereomer

Full text of DOI:10.1021/jo010537a

J . Org. Chem. 2001, 66, 7227-7230
7227
Sch em e 1
P ola r -π a n d Ca tion -π Sta bilizin g
In ter a ction s betw een Con str a in ed Cofa cia l
Ar om a tic Rin gs F a vor in g th e Mor e
Ster ica lly Hin d er ed Dia ster eom er
Sophie Lavieri
Faculty of Pharmacy, Universidad Central de Venezuela,
Caracas 1048-A Venezuela
J ohn A. Zoltewicz*
We prepared two series of positional cofacial isomers
and examined their syn-anti population ratios by proton
NMR at 300 MHz at ambient temperatures. These
include three additional 8-aryl-and 8-hetaryl-1,1′-bi-
naphythyls to supplement our earlier study of such
compounds29 and seven new, isomeric 8-aryl- and 8-hetar-
yl-1,2′-binaphthyls (Scheme 1). The 8-arenes consisted
of 3′-substituted benzenes and the 8-hetaryls contained
a 3′-pyridyl ring. Arene substituents studied include
methoxy (1, 2), methylthio (3, 4), dimethylsulfonio (5, 6),
dimethylamino (7), and trimethylammonio (8). The py-
ridyl ring existed either as the free base 9 or the
N-methyl-quaternized ionic product 10. Examples are
given in Table 1. The results for these two series of
neutral and ionic compounds allowed us to determine the
influence of different groups and new geometries for the
interacting cofacial rings on the preference for the more
sterically hindered syn atropisomers induced by π-π,
polar-π, or cation-π interactions.
Population ratios for the compounds are considered in
pairs, each constitutional isomer of the pair having the
same group at position 3′ of the arene while differing in
the geometry of the cofacial 1′- or 2′-naphthyl ring. The
syn diastereomer is defined as that rotational form
having the group at position 3′ of the arene or hetarene
directed toward the B-ring of the cofacial 1′- or 2′-
naphthalene ring while the anti isomer is that structure
having this group directed away from the B-ring of the
naphthalene.
Department of Chemistry, University of Florida,
Gainesville, Florida 32611-7200
jaz@chem.ufl.edu
Received May 25, 2001
1,8-Diaryl cofacial naphthalenes1-7 as well as cyclo-
phanes1 continue to be useful model compounds to study
the interactions between aromatic rings held near or
below van der Waals interatomic distances. In such
naphthalenes, the two aromatic rings are held cofacial
but are splayed out from each other and are able to rotate
about the bonds attaching them to the rigid naphthalene
frame, thereby giving rise to atropisomers.4,8-10They are
readily prepared by a number of metal-catalyzed cross-
coupling reactions.11,12 Magnetic resonance10,13-15 contin-
ues to offer a means of facile study of the consequences
of π-π, π-dipole, and π-cation interactions, predomi-
nantly electrostatic in nature, on isomer populations.16-22
Cation-π interactions play a role in molecular recogni-
tion and in substrate-protein binding.23-28
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Syn th eses. A common palladium-catalyzed cross-
coupling approach was used to prepare all the cofacial
compounds as in our earlier studies.5,6,29 Usually, either
an 8-bromo-1,1′-binaphthyl or an 8-bromo-1,2′-binaphthyl
was coupled under Suzuki conditions30-32 with a 3-sub-
stituted benzeneboronic acid or diethyl(3-pyridyl)borane
in the presence of Pd(PPh3)4. An alternate route inter-
changed the positions of the bromo and boronic acid
groups. Thus, 1,1′-binaphthy-8-boronic acid ester and
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1972, 37, 1003-1009.
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41, 2252-2255.
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Reactions; Wiley-VCH: New York, 1998.
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35, 1815-1819.
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Am. Chem. Soc. 1992, 114, 5729-5733.
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Chem. Soc. 1993, 115, 5330-5331.
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Angew. Chem., Int. Ed. Engl. 1995, 34, 1019-1020.
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10.1021/jo010537a CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/13/2001

7228 J . Org. Chem., Vol. 66, No. 21, 2001
Notes
Ta ble 1. Ch em ica l Sh ifts for Ster eoisom er ic Meth yl P r oton s a n d Associa ted Isom er Qu otien ts for Cofa cia l Com p ou n d s
in Deu ter ioch lor ofor m
(area high field)/
compd
naphthyl
Z
G
low field, ppm
high field, ppm
(area low field)
1
2
3
1′
2′
1′
2′
1′
2′
1′
2′
1′
2′
2′
1′
2′
C
C
C
C
C
C
C
C
C
C
N
+N
+N
OMe
OMe
SMe
SMe
3.63
3.54
2.35
2.27
3.09
3.21
1.95
1.96
1.2
1.3
1.0
1.1
2.3
2.5
1.5
1.6
3.1
2.8
1.6
2.2
1.5
4
5a
+S(Me)2
+(SMe)2
N(Me)2
N(Me)2
+N(Me)3
+N(Me)3
-
3.31; 3.18b
3.05; 3.01b
2.78
2.98; 2.92b
2.84; 2.34b
2.30
6a
7Ad
7
2.68
3.80
2.37
3.41
8Ac,d
8c
3.64
3.29
9
6.50e
4.30
6.25e
3.95
10Ac,d
10c
Me
Me
4.38
3.94
a
b
d
Triflate. Diastereotopic methyl groups. c Iodide. Reference 29. e Ring proton.
1-bromo-3-methythiobenzene as well as N,N-dimethyl-
3-bromoaniline were coupled using Pd(PPh3)4. The meth-
ylthio cofacial product then was S-methylated with
methyl triflate while quaternization of the aniline and
pyridine employed MeI.
For the unquaternized 1-(2′-naphthyl)-8-(3′-pyridyl) 9,
the broadened multiplets at 6.25 and 6.50 ppm were in
a 1.6 to 1 area ratio, respectively. The higher field more
abundant signal is due to a ring proton, in contrast to
the other substrates studied here where the higher field
signals are due to methyl protons. These signals are
easily identified as being due to the H-5′ pyridyl ring
protons by their chemical shifts and by the presence of
two large ortho coupling constants in each of the two
atropisomers.7 The higher field multiplet is associated
with H-5′ which is directed over the B-ring of the
naphthalene, and this is the anti isomer where the
annular nitrogen atom of the pyridyl ring is directed
away from the B-ring of its neighbor. With 9 the more
highly populated atropisomer is anti as in classical
studies. This result stands in contrast with those found
for the other compounds in this study where the syn
isomer is favored. Thus, the identity of the major di-
astereomer changes with the presence or absence of a
positive charge, 10 versus 9, interesting differences.
P r oton NMR Stu d ies. Spectra for all the compounds
were taken at probe temperature at 300 MHz using
CDCl3 as the solvent, previously found to give the largest
difference between the populations of the syn and anti
isomers,29 the area of the methyl signal serving as the
primary population reporter group. The chemical shifts
of the methyl reporter groups for the 1,1′- and 1,2′-
binaphthyl series are in general agreement, Table 1. In
general, the aromatic region suffered from signal overlap
and gave little information except in the case of the
pyridyl ligand 9 that provided a larger separation in
proton signal positions for this ring. Area ratios based
on the signals for the methyl protons and also the ring
protons of 9 are summarized in Table 1. As expected, the
sulfonium salts demonstrated a pair of signals in equal
areas for the two diastereotopic methyl groups in each
of the syn and anti atropisomers for a total of four singlet
signals. Results in Table 1 for compounds denoted by a
number and also the letter A are from our earlier study.29
Syn /An t i P op u la t ion R a t ios. As in our29 and
other10,13,14 studies, we assign in Table 1 the higher field
singlet to the more shielded methyl group that is posi-
tioned over the cofacial 1′- or 2′-naphthyl B-ring in the
more sterically hindered syn atropisomer. The preference
for this more hindered diastereomer is small for the
neutral compounds having a 3′-OMe (1, 2), a 3′-SMe (4),
or a 3′-NMe2 (7, 7A) group, the ratio being only slightly
greater than one except for the SMe compound 3 in the
1′-naphthyl series where the value appears to be about
one. There is no substantial difference in these population
ratios between the 1′- and 2′-naphthyl constitutional
isomers having π-π and polar-π interactions. However,
when the substitutent at position 3′ has a positive charge
as in 5, 6, 8, and 8A, the preference for the syn
atropisomer increases noticeably, more than a factor of
2. When the positive charge is located on the ring as in
the 1-(2′-naphthyl)-8-(3′-pyridylium) ion 10, the value is
1.5, and this is smaller than that found earlier for the
corresponding 1′-naphthyl structural isomer 10A (2.2)
under similar conditions. The largest preference was
found for the ions with the largest group, trimethylam-
monio 8 and 8A, where the syn/ anti ratio is 2.8 to 1 and
3.1, respectively.
Con clu sion s
1,8-Disubstituted naphthalenes having two cofacial
aromatic rings demonstrate either one of two preferred
ground state syn or anti geometries due to restricted
rotation about their substituent-naphthalene bonds.
Two monocyclic aromatic rings, whether carbocyclic or
heterocyclic, with uncharged or charged groups, adopt the
expected classically favored anti geometry to minimize
steric and electrostatic repulsive interactions between
dipoles and/or charges.2-7,16-22 The same is true for two
cofacial 1- and 1′-naphthalene rings where again the less
sterically hindered anti form is more abundant.5 How-
ever, we find that when one of the cofacial aromatic rings
is a fused bicyclic 1′-naphthalene29 or a 2′-naphthalene
ring and the other is a monosubstituted monocyclic ring,
the syn diastereomer generally is favored in the ground
state. Here favorable π-π, dipole-π, and charge-π
interactions between the two cofacial sites are large
enough to overcome classically unfavorable interactions,
even when one of the rings contains a site manifesting a
considerable steric, repulsive, destabilizing interaction
with its neighboring ring.
Exp er im en ta l Section
Gen er a l Meth od s. For flash chromatography, the crude
coupled product was dissolved in a small amount of solvent and
added to some silica gel. After removal of the solvent by

Notes
J . Org. Chem., Vol. 66, No. 21, 2001 7229
evaporation, the resultant powder then was added to the top of
a silica gel column that then was eluted. Those compounds
consisting of a mixture of syn-anti isomers in unequal amounts
at probe temperature (ca. 20 °C) do not show integral peaks
areas, and so areas are not reported for their NMR spectra.
1-(1′-Na p h th yl)-8-(3′-m eth oxyp h en yl)n a p h th a len e (1). To
a degassed solution of 70.9 mg (0.213 mmol) of 8-bromo-1-(1′-
naphthyl)naphthalene29 and 12.4 mg (0.0107 mmol, 5 mol %) of
Pd(PPh3)4 in 5 mL of DME was added 35.6 mg (0.234 mmol) of
3-methoxyphenylboronic acid followed by 50 mg (0.49 mmol) of
Na2CO3 in 2 mL of degassed water. The mixture was stirred at
reflux under nitrogen for 3 h and then cooled to room temper-
ature. The mixture was filtered and treated consecutively with
CH2Cl2 (25 mL) and water (10 mL), and the aqueous layer was
extracted with CH2Cl2 (2 × 25 mL). The combined organic phases
were applied to a silica column equilibrated with hexanes/EtOAc
(1:1). Elution with the same solvent gave 63.8 mg (0.177 mmol,
6.84-6.68 (m), 6.54-6.30 (m), 2.27 (Me), 1.96 (Me). Anal. Calcd
for C27H20S‚0.4H2O: C, 84.51; H, 5.46. Found: C, 84.62, H, 5.90.
1-(1′-Na p h th yl)-8-[(3′-d im eth ylsu lfon io)p h en yl]n a p h th a -
len e Tr ifla te (5). To a solution of 1-(1′-naphthyl)-8-[(3′-meth-
ylthio)phenyl]naphthalene 0.4 hydrate (10.0 mg, 0.0259 mmol)
in dry hexanes (3 mL) was added at room-temperature methyl
trifluoromethanesulfonate (0.05 mL, 0.45 mmol). The white
precipitate was filtered and washed with hexanes and allowed
to dry under reduced pressure. The yellowish precipitate then
was dissolved in chloroform, and the organic phase was washed
with aqueous 0.01 N K2CO3 and then with water until neutral.
After drying over MgSO4, the solvent was removed under
reduced pressure to give 11.5 mg (0.019 mmol, 73%) of a
yellowish solid, mp 127-130 °C. 1H NMR (CDCl3) δ 8.2-8.07
(m), 7.71-7.06 (m), 6.87 (m), 3.31 (Me), 3.18 (Me), 2.98 (Me),
2.92 (Me). Anal. Calcd C29H23S2F3O3‚3.5H2O: C, 57.70; H, 5.01.
Found: C, 57.90; H, 4.79.
1
83%) of white crystals, mp144-145 °C. H NMR (CDCl3) δ 8.01
1-(2′-Na p h th yl)-8-[(3′-d im eth ylsu lfon io)p h en yl]n a p h th a -
len e Tr ifla te (6). To a solution of 1-(2′-naphthyl)-8-[(3′-meth-
ylthio)phenyl]naphthalene 0.4 hydrate (17 mg, 0.044 mmol) in
dry hexanes (3 mL) was added at room-temperature methyl
trifluoromethanesulfonate (0.1 mL, 0.9 mmol). The hexane phase
was removed, and the remaining phase was washed twice with
hexanes. The combined hexanes phases were concentrated, the
yellowish precipitate was dissolved in chloroform, and K2CO3
was added. After being dried over Na2SO4, the solvent was
removed to give 18 mg (0.033 mmol, 75%) of a yellowish product,
(2H, m), 7.70-7.10 (m), 6.71 (dd, J ) 7.8, 8.1 Hz), 6.45 (dt, J )
1.5, 7.5 Hz), 6.32 (m), 5.95-5.99 (m), 5.87 (dd, J ) 1.5, 2.4), 3.63
(Me), 3.09 (Me). Anal. Calcd for C27H20O: C, 89.97; H, 5.59.
Found: C, 89.63; H, 5.61.
1-(2′-Na p h th yl)-8-(3′-m eth oxyp h en yl)n a p h th a len e (2). To
a degassed solution of 71.0 mg (0.213 mmol) of 8-bromo-1-(2′-
naphthyl)naphthalene and 12 mg (0.011 mmol, 5 mol %) of Pd-
(PPh3)4 in 3 mL of DME was added 35.6 mg (0.234 mmol) of
3-methoxyphenylboronic acid followed by 50 mg (0.49 mmol) of
Na2CO3 in 1 mL of degassed water. The contents of the sealed
tube under nitrogen were magnetically stirred at 100 °C. After
30 min, to the black mixture was added an additional 6 mg of
Pd(PPh3)4 and 4 mL of degassed DME-water (3:1). Further
stirring, heating at reflux under nitrogen for 3 more hours,
cooling, and filtering were followed by diluting with CH2Cl2 (25
mL) and then water (10 mL). After separating the phases, the
water layer was extracted with CH2Cl2 (3 × 10 mL). The
combined organic phases were chromatographed on a silica
column equilibrated with hexanes/EtOAc (1:1) and eluted with
the same solvent. Rechromatographing with hexanes by gravity
gave 46.3 mg (12.8 mmol, 60%) of a yellow oil. 1H NMR (CDCl3)
δ 7.97 (d, 2H, J ) 8.1 Hz), 7.70-7.22 (m), 7.08 (d, J ) 8.4 Hz),
6.75-6.45 (m), 6.43 (s), 6.35 (s), 6.08 (m), 3.54 (Me), 3.21 (Me).
Anal. Calcd for C27H20O: C, 89.97; H, 5.59. Found: C, 89.83; H,
5.77.
1-(1′-Na p h th yl)-8-(3′-m eth ylth iop h en yl)n a p h th a len e (3).
A solution of 0.186 g (0.453 mmol) of di-n-butyl 1-(1′-naphthyl)-
8-naphthaleneboronate in 7 mL of DME was added to 0.140 g
(0.689 mmol) of 1-bromo-3-(methylthio)benzene (Lancaster), and
after degassing, 26 mg (0.023 mmol, 5 mol %) of Pd(PPh3)4
followed by 70 mg (0.66 mmol) of Na2CO3 in 2 mL of degassed
water was added. The mixture was heated at reflux with stirring
under nitrogen for 5 h and then allowed to reach room temper-
ature under nitrogen overnight. The solvent was removed, and
the residue was diluted with a mixture of CH2Cl2 (25 mL) and
water (10 mL). The organic layer was separated, and the
aqueous phase was extracted with CH2Cl2 (2 × 25 mL). The
combined organic phases were concentrated, and the residue was
applied to a silica column equilibrated with hexanes and eluted
with the same solvent. The pure fraction (identified by TLC) gave
0.128 g (0.340 mmol, 75%) of a white solid, mp 91-93 °C. 1H
NMR (CDCl3) δ 8.01 (2H, m), 7.7-7.12 (m), 6.65 (m), 6.58 (m),
6.50 (dt, J ) 2, 7.5 Hz), 6.25-6.13 (m), 2.35 (Me), 1.95 (Me).
Anal. Calcd. for C27H20S: C, 86.13; H, 5.35. Found: C, 86.12;
H, 5.97.
1
mp 123-125 °C. H NMR (CDCl3) δ 8.05 (t, J ) 8 Hz), 7.8-7.0
(m), 3.05 (Me), 3.01 (Me), 2.84 (Me), 2.34 (Me). Anal. Calcd for
C
29H23S2F3O3‚0.5HOSO2CF3: C, 57.74; H, 4.27. Found: C, 57.55;
H, 3.85. Mass spectrum (positive FAB): m/z 391.1531 (C28H23S,
391.1520).
Di-n -b u t yl 1-(2′-Na p h t h yl)-8-n a p h t h a len eb or on a t e. A
magnetically stirred solution of 1-bromo-8-(2′-naphthyl)naph-
thalene (100 mg, 0.300 mmol) in 30 mL of dry THF under
nitrogen was cooled to -74 °C, and 1.8 N n-BuLi (hexane) (0.20
mL, 0.36 mmol) was added dropwise, keeping the temperature
below -70 °C. The green-brown solution was stirred for 30 min
at this temperature, and then tri-n-butyl borate (0.10 mL, 0.37
mmol) was added slowly by syringe keeping the temperature
below -70 °C. The mixture was allowed to reach room temper-
ature gradually (12 h). After quenching with 15 mL of saturated
NH4NO3 and separating the phases, the organic layer was
extracted with ether (3 × 20 mL) and dried with Na2SO4.
Evaporation of the organic solvent gave a yellow oil which was
preadsorbed onto 0.5 g of silica and purified by flash chroma-
tography first using hexanes as eluent and then increasing the
polarity to 20% ethyl acetate. Flash chromatography was
performed again to the preadsorbed mixture onto 0.5 g silica
using hexanes/EtOAc (4:1) to give 53 mg (0.13 mmol, 41%) of a
yellow oil. Anal. Calcd for C28H31BO2‚H2O: C, 78.51; H, 7.76.
Found: C, 78.44; H, 7.72. 1,2′-Binaphthyl (27.7 mg, 0.11 mmol,
37%) mp 74-76 °C (lit.33 mp 79-81 °C) was also obtained as a
side product by washing the column with the same eluent.
1-(2′-Na p h th yl)-8-[3′-(N,N-d im eth yla m in o)p h en yl]n a p h -
th a len e (7). To a degassed solution of 40 mg (0.093 mmol) of
di-n-butyl 1-(2′-naphthyl)-8-naphthaleneboronate and 5.4 mg
(0.0047 mmol, 5 mol %) of Pd(PPh3)4 in 5 mL of DME was added
26.9 mg (0.134 mmol) of N,N-dimethyl-3-bromoaniline followed
by a degassed solution of 130 mg (3.61 mmol) of KOH and 2.4
mg (0.0074 mmol) of tetra-n-butylammonium bromide in 2 mL
of water. The mixture was stirred at reflux under nitrogen for
3 h, cooled to room temperature and diluted with CH2Cl2 (20
mL) and water (10 mL). The aqueous layer was extracted with
CH2Cl2 (2 × 15 mL). The combined organic phases were added
to 0.5 mg silica, concentrated, and applied to a silica column
equilibrated with hexanes. Elution with EtOAc in hexanes (0-
6%) gave 30 mg (0.073 mmol, 79%) of a yellowish oil. 1H NMR
(CDCl3) δ 7.97 (2H, m), 7.68-7.24 (m), 7.04 (d, J ) 8.1 Hz), 6.74
(t, J ) 7 Hz), 6.47 (m), 6.16 (m), 5.92 (d, J ) 7.2 Hz), 5.81 (m),
2.68 (Me), 2.37 (Me). Anal. Calcd for C28H23N‚ 2H2O: C, 82.12;
H, 6.64; N, 3.42. Found: C, 81.95; H, 6.25; N: 3.60.
1-(2′-Na p h th yl)-8-(3′-m eth ylth iop h en yl)n a p h th a len e (4).
To a degassed solution of 103 mg (0.309 mmol) of 8-bromo-1-
(2′-naphthyl)naphthalene and 17.9 mg (0.015 mmol, 5% mol) of
Pd(PPh3)4 in 5 mL of DME was added 50.8 mg (0.113 mmol) of
the boroxine trimer of 3-(methylthio)benzeneboronic followed by
0.113 g (1.07 mmol) of Na2CO3 in 2 mL of degassed water. After
15 min, additional Pd(PPh3)4 was added, and stirring was
continued for 3.25 more hours. The cooled mixture was diluted
with CH2Cl2 (25 mL) and then with water (10 mL). The water
layer was extracted with CH2Cl2 (2 × 25 mL). The combined
organic phases were chromatographed on
a silica column
equilibrated with hexanes and eluted with the same solvent to
give 47.0 mg (0.125 mmol, 40%) of a yellow oil. 1H NMR (CDCl3)
δ 7.97 (dd, J ) 1.2, 8.4 Hz), 7.70-7.30 (m), 7.22 (m), 7.08 (m),
(33) Dobbs, T. K.; Hertzler, D. V.; Keen, G. W.; Eisenbraun, E. J .;
Fink, R.; Hossain, M. B.; Helm, D. vd. J . Org. Chem. 1980, 45, 4769-
4774.

7230 J . Org. Chem., Vol. 66, No. 21, 2001
Notes
1-(2′-Na p h th yl)-8-[3′-(tr im eth yla m m on io)p h en yl]n a p h -
th a len e Iod id e (8). To 17 mg (0.042 mmol) of 1-(2′-naphthyl)-
8-[3′-(N,N-dimethylamino)phenyl]naphthalene in 2 mL of chlo-
roform was added 0.05 mL (0.8 mmol) of iodomethane. After
standing for 24 h at room temperature, the solvent was removed,
and the yellowish solid was suspended in ether and filtered. The
collected precipitate was washed with ether and dried to give
18.7 mg (0.0345 mmol, 82%) of a yellowish solid, mp 119-121
°C. 1H NMR (CDCl3) δ 8.07 (2H, t, J ) 8 Hz), 7.75-7.24 (m),
8.34 (s), 7.99 (td, J ) 1.2, 6.6 Hz), 7.79 (m), 7.70-7.30 (m), 7.20-
6.97 (m), 6.50 (m), 6.25 (m). Anal. Calcd for C25H17N‚0.25H2O:
C, 89.39; H, 5.25; N, 4.17. Found: C, 89.40, H, 5.24; N, 4.20.
1-(2′-Na p h t h yl)-8-(1′-m e t h yl-3′-p yr id yliu m )n a p h t h a -
len e Iod id e (10). To a solution of 12.6 mg (0.0381 mmol) of 1-(2′-
naphthyl)-8-(3′-pyridyl)naphthalene in 0.5 mL of methanol was
added 0.050 mL (0.11 g, 0.80 mmol) of CH3I. Concentration of
the mixture after 24 h at room temperature gave a yellow oil
that subsequently crystallized. Recrystallization from ethanol/
water gave 5.1 mg (0.011 mmol, 29%) of yellow crystals, mp193-
7.03 (m), 6.92 (m), 3.64 (Me), 3.29 (Me). Anal. Calcd for C29H26
-
IN‚1.5H2O: C, 64.21; H, 5.39; N, 2.58. Found: C, 64.07; H, 5.31;
N: 2.21.
1
194 °C. H NMR (CDCl3) δ 8.54 (s), 8.44 (s), 8.19 (m), 8.14 (dd,
J ) 2.1, 7.5 Hz), 8.08 (dd, J ) 1.2, 8.1 Hz), 7.84-7.48 (m), 7.36
(m), 7.19 (m), 7.01 (m), 4.38 (Me), 3.94 (Me). Anal. Calcd for
1-(2′-Na p h th yl)-8-(3′-p yr id yl)n a p h th a len e (9). To a de-
gassed solution of 100 mg (0.300 mmol) of 8-bromo-1-(2′-
naphthyl)naphthalene and 17 mg (0.013 mmol, 5 mol %) of
Pd(PPh3)4 in 2 mL of DME was added 48 mg (0.33 mmol) of
diethyl(3-pyridyl)borane followed by 50 mg (0.47 mmol) of Na2-
CO3 in 1 mL of water. The mixture was magnetically stirred in
a tube sealed under nitrogen at 100 °C for 2 h. The cooled
mixture was diluted with 50 mL of CH2Cl2 and 100 mL of water.
The organic phase was separated, and the water layer was
extracted with CH2Cl2 (10 mL). The combined organic phases
were chromatographed on silica using hexanes/EtOAc (1:1) to
give 84.2 mg (0.254 mmol, 85%) of a yellow oil which after
standing in hexanes in a freezer for 3 days gave white crystals,
73.8 mg (0.223 mmol, 74%), mp 86-88 °C. 1H NMR (CDCl3) δ
C
26H20NI: C, 65.97; H, 4.26; N, 2.97. Found: C, 66.34; H, 4.49;
N, 3.08.
Ack n ow led gm en t. S.L. kindly received stipends
from Consejo de Desarrollo Cientifico y Humanistico de
la Universidad Central de Venezuela and the Organiza-
tion of American States. Prof. W. M. F. Fabian kindly
carried out semiempirical computations on our com-
pounds.
J O010537A