Synthesis of Functionalized Phenanthrenes via Regioselective Oxidative Radical Cyclization

Article abstract of DOI:10.1021/acs.joc.5b01014

The majority of Sn-mediated cyclizations are reductive and, thus, cannot give a fully conjugated product. This is a limitation in the application of Sn-mediated radical cascades for the preparation of fully conjugated molecules. In this work, we report an oxidatively terminated Bu₃Sn-mediated cyclization of an alkyne where AIBN, the commonly used initiator, takes on a new function as an oxidative agent. Sn-mediated radical transformation of biphenyl aryl acetylenes into functionalized phenanthrenyl stannanes can be initiated via two potentially equilibrating vinyl radicals, one of which can be trapped by the fast 6-endoclosure at the biphenyl moiety in good to excellent yields. The efficient preparation of Sn-substituted phenanthrenes opens access to convenient building blocks for the construction of larger polyaromatics.

Full text of DOI:10.1021/acs.joc.5b01014

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Synthesis of Functionalized Phenanthrenes via
Regioselective Oxidative Radical Cyclization
Kamalkishore Pati, Christopher Michas, David Allenger, Ilya Piskun, Peter S. Coutros, Gabriel
dos Passos Gomes, and Igor V. Alabugin*
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Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
ABSTRACT: The majority of Sn-mediated cyclizations are reductive and, thus, cannot give a
fully conjugated product. This is a limitation in the application of Sn-mediated radical cascades
for the preparation of fully conjugated molecules. In this work, we report an oxidatively
terminated Bu3Sn-mediated cyclization of an alkyne where AIBN, the commonly used initiator,
takes on a new function as an oxidative agent. Sn-mediated radical transformation of biphenyl
aryl acetylenes into functionalized phenanthrenyl stannanes can be initiated via two potentially
equilibrating vinyl radicals, one of which can be trapped by the fast 6-endo-closure at the
biphenyl moiety in good to excellent yields. The efficient preparation of Sn-substituted
phenanthrenes opens access to convenient building blocks for the construction of larger
polyaromatics.
INTRODUCTION
In our continuing efforts to expand the synthetic utility of radical cyclizations1,2 toward
the preparation of precisely functionalized and shaped polyaromatic building blocks, we
developed multiple ways for taking advantage of carbon-rich character of the alkyne
functionality for the preparation of cyclic conjugated molecules.3 This work addressed the
questions of regio- and chemoselectivity of activation and exo/endo-selectivity for the ring
forming steps. In this work, we address manipulation of the oxidation state of the final products.
In our earlier work, we found that cyclizations of fully conjugated oligoalkynes lead to
reduction of two alkyne carbons: the place of initial Sn-attack and the place of final ring closure
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(Scheme 1). As a result, these sequences form polycylic system with two partially reduced five-
membered rings. In a more recent work, we avoided both the formation of one of the five-
membered rings and the partial reduction at the cascade initiation point by utilizing “skipped”
oligoalkynes equipped with a traceless directing group.4 Loss of the directing group proceeds via
C-O bond fragmentation driven by aromatization of the top ring in the ribbon (Scheme 1), the
process that adjusts the oxidation state and assists in avoiding the reduced product formation.
However, the termination point of the cascade still includes a partially reduced five-membered
cycle.
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Scheme 1. Reductive and oxidative Sn-mediated radical cascades. Alkyne carbons
that will be reduced in the product are indicated with gray circles.
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Guided by the hypothesis that such reduction can be avoided by terminating the cascade
by an oxidizing step, we designed the new radical cascade reported in this work. This cascade
features an intermolecular attack at the alkyne that, albeit not necessarily selective itself, can still
lead to selective 6-endo cyclization followed by an oxidative termination step that uses AIBN, a
commonly used radical initiator as an oxidant. This reaction provides a simple and efficient
strategy for the synthesis of substituted phenanthrenyl stannanes from 2-(1-alkynyl)-biphenyls
via Bu3SnH/AIBN mediated radical cyclization. The products are conveniently functionalized
for further transformations.
RESULTS AND DISCUSSION
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The required starting materials 1a-l are readily prepared from the respective 2-
bromobiphenyls via the Sonogashira cross-coupling (Scheme 2). The cross-coupling proceeded
in good yields to produce the library of 2-(arylethynyl)biphenyls (1a-l) in 70-84% yields.
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Scheme 2. Synthesis of requisite 2-(arylethynyl) biphenyls
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Table 1. Screening of Reaction Conditions:
Entry
Reagent(eq)/Initiator(eq)
Condition
Conversiona
Yieldb
1
2
Bu3SnH(1.0)/AIBN(0.2)
Bu3SnH(1.5)/AIBN(1.0)
--
SM
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
100%
90%
3
Ph3SnH(1.5)/AIBN(1.0)
No Reagent/Initiator
100%
0%
80%
SM
--c
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Benzene, 14 h, 80°C
THF, 14 h, 66°C
4
5
Et3SiH (1.5)/AIBN(1.0)
(Me3Si)3SiH (1.5)/AIBN(1.0)
Bu3SnH (1.5)/ABCN(1.0)
Bu3SnH (1.5)/DTBPB(1.0)
Bu3SnH(1.5)/AIBN(1.0)
Bu3SnH(1.5)/AIBN(1.0)
30%
20%
100%
40%
80%
100%
6
--c
7
70%
60%
65%
70%
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10
11
12
Bu3SnH(2.0)/AIBN(1.0)
Bu3SnH(1.8)/AIBN(1.0)
100%
100%
90%
90%
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
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Bu3SnH(1.2)/AIBN(1.0)
100%
100%
70%
40%
60%
--
90%
70%
60%
30%
40%
S.M
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 14 h, 110°C
Toluene, 16 h, rt
Bu3SnH(1.0)/AIBN(1.5)
Bu3SnH(1.0)/AIBN(1.0)
Bu3SnH(1.0)/AIBN(0.5)
Bu3SnH(0.6)/AIBN(1.0)
Bu3SnH(1.5)/Et3B(1.0)
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0.04M concentration of [1a] was used unless stated otherwise. SM=starting material. a Conversion rate
reported based on H-NMR. bYields are based on H-NMR (see Experimental Section for the details). The
product yields are lower than conversion of the starting material due to the formation of small amounts of
unidentified side products. cSubstrate 1a remained unreacted.
As shown in table 1, when we tried with 20 mol% of AIBN we didn’t observe any
transformation of 1a to 2a (entries 1), we recovered only starting material. Tin-containing
reagents (Bu3SnH/AIBN and Ph3SnH/AIBN) promote the radical cyclization of substrate 1a to
phenanthrene 2a in refluxing toluene in good yields (entries 2 and 3). On contrary, Et3SiH and
(Me3Si)3SiH do not transform 1a into 2a (entries 5 and 6). We also examined the effect of
solvents. Reaction proceeded more efficiently in toluene than in other solvents, such as benzene
and THF (65% and 70%, respectively, entries 9 and 10). Once suitable conditions for this
transformation were determined, we concentrated our efforts on optimizing the amounts of
reagent and initiator. The yields were lower when the amount of Bu3SnH reagent was reduced to
less than 1.2 molar equivalents (entry 14, 15) or when the amount of initiator was reduced to less
than 1.0 equivalents (entry 16). The relatively high amount of initiator is particularly noteworthy.
More than 90% of starting material was recovered when less than 0.2 equivalents of AIBN was
used. On the other hand, reaction proceeded to the full conversion with 1.0 equivalents of AIBN,
providing up to 90% of the phenanthrene product.
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With the optimal reaction conditions in hand, we explored the substrate scope of this
transformation. We tested the reactions of additional 2-(arylethynyl) biphenyls 1b–1i under the
optimized conditions (Table 2). The radical cyclization is fully compatible with acceptor (1c-e
and 1p) and donor (1b, 1h) substituents at the alkyne termini. The process also tolerates
heteroaromatics and alkyl substitution. The corresponding products 2i-2m that incorporate
pyridine, thiophene, benzothiophene and n-butyl groups were obtained in high yields (70-81%).
Furthermore, alterations at the biphenyl part of the substrate are also possible, i.e., the reaction of
benzofuran 1j gave 70% of 6-(4-methoxyphenyl)-3-methylnaphtho[1,2-b]benzofuran 2j. In a
similar manner, reactions of alkynes 1n and 1o with additional substitution in the biphenyl
moiety provided the respective products 2n-2o in high yields (76% and 82%). These results
highlight the broad scope and selectivity of this method.
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Table 2. Radical cyclization of 2-(1-Arylethynyl) biphenyls.
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Isolated yields after acid hydrolysis and silica column chromatography. Concentration of ethynyl
biphenyls reactants was 0.04M.
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The structure of the products was confirmed with a combination of NMR techniques, and
in the case of iodinated compound 3a with X-ray crystallography5 (Figure 1). The position of
iodo-substituent unambiguously confirms the presence and the position of the Sn-moiety.
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Figure 1: The ORTEP for 3a (50%).
Computational Details:
Potential energy profiles for this cascade transformation were evaluated with Gaussian
096 using the UM06-2X functional,7 capable of relatively accurate description of reaction and
activation energies for a variety of chemical processes including radical reactions.8 The
LanL2DZ basis set was used due to the need to study Sn-substituted molecules. Chemcraft 1.79
and CYLView10 were used to render the molecules and orbitals. Frequency calculations were
performed to confirm each stationary point as either a minimum or a first-order saddle point.
NBO 3.0 program was used to analyze electronic properties of reactive intermediates.11 The G
values for all reactions were calculated at 110˚C, the experimental temperature. A truncated
version of the attacking radical (SnMe3) was used instead of SnBu3.
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Two sources of selectivity:
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The selectivity of the new transformation depends on the two following factors: a) the
selectivity of initial radical attack and b) the selectivity of the subsequent cyclizations. In order to
understand the origin for the exclusive attack at the carbon adjacent to the biphenyl moiety, we
evaluated the activation barriers for the two alternative intermolecular attack directions (Scheme
3). Interestingly, at the present level of theory, the formation of “unproductive” radical B is
predicted to be marginally faster (G≠ 0.8 kcal/mol). However, the “productive” radical A is
also predicted to be 2.2 kcal/mol more stable than radical B. Formation of both radicals is only
weakly exergonic and can be considered reversible under the reaction conditions.
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Scheme 3: Potential energy diagram for the formation of radicals A and B from the
biphenyl phenyl alkyne
Because the transformation of unproductive radical B to the productive radical A is
exergonic, we have also explored the additional ways that can take advantage of the well-known
weakness of C-Sn bonds for interconverting the two radicals. The additional analysis identified a
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radical 1,2-Sn-shift as a feasible direct route for formation of the productive radical A directly
from the unproductive radical B. Figure 2 illustrates geometry for the 1,2-shift Transition State
(TS). Due to the relatively low accuracy of the presently available computational methods, the
absolute energy for the 1,2-shift TS (16.9 kcal/mol) and the TS leading to the direct formation of
radical A from the alkyne reactant (16.5 kcal/mol) should be considered, within the
computational margin of error, as identical. For comparison, we had also calculated activation
energy for the analogous shift of the SiMe3 (TMS) group and found that the respective 1,2-shift
TS lies much higher (27.0 kcal/mol higher than the alkyne and TMS radical and 41.5 kcal/mol
higher than the Si-analogue of radical B, se the SI part).
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Figure 2: Transition state geometry for 1,2-Sn shift that interconverts the two vinyl
radicals
The situation where radicals are dynamically interconverted via relatively fast reactions
can be referred to as “a pool of radicals”.12 When coupled with kinetic self-sorting via a low
barrier irreversible reaction, this kinetic scenario provides an unorthodox approach to the control
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of radical processes that provides a convenient alternative to the use of electronic effects and
traceless directing groups.4
In order to evaluate the possibility of kinetic self-sorting, we investigated reaction
possibilities diverging from the two radicals (Scheme 4). Radical B has to overcome a relatively
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high barrier of ~17 kcal/mol to reach the 5-exo cyclization product C. The absolute value for this
barrier is within 1 kcal/mol for the calculated barriers for the two routes (-scission and 1,2-Sn
shift) that convert this radical into the productive radical A. Lack of products derived from this
path in the experimental work provides a much needed benchmark for theory, suggesting that the
computational analysis either overestimates the barrier for B→A conversion or underestimates
the barrier for the cyclization of B.
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In contrast, the radical A was found to have a much lower “escape route” via the
relatively low 8.2 kcal/mol activation barrier for the 6-endo cyclization. The cyclic radical D
formed in the latter step is ~7 kcal/mol more stable than its vinyl radical precursor and ~10
kcal/mol more stable than the two reactants (Sn-radical and alkyne).
Scheme 4: The calculated Gibbs free energy surface for the Sn-radical mediated
transformation of biphenyl phenyl alkyne at 110˚C. Energies are in kcal/mol relative to the
isolated alkyne and Me3Sn radical
Routes to the final hydrogen loss: the key oxidizing step
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There are two main routes for the oxidative (the formal loss of H-atom) aromatization of 6-
endo radical D into the final product. The direct H-abstraction at the relatively weak C-H bond at
the ring junction is a straightforward one-step approach and we have considered several possible
routes for the final H-atom abstraction mediated by the radicals present in the reaction mixture
(Scheme 5). As the first step, we located a TS for C-H abstraction by the carbon-centered radical
derived from AIBN (Scheme 5). Although this process is highly exergonic (G = -76.5
kcal/mol) and clearly irreversible, the 19.5 kcal/mol barrier is fairly high, with the absolute
energy ~5 kcal/mol higher than TS for the phenanthrene ring opening back to the acyclic vinyl
species.
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Scheme 5: Mechanistic possibilities for aromatization of polycyclic radical D
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Considering the possible role of steric hindrance in the barrier for this H-abstraction, we
investigated reaction at the nitrogen atom of the -CN-radicals derived from AIBN. Not only do
such radicals have significant radical density at the nitrogen, the nitrogen atom has no other
substituents and its approach to the targeted C-H bond is not hindered. Indeed, we were able to
find the respective TS. However, the process is ~25 kcal/mol less exergonic (G=-50.4) and the
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activation barrier for this step is ~9 kcal/mol higher (G≠ = 28.2 kcal/mol), in a good agreement
with the known correlation between the thermodynamics and kinetics of radical reactions.14 The
relatively low efficiency of these reactions is consistent with the experimental findings that
reaction needs ~2 equivalents of such radicals per molecule of product in order to proceed to
completion.
Finally, we investigated the possibility of H-abstraction from D by another SnBu3 radical.
The calculated transition state energy was surprisingly low even considering the relatively high
exergonicity (~70 kcal/mol) of this process. Furthermore, the transition state energy was negative
and was located ~15 kcal/mol lower than the reactants. A negative barrier in a chemical reaction
generally suggests precomplexation between the reactants and, indeed, the further computational
analysis located an additional minimum corresponding to the coupling product between SnR3
and the cyclic radicals. The transition state for the transformation of this intermediate to the final
product corresponds to 1,4-elimination of Bu3SnH via a concerted retro [4s+2s] path (Scheme
7). Such 1,4-eliminations are known but much more rare15 than 1,2-elimination of metal-
hydrides.16 Aromatization energy is likely to be important in the assisting this process in the
present system.
From the kinetic point of view, formation of Bu3SnH is significant because it terminates
the radical chain, accounting for the very low conversions in the absence of sufficient excess of
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AIBN. In this scenario, Bu3Sn radical serves as a primary oxidant that is directly involved in the
aromatization/oxidation step whereas AIBN plays a secondary role by converting Bu3SnH to
Bu3Sn radical and restarting the radical chain process.
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Scheme 6: Left: Comparison between 1,2 and 1,4-eliminations. Right: Transition State
Geometry for concerted elimination of Bu3SnH.
The new radical route to phenanthrenes starts with the regioselective Bu3Sn radical attack at
the alkyne and formation of vinyl radical intermediate A from substrate 1a (Scheme 6). The
vinyl radical A attacks π-system of the neighboring phenyl group via 6-endo cyclization to form
the cyclic radical intermediate D. A second Bu3Sn radical assists in the removal of hydrogen
from C-H bond from intermediate D, which leads to the formation of the desired product
phenanthrene 2a.
Scheme 7: Proposed mechanism for radical cyclization
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Synthetic Applications:
Phenanthrenes are an important class of polycyclic aromatic compounds and appear in
many natural products17 and biologically active molecules with antimicrobial,18 anticancer,19 and
anti-HIV activities.20 Moreover, phenanthrene is an important structural motif in materials
science21 due to its optical and electronic properties. Consequently, in the past two decades,
extensive efforts have been focused on the development of new protocols for the construction of
the phenanthrenes (Scheme 8).22
Scheme 8: Regioselective alkyne ring closures of 2-(1-alkynyl)-biphenyl systems
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In particular, electrophile-assisted23 and transition metal-catalyzed reactions of 2-
(arylethynyl)biphenyl derivatives represent a frequently utilized atom-economical strategy for
the preparation of such compounds.24 Swager and coworkers reported several acid- and
electrophile promoted cyclizations for the preparation of extended fused polycyclic aromatics.25
Larock group reported the electrophile assisted cyclization of 2-(arylethynyl)biphenyls with ICl,
NBS, or arylsulfenyl chloride for the synthesis of phenanthrene derivatives.26 More recently,
several metal-catalyzed (Fe, In, Au, Pt, Pd) protocols have emerged.27 In earlier works, the
presence of EDG and EWG on the bottom ring of the biphenyl system has been shown to affect
the regioselectivity of intramolecular hydroarylation. As reported by Gevorgyan, o-alkynylated
biphenyls containing electron-withdrawing substituents undergo 5-exo-dig cyclization via Pd-
catalyzed C-H activation pathway. In contrast, Fürstner found the 6-endo-dig preference for the
transition-metal (PtCl2, InCl3, GaCl3, AuCl) catalyzed cyclization of o-alkynylbiphenyls bearing
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an electron-rich aryl ring. The latter reaction proceeds via a Friedel-Crafts-type electrophilic
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aromatic substitution pathway following initial π-coordination of the metal to the alkyne unit.
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Our work complements the literature methods by providing ready access to nucleophilic
phenantrenyl building blocks via a radical pathway. The polycyclic aromatic stannanes can be
further elaborated using a variety of palladium-catalyzed processes where they can be either used
directly as nucleophilic components (i.e., in the Stille cross-coupling) in Pd-catalyzed cross-
coupling or converted into the respective iodides that can serve as electrophilic building blocks
in Suzuki or Sonogashira cross-coupling. Furthermore, a variety of other interesting
transformations are reported in the recent literature (Sn→CN, F, OCF3 etc. as outlined in Scheme
9).
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Scheme 9: Derivatization of phenanthryl stannanes28
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Furthermore, the cascade can involve more than one biphenyl arylacetylene moiety as described
in Scheme 10.
Scheme 10: Double phenanthrene-forming cascade
In summary, we have developed a new approach to substituted phenanthrene derivatives
from 2-(arylethynyl)biphenyls through a selective radical cascade which involves formation of
the central ring of phenanthrene via regioselective vinyl radical formation followed by a 6-endo
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cyclization. Subsequent removal of hydrogen atom aromatizes the intermediate products and
furnishes the final phenanthrenes in high yields. This radical cyclization opens a new avenue for
the preparation of substituted polyaromatics. Future work will include expansion of this radical
cascade toward the preparation of larger conjugated molecules and materials.
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Experimental Section:
Unless otherwise noted, all reactions were carried out under nitrogen atmosphere in oven-
dried glassware using standard syringe, cannula, and septa apparatus. Benzene, diethyl ether,
toluene, tetrahydrofuran, and hexane were dried with a dry solvent system before use.
Dichloromethane was dried over CaH2 before use. Reagents were purchased from commercial
sources and used without purification, unless otherwise stated. Reactions were magnetically
stirred and monitored by thin layer chromatography on 0.25 mm silica gel plates (60f-254) using
UV light as visualizing agent. Time-of-flight mass spectrometer used for the analysis of HRMS. NMR
spectra were recorded on a 400 and 600 MHZ NMR-spectrometer. Column chromatography was
performed using Kieselgel 60 (70-230 mesh) or Kieselgel 60 (230-400 mesh). Preparative thin-
layer chromatography (PTLC) separations were carried out on 0.25 or 0.55 mm silica gel plates
(60F-254) in ethyl acetate/hexanes system.
Procedure for NMR experiments to determine conversion rate and yields: The 8.8 ppm peak in
H-NMR spectra characteristic for the phenanthrene product and characteristic peak at 7.7 ppm
for the starting material were compared with the peaks of triphenyl methane as internal standard.
And we also monitored C-NMR data to confirm starting material consumption from the
disappearance of alkyne carbon peaks. H-NMR integration used to quantify reaction conversions
and yields by using the peak at 8.8 characteristic for the phenanthrene products. We used
triphenyl methane as standard.
Synthetic Scheme (A1) for the Preparation of 2-(phenylethynyl)-1,1'-biphenyl (1a):
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A. Procedure for synthesis of 2-(phenylethynyl)-1,1'-biphenyl 1a:
2-bromo-1,1'-biphenyl (1.00 g, 5.43 mmol) was added in one portion to a solution of CuI
(0.10 g, 10 mol%) in Et3N (30 mL) and degassed with nitrogen for 15 min at 23 oC. PdCl2(PPh3)2
(0.32 g, 5 mol %) was added to the mixture and was stirred for 15 min before being treated with
ethynylbenzene (0.63 g, 6.2 mmol) dropwise. The resulting solution was stirred at room
temperature for 12 h and then filtered through a celite pad, concentrated, and eluted (3% ethyl
acetate/hexanes mixture used as eluent) through a silica column to give the desired 2-
(phenylethynyl)-1,1'-biphenyl(1a) (0.94 g, 3.6 mmol, 86%).
Synthetic Scheme (A2) for the Preparation of 2-(arylethynyl)-1,1'-biphenyls 1a-q:
General Procedure:
2-bromo-1,1'-biphenyl (1.7 g, 7.2 mmol), Pd(PPh3)4 (0.51 g, 0.44 mmol), and CuI (0.084
g, 0.44 mmol) were charged into a round flask and pumped under vacuo. Triethylamine (50 mL)
was added into the flask. The mixture was stirred at rt, and trimethylsilylacetylene (1.2 mL, 8.7
mmol) was added dropwise to the mixture. The resulting mixture was stirred at rt for 10-14 h.
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The resulting material was passed through a short celite bed with EtOAc:Hexane (1:1 ; 50 mL),
and then washed with sat. NH4Cl (50 mL), H2O (50 mL x 2), and brine (50 mL). After the
material was dried over Na2SO4, the solvent was removed by evaporation. The resulting material
was dissolved in a mixture of DCM (20 mL) and MeOH (20 mL). K2CO3 (2.0 g, 14.6 mol) was
added to the mixture, and then stirred at rt for 5-6 h. The solid material was removed by
filtration. The filtrate was concentrated by evaporation. The resulting crude material was purified
with SiO2 column chromatography (5 % ethyl acetate/hexanes mixture used as eluent) to afford a
desired product 1-1.
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Synthetic Scheme (A3) for the Preparation of 2-(arylethynyl)-1,1'-biphenyls 1n and 1o:
To a solution of Na2CO3 (3.26 g, 31.1 mmol) in toluene (45 mL), ethanol (15 mL), and
water (15 mL) was added 1-bromo-2-(phenylethynyl)benzene (2.0 g, 7.8 mmol) at room
temperature, and the solution was degassed with nitrogen. To this mixture was added 4-methyl
phenylboronic acid (1.37 g, 10.1 mmol) and Pd(PPh3)4 (0.63 g, 7 mol %), and the resulting
mixture was heated to 100 oC for 10 h. After completion of the reaction, the solution was cooled
to room temperature and washed with water, and the organic layer was separated. The aqueous
layer was extracted with ethyl acetate, washed with brine solution, dried over MgSO4, and
concentrated. The residues were eluted (5-10% ethyl acetate/hexanes mixture used as eluent)
through a silica column to give the desired compound (1n-o).
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General Procedure Synthetic Scheme (A4) for the Synthesis of 9-phenylphenanthrenes (2a-
2p):
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Solution of 0.10 g (0.39 mmol) of 2-(phenylethynyl)-1,1'-biphenyl 1a in 10 ml of toluene
(0.04M solution) was fitted with a condenser and degassed by purging with argon gas. AIBN
(0.064 g, 0.39 mmol) and Bu3SnH (0.137 g, 0.47 mmol) were dissolved separately in dry toluene
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and added slowly (flow rate 1 mL/hr) to the reaction mixture by using a syringe pump at 110 C.
The progress of reaction was monitored by TLC. After consumption of the starting material, the
reaction mixture was allowed to cool down to room temperature and filtered through a small
celite bed. Solvent was removed under reduced pressure. The crude reaction mixture was
dissolved in 20 mL DCM. Aq. HCl (3 M) (15 mL) was added to above mixture and stirred for 4
h. The reaction mixture was extracted with DCM (30 mL). The extract was washed with brine,
dried over Na2SO4, and concentrated under reduced pressure. The residue was eluted through a
silica column to afford compound purified by column chromatography over silica gel (1% ethyl
acetate/hexanes mixture used as eluent), which yielded 9-phenylphenanthrene 2a (0.090 g, 0.33
mmol, 90%).
2-(phenylethynyl)-1,1'-biphenyl (1a): NMR data for this compound are identical to those reported
in the literature22d. Yield: 0.94 g (87%). Compound 1a prepared using synthetic scheme A1. 2%
ethyl acetate/hexanes mixture used as eluent. Pale yellow liquid. 1H NMR (400 MHz, CDCl3): δ
7.72-7.67 (m, 3H), 7.50-7.30 (m, 11H). 13C NMR (100 MHz, CDCl3): 143.9, 140.5, 132.8,
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131.3 (2xCH), 129.4, 129.37 (2xCH), 128.5, 128.2 (2xCH), 128.1, 127.8 (2xCH), 127.4, 127.0,
123.4, 121.5, 92.2, 89.4.
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2-(p-tolylethynyl)-1,1'-biphenyl (1b): NMR data for this compound are identical to those reported
in the literature22d. Yield: 0.129 g (86%). Compound 1b prepared using synthetic scheme A2. 1%
ethyl acetate/hexanes mixture used as eluent. Pale yellow liquid. 1H NMR (400 MHz, CDCl3): δ
7.69-7.63 (m, 3H), 7.48-7.31 (m, 6H), 7.23 (d, J =8 Hz, 2H), 7.10 (d, J =8 Hz, 2H), 2.34 (s, 3H).
13C NMR (100 MHz, CDCl3): 143.7, 140.5, 138.2, 132.7, 131.2 (2xCH), 129.4 (2xCH), 129.3,
128.9 (2xCH), 128.3, 127.8 (2xCH), 127.3, 127.0, 121.7, 120.3, 92.4, 88.7, 21.5.
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2-((4-fluorophenyl)ethynyl)-1,1'-biphenyl (1c):29 Yield: 0.119 g (78%). 12% ethyl acetate
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hexanes mixture used as eluent. H NMR (400 MHz, CDCl3): δ 7.70- 7.65 (m, 3H), 7.47-7.31
(m, 8H), 7.03-6.99 (m, 2H). 13C NMR (100 MHz, CDCl3): 162.3 (d, Jf = 247.41 Hz), 143.8,
140.5, 133.2, 133.1, 132.7 (2xCH), 129.4, 129.3 (2xCH), 128.5, 127.8, 127.4, 127.8, 127.4,
127.0, 120.4 (d, Jf = 190.29 Hz), 115.6, 115.4, 90.1 (d, Jf = 206.18 Hz).
4-([1,1'-biphenyl]-2-ylethynyl)benzonitrile (1d):22d Yield: 0.113 g (72%). Synthetic Scheme A2.
8% ethyl acetate/hexanes mixture used as eluent. Pale yellow oil. 1H NMR (600 MHZ, CDCl3): δ
7.66 (d, J = 7.68 Hz, 1H), 7.64-7.62 (m, 2H), 7.56 (d, J =10.86 Hz, 2H), 7.48-7.41 (m, 5H), 7.38-
7.35 (m, 3H). 13C NMR (100 MHz, CDCl3): 144.5, 140.3, 133.0, 132.0 (2xCH), 131.8 (2xCH),
129.6, 129.4, 129.4 (2xCH), 128.4, 128.0, 127.7, 127.2 (2x qC), 120.6, 118.6, 111.2, 93.9, 90.5.
HRMS calcd for C21H13N : 279.1048, found [M]+: 279.1056.
2-((4-(trifluoromethyl)phenyl)ethynyl)-1,1'-biphenyl (1e): NMR data for this compound are
identical to those reported in the literature22d. Yield: 0.145 g (80%). Synthetic Scheme A4. 10%
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ethyl acetate/hexanes mixture used as eluent. Pale brown liquid. H NMR (600 MHz, CDCl3): δ
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7.67-7.64 (m, 3H), 7.54 (d, J = 8.3 Hz, 2H), 7.48-7.40 (m, 7H), 7.38-7.35 (m, 1H). 13C NMR
(150 MHz, CDCl3): δ 144.3, 140.4, 132.9, 131.5, 129.8, 129.5, 129.3, 129.1, 127.9, 127.6, 127.2,
127.1, 125.2, 125.18, 125.15, 125.1, 124.8, 123.0, 120.9, 91.8, 90.7; HRMS calcd for C21H13F3 :
322.0969, found [M]+: 322. 0983.
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1-([1,1'-biphenyl]-2-ylethynyl)naphthalene (1f): NMR data for this compound are identical to
those reported in the literature.22d 5% ethyl acetate/hexanes mixture used as eluent. Yield: 0.157
g (92%). 1H NMR (400 MHz, CDCl3): δ. 7.94 (d, J=8 Hz, 1H), 7.87-7.82 (m, 3H), 7.79-7.76 (m,
2H) 7.68 (dd, J =1.12 Hz, 6 Hz, 1H), 7.59-7.42 (m, 9H). 13C NMR (100 MHz, CDCl3): 144.1,
140. 9, 133.1, 133.0, 132.9, 130.1, 129.5, 129.4 (2xCH), 128.5, 128.5, 128.1 (2xCH), 128.0,
127.4, 127.1, 126.5, 126.3, 126.2, 125.1, 121.9, 121.0, 94.1, 90.5.
2-(hex-1-yn-1-yl)-1,1'-biphenyl (1g): NMR data for this compound are identical to those reported
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in the literature.26 2% ethyl acetate/hexanes mixture used as eluent. Yield: 0.118 g (90%). H
NMR (400 MHz, CDCl3): δ 7.61-7.59 (m, 2H), 7.54-7.52 (m, 1H), 7.44-7.27 (m, 6H), 2.31 (t, J
=6.88 Hz , 2H), 1.48-1.30 (m, 4H), 0.88 (t, J =7.32 Hz, 3H). 13C NMR (100 MHz, CDCl3):
143.6, 140.8, 132.9, 129.3, 129.2 (2xCH), 127.7 (2xCH), 127.6, 127.1, 126.8, 122.3, 93.4, 80.0,
30.4, 21.8, 19.1, 13.6. HRMS calcd for C18H18: 234.1409, found [M]+: 234.1407.
2-((4-methoxyphenyl)ethynyl)-1,1'-biphenyl (1h): NMR data for this compound are identical to
those reported in the literature22d. Yield: 0.144 g (90%) Synthetic Scheme A2. 8% ethyl
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acetate/hexanes mixture used as eluent. Clear oil (with a very slight hint of yellow). H NMR
(400 MHz, CDCl3): δ 7.69-7.68 (m, 2H), 7.65-7.63 (m, 1H), 7.48-7.37 (m, 5H), 7.33 (t of d, J1
=7.5 Hz , J2=1.44 Hz, 1H), 7.29-7.27 (m, 2H), 6.83-6.82 (m, 2H), 3.80 (s, 3H). 13C NMR(100
MHz, CDCl3): 159.5, 143.6, 140.7, 132.8 (2xCH), 132.6, 129.4, 129.39, 128.1, 127.8 (2xCH),
127.4, 127.0 (2xqC), 121.9, 115.6, 113.9 (2xCH), 92.2, 88.0, 55.2 .
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2-([1,1'-biphenyl]-2-ylethynyl)thiophene(1i): NMR data for this compound are identical to those
reported in the literature26. Yield: 0.111 g (76%). Synthetic Scheme A2. 6% ethyl
acetate/hexanes mixture used as eluent. Yellow oil. 1H NMR (600 MHZ, CDCl3): δ 7.67-7-66
(m, 2H), 7.64 (d, J = 7.56 Hz, 1H), 7.49-7.44 (m, 3H), 7.43-7.39 (m, 2H), 7.34 (dd, J1 =7.5 Hz,
J2 =1.5 Hz 1H), 7.24 (dd, J1 =5.2 Hz, J2=1.0 Hz 1H), 7.11 (dd, J1= 3.5 Hz, J2=1 Hz, 1H), 6.97-
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6.96 (m, 1H). C NMR(100 MHz, CDCl3): 143.7, 140.4, 132.5, 131.5, 129.5, 129.3 (2xCH),
128.7, 128.0 (2xCH), 127.5, 127.2, 127.1, 127.0, 123.5, 121.3, 93.2, 85.6. HRMS calcd for
C18H12S: 260.0660, found [M]+: 260.0684.
2-(2-((4-methoxyphenyl)ethynyl)-4-methylphenyl)benzofuran (1j):33 10% ethyl acetate/hexanes
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mixture used as eluent. Yield: 0.109 g (75%). H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 8.12
Hz, 1H), 7.75 (s, 1H), 7.64 (d, J = 7.44 Hz, 1H), 7.58-7.55 (m, 3H), 7.50 (s, 1H), 7.34-7.30 (m,
1H), 7.28-7.24 (m, 2H), 6.97-6.94 (m, 2H), 3.86 (s, 3H), 2.41 (s, 3H). 13C NMR (100 MHz,
CDCl3): 159.8, 154.2, 154.1, 137.7, 134.1, 132.9 (2xCH), 129.4, 129.3, 128.5, 126.5, 124.3,
122.7, 121.1, 119.7, 115.4, 114.1 (2xCH), 110.9, 105.0, 94.2, 88.2, 55.3, 20.9. HRMS calcd for
C24H18O2: 338.1307, found [M]+: 338.1305.
4-([1,1'-biphenyl]-2-ylethynyl)pyridine (1k): 15% ethyl acetate/hexanes mixture used as eluent.
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Yield: 0.100 g (70%). H NMR (600 MHz, CDCl3): δ 8.54 (s, 2H), 7.66 (d, J =7.62 Hz, 1H),
7.63 (d, J = 7.98 Hz, 2H) 7.48-7.41(m, 5H), 7.36-7.33 (m, 1H), 7.15 (d, J = 5.64 Hz, 2H). 13C
NMR (150 MHz, CDCl3): 149.5(2xC), 144.4, 140.0, 133.0, 131.3, 129.4, 129.4, 129.2 (2xCH),
127.8 (3xCH), 127.6, 127.0, 125.1, 120.2, 93.9, 89.2. HRMS calcd for C19H13N : 255.1048,
found [M]+: 255.1036.
5-([1,1'-biphenyl]-2-ylethynyl)benzo[d][1,3]dioxole (1l): Yield: 0.137 g (82%). Synthetic
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Scheme A1. 9% ethyl acetate/hexanes mixture used as eluent. Pale orange semisolid. H NMR
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(400 MHz, CDCl3): δ 7.69-7.63 (m, 3H), 7.51-7.33 (m, 6H), 6.88 (dd, J = 1.5 Hz, 1.5 Hz, 1H),
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108.5, 101.3, 92.3, 88.0; HRMS calcd for C21H14O2: 298.0994, found [M]+: 298.1002.
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2-([1,1'-biphenyl]-2-ylethynyl)benzo[b]thiophene (1m):40 Yield: 0.136 g (78%). Synthetic
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Scheme A1, 10% ethyl acetate/hexanes mixture used as eluent. Orange liquid. H NMR (400
MHz, CDCl3): 7.77-7.68 (m, 5 H), 7.54-7.43 (m, 5 H), 7.39-7.35 (m, 4 H). 13C NMR (100 MHz,
CDCl3): δ 144.0, 140.3, 140.3, 139.1, 132.8 (2xCH), 129.6, 129.3 (2xCH), 129.1, 128.3, 128.1,
127.7, 127.1, 125.3, 124.7, 123.8, 123.5, 122.0, 121.0, 95.1, 85.9.; HRMS calcd for C22H14S:
310.0816, found [M]+: 310.0828
4'-methyl-2-(phenylethynyl)-1,1'-biphenyl (1n): 3% ethyl acetate/hexanes mixture used as eluent.
Yield: 0.140 g (72%). 1H NMR (400 MHz, CDCl3): δ 7.73 (dd, J = 1 Hz, 6.56 Hz, 1H), 7.67 (d, J
= 8.08 Hz, 2H) 7.55-7.33 (m, 10H), 2.51 (s, 3H). 13C NMR (100 MHz, CDCl3): 143.7, 137.6,
137.1, 132.9, 131.3 (2xCH), 129.4, 129.2 (2xCH), 128.6 (2xCH), 128.5, 128.2 (2xCH), 128.0,
126.7, 123.5, 121.4, 92.0, 89.5, 21.2. HRMS calcd for C21H16: 268.1252, found [M]+: 268.1274.
4'-fluoro-2-(phenylethynyl)-1,1'-biphenyl (1o): 12% ethyl acetate/hexanes mixture used as eluent.
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Yield: 0.210 g (76%). H NMR (400 MHz, CDCl3): δ 7.67-7.63 (m, 3H), 7.42 (d, J =8.68 Hz,
2H), 7.38-7.30 (m, 6H), 7.16 (t, J =8.76 Hz, 2H). 13C NMR (100 MHz, CDCl3): 162.38 (d, Jf =
245.34 Hz), 142.77, 136.5, 132.9, 131.3 (2xCH), 131.0, 130.9, 129.3, 128.5, 128.3 (2xCH),
128.2, 127.1, 123.2, 121.5, 114.7 (d, Jf =21.25 Hz), 92.3, 89.0. Peaks for several chemically
nonequivalent carbons overlap with each other. HRMS calcd for C20H13F: 272.1001, found [M]+:
272.1011.
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1-(4-([1,1'-biphenyl]-2-ylethynyl)phenyl)ethan-1-one (1p): 4% ethyl acetate/hexanes mixture
used as eluent. Yield: 0.141 g (85%). 1H NMR (400 MHz, CDCl3): δ 7.87 (m, 2H), 7.66-7.64 (m,
3H), 7.47-7.36 (m, 8H), 2.59 (s, 3H). 13C NMR (100 MHz, CDCl3): 197.3, 144.3, 140.4, 137.9,
136.0, 132.9, 131.4 (2xCH) , 129.5, 129.4 (2xCH), 129.1, 128.4 (2xCH), 128.2, 127.9, 127.6,
127.1, 121.1, 92.8, 91.4, 26.6. HRMS calcd for C22H16O: 296.1201, found [M]+: 296.1206.
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1,4-bis([1,1'-biphenyl]-2-ylethynyl)benzene (1q): 10% ethyl acetate/hexanes mixture used as
eluent. Yield: 0.230 g (64%). NMR data for this compound are identical to those reported in the
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literature.35 Pale yellow thick syrup. H NMR (400 MHz, CDCl3): δ 7.72-7.71 (m, 3H), 7.69-
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7.43 (m, 5H), 7.39-7.30 (m, 1H), 7.26 (s, 2H). C NMR (100 MHz, CDCl3): 143.9, 140.4,
132.8,132.1 (2xCH), 129.4 (2xCH), 129.3, 128.6 (2xCH), 127.8, 127.4, 127.0, 123.0, 121.3,
91.9, 91.2. HRMS calcd for C34H22: 430.1722, found [M]+: 430.1746.
9-phenylphenanthrene (2a): (NMR data for this compound are identical to those reported in the
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literature).30 1% ethyl acetate/hexanes mixture used as eluent. Yield 0.090 g (90%). H NMR
(400 MHz, CDCl3): δ 8.81-8.79 (m, 2H), 7.93-7.90 (m, 2H), 7.71-7.55 (m, 4H), 7.53-7.46 (m,
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6H). C NMR (100 MHz, CDCl3): 140.7, 138.7, 131.5, 131.1, 130.6, 130.0 (2xCH), 129.9,
128.6, 128.3 (2xCH), 127.5, 127.3, 126.9, 126.8, 126.5, 126.47, 126.42, 122.9, 122.5.
Tributyl(10-phenylphenanthren-9-yl)stannane (2a-Sn): This compound was prepared using the
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same procedure as shown in general procedure A4. Hexanes was used as the eluent. H NMR
(400 MHz, CDCl3): δ 8.89-8.81 (m, 2H), 8.07 (d, J = 7.98 Hz, 1H), 7.71-7.62 (m, 2H), 7.50-
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7.34(m, 3H), 7.33-7.27(m, 5H), 1.38-1.35 (m, 6H), 1.24-1.21 (m, 6H), 0.82-0.73 (m, 15H). C
NMR (100 MHz, CDCl3): 148.1, 143.5, 141.8, 136.7, 131.8, 131.0, 130.8, 130.5, 129.8, 128.3,
127.4, 127.3, 126.3, 126.2, 125.8, 122.9, 122.3, 29.07, 27.1, 13.6, 11.9. Peaks for several
chemically nonequivalent carbons overlap with each other.
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9-(p-tolyl)phenanthrene (2b): NMR data for this compound are identical to those reported in the
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literature26c. 2% ethyl acetate/hexanes mixture used as eluent. Yield: 0.049 g (82%). H NMR
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(400 MHz, CDCl3): δ 8.78 (dd, J = 0.44 Hz, 8.26 Hz,1H), 8. 73 (d, J =8.16 Hz, 1H), 7.95 (d, J =
8.24 Hz, 1H), 7.89 (dd, J = 0.6 Hz, 7.48 Hz, 1H), 7.69-7.59 (m, 4H), 7.56-7.51 (m, 1H), 7.45 (d,
J =7.92 Hz, 2H), 7.34-7.32 (m, 2H), 2.48 (s, 3H). 13C NMR (150 MHz, CDCl3): 138.8, 137.9,
137.1, 131.6, 131.3, 130.6, 129.9, 129.0 (2xCH), 128.6, 127.4, 127.0, 126.8, 126.5, 126.4, 126.4,
122.9, 122.5, 21.3.
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9-(4-fluorophenyl)phenanthrene (2c): NMR data for this compound are identical to those
reported in the literature26c. 12% ethyl acetate/hexanes mixture used as eluent. Yield: 0.068 g
(85%). 1H NMR (600 MHz, CDCl3): δ 8.78 (d, J =8.22 Hz, 1H), 8.73 (d, J = 8.16 Hz, 1H), 7.90
(d, J = 7.74 Hz, 1H), 7.86 (d, J = 7.92 Hz, 1H), 7.70-7.62 (m, 4H), 7.57-7.50 (m, 3H), 7.21 (t, J =
8.52 Hz, 2H). 13C NMR (150 MHz, CDCl3): 162.31 (d, Jf = 245.01 Hz), 137.65, 136.65, 131.60,
131.55, 131.42, 131.08, 130.62, 129.96, 128.62, 127.64, 126.90, 126.69, 126.65, 126.57, 126.52,
122.95, 122.53, 115.29, 115.15.
4-(phenanthren-9-yl)benzonitrile (2d): NMR data for this compound are identical to those
reported in the literature31. Yield: 0.032 g (64%). Synthetic Scheme A4. 9% ethyl
acetate/hexanes mixture used as eluent. White solid. 1H NMR (600 MHZ, CDCl3): δ 8.80 (d, J =
8.28 Hz, 1H), 8.74 (d, J = 8.34 Hz, 1H), 7.91 (d, J = 7.86 Hz, 1H), 7.82 (d, J = 8.10 Hz, 2H),
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7.78 (d, J = 8.22 Hz, 1H), 7.73-7.70 (m, 2H), 7.68-7.63 (m, 4H), 7.57 (t, J = 7.56 Hz, 1H). C
NMR (150 MHz, CDCl3): 145.8, 136.8, 132.2 (2xCH), 131.2, 130.8 (2xCH), 130.7, 130.3,
130.2, 128.9, 127.9, 127.3, 127.2, 126.9, 126.8, 126.2, 123.2, 122.6, 118.9, 111.3. HMRS-DART
calcd for C21H13N+NH4: 297.1392, found [M+NH4]+: 297.1378.
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9-(4-(trifluoromethyl)phenyl)phenanthrene(2e): NMR data for this compound are identical to
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those reported in the literature32. 10 % ethyl acetate/hexanes mixture used as eluent. Yield: 0.
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080 g (80%). White solid (m.p.: 162-163 oC). H NMR (600 MHz, CDCl3): δ 8.78 (dd, J = 8.3
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Hz, 26.6 Hz, 2H), 7.92 (d, J = 7.8 Hz, 1H), 7.83 (d, J =8.2 Hz, 1H), 7.79 (d, J = 8.0 Hz, 2H),
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7.73-7.65 (m, 6H), 7.58-7.56 (m, 1H). C NMR (150 MHz, CDCl3): δ 144.6, 137.3, 131.3,
130.7, 130.6, 130.4, 130.2, 129.9, 129.8, 128.2, 127.8, 127.07, 127.05, 126.8, 126.6, 126.5,
125.33, 125.30, 123.1, 122.6; CF3 carbons are merging with other peaks.
9-(naphthalen-1-yl)phenanthrene (2f): NMR data for this compound are identical to those
reported in the literature26. 4% ethyl acetate/hexanes mixture used as eluent. Yield: 0. 067 g
(84%). 1H NMR (600 MHz, CDCl3): δ 8.84 (d, J =8.4 Hz, 1H), 8.82 (d, J = 8.4 Hz, 1H), 8.00 (d,
J =8.16 Hz, 1H), 7.99 (d, J =8.04 Hz, 1H), 7.92 (d, J =7.74 Hz, 1H), 7.81 (s, 1H), 7.75- 7.73 (m,
1H), 7.68-7.63 (m, 3H), 7.60-7.59 (m, 1H), 7.51-7.46 (m, 3H), 7.43-7.40 (m, 1H), 7.31-7.29 (m,
1H). 13C NMR (150 MHz, CDCl3): 138.4, 137.0, 133.5, 132.9, 132.1, 131.5, 130.2, 130.2,
128.6, 128.4, 128.1, 128.0, 127.8, 127.4, 126.8, 126.7, 126.6, 126.5, 126.4, 126.0, 125.8, 125.4,
122.7, 122.6.
9-(4-butylphenyl)phenanthrene (2g): NMR data for this compound are identical to those
reported in the literature.33 1% ethyl acetate/hexanes mixture used as eluent. Yield: 0.075 g
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(75%). H NMR (600 MHz, CDCl3): δ 8.75-8.73 (m, 1H), 8.66 (d, J =8.04 Hz, 1H), 8.13-8.11
(m, 1H), 7.83-7.82 (m, 1H), 7.67-7.56 (m, 5H), 3.12 (t, J =7.8 Hz, 2H), 1.82-1.78 (m, 2H), 1.53-
1.50 (m, 2H), 1.00 (t, J = 7.32 Hz, 3H). 13C NMR (150 MHz, CDCl3): 136.9, 131.9, 131.3,
130.7, 129.6, 128.0, 126.5, 126.4, 126.0, 125.9, 125.8, 124.5, 123.2, 122.1, 33.2, 32.4, 22.9, 14.0.
9-(4-methoxyphenyl)phenanthrene (2h): NMR data for this compound are identical to those
reported in the literature26. 6% ethyl acetate/hexanes mixture used as eluent. Yield: 0.80 g
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(80%). White solid. H NMR (600 MHZ, CDCl3): δ 8.78 (d, J = 2.82 Hz, 1H) 8.73 (d, J = 8.16
Hz, 1H), 7.95 (d, J= 8.28 Hz, 1H), 7.89 (d, J =7.62 Hz, 1H), 7.69-7.65 (m, 3H), 7.62 (t, J = 7.44
Hz, 1H), 7.55 (t, J = 7.29 Hz, 1H), 7.50-7.47 (m, 2H), 7.08-7.06 (m, 2H), 3.92 (s, 3H). 13C NMR
(150 MHz, CDCl3): 159.0, 138.4, 133.2, 131.7, 131.4, 131.1 (2xCH), 130.7, 129.9, 128.6, 127.4,
126.9, 126.8, 126.5, 126.4, 122.9, 122.5, 113.8. 55.4. Chemically nonequivalent carbons are
merging with other peaks. LRMS-EI calcd for C21H16O: 284.12, found [M]+: 282.26.
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2-(phenanthren-9-yl)thiophene (2i): NMR data for this compound are identical to those reported
in the literature.34 5% ethyl acetate/hexanes mixture used as eluent. Yield: 0.074 g (74%).
Synthetic Scheme A4. White solid. 1H NMR (600 MHZ, CDCl3): δ 8.78 (d, J =8.2 Hz, 1H), 8.71
(d, J =8.3 Hz, 1H), 8.26 (d, J =8.2 Hz, 1H), 7.90 (d, J =7.8 Hz, 1H), 7.86 (s, 1H), 7.69 (q, J =
7.5Hz 1H), 7.64-7.59 (m, 2H) 7.46 (d, J =5.0 Hz, 1H) 7.30 (d, J =3.3 Hz, 1H) 7.23-7.22 (m, 1H).
13C NMR (150 MHz, CDCl3): 141.7, 131.3, 131.1, 131.0, 130.7, 130.2, 129.1, 128.8, 127.6,
127.3, 127.1, 127.0, 126.8, 126.7, 126.6, 125.6, 122.9, 122.6. (solvent (DCM) peak at 53.4).
6-(4-methoxyphenyl)-3-methylnaphtho[1,2-b]benzofuran (2j): NMR data for this compound are
identical to those reported in the literature.35 15% ethyl acetate/hexanes mixture used as eluent.
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Yield: 0.035 g (70%). H NMR (400 MHz, CDCl3): δ 7.44-7.40 (m, 2H), 7.38-7.36 (m, 1H),
7.32-7.28 (m, 1H), 7.15-7.12 (m, 2H), 7.09 (s, 1H), 7.00-6.97 (m, 3H), 6.80 (t, J =3.56 Hz, 2H),
3.86 (s, 3H), 2.35 (s, 3H). 13C NMR (100 MHz, CDCl3): 159.2, 152.8, 143.6, 143.5, 142.2,
138.9, 131.3, 130.6 (2xCH). 130.1, 130.1, 129.6, 128.1, 126.8, 125.9, 123.2, 121.5, 120.6, 115.9,
113.9 (2xCH), 53.3, 21.6. Chemically nonequivalent carbons are merging with other peaks.
HRMS-DART calcd for C24H18O2+H: 339.1385, found [M+H]+:339.1387.
4-(10-(tributylstannyl)phenanthren-9-yl)pyridine(2k-Sn): This compound prepared same
procedure as general procedure synthetic scheme (A4). 10% ethyl acetate/hexanes mixture used
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