Biphenyl- and fluorenyl-based potential molecular electronic devices

Tetrahedron 59 (2003) 3131–3156

Biphenyl- and ﬂuorenyl-based potential molecular

electronic devices

*

David W. Price, Jr. and James M. Tour

Department of Chemistry and Center for Nanoscale Science and Technology, MS 222, Rice University, 6100 Main St.,

Houston, TX 77005, USA

Received 16 January 2003; revised 1 March 2003; accepted 1 March 2003

Abstract—New potential molecular electronics devices have been synthesized based on our knowledge of systems that we previously

studied. Research has shown that simple molecular systems demonstrate negative differential resistance (NDR) and memory characteristics.

The new molecules rely primarily on the redox properties of the compounds to improve upon the solid-state characteristics already observed.

Electrochemical tests have been performed in order to evaluate the redox properties with the hope that the electrochemical results can be used

1. Introduction

It is for these reasons and others that work continues to

develop molecular electronics candidates. Of course, there

are numerous problems that will need to be solved before

molecular computing will be realized, including addressing

single molecules in circuits and the need for heat dissipation

at these packing levels.³

Molecular electronics is currently a topic of considerable

interest among a diverse community of scientists and

engineers as well as the general population and popular

press.¹Much effort and capital has been expended to

improve and further miniaturize the components of

computers. The methods currently used to make the

microchips have been commercially scaled down to

0.13 mm (130 nm) feature size (interconnect metal line

width, for instance). The lower limit is expected to be about

30 nm.²Experts in the semiconductor ﬁeld estimate that this

limit will be reached in 10–15 years.^2b

Many molecular structures have been synthesized for use as

molecular devices, including switches, wires, controllers,

and gates.^4,5Molecules in the oligo(phenylene ethynylene)

(OPE) class having a negative differential resistance (NDR)

effect were discovered when nitro-bearing OPE molecules

were tested. The deﬁning characteristic of NDR is that the

device will only carry signiﬁcant current in a narrow voltage

range. When sandwiched between metal contacts, both the

nitro-amino containing compound 1⁶and the mono-nitro

compound 2^7,8were shown to demonstrate this NDR effect

(Fig. 1).

If electronics and computer components are to continue

decreasing in size beyond the 30 nm limit, new technologies

must be invented and explored. Molecular scale devices

seem to be a logical approach to reduce the size of current

electronic devices. A typical organic ‘molecular wire’

synthesized in our laboratory is about 2.5 nm long and

0.3 nm wide, 10 times smaller in width than the presumed

ultimate 30 nm width of metal lines in solid-state-based

devices. Present day personal computers utilize components

that contain approximately 10⁷transistors per cm². Self-

assembled monolayers (SAMs) of molecular scale wires can

achieve ordering of approximately 10¹⁴molecules/cm²,

seven orders of magnitude greater. Also, one can manu-

facture one mole of these molecules in a large laboratory

ﬂask, which amounts to 6£10²³devices, or more than the

number of transistors ever made in the history of the world.

One proposed mechanism for the NDR effect involves the

reduction of the molecules. It was thought that the ‘turn-on’

voltage, that is, the potential where current began to increase

dramatically, was the result of a single-electron reduction of

the molecules. The ‘turn-off’ voltage, where the current

essentially stopped, occurred because of a second single-

electron reduction. In an effort to understand the mechanism

behind the NDR effect, calculations⁹and cyclic voltam-

metric measurements¹⁰on the nitro-only compound 2 and

its derivatives were performed, both of which are generally

in good agreement. In addition, both 1 and 2 demonstrate

molecular dynamic random access memory (molecular

DRAM).¹¹That is, the nanopore devices containing either

of these compounds can store conductive states that differ

enough from one another to be recognizable. This

Keywords: molecular electronics; biphenyl; ﬂuorenyl.

*

Corresponding author. Tel.: þ1-7133486246; fax: þ1-7133486250;

e-mail: tour@rice.edu

doi:10.1016/S0040-4020(03)00334-X

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Figure. 1. Both the nitro-amino functionalized OPE 1 and the nitro functionalized 2 demonstrated the NDR effect.

essentially constitutes DRAM as used in modern computers,

an interesting achievement. To fully develop the structure–

activity relationship (SAR) among this class of compounds,

we designed and synthesized a number of compounds that

structurally differed from 1 and 2. We report on those

syntheses in this paper.

through an alternative method and therefore not isolated

here.

Coupling of 3 with 4-ethynyl-1-benzenethioacetate

afforded monocoupled product (not shown) in low 14%

yield. This has been a problem common to many couplings

of nitro-containing compounds with thioacetate-containing

alligator clip molecules (molecules bearing moieties that

adhere to metal surfaces³). Coupling of compound 3 with

trimethylsilylacetylene (TMSA) afforded 4 in a modest

yield. Coupling of 4 with phenylacetylene provided 5 in a

higher yield. Coupling of nitro compounds can be

problematic because of the potential for intramolecular

reaction between the nitro group and an adjacent alkyne to

form cyclic isatogens, as seen by Rosen and coworkers.¹⁴

Lower temperatures and shorter reaction times as well as the

use of lower concentrations of base help to reduce or

prevent such side reactions. Deprotection of the

alkyne using potassium carbonate and methanol afforded

6 in high yield. Coupling of the terminal alkyne with

the alligator clip 7 afforded ﬁnal product 8 in good

yield.

2. Biphenyl cores: synthesis of 2,3⁰-dintro system

Scheme 1 shows the complete synthesis of a 2,3⁰-

dinitrobiphenyl system. Preliminary data indicate that this

compound shows a well-deﬁned room temp₀erature NDR as

well as long-term (hours) memory.¹²4,4 -Biphenyl was

nitrated using the conditions of Shaw and Turner¹³to give

the 2,3⁰-dinitro product 3. By literature precedent and by

1

our own H NMR analysis of the crude product mixture,

there was approximately 85% of the desired product and

15% of the 2,2⁰-dinitro product. Recrystallization from

ethanol/acetone would only allow for isolation of 70% of

pure 3. Although the 2,2⁰-product is useful and is currently

being used in making a device, it is obtained in higher yields

Scheme 1. Synthesis of 2,3⁰-dinitrobiphenyl system 8.

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Scheme 2. Synthesis of isonitrile 11.

The 2,3⁰-dinitro biphenyl compound 8 shows NDR behavior

similar to the mono-nitro and nitro-amino devices 1 and 2.

However, 8 shows an NDR effect that is far more

pronounced at room temperature that the NDR effect of 1

or 2.⁷This supports our theory that the nitro group

functionality plays a key role in the NDR switching

mechanism and memory effects. A full account of the

electrical characteristics will be published separately.

higher delocalization within the molecular system and better

overlap of the molecular orbitals with the metals’ Fermi

levels.³Scheme 2 shows the synthesis of the 2,3⁰-

dinitrobiphenyl device synthesized with an isonitrile

alligator clip. 4⁰-Ethynyl-2,3⁰-dinitro-4-phenylethynyl-

biphenyl (6) was coupled with formamide 9 to provide 10.

The exact yield was not determined since ¹H NMR analysis

showed some impurities. In addition, slow rotation about the

formamide C–N bond, on the NMR time scale, due to its

partial double bond character (tautomerization),¹⁵produced

complex absorbances that made it difﬁcult to assign peaks in

the ¹H NMR. Compound 10 was dehydrated using

triphosgene to provide 11 in a yield of 91% over the two

steps.

2.1. Biphenyl systems with one or two thioacetyl or

isonitrile alligator clips

We are exploring the use of isonitriles as alligator clips for

attaching these compounds to metal surfaces. Isonitriles

form weaker bonds to gold and other metal substrates than

thiols; weaker chemisorption might make for a better

alligator clip and thereby better conduction due to changes

in the molecular orbital overlap with the Fermi level of the

metal. Also, the SAMs that are formed using isonitriles may

be more perpendicular to the surface than thiol-based

compounds, which might allow for better conduction due to

Scheme 3 shows the complete synthesis of the 2,3⁰-

dinitrobiphenyl compound with two alligator clips. Com-

pound 3 was coupled with an excess of TMSA at room

temperature to provide 12 in good yield. If the reaction was

heated to 458C for only a few hours, the yield was reduced,

possibly due to cyclization between the 3⁰-nitro group and

Scheme 3. Synthesis of 14 containing two protected thiol alligator clips.

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Scheme 4. Synthesis of 16 containing two isonitrile alligator clips.

the alkyne.¹⁴Deprotection of the alkynes provided 13,

which was coupled with 2 equiv. of alligator clip 7 to

provide 14 in good yield. No electronic tests have yet been

done with this compound. As we have long experienced, the

synthesis of the candidate molecules moves far more swiftly

than the detailed electrical testing.

Scheme 5 shows the complete ₀synthesis of another

dinitrobiphenyl compound, the 2,2 -isomer. We made this

compound since we have yet to determine how regio-

isomerism affects the electronic characteristics of the

molecules. 2,5-Dibromonitrobenzene was subjected to Ull-

man coupling conditions to give the biphenyl compound 17

in good yield.¹⁶Coupling of 17 with TMSA afforded 18 in

moderate yield. Subsequent coupling with phenylacetylene

gave 19. Deprotection of the alkyne using potassium

carbonate and methanol afforded terminal alkyne 20 in

high yield. Coupling of 20 with 7 afforded 21 in a surprising

72% yield. This yield is much higher than some other yields

of couplings with nitro compounds and thioacetates. It may

result from the inability of the nitro group to internally

cyclize with the adjacent alkyne, thereby giving fewer by-

products.

Scheme 4 depicts the synthesis of the 2,₀3⁰-dinitro device

with two isonitrile alligator clips. 4,4 -Diethynyl-2,3⁰-

dinitro-biphenyl (13) was coupled with 2 equiv. of for-

mamide 9 to provide 15. The precise yield could not be

ascertained due to the same reasons described earlier.

Therefore, crude 15 was taken onto the dehydration step to

afford ﬁnal product 16 in a moderate yield. This is actually

an encouraging yield considering the poor solubility of the

bis-formamide precursor.

Scheme 5. Synthesis of regioisomeric 2,2⁰-dinitrobiphenyl compound 21.

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Scheme 6. Synthesis of compounds 24 with two alligator clips.

Scheme 6 shows the complete synthesis of the 2,2⁰-

dinitrobiphenyl compound containing two alligator clips

for possible use in contacting two metal surfaces or

crosslinking nanoparticles. Compound 22 was made by

coupling 2 equiv. of TMSA with 17. Deprotection of the

alkynes provided 23, which was then coupled with 2 equiv.

of 7 to provide 24 in low yield.

with 1 equiv. of phenylacetylene provided an inseparable

mixture of starting material, monocoupled product and

dicoupled product, which was taken onto the next step.

Hypoﬂuorous acid (HOF, formed from the reaction of F₂

and H₂O) oxidation¹⁷afforded tetranitro compound 28 in

11% yield over 2 steps. Final coupling of 28 with the

alkynyl alligator clip 29¹⁸afforded 30 in an expectedly low

yield of 24% due to the nitro moieties’ proximity to the

alkynes. No electrical tests on this compound have yet been

conducted.

Scheme 7 shows the complete synthesis of another

biphenyl-based candidate. If two nitro groups are good,

will a molecule containing four nitro groups have longer

lifetime memory states when tested?³17 was reduced to the

corresponding diamine. The amines were then protected as

acetamides to give 25 in 89% yield over two steps. Mixed

acid nitration at 08C afforded compound 26 in good yield.

Potassium carbonate/methanol-promoted deprotection⁷of

26 failed to remove the acetyl groups, but acidic hydrolysis

using H₂SO₄and water easily provided 27. Coupling of 27

Scheme 8 shows a synthesis that was designed with the

thought that 33 would couple more selectively with

phenylacetylene than would 27, as used in the prior

synthesis. Reduction of 3 followed by acetyl protection of

the amines afforded 31 in 100% yield over two steps. This

yield is higher than that for the previous scheme because

some of the 2,2⁰-dinitrobiphenyl is converted to the

Scheme 7. Synthesis of tetranitro compound 30.

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Scheme 8. Improved synthesis of intermediate 28.

benzo[c]cinnoline product instead of the diamine, a

conversion that cannot occur for the 2,3⁰-dinitro isomer.

Mixed acid nitration afforded 32 in a modest yield. TLC and

proton NMR detected other isomers although they were not

isolated. Compound 32 was then deprotected in high yield

using 3N HCl in THF to afford 33 with the free amines. The

biphenyl core 33 was then coupled with phenylacetylene to

give an inseparable mixture of starting material, desired

product, and dicoupled material. After some attempt to

purify (column chromatography), the mixture was taken

onto the oxidation step. The HOF oxidation was used to

afford 28 in 45% yield (over two steps).¹⁷This is an

improvement over the prior route that afforded 28 in 11%

over two steps from the symmetric biphenyl 27. Indeed the

Scheme 9. Synthesis of mononitro biphenyl molecule 41.

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3137

Scheme 10. Synthesis of candidate 43.

unsymmetrical nature of 33 led to an increase in yield in the

Sonogashira coupling.¹⁹

again in high yield. The production of the second raw

material in the parallel synthesis began with the stannylation

of 37²¹to give 38. This was then subjected to a Stille

coupling²²with 36 to give the biphenyl product 39 in good

yield. 39 was deprotected using potassium carbonate and

methanol to liberate the terminal alkyne 40 in high yield. 40

was coupled with 7 to give 41 in good yield.

Scheme 9 shows the complete synthesis of a mononitro

biphenyl core-based molecule 41 synthesized to compare its

properties to 2 and 14. The comparison to 2 should reveal

any differences produced by adding a barrier (i.e. the

biphenyl twist) and length to the molecule. The comparison

to 14 should determine what difference exists between

having one or two nitro groups on a biphenyl core. The

synthesis of 41 began with the iodination of 2-nitroaniline to

give 34 in high yield.²⁰Coupling of 34 with phenyl-

acetylene provided 35 in high yield. Note that this

methodology allows one to generate derivatives of the

mononitro device in high yield by coupling of a terminal

alkyne at only one available halogen site; a route not easily

attainable through other means. Next, the amine was

replaced by an iodide via the diazonium salt to give 36,

Scheme 10 shows the synthesis of a mononitro biphenyl

molecule 43 with an isonitrile alligator clip. 4⁰-Ethynyl-2-

nitro-4-phenylethynyl-biphenyl (40) was coupled with

formamide 9 to give 42 in high yield. Formamide 42 was

then dehydrated using triphosgene to afford isonitrile 43 in a

good yield of 73%.

Scheme 11 shows the synthesis of a biphenyl-based device

containing two amino groups and two nitro groups. The

reasoning behind this design is that if each ring of the

Scheme 11. Synthesis of diamino dinitro biphenyl-based molecule 46.

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Figure. 2. Schematically depicting the alignment of the internal dipoles and interactions of 46 that may occur in a solid-state device.

biphenyl is in a zwitterionic or pseudo-quinoidal form, the

two rings may interact in an interesting manner not seen in

any previous devices (Fig. 2). Until some data is generated

from the solid-state testing of this compound, it is difﬁcult to

speculate on how this system may truly behave.

could not be fully puriﬁed via column chromatography.

Therefore, after limited puriﬁcation, the product was

coupled with phenylacetylene and puriﬁed to give 44

(Scheme 11) in a low, yet statistically expected, yield over

the two steps. Deprotection of the terminal alkyne yielded

45, which was puriﬁed by simple ﬁltration through a silica

plug. This alkyne was then coupled with 7 to afford 46 in

low yield. As we have discussed previously, in our hands the

The synthesis began with compound 27 (Scheme 7). 27 was

coupled with 1 equiv. of TMSA to give an intermediate that

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3139

Scheme 12. Synthesis of ﬂuorene-based molecule 51.

Scheme 13. Synthesis of ﬂuorene-based molecule 53.

coupling of nitrated molecules with thioacetyl-containing

compounds rarely gives high yields when the nitro moieties

are in the 2-position relative to the alkyne.¹⁴

an inseparable mixture of products. Deprotection of the

terminal alkyne afforded 52 which was .90% pure after

column chromatography. The determination of the order of

coupling was based on a prior knowledge of Sonogashira

couplings.²¹The palladium oxidatively adds to the C–Br

bond that is closest and most affected by the electron-

withdrawing nitro group. In this case it is the C–Br bond

that is in the 3-position relative to the nitro group.

Compound 52 was then coupled with 7 to provide ﬁnal

compound 53 in an overall yield of 23% (over 4 steps). The

structure of 52 was conﬁrmed via X-ray crystallographic

analysis of 53 that provided the ORTEP shown in Figure 3.

2.2. Fluorene systems

Scheme 12 shows the ﬁrst synthesis of a new class of

potential molecular electronics devices: ﬂuorene-based

compounds. Because the non-planarity of biphenyl cores

can create a barrier to conduction (the twist between the

rings averages 708), forcing the rings nearer to planarity by

connecting the 2- and 2⁰-carbons with a methylene bridge, as

in ﬂuorene, could lead to molecules with better conduction.

Scheme 14 shows the synthesis of 55, an isomer of 53,

accomplished by simple reversal of the ﬁrst two coupling

steps. Compound 48 was ﬁrst coupled with phenylacetylene

followed by the addition of TMSA in the same reaction

The synthesis began with the bromination of ﬂuorene to

give 47 in quantitative yield.²³Next, 47 was nitrated using

mixed acid conditions to give 48.²⁴48 was coupled with

2 equiv. of TMSA to give 49 in moderate yield. The

terminal alkynes were deprotected to give compound 50 in

high yield. Finally, the diyne was coupled with 2 equiv. of 7

to afford 51 in a reasonable yield.

Scheme 13 depicts the synthesis of a nitro-ﬂuorene

molecule with only one alligator clip. Compound 48 was

coupled with TMSA to afford an inseparable mixture of

products. After a limited degree of puriﬁcation, the impure

product was coupled with phenylacetylene, again providing

Figure. 3. ORTEP of 53 from X-ray crystallography.

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Scheme 14. Synthesis of the isomer of 51.

Scheme 15. Synthesis of ﬂuorene-based molecule 57 with isonitrile alligator clip.

Scheme 16. Synthesis of ﬂuorenone 61.

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3141

Scheme 17. Synthesis of nitroﬂuorenone 65 with two alligator clips.

apparatus. Again, this product could not be puriﬁed so was

taken onto the next step with limited puriﬁcation. Deprotec-

tion of the alkyne afforded 54 in ,38% yield (.90% purity)

over the two steps. Coupling of 54 with 7 afforded ﬁnal

compound 55 in 25% yield over the three steps.

alkynes in high yield.²⁷Diyne 60 was coupled with 2 equiv.

7 in a modest yield.

Scheme 17 shows the synthesis of 65 containing a nitrated

ﬂuorenone core, combining both nitro and carbonyl

functionality. This could provide new and interesting

electronic properties in a solid-state device in that there

could be two modes of switching and perhaps multiple

memory states. The synthesis began with the oxidation of

2,7-dibromo-4-nitroﬂuorene (48) using the catalytic chro-

mium(VI) method described for the previous synthesis²⁵but

in lower yield, possibly because 48 is more electron-

deﬁcient and therefore less susceptible to oxidation.¹⁷62

could not be completely puriﬁed so it was taken onto the

next step, where it was coupled with 2 equiv. of TMSA to

afford 63 in a modest yield over the two steps. 63 was then

deprotected to afford 64 in high yield. The liberated alkynes

were then coupled with 2 equiv. of 7 to afford 65 in a good

yield.

Scheme 15 shows the synthesis of a nitro-ﬂuorene

compound containing an isonitrile alligator clip. The

synthesis began with the coupling of formamide 9 with

7-ethynyl-4-nitro-2-phenylethynyl-9H-ﬂuorene (54) to

provide 56 in approximately 90% yield (the starting alkyne

was not pure). This compound could not be fully puriﬁed by

column chromatography. Therefore, the slightly impure 56

was dehydrated to give the isonitrile 57 in an overall yield of

31% over two steps.

Scheme 16 shows the synthesis of a molecule containing a

ﬂuorenone core. This compound was designed and syn-

thesized based on the concept that the carbonyl functionality

of the ﬂuorenone may act as an electron sink and allow for

facile reductions. If it demonstrates switching capabilities,

61 would be the ﬁrst device-like system that we have

identiﬁed which contains no nitro functionalities. Degra-

dation of the nitro-based devices has been a problem and

ﬂuorenones might prove to be more stable. The synthesis

began with the oxidation of 2,7-dibromoﬂuorene using a

catalytic amount of chromium(VI) oxide and t-butyl

hydroperoxide to regenerate the catalyst.²⁵The reaction

proceeded smoothly to afford 2,7-dibromo-9-oxo-ﬂuorene

(58).²⁶Next, 58 was coupled with 2 equiv. of TMSA to

afford 59 in unoptimized yield.²⁷59 was deprotected using

potassium carbonate and methanol to liberate the free

3. Cyclic voltammetry results

We have used cyclic voltammetry (CV) to help us

understand how some of our molecules might behave as

switches and memory elements.¹⁰We used the same CV

testing methods on the new products in order to predict how

these nanoscale structures may behave in a solid-state

device. We concede that the comparisions would only be

qualitative since the electrochemical (solvent-based with

electrolyte) and solid-state (solvent-free, no electrolyte) are

dramatically different.

Scheme 18. Synthesis of compound 66 with no alligator clips.

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molecular orbitals overlap, producing conduction. As the

potental becomes higher, the molecules get reduced a

second time thereby changing the electronic properties

again. This leads to the switching OFF of the device putting

it in a lower conductivity state.¹⁰The CV data lends more

support to this proposed theory of switching operation.

Scheme 19 shows the synthesis of the 2,2⁰-dinitro-biphenyl

compound 67 with no alligator clips for further CV

experiments. 17 was coupled with an excess of phenyl-

acetylene to afford compound 67 in good yield. CV

measurements were performed and can be seen in

Figure 5. The quasi-reversible reduction potentials are

almost identical to the ﬁrst two reductions of 66. However,

there is no third reduction at 22.0 to 22.2 V, as was seen

with 66. One could reason that the third reduction of 6₀6

leads to a reaction between the 3⁰-nitro group and the 4 -

Figure. 4. CV of 66. The reduction potentials were found to be 21.37,

21.60, and 22.26 V.

Scheme 19. Synthesis of 67 for CV studies.

Scheme 18 shows the synthesis of the 2,3⁰-dinitrobiphenyl

compound 66 with no alligator clips, similar to 8, but

without the S–Ac. It is beneﬁcial to study similar

compounds that differ only by the presence or absence of

the S–Ac group since hydrolysis of the acetate under

conditions of the CV testing could skew the results. 66 was

therefore synthesized for the sole purpose of our electro-

chemical testing. 3 was coupled with an excess of

phenylacetylene to afford compound 66 in a yield of 80%.

The CV for this compound is shown in Figure 4. There are

three distinct reduction peaks, although they are only quasi-

reversible. The ﬁrst and third potentials are approximately

the same as the ﬁrst and second potentials of 2 studied

previously.¹⁰Interestingly, 66 has a third reduction not seen

in any of the previous devices. It is reasonable that the new

reduction is due to the presence of the second nitro group.

This new reduction potential is 21.60 V, which is

approximately 0.2 V difference from the ﬁrst potential.

From this data 66 should have better electronic properties

than previous systems, and this is precisely what has been

observed. From preliminary solid-state testing of 8, the

switching ON potential of the 2,3⁰-dinitro biphenyl device is

approximately 2.7 V and the switching ‘OFF’ potential is

approximately 2.9 V.^28,25The difference between these

ON–OFF voltages is approximately 0.2 V, closely corre-

sponding to the difference in the ﬁrst two CV reduction

potentials.

alkyne of 66. This is reasonable because nitro groups and

alkynes are known to reac₀t in an intramolecular fashion to

form isatogens.¹⁴The 2,2 -dinitro compound 67 does not

have such a 3⁰-nitro-4⁰-alkyne relationship and therefore

cannot form isatogen side-products.

Figure 6 shows results from the CV testing of tetranitro

compound 30. The two voltammagrams 6a and 6b represent

the same compound from different synthetic batches. As can

be seen, the CVs look similar but are not exactly the same.

This could be because the tetra-nitro device is very redox

reactive and is not stable. Upon close examination, there

appear to be several reductions in both CVs between 20.7 V

and 21.4 V. Since there are four nitro groups located in this

system, several reductions may overlap, thereby making the

voltammagrams difﬁcult to interpret. Based on this analysis,

Our working theory of how these molecules behave as

switches is based on the idea that the molecules in the solid

state get reduced as the voltage is increased and the

reduction is concomitant with a conformational change.

This gives rise to the switching ON of the device because of

changes to the molecular orbitals of the molecule and

delocalization of the charge over the entire molecule as

Figure. 5. CV of 67. The reduction potentials were found to be 21.32,

1.61 V.

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Figure. 8. CV of dinitro–diamino molecule 46.

4⁰-alkyne in compound 41. Because there is no possibility of

an intramolecular cyclization reaction between those

groups, the second reduction might be rather weak because

it is due to an intermolecular coupling.

The CV for dinitro-diamino device 46 is shown in Figure 8.

Although this compound was not designed to rely on its

redox properties to behave as a functional device (it should

rely on the ability of dipole moments of the internal rings to

align with an applied electric ﬁeld as shown in Fig. 2), the

electrochemical properties were measured to compare with

the other devices. Two reductions are present, in what

appears to be overlapping peaks. It is estimated that there

are two reductions at 21.71 V and 21.80 V, probably due

to the presence of two nitro groups on the system.

Figure. 6. CVs (a) and (b) of different batches of tetranitro compound 30.

this device may be an excellent redox center for use in our

molecular electronics studies; however, its lack of stability

may be a problem.

Figure 9 shows the CV of nitro-ﬂuorene compound 55.

There is a clearly visible reduction peak at 21.40 V and

another reduction, which is not so clear, at 22.0 V. These

are similar to the results for the mono-nitro biphenyl

compound 41 which showed reductions at 21.47 V and

22.19 V. The second reduction of the 41 was likewise not

well-deﬁned. These compounds have very similar CVs with

only a minor shift in reduction potentials.

Figure 7 shows the CV results of the mononitro biphenyl

device 41. As can be seen in the plot, there are again two

reductions, one at 21.47 V and another at 22.19 V. These

potentials are close to those of 2, however, the second

reduction here is much less pronounced than that for 2. As

was seen with the 2,2⁰-dinitro biphenyl device 67, there is no

spatially close relationship between a 3⁰-nitro group and a

Figure 10 shows the CV for ﬂuorenone compound 61. The

graph shows a single reduction at 21.45 V that appears to

Figure. 7. CV of mononitro biphenyl molecule 41.

Figure. 9. CV for compound 55.

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state results we have received from collaborators. Although

absolute values of the reduction potentials cannot be

compared between the nanopore (pseudo-solid state) and

solution experiments, solution CV helps to support the

proposed mechanism wherein reduction of the system

occurs to open or close a transport channel. Also, it is

hoped that CV testing may prove to be a method of quick-

screening compounds prior to solid-state testing as well as a

way to predict solid-state electronic properties. However,

more data needs to be obtained before this can be ﬁrmly

established.

5. Experimental

5.1. General

Figure. 10. CV of ﬂuorenone molecule 61.

All reactions were performed under an atmosphere of

nitrogen unless stated otherwise. N,N-dimethylformamide

(DMF) was distilled over calcium hydride and stored over

˚

4 A molecular sieves. Tetrahydrofuran (THF) was distilled

from sodium benzophenone ketyl. Hexanes were distilled.

N,N-Diisopropylethylamine (DIEA) was distilled over

calcium hydride. Silica gel plates were 250 mm thick, 40

F₂₅₄grade from EM Science. Silica gel was grade 60 (230–

400 mesh) from EM Science. ¹H NMR spectra were

observed at 400 MHz and ¹³C NMR spectra were observed

at 100 MHz on a Bru¨ker Avance 400 spectrometer. IR

spectra were obtained on a Nicolet Avatar 360 FTIR.

Melting points were determined on a Bu¨chi melting point

apparatus. Mass spectrometry was performed at Rice

University’s mass spectrometry lab. All new compounds

were named using the Beilstein AutoNom feature of

Beilstein Commander software. The synthesis of compound

7 was described previously²⁹as was the synthesis of

compound 9.³⁰

Figure. 11. CV of compound 65.

be quasi-reversible. This is almost the same value for the

reduction potential for the nitro-ﬂuorene 55. One could

argue that there is a second reduction at 22.1 V but it is not

clear. This data suggests that this device may give similar

results to previously tested compounds when tested in a

solid-state testbed such as the nanopore device.

5.2. General procedure for the coupling of a terminal

alkyne with an aryl halide utilizing a palladium–copper

cross-coupling (Castro–Stephens/Sonogashira

Protocol)^19,31

The CV for the nitro-ﬂuorenone molecule 65 is shown in

Figure 11. This compound shows two obvious reduction

peaks. The reduction potentials are 21.26 V and

21.66 V. Other than the tetra-nitro device, the ﬁrst

reduction is the lowest reduction potential observed for

any biphenyl or ﬂuorenyl-based compound. It appears that

the ﬁrst reduction peak may be two close, overlapping

peaks, with the ﬁrst reduction being approximately

21.16 V.

To an oven-dried screw cap tube or a round bottom ﬂask

equipped with a water cooled West condenser and a

magnetic stir bar were added the aryl halide, bis(triphenyl-

phosphine)palladium(II) dichloride (5 mol% based on aryl

halide), and copper(I) iodide (10 mol% based on aryl

halide). Alternately, bis(dibenzylideneacetone)palladium(0)

(2 mol% based on aryl halide), copper(I) iodide (2 mol%

based on aryl halide) and triphenylphosphine (2.5 equiv. per

palladium) were used. The vessel was then sealed with a

rubber septum, evacuated and backﬁlled with nitrogen (3£).

A co-solvent system of THF was added followed by DIEA.

The terminal alkyne was then added and the reaction heated,

if necessary, until complete. The reaction vessel was cooled

to room temperature and the mixture quenched with water

or a saturated solution of NH₄Cl. The organic layer was

diluted with CH₂Cl₂and washed with a saturated solution of

NH₄Cl (3£). The combined aqueous layers were extracted

with CH₂Cl₂(3£). The combined organic layers were dried

over anhydrous MgSO₄and the solvent removed in vacuo.

The crude product was then puriﬁed by ﬂash or column

chromatography (silica gel).

We made minimal effort to exclude air in any of our CV

work, therefore repeatability was generally poor, especially

with the products containing the S–Ac group.

4. Conclusions

Many different molecular electronics device candidates

have been synthesized with a few tested to date in full

device embodiments. These device candidates were ration-

ally designed based on chemical intuition using the solid-

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3145

5.3. General procedure for the deprotection of a

trimethylsilyl (TMS) protected alkyne

0.061 mmol), copper(I) iodide (0.023 g, 0.121 mmol),

triphenylphosphine (0.032 g, 0.121 mmol), THF (20 mL),

DIEA (0.84 mL, 4.84 mmol), and phenylacetylene

(0.20 mL, 1.82 mmol) were used following the general

procedure for couplings. The tube was capped and the

solution was heated in a 708C oil bath for 1 d. Flash column

chromatography (silica gel using 1:1 hexanes/CH₂Cl₂as

eluent) afforded the desired product as brown oil (0.355 g,

67% yield). IR (KBr) 3065.8, 2958.3, 2883.6, 2213.7,

2160.5, 1530.7, 1490.9, 1347.7, 1249.5, 1078.8, 891.0,

To a round bottom ﬂask equipped with a magnetic stir bar

were added the TMS-protected alkyne, 4–6 equiv. of

potassium carbonate, and a 1:1 mixture of methanol and

CH₂Cl₂. The reaction vessel was sealed with a rubber

septum and then ﬁlled with nitrogen. The reaction was

allowed to go to completion at which time the reaction was

quenched with a saturated solution of NaCl. The resulting

solution was extracted as stated in the previous section with

the resulting terminal alkyne quickly employed in the next

palladium/copper cross-coupling step.

844.6, 756.4, 689.6, 527.2 cm²^{1 1}H NMR (400 MHz,

.

CDCl₃) d 8.11 (d, J¼1.6 Hz, 1H), 8.00 (d, J¼1.8 Hz, 1H),

7.78 (dd, J¼8.0, 1.6 Hz, 1H), 7.68 (d, J¼8.0 Hz, 1H), 7.55

(m, 2H), 7.45 (dd, J¼8.0, 1.8 Hz, 1H), 7.39 (m, 4H), 0.29 (s,

9H). ¹³C NMR (100 MHz, CDCl₃) d 150.5, 148.8, 138.5,

135.9, 135.7, 133.2, 132.5, 132.3, 132.2, 129.7, 129.0,

128.0, 125.9, 124.5, 122.3, 118.8, 105.9, 99.4, 93.8, 86.4,

0.0. HRMS calcd for C₂₅H₂₀N₂O₄Si: 440.1192. Found:

440.1187 (Error¼1.2 ppm).

5.4.4. 4⁰-Ethynyl-2₀,3⁰-dinitro-4-phenylethynyl-biphenyl

(6). (3,2⁰-Dinitro-4 -phenylethynyl-biphenyl-4-ylethynyl)-

trimethyl-silane (5) (0.334 g, 0.758 mmol), potassium

carbonate (0.524 g, 3.79 mmol), methanol (20 mL), and

CH₂Cl₂(20 mL) were used following the general procedure

for deprotection to afford the desired product as brown oil

(0.274 g, 98% yield). ¹H NMR (400 MHz, CDCl₃) d 8.11 (d,

J¼1.5 Hz, 1H), 8.02 (d, J¼1.7 Hz, 1H), 7.78 (dd, J¼8.0,

1.6 Hz, 1H), 7.71 (d, J¼8.0 Hz, 1H), 7.55 (m, 2H), 7.48 (dd,

J¼8.0, 1.8 Hz, 1H), 7.38 (m, 4H), 3.58 (s, 1H).

5.4. General procedure for electrochemical testing of

potential moletronics devices

The CVs were performed on a BAS CV-50W using a glassy

carbon electrode as working electrode, platinum wire as

auxiliary electrode, with a Ag/AgNO₃non-aqueous refer-

ence electrode. The solutions were 1 mM in DMF and 0.1 M

n-Bu₄NBF₄. The scan rate was 0.1 V/s at 258C.

5.4.1. 4,4⁰-Dibromo-2,3⁰-dinitro-biphenyl (3).¹³Nitric

acid (70%, 30.6 mL) was added to a 100 mL round bottom

ﬂask containing a stir bar and cooled to approximately 08C

in an ice bath. 4,4⁰-Dibromobiphenyl (4.01 g, 12.8 mmol)

was then slowly added to the acid and stirred at 08C for

40 min. Ice water was then added to the mixture at which

point a light yellow solid precipitated out of the solution.

The solid was ﬁltered and washed with water then air-dried.

Recrystallization from ethanol/acetone afforded the desired

product as yellow needles (3.59 g, 70% yield): mp 150–

1518C (lit. mp 152–1538C). ¹H NMR (400 MHz, CDCl₃) d

8.15 (d, J¼2.0 Hz, 1H), 7.82 (dd, J¼8.3, 2.0 Hz, 1H), 7.79

(d, J¼0.4 Hz, 1H), 7.78 (d, J¼6.8 Hz, 1H), 7.30 (dd, J¼8.2,

2.2 Hz, 1H), 7.29 (d, J¼8.1 Hz, 1H).

5.4.2. (4⁰-Bromo-3,2⁰-dinitro-biphenyl-4-ylethynyl)-tri-

methyl-silane (4). 4,4⁰-Dibromo-2,3⁰-dinitrobiphenyl (3)

(1.00 g, 2.49 mmol), bis(triphenylphosphine)palladium(II)

dichloride (0.088 g, 0.125 mmol), copper(I) iodide (0.047 g,

0.249 mmol), THF (10 mL), DIEA (1.73 mL, 9.96 mmol),

and TMSA (0.39 mL, 2.7 mmol) were used for 4 h at RT

following the general procedure for couplings. Flash

column chromatography (silica gel using 1:1 hexanes/CH₂-

Cl₂as eluent) afforded the desired product as a brown solid

(0.605 g, 58% yield): mp 106–1088C. IR (KBr) 3098.7,

3068.3, 2955.3, 2852.9, 2069.4, 1597.9, 1525.5, 1462.9,

1347.1, 1250.9, 1152.4, 1099.1, 1036.9, 866.9, 840.2, 826.6,

760.3, 536.4 cm²¹. ¹H NMR (400 MHz, CDCl₃) d 8.11 (d,

J¼1.8 Hz, 1H), 7.93 (d, J¼1.8 Hz, 1H), 7.80 (dd, J¼8.1,

1.9 Hz, 1H), 7.66 (d, J¼7.9 Hz, 1H), 7.42 (dd, J¼8.0,

1.8 Hz, 1H), 7.30 (d, J¼8.3 Hz, 1H), 0.26 (s, 9H). ¹³C NMR

(100 MHz, CDCl₃) d 150.4, 149.0, 138.0, 136.6, 135.8,

133.5, 132.9, 132.5, 128.2, 124.4, 123.5, 118.9, 106.0, 99.3,

0.0. HRMS calcd for C₁₇H₁₅N₂O₄BrSi: 419.9967. Found:

419.9963 (Error¼0.9 ppm).

5.4.5. Thioacetic acid S-[4-(3,2⁰-dinitro-4⁰-p₀henylethynyl-

biphenyl-4-ylethynyl)-phenyl] ester (8). 4 -Ethynyl-2,3⁰-

dinitro-4-phenylethynyl-biphenyl (6) (1.10 g, 2.99 mmol))

was coupled with 4-thioacetyl-1-iodobenzene (7)²⁶(0.831 g,

2.99 mmol) using the Pd/Cu cross coupling method described

earlierusingbis(dibenzylideneacetone)palladium(0)(0.086 g,

0.149 mmol), copper(I) iodide (0.057 g, 0.30 mmol), tri-

phenylphosphine (0.157 g, 0.60 mmol), THF (20 mL), and

DIEA (2.1 mL, 12.0 mmol) in a screw cap tube under

nitrogen. The solution was stirred in a 508C oil bath for 3 h.

Column chromatography (silica gel using CH₂Cl₂as eluent;

R_f¼0.70) afforded the desired product as an orange solid

(0.981 g, 63% yield): mp 156–1588C. IR (KBr) 3078.2,

2924.6, 2858.0, 2207.6, 1709.0, 1528.4, 1495.7, 1346.2,

1

1280.9, 1112.6, 846.6, 827.0, 760.8, 691.0, 618.5 cm²¹. H

NMR (400 MHz, CDCl₃) d 8.13 (d, J¼1.6 Hz, 1H), 8.09 (d,

J¼1.9 Hz, 1H), 7.79 (dd, J¼8.0, 1.7 Hz, 1H), 7.74 (d,

J¼8.1 Hz, 1H), 7.62 (dt, J¼8.2, 1.8 Hz, 2H), 7.56 (m, 2H),

7.51 (dd, J¼8.1, 1.8 Hz, 1H), 7.43 (m, 3H), 7.38 (m, 3H), 2.43

(s, 3H). ¹³C NMR (100 MHz, CDCl₃) d 193.5, 150.0, 148.8,

138.5, 136.0, 135.3, 134.7, 133.2, 133.0, 132.7, 132.3, 132.3,

130.0, 129.7, 129.0, 128.0, 126.0, 124.8, 123.8, 122.4, 118.4,

98.0, 93.8, 86.7, 86.4, 30.8. HRMS calcd for C₃₀H₁₈N₂O₅S:

518.0936. Found: 518.0947 (Error¼2.0 ppm).

5.4.6. N-[4-(3,2⁰-Dinitro-4⁰-phenylethynyl-biphenyl-4-

ylethynyl)-phenyl]-formamide (10). 4⁰-Ethynyl-3,2⁰-

dinitro-4-phenylethynyl-biphenyl (6) (1.10 g, 2.99 mmol)

was coupled with N-(4-iodo-phenyl)-formamide (9)²⁷

(0.739 g, 2.99 mmol) following the Pd/Cu protocol using

5.4.3. (3,2⁰-Dinitro-4⁰-phenyle₀thynyl-biphenyl-4-ylethy-

nyl)-trimethyl-silane (5). (4 -Bromo-3,2⁰-dinitro-biphe-

nyl-4-ylethynyl)-trimethyl-silane (4) (0.509 g, 1.21 mmol),

bis(triphenylphosphine)palladium(II) dichloride (0.043 g,

bis(dibenzylideneacetone)

0.150 mmol), copper(I) iodide (0.057 g, 0.300 mmol),

palladium(0)

(0.086 g,

3146

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

triphenylphosphine (0.157 g, 0.600 mmol), DIEA (2.1 mL,

12 mmol), and THF (20 mL). After stirring at 558C for 4 h,

the reaction mixture was washed with NH₄Cl (aq) and

CH₂Cl₂. The resulting solution was diluted with hexanes to

precipitate the desired compound (1.48 g) that was taken

onto the next step with no further puriﬁcation. IR (KBr)

3361.9, 3073.1, 2202.5, 1692.6, 1600.5, 1520.1, 1405.4,

5.4.9. 4,4⁰-Diethynyl-2,3⁰-dinitro-biphenyl (13). 2,3⁰-Dini-

tro-4,4⁰-bis-trimethylsilanylethynyl-biphenyl (12). (0.815 g,

1.87 mmol), potassium carbonate (1.55 g, 11.2 mmol), metha-

nol (50 mL), and CH₂Cl₂(50 mL) were used following the

generalprocedurefordeprotectiontoaffordthedesiredproduct

(0.508 g, 93% yield). ¹H NMR (400 MHz, CDCl₃) d 8.14 (d,

J¼1.3 Hz, 1H), 8.06(d, J¼1.7 Hz, 1H), 7.79 (m, 2H), 7.51(dd,

J¼7.9, 1.7 Hz, 1H), 7.44 (d, J¼8.0 Hz, 1H), 3.63 (s, 1H), 3.33

(s, 1H).

1337.3, 1282.2, 1238.6, 1144.5, 834.0, 753.7, 685.6 cm²¹

.

¹H NMR (400 MHz, acetone-d₆) d 8.43 (s, 0.73H), 8.26 (d,

J¼1.7 Hz, 1H), 8.22 (d, J¼1.6 Hz, 1H), 8.00 (dd, J¼8.1,

1.7 Hz, 1H), 7.94 (d, J¼8.1 Hz, 1H), 7.82–7.76 (m, 4.1H),

7.67–7.60 (m, 4.63H), 7.49 (m, 3.43H).

5.4.10. Thioacetic acid S-{4-[4⁰-(4-acetylsulfanyl-phenyl-

ethynyl)-3,2⁰₀-dinitro-biphenyl-4-ylethynyl]-phenyl}

ester (14). 4,4 -Diethynyl-2,3⁰-dinitro-biphenyl (13) (1.26 g,

4.31 mmol),bis(dibenzylideneacetone)palladium(0)(0.124 g,

0.216 mmol), copper(I) iodide (0.082 g, 0.431 mmol),

triphenylphosphine (0.226 g, 0.862 mmol), THF (20 mL),

DIEA (4.5 mL, 25.9 mmol), and 4-(thioacetyl)iodobenzene

(7)²⁹(2.40 g, 8.62 mmol) were used following the general

procedure for couplings. The tube was capped and the

solution was stirred at 558C for 4.5 h. Flash column

chromatography (silica gel using CH₂Cl₂as eluent;

R_f¼0.45) followed by precipitation from CH₂Cl₂/hexanes

afforded the desired product as a slightly yellow solid

(1.52 g, 59% yield): mp 176–1798C (decomp.). IR (KBr)

3073.1, 2211.7, 1709.3, 1534.1, 1348.8, 1118.5, 951.2,

827.0, 623.5 cm²¹. ¹H NMR (400 MHz, CDCl₃) d 8.15 (d,

J¼1.7 Hz, 1H), 8.11 (d, J¼1.8 Hz, 1H), 7.82 (dd, J¼8.0,

1.6 Hz, 1H), 7.77 (d, J¼8.1 Hz, 1H), 7.64 (dt, J¼8.2, 1.7 Hz,

2H), 7.59 (dt, J¼8.2, 1.7 Hz, 2H), 7.53 (dd, J¼8.0, 1.8 Hz,

1H), 7.45 (m, 5H), 2.452 (s, 3H), 2.446 (s, 3H). ¹³C NMR

(100 MHz, CDCl₃) d 193.5, 150.0, 148.8, 138.4, 136.1, 135.3,

134.8, 134.7, 133.5, 133.0, 132.8, 132.7, 132.3, 130.0, 129.9,

128.1, 125.6, 124.8, 123.8, 123.5, 118.9, 98.0, 92.9, 88.2, 86.4,

30.8. MALDI-MS calcd for C₂₂H₂₄N₂O₄Si₂: 593. Found: 593.

5.4.7. 4⁰-(4-Isocyano-phenylethynyl)-2,3⁰-dinitro-4-

phenylethynyl-biphenyl (11).₀To a large test tube was

added

N-[4-(3,2⁰-dinitro-4 -phenylethynyl-biphenyl-4-

ylethynyl)-phenyl]-formamide (10) (0.500 g, 1.03 mmol).

Air was removed and N₂backﬁlled (3£). CH₂Cl₂(40 mL)

and triethylamine (10 mL) was added and the solution was

cooled to 08C. Triphosgene (0.278 g, 1.03 mmol) was then

added. After 2 h starting material remained by TLC. An

additional 0.139 g (0.51 mmol) of triphosgene was added.

After 45 min, an additional 0.139 g (0.51 mmol) of

triphosgene was added. After 15 additional min, 0.278 g

(1.03 mmol) of triphosgene was added (total of 3 equiv.).

After 4.5 h (total time), the reaction was complete by TLC.

The mixture was washed with NaCl (aq) and CH₂Cl₂.

Column chromatography (silica gel using CH₂Cl₂as eluent;

R_f¼0.84) afforded the product as a yellow solid (0.438 g,

91% yield): mp 1608C (decomp.). IR (KBr) 2119.7, 1525.6,

1341.3, 840.4, 761.6, 691.6, 543.4 cm²¹

.

¹H NMR

(400 MHz, CDCl₃) d 8.14 (d, J¼1.4 Hz, 1H), 8.10 (d,

J¼1.6 Hz, 1H), 7.80 (dd, J¼8.0, 1.3 Hz, 1H), 7.75 (d,

J¼8.1 Hz, 1H), 7.62 (d, J¼8.3 Hz, 2H), 7.57–7.52 (m, 3H),

7.43 (d, J¼7.9 Hz, 1H), 7.40–7.38 (m, 5H). ¹³C NMR

(100 MHz, CDCl₃) d 166.9, 150.0, 148.8, 138.9, 136.0,

135.2, 133.5, 133.1, 132.8, 132.3, 132.2, 129.8, 129.0,

128.0, 127.2, 127.0, 126.1, 124.9, 124.1, 122.3, 118.4, 96.7,

93.9, 87.4, 86.7. HRMS calcd for C₂₉H₁₅N₃O₃: 469.106256.

Found: 469.107078 (Error¼1.8 ppm).

5.4.8. 2,3⁰-Dinitro-4,4⁰-bis-trimethylsilanylethynyl-

biphenyl (12). 4,4⁰-Dibromo-2,3⁰-dinitro-biphenyl¹³(3)

(1.50 g, 3.73 mmol), bis(triphenylphosphine)palladium(II)

dichloride (0.131 g, 0.187 mmol), copper(I) iodide (0.071 g,

0.373 mmol), THF (20 mL), DIEA (5.2 mL, 30 mmol) and

TMSA (1.32 mL, 9.33 mmol) were used following the

general procedure for couplings. The tube was capped and

the solution was stirred at ambient temperature for 17 h.

Flash column chromatography (silica gel using 1:1 CH_2-

Cl₂/hexanes as eluent; R_f¼0.59) afforded the desired

product (1.20 g, 74% yield): mp 82–908C. IR (KBr)

3073.1, 2960.4, 2899.2, 2164.0, 1533.8, 1477.8, 1348.8,

1250.8, 1219.9, 1079.1, 847.5, 760.3, 643.0 cm²¹. ¹H NMR

(400 MHz, CDCl₃) d 8.07 (d, J¼1.6 Hz, 1H), 8.00 (d,

J¼1.8 Hz, 1H), 7.74 (dd, J¼8.0, 1.6 Hz, 1H), 7.70 (d,

J¼8.0 Hz, 1H), 7.46 (dd, J¼8.0, 1.9 Hz, 1H), 7.39 (d,

J¼7.9 Hz, 1H), 0.31 (s, 9H), 0.30 (s, 9H). ¹³C NMR

(100 MHz, CDCl₃) d 150.5, 148.6, 138.4, 136.3, 135.7,

133.5, 132.4, 132.1, 128.4, 125.7, 124.5, 118.8, 105.9,

101.8, 99.7, 99.3, 0.1, 20.01. HRMS calcd for

5.4.11. N-{4-[4-(4-Formylamino-phenylethynyl)-3,2⁰₀-

dinitro-biphenylethynyl]-phenyl}-formamide (15). 4,4 -

Diethynyl-2,3⁰-dinitro-biphenyl (13) (1.25 g, 4.28 mmol)

was coupled with N-(4-iodo-phenyl)-formamide (9)³⁰

(2.22 g, 8.99 mmol) following the Pd/Cu protocol using

bis(dibenzylideneacetone)palladium(0) (0.123 g, 0.214

mmol), copper(I) iodide (0.082 g, 0.43 mmol), triphenyl-

phosphine (0.226 g, 0.86 mmol), THF (25 mL), and DIEA

(4.5 mL, 25.7 mmol). The reaction was stirred at 558C for

4 h. The tube was ﬁlled with solid that was ﬁltered and

washed with CH₂Cl₂to remove salts and starting materials

to afford the desired product (2.13 g, 94% yield): mp 2408C

(decomp.). (The desired product has poor solubility in most

common organic solvents due to the hydrogen bonding

nature of the formamides. The presence of two formamide

groups allows the molecules to become a hydrogen-bonded

polymer, thus, having poor solubility.) IR (KBr) 3362.2,

3231.9, 3073.1, 2883.6, 2204.7, 1690.4, 1601.0, 1521.3,

1406.2, 1336.6, 1285.9, 1245.0, 1144.1, 836.9, 691.9,

1

533.1 cm²¹. H NMR (400 MHz, DMSO-d₆) d 10.47 (d,

J¼9.1 Hz, 1.4H), 10.40 (t, J¼9.4 Hz, 0.49H), 8.93 (d,

J¼10.4 Hz, 0.44H), 8.33 (s, 1.5H), 8.26 (d, J¼17.1 Hz, 2H),

7.97 (d, J¼7.8 Hz, 1H), 7.92 (d, J¼8.1 Hz, 1H), 7.79 (d,

J¼8.0 Hz, 1.16H), 7.72–7.68 (m, 4H), 7.61–7.55 (m, 4H),

7.32 (m, 1H).

C₂₂H₂₄N₂O₄Si₂:

(Error¼2.2 ppm).

436.127465.

Found:

436.126508.

5.4.12. 4,4⁰-Bis-(4-isocyano-phenylethynyl)-2,3⁰-dinitro-

biphenyl (16). To a 500 mL round bottom ﬂask was

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3147

added N-{4-[4-(4-formylamino-phenylethynyl)-3,2⁰-dini-

tro-biphenylethynyl]-phenyl}-formamide (15) (1.00 g,

1.89 mmol). Air was removed and N₂backﬁlled (3£).

CH₂Cl₂(200 mL) and triethylamine (20 mL) was added and

the solution was cooled to 08C. Triphosgene (0.560 g,

1.89 mmol) was then added. After 30 min starting material

remained by TLC. An additional 0.280 g (0.95 mmol) of

triphosgene was added. After 60 min an additional 0.280 g

(0.95 mmol) of triphosgene was added. After 40 min an

additional amount of triphosgene (0.280 g, 0.95 mmol) was

added. After 2.25 h (total time), the reaction was warmed to

ambient temperature. An additional 0.25 equiv. of tri-

phosgene (0.140 g, 0.48 mmol) was added and stirred for

1.5 h. The solvents were then removed under reduced

pressure. Column chromatography (silica gel using CH₂Cl₂

as eluent; R_f¼0.84) afforded the product (0.478 g, 51%

yield): mp 140–1508C (decomp.). IR (KBr) 2122.8, 1531.5,

5.4.15. (2,2⁰-Dinitro-4⁰-phenylethynyl-biphenyl-4-ylethy-

nyl)-trimethyl-silane (19). (4⁰-Bromo-2,2⁰-dinitro-bi-

phenyl-4-ylethynyl)-trimethyl-silane

(18)

(1.91 g,

4.55 mmol), bis(triphenylphosphine)palladium(II) dichlor-

ide (0.095 g, 0.136 mmol), copper(I) iodide (0.052 g,

0.273 mmol), THF (20 mL), DIEA (3.2 mL, 18 mmol),

and phenylacetylene (0.60 mL, 5.5 mmol) were used

following the general procedure for couplings. The tube

was capped and the solution was stirred at RT for 1 d,

followed by heating to 508C for 2 h. Flash column

chromatography (silica gel using 1:1 hexanes/CH₂Cl₂as

eluent) afforded the desired product as a yellow-brown solid

(1.54 g, 77% yield): 143–1468C. IR (KBr) 3083.4, 2957.7,

2888.8, 2207.7, 2161.6, 1529.3, 1349.0, 1249.4, 1217.1,

1004.2, 843.8, 756.2, 689.2, 517.8 cm²¹

.

¹H NMR

(400 MHz, CDCl₃) d 8.32 (d, J¼1.5 Hz, 1H), 8.28 (d,

J¼1.5 Hz, 1H), 7.76 (dd, J¼7.9, 1.6 Hz, 1H), 7.71 (dd,

J¼7.9, 1.5 Hz, 1H), 7.56 (m, 2H), 7.37 (m, 3H), 7.22 (d,

J¼7.9 Hz, 1H), 7.21 (d, J¼7.9 Hz, 1H), 0.30 (s, 9H). ¹³C

NMR (100 MHz, CDCl₃) d 147.4, 147.3, 136.8, 136.4,

133.8, 133.4, 132.3, 131.4, 131.3, 129.7, 129.0, 128.5,

128.0, 125.6, 125.4, 122.5, 102.2, 99.2, 93.3, 87.0, 0.2.

HRMS calcd for C₂₅H₂₀N₂O₄Si: 440.1192. Found:

440.1187 (Error¼1.3 ppm).

5.4.16. 4⁰-Ethynyl-2,2⁰-dinitro-4-phenylethynyl-biphenyl

(20). (2,2⁰-Dinitro-4⁰-phenylethynyl-biphenyl-4-ylethynyl)-

trimethyl-silane (19) (1.50 g, 3.41 mmol), potassium car-

bonate (1.89 g, 13.7 mmol), methanol (20 mL), and CH₂Cl₂

(20 mL) were used following the general procedure for

deprotection to afford the desired product as a viscous

brown oil (1.21 g, 97% yield). ¹H NMR (400 MHz, CDCl₃)

d 8.35 (d, J¼1.6 Hz, 1H), 8.31 (d, J¼1.6 Hz, 1H), 7.77 (m,

2H), 7.57 (m, 2H), 7.38 (m, 3H), 7.25 (m, 2H), 3.27 (s, 1H).

1

1505.5, 1338.1, 841.9, 528.0 cm²¹. H NMR (400 MHz,

CDCl₃) d 8.15 (d, J¼1.6 Hz, 1H), 8.10 (d, J¼1.8 Hz, 1H),

7.81 (dd, J¼7.9, 1.6 Hz, 1H), 7.76 (d, J¼8.1 Hz, 1H), 7.62

(dt, J¼8.4, 1.9 Hz, 2H), 7.58 (dt, J¼8.4, 1.9 Hz, 2H), 7.53

(dd, J¼7.9, 1.8 Hz, 1H), 7.46 (d, J¼8.0 Hz, 1H), 7.41–7.38

(m, 4H). ¹³C NMR (125 MHz, CDCl₃) d 167.0, 166.9,

150.0, 148.8, 138.6, 136.1, 135.3, 133.7, 133.5, 133.3,

132.8, 132.4, 128.2, 127.1, 127.1, 125.2, 124.9, 124.0,

123.7, 118.6, 96.9, 91.9, 89.1, 87.3. LRMS calcd for

C₃₀H₁₄N₄O₄: 494.1 Found: 494.0.

5.4.13. 4,4⁰-Dibromo-2,2⁰-dinitro-biphenyl (17).¹³2,5-

Dibromonitrobenzene (18.0 g, 64.1 mmol), copper pow-

der (9.00 g, 141 mmol), DMF (120 mL), and a stir bar

were added to a 250 mL round bottom ﬂask equipped

with a West condenser. The ﬂask was heated in a 1208C

oil bath for 2 h. The solution was ﬁltered and diluted with

water to precipitate yellow-brown crystals. Flash chro-

matography (silica gel using 1:1 hexanes/CH₂Cl₂as

eluent) afforded pale yellow crystals (4.8 g, 75% yield):

mp 149–1508C (lit. mp 146–1488C).¹³¹H NMR

(400 MHz, CDCl₃) d 8.36 (d, J¼2.0 Hz, 2H), 7.81 (dd,

J¼8.2, 2.0 Hz, 2H), 7.14 (d, J¼8.2 Hz, 2H). ¹³C NMR

(100 MHz, CDCl₃) d147.8, 137.0, 132.5, 132.4, 128.5,

123.3.

5.4.17. Thioacetic acid S-[4-(2,2⁰-dinitro-4⁰-phenyl-

ethynyl-biphenyl-4-ylethynyl)-phenyl] ester (21). 4⁰-

Ethynyl-2,2⁰-dinitro-4-phenylethynyl-biphenyl

(20)

(1.21 g, 3.30 mmol) was coupled with 4-thioacetyl-1-

iodobenzene (7)²⁹(0.917 g, 3.30 mmol) using the Pd/Cu

cross coupling method described earlier using bis(dibenzyl-

ideneacetone)palladium(0) (0.380 g, 0.660 mmol), cop-

per(I) iodide (0.126 g, 0.660 mmol), triphenylphosphine

(0.433 g, 1.65 mmol), THF (25 mL), and DIEA (1.15 mL,

6.60 mmol) in a 100 mL round bottom ﬂask under nitrogen.

The solution was stirred in a 408C oil bath for 1 d. Column

chromatography (silica gel using 2:1 CH₂Cl₂/hexanes as

eluent) afforded the desired product as a green-yellow solid

(1.23 g, 72% yield). IR (KBr) 3078.2, 2919.5, 2842.7,

2207.7, 1698.9, 1526.2, 1350.6, 1111.8, 1088.9, 826.4,

5.4.14. (4⁰-Bromo-2,2⁰-dinitro-biphenyl-4-ylethynyl)-tri-

methyl-silane (18). 4,4⁰-Dibromo-2,2⁰-dinitrobiphenyl (17)

(4.00 g, 9.95 mmol), bis(triphenylphosphine)palladium(II)

dichloride (0.211 g, 0.300 mmol), copper(I) iodide (0.114 g,

0.597 mmol), THF (20 mL), DIEA (6.9 mL, 40 mmol), and

TMSA (1.49 mL, 10.5 mmol) were used following the

general procedure for couplings. The tube was capped and

the solution was stirred at RT for 5 h. Flash column

chromatography (silica gel using 1:1 hexanes/CH₂Cl₂as

eluent) afforded the desired product as a viscous brown oil

(1.923 g, 46% yield). IR (KBr) 3083.4, 2958.5, 2899.0,

1

762.0, 691.1, 617.5 cm²¹. H NMR (400 MHz, CDCl₃) d

8.36 (d, J¼1.5 Hz, 2H), 7.79 (dd, J¼8.0, 1.7 Hz, 2H), 7.58

(m, 4H), 7.43 (dt, 8.0, 1.7 Hz, 2H), 7.39 (m, 3H), 7.28 (d,

J¼8.0 Hz, 1H), 7.27 (d, J¼7.9 Hz, 1H), 2.44 (s, 3H). ¹³C

NMR (100 MHz, CDCl₃) d 193.6, 147.5, 147.5, 136.5,

136.4, 134.7, 133.8, 133.4, 132.8, 132.3, 131.4, 131.3,

129.7, 129.6, 129.0, 128.2, 128.1, 125.7, 125.2, 126.6,

122.5, 93.3, 92.4, 88.4, 86.9, 30.8. HRMS calcd for

C₃₀H₁₈N₂O₅S: 518.0936. Found: 518.0941 (Error¼0.79

ppm).

2868.3, 2177.0, 1530.8, 1346.2, 1249.7, 845.4, 760.2 cm²¹

.

¹H NMR (400 MHz, CDCl₃) d 8.34 (d, J¼2.0 Hz, 1H), 8.26

(d, J¼1.6 Hz, 1H), 7.79 (dd, J¼8.1, 2.0 Hz, 1H), 7.71 (dd,

J¼7.9, 1.7 Hz, 1H), 7.19 (d, J¼8.1 Hz, 1H), 7.14 (d,

J¼8.1 Hz, 1H), 0.27 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) d

147.8, 147.2, 137.0, 136.8, 133.2, 133.0, 132.5, 131.2,

128.5, 128.4, 125.6, 123.1, 102.0, 99.4, 0.1. HRMS calcd for

C₁₇H₁₅N₂O₄BrSi: 417.9985. Found: 417.9989 (Error¼1.0

ppm).

5.4.18. 2,2⁰-Dinitr₀o-4,4⁰-bis-trimethylsilanylethynyl-

biphenyl (22). 2,2 -Dinitro-4,4⁰-dibromobiphenyl¹³(17)

3148

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

(1.50 g, 3.73 mmol), bis(triphenylphosphine)palladium(II)

dichloride (0.131 g, 0.187 mmol), copper(I) iodide (0.071 g,

0.373 mmol), THF (20 mL), DIEA (5.20 mL, 29.8 mmol)

and TMSA (1.32 mL, 9.33 mmol) were used following the

general procedure for couplings. The tube was capped and

heated in a 458C oil bath for 3 h. Flash column

chromatography (silica gel using 1:1 hexanes/CH₂Cl₂as

eluent) afforded the desired product (1.3 g, 80% yield): mp

82–908C. IR (KBr) 3083.4, 2959.3, 2899.0, 2166.8, 1530.8,

acetate as eluent; R_f¼0.46) afforded the desired compound

(5.17 g, 85% yield): mp 127–1298C. IR (KBr) 3412.0,

3277.6, 3109.0, 3047.5, 3011.7, 1675.5, 1564.9, 1510.4,

1450.2, 1397.4, 1367.8, 1278.7, 1083.9, 1003.0, 879.6,

813.2, 686.1, 602.9, 502.4 cm²^{1 1}H NMR (400 MHz,

.

CDCl₃) d 8.28 (br s, 2H), 7.35 (dd, J¼8.2, 1.9 Hz, 2H), 7.01

(d, J¼8.1 Hz, 2H), 6.91 (br s, 2H), 1.96 (s, 6H). ¹³C NMR

(100 MHz, CDCl₃) d 169.5, 137.0, 132.0, 128.9, 127.4,

126.9, 123.8, 24.5. HRMS calcd for C₁₆H₁₄N₂O₂Br₂:

425.940305. Found: 425.940263 (Error¼0.099 ppm).

1350.2, 1250.3, 1219.2, 930.2, 844.7, 753.3, 644.5 cm²¹

.

¹H NMR (400 MHz, CDCl₃) d 8.31 (d, J¼1.6 Hz, 2H), 7.75

(dd, J¼7.9, 1.7 Hz, 2H), 7.23 (d, J¼8.0 Hz, 2H), 0.31 (s,

18H). ¹³C NMR (100 MHz, CDCl₃) d 147.1, 136.5, 133.5,

131.0, 128.3, 125.2, 101.9, 99.0, 20.1. HRMS calcd for

5.4.22. N-(2⁰-Acetylamino-4,4⁰-dibromo-5,5⁰-dinitro-

biphenyl-2-yl)-acetamide (26). To a 500 mL round-bottom

ﬂask was added conc. H₂SO₄(85 mL) followed by the slow

addition of N-(2⁰-acetyamino-4,4⁰-dibromo-biphenyl-2-yl)-

acetamide (25) (8.90 g, 20.9 mmol). The mixture was

cooled to 2108C and a solution of conc. H₂SO₄(50 mL)

and conc. HNO₃(50 mL) was added slowly over 2.25 h. The

mixture was allowed to warm to 108C over 1 h before being

poured onto ice and extracted with ethyl acetate. Column

chromatography (silica gel using 2:1 CH₂Cl₂/ethyl acetate;

R_f¼0.49) afforded the desired compound (8.11 g, 75%

yield): mp 252–2548C. IR (KBr) 3385.5, 3355.1, 3114.1,

3073.1, 3037.3, 1704.7, 1599.3, 1552.2, 1533.0, 1495.2,

C₂₂H₂₄N₂O₄Si₂:

(Error¼1.3 ppm).

436.127465.

Found:

436.126915.

5.4.19. 4,4⁰-Diethynyl-2,2⁰-dinitro-biphenyl (23). 2,2⁰-

Dinitro-4,4⁰-bis-trimethylsilanylethynyl-biphenyl

(22)

(1.31 g, 3.00 mmol), potassium carbonate (2.49 g,

18.0 mmol), methanol (50 mL), and CH₂Cl₂(50 mL) were

used following the general procedure for deprotection to

1

afford the desired product (0.825 g, 94% yield). H NMR

(400 MHz, CDCl₃) d 8.36 (d, J¼1.5 Hz, 2H), 7.80 (dd,

J¼7.9, 1.6 Hz, 2H), 7.27 (d, J¼7.9 Hz, 2H), 3.31 (s, 2H).

1329.1, 1233.8, 1049.2, 1004.6, 839.3, 666.8 cm²^{1 1}H

.

NMR (200 MHz, acetone-d₆) d 9.03 (br s, 2H), 8.70 (m,

2H), 8.06 (s, 2H), 1.97 (s, 6H). ¹³C NMR (100 MHz,

acetone-d₆) d 169.7, 145.5, 141.6, 129.2, 128.7, 128.6,

126.9, 115.1, 23.5. HRMS calcd for C₁₆H₁₂Br₂N₄O₆:

513.912380. Found: 513.912528 (Error¼0.29 ppm).

5.4.20. Thioacetic acid S-{4-[4⁰-(4-acetylsulfanyl-phenyl-

ethynyl)-2,2⁰-dinitro-biphenyl₀-4-ylethynyl]-phenyl}

ester (24). 4,4⁰-Diethynyl-2,2 -dinitro-biphenyl (23)

(0.825 g,2.82 mmol),bis(dibenzylideneacetone)palladium(0)

(0.324 g, 0.564 mmol), copper(I) iodide (0.107 g,

0.564 mmol), triphenylphosphine (0.370 g, 1.41 mmol),

THF (20 mL), DIEA (2.0 mL, 11.3 mmol), and 4-(thio-

acetyl)iodobenzene (7)²⁶(1.65 g, 5.92 mmol) were used

following the general procedure for couplings. The tube was

capped and the solution was stirred at ambient temperature

for 1 d. Flash column chromatography (silica gel using

CH₂Cl₂as eluent; R_f¼0.46) followed by precipitation from

CH₂Cl₂/hexanes afforded the desired product as slightly

yellow solid (0.434 g, 26% yield): mp 160–1738C

(decomp.). IR (KBr) 3083.4, 2202.6, 1716.5, 1524.4,

5.4.23. 4,4⁰-Dibromo-5,5⁰-dinitro-biphenyl-2,2⁰-diamine

(27). To a 100 mL round-bottom ﬂask was added conc.

H₂SO₄(30 mL) followed slowly by N-(2⁰-acetylamino-4,4⁰-

dibromo-5,5⁰-dinitro-biphenyl-2-yl)-acetamide (26) (1.0 g,

1.94 mmol). Water (20 mL) was then slowly added while

stirring over 30 min (exotherm; temperature reached 908C).

The ﬂask was placed in a 908C oil bath for 1 h, at which

point water (30 mL) was added and the reaction mixture

cooled to ,508C. The mixture was then poured onto ice and

the solid was ﬁltered to give the desired product as a yellow

solid (0.805 g, 96% yield): mp .3008C. IR (KBr) 3463.3,

3375.0, 1628.5, 1586.0, 1541.8, 1500.5, 1297.9, 1250.1,

1

1347.7, 1117.3, 828.6, 597.6 cm²¹. H NMR (400 MHz,

CDCl₃) d 8.40 (d, J¼1.5 Hz, 2H), 7.83 (dd, J¼8.0, 1.7 Hz,

2H), 7.62 (dt, J¼8.5, 1.8 Hz, 4H), 7.47 (dt, J¼8.5, 1.8 Hz,

4H), 7.32 (d, J¼7.9 Hz, 2H), 2.47 (s, 6H). ¹³C NMR

(100 MHz, CDCl₃) d 193.6, 147.4, 136.5, 134.7, 133.7,

132.8, 131.4, 129.7, 128.2, 125.3, 123.6, 92.4, 88.4, 30.8.

1

1116.9, 1060.6 cm²¹. H NMR (400 MHz, acetone-d₆) d

7.94 (s, 2H), 7.23 (s, 2H), 6.01 (br s, 4H). ¹³C NMR

(125 MHz, acetone-d₆) d 152.1, 130.9, 120.0, 119.2, 117.1.

HRMS calcd for C₁₂H₈N₄O₄Br₂: 429.891251. Found:

429.891129 (Error¼0.28 ppm).

5.4.21. N-(2⁰-Acetyamino-4,4⁰-dibromo-biphenyl-2-yl)-

acetamide (25). 4,4⁰-Dibromo-2,2⁰-dinitro-biphenyl (17)

(5.75 g, 14.3 mmol), ethanol (70 mL) and concentrated

HCl (25 mL) were added to a 250 mL round-bottom ﬂask.¹⁶

Tin powder (6.79 g, 57.2 mmol) was then added slowly

while stirring. The mixture was then heated to reﬂux for

30 min before being poured into ice and water. The product

was extracted with ethyl acetate and washed with NaOH

(aq). The crude diamine was then placed in a 250 mL round-

bottom ﬂask with glacial acetic acid (6.2 mL) and a stir bar.

Acetic anhydride (5.4 mL, 57.2 mmol) was then added and

the solution was heated in a 708C oil bath for 40 min. Water

was then added and the mixture neutralized with NaOH

(aq). The crude product was extracted with ethyl acetate.

Column chromatography (silica gel using 1:1 CH₂Cl₂/ethyl

5.4.24. 4⁰-Bromo-2,5,2⁰,5⁰-tetranitro-4-phenylethynyl-

biphenyl ₀(28) from 27. 4,4⁰-Dibromo-5,5⁰-dinitro-bi-

phenyl-2,2 -diamine (27) (0.900 g, 2.08 mmol), bis(tri-

phenylphosphine)palladium(II)

dichloride

(0.073 g,

0.104 mmol), copper(I) iodide (0.040 g, 0.208 mmol),

THF (25 mL), DIEA (1.45 mL, 8.32 mmol), and phenyl-

acetylene (0.25 mL, 2.29 mmol) were used following the

general procedure for couplings. The tube was capped and

the solution was stirred at RT for 1 d. Flash column

chromatography (silica gel using 1:1 hexanes/ethyl acetate

as eluent; R_f¼0.51) afforded an inseparable mixture of

products and starting material (0.784 g) which was taken

onto the next step. To a small plastic bottle with a stir bar

was added acetonitrile (90 mL) and water (3 mL). The

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3149

solution was cooled to 2258C and 20% F₂in He was

bubbled through at 70 cc/min for 2.5 h. The F₂ﬂow was

turned off and He was bubbled through for ₀15 min at

70 cc/min to remove any excess F₂. 4-Bromo-5,5 -dinitro-4-

phenylethynyl-biphenyl-2,2⁰-diamine (0.784 g as a mixture

from previous reaction) in acetone (10 mL) was then added

to the solution and stirred for 2.5 min before being poured

into a saturated sodium bicarbonate solution. The material

was washed with water and extracted with CH₂Cl₂. Column

chromatography (silica gel using 2:1 CH₂Cl₂/hexanes as

eluent) afforded the desired product as an orange solid

(0.120 g, 11% yield over 2 steps). IR (KBr) 3098.7, 2202.6,

5.4.27. N-(3⁰-Acetylamino-4,4⁰-dibromo-biphenyl-2-yl)-

acetamide (31).

4,4⁰-Dibromo-biphenyl-2,3⁰-diamine

(5.28 g, 12.4 mmol) and acetic acid (6.8 mL) were added

to a 100 mL round bottom ﬂask followed by acetic

anhydride (5.73 mL, 60.7 mmol). The ﬂask was placed in

a 708C oil bath for 40 min. The solution was neutralized

with 50% NaOH (aq) and extracted with CH₂Cl₂. Removal

of the solvent gave the desired product (6.47 g, 100% over 2

steps). mp: 168–1718C. IR (KBr) 3386.2, 3260.8, 3022.9,

1685.9, 1575.7, 1510.2, 1449.5, 1386.2, 1275.8, 1050.3,

1025.8, 806.8 cm²¹. ¹H NMR (400 MHz, CDCl₃) d 8.55 (br

s, 1H), 8.22 (br s, 1H), 7.68 (m, 2H), 7.50 (br s, 1H), 7.30

(dd, J¼8.2, 1.7 Hz, 1H), 7.11 (d, J¼8.2 Hz, 1H), 6.99 (dd,

J¼8.2, 2.2 Hz, 1H), 2.28 (s, 3H), 2.13 (s, 3H). ¹³C NMR

(100 MHz, CDCl₃) d 169.2, 168.9, 137.7, 136.2, 133.7,

131.4, 129.6, 127.8, 126.5, 125.1, 123.6, 123.0, 114.0, 25.8,

25.0. HRMS calcd for C₁₆H₁₄N₂O₂Br₂: 425.940266. Found:

425.939783 (Error¼1.1 ppm).

1544.6, 1341.8, 1265.4, 912.1, 835.3, 753.3, 681.6 cm²¹

.

¹H NMR (400 MHz, CDCl₃) d 8.70 (s, 1H), 8.62 (s, 1H),

8.08 (s, 1H), 7.88 (s, 1H), 7.69 (m, 2H), 7.48 (m, 3H).

HRMS calcd for C₂₀H₉N₄O₈Br: 511.960386. Found:

511.959830 (Error¼1.1 ppm).

5.4.25. Thioacetic acid S-[4-2,5,2⁰5⁰-tetranitro-4⁰-phenyl-

ethynyl-biphenyl-4-ylethynyl)-phenyl] ester (30). 4⁰-

Bromo-2,5,2⁰,5⁰-tetranitro-4-phenylethynyl-biphenyl (28)

5.4.28. N-(5⁰-Acetylamino-4,4⁰-dibromo-5,2⁰-dinitro-

biphenyl-2-yl)-acetamide (32). To a 500 mL round bottom

ﬂask was added N-(3-acetylamino-4,4-dibromo-biphenyl-2-

yl)-acetamide (31) (2.45 g, 5.75 mmol), CH₂Cl₂(20 mL)

and conc. H₂SO₄(70 mL) and the mixture was cooled to

2158C. Next, an ice cold solution of HNO₃(15 mL, 70%)

and conc. H₂SO₄(15 mL) were added dropwise over 1 h.

The mixture was allowed to warm to 08C over 2 h at which

point the reaction was poured onto ice and washed with

water and ethyl acetate. Column chromatography (silica gel

using 3:1 CH₂Cl₂/ethyl acetate; R_f¼0.21) afforded the

desired product (1.29 g, 43% yield): mp 229–2328C. IR

(KBr) 3387.3, 3338.3, 1699.0, 1570.7, 1533.1, 1507.5,

(0.110 g,

0.214 mmol),

bis(dibenzylideneacetone)-

palladium(0) (0.025 g, 0.043 mmol), copper(I) iodide

(0.008 g, 0.043 mmol), triphenylphosphine (0.023 g,

0.086 mmol),

THF

(15 mL),

DIEA

(0.075 mL,

0.43 mmol), and 4-thioacetyl-1-ethynylbenzene¹⁸(29)

(0.049 g, 0.278 mmol) were used following the general

procedure for couplings. The tube was capped and the

solution was stirred at RT for 2 h and then at 508C for 1 h.

Flash column chromatography (silica gel using 1:2

hexanes/CH₂Cl₂as eluent) followed by precipitation from

CH₂Cl₂/hexanes afforded the desired product as an orange

solid (0.031 g, 24% yield): mp 130–1508C (decomp.). IR

(KBr) 3073.1, 2212.7, 1707.9, 1548.8, 1340.8, 1270.9,

1

1466.7, 1371.3, 1335.1, 1236.9, 1074.0, 895.0 cm²¹. H

NMR (400 MHz, CDCl₃) d 8.19 (br s, 2H), 7.33 (dd, J¼8.2,

2.0 Hz, 2H), 7.15 (br s, 2H), 6.98 (d, J¼8.2 Hz, 2H), 1.92 (s,

6H). ¹³C NMR (125 MHz, acetone-d₆) d 169.6, 169.4,

144.9, 143.9, 142.1, 141.1, 130.9, 130.2, 129.3, 127.6,

127.1, 125.6, 114.7, 113.7, 24.0, 23.6. HRMS calcd for

1

1118.3, 912.1, 829.3, 759.1, 681.6, 615.1 cm²¹. H NMR

(400 MHz, CDCl₃) d 8.63 (s, 2H), 8.13 (s, 1H), 8.11 (s, 1H),

7.70 (m, 4H), 7.49 (m, 5H), 2.49 (s, 3H). ¹³C NMR

(100 MHz, CDCl₃) d 193.00, 151.13, 148.49, 134.59,

133.08, 132.68, 131.71, 131.42, 131.23, 131.14, 130.71,

128.94, 127.65, 127.55, 122.27, 121.62, 121.29, 121.17,

102.87, 101.60, 84.11, 82.88, 30.64.

C₁₆H₁₂Br₂N₄O₆:

(Error¼0.22 ppm).

515.910536.

Found:

515.910650

5.4.29. 4,4⁰-Dibromo-5,6⁰-dinitro-biphenyl-2,3⁰-diamine

(33). To a 100 ₀mL round-bottom ﬂask was added N-(5⁰-

acetylamino-4,4 -dibromo-5,2⁰-dinitro-biphenyl-2-yl)-acet-

amide (32) (0.441 g, 0.854 mmol), 3N HCl (20 mL), and

THF (20 mL). The solution was heated to reﬂux for 3 h

before being neutralized with NaOH and extracted with

ethyl acetate to give the desired product as a yellow solid

(0.356 g, 96% yield): mp 250–2708C (decomp.). IR (KBr)

3472.6, 3446.7, 3353.5, 3234.0, 1624.4, 1588.7, 1556.8,

5.4.26. 4,4⁰-Dibromo-biphenyl-2,3⁰-diamine. 4,4⁰-Di-

bromo-2,3⁰-dinitro-biphenyl¹³(3) (6.10 g, 15.2 mmol) was

added to a 250 mL round bottom ﬂask containing

concentrated HCl (30 mL), EtOH (80 mL) and a stir bar.

Tin powder (7.21 g, 60.7 mmol) was slowly added to the

solution with stirring. The solution was heated to reﬂux for

30 min and then poured into ice water. The mixture

was extracted with ethyl acetate and washed with

50% NaOH (aq). Removal of the solvent provided

the crude product, which was taken onto the next step

with no further puriﬁcation (5.28 g): mp 87–908C. IR

(KBr) 3423.0, 3408.6, 3324.0, 3304.2, 3190.9, 1616.1,

1590.3, 1559.6, 1478.1, 1402.1, 1301.3, 1241.3, 1037.4,

1496.9, 1300.5, 1255.8, 1126.4, 1055.6, 903.1, 841.6 cm²¹

.

¹H NMR (400 MHz, acetone-d₆) d 8.34 (s, 1H), 7.84 (s, 1H),

7.17 (s, 1H), 6.82 (s, 1H), 6.30 (br s, 2H), 5.90 (br s, 2H).

¹³C NMR (100 MHz, acetone-d₆) d 151.8, 151.7, 137.7,

137.6, 133.5, 131.2, 128.1, 123.7, 119.1, 117.2, 116.5,

106.1.

908.9, 799.8, 661.8, 461.4 cm²^{1 1}H NMR (400 MHz,

.

CDCl₃) d 7.46 (d, J¼8.1 Hz, 1H), 6.91 (m, 2H), 6.86 (m,

1H), 6.75 (d, J¼2.0 Hz, 1H), 6.64 (dd, J¼8.1, 2.0 Hz, 1H),

4.18 (br s, 2H), 3.84 (br s, 2H). ¹³C NMR (100 MHz,

CDCl₃) d 145.3, 145.0, 139.2, 133.5, 131.8, 126.0, 122.6,

121.8, 120.3, 118.5, 116.4, 108.8. HRMS calcd for

C₁₂H₁₀N₂Br₂: 341.919157. Found: 341.918664 (Error¼1.4

ppm).

5.4.30. 4⁰-Bromo-2,5,2⁰,5⁰-tetranitro-4-phenylethynyl-

biphenyl ₀(28) from 33. 4,4⁰-Dibromo-5,6⁰-dinitro-bi-

phenyl-2,3 -diamine (33) (1.04 g, 2.41 mmol) and phenyl-

acetylene (0.290 mL, 2.65 mmol) were coupled following

the Pd/Cu protocol using bis(triphenylphosphine)pal-

ladium(II) dichloride (0.085 g, 0.121 mmol), copper(I)

3150

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

iodide (0.046 g, 0.241 mmol), THF (20 mL), and DIEA

(1.7 mL, 9.64 mmol). The tube was capped and the solution

was stirred in a 408C oil bath for 1.5 h. The temperature was

then increased to 508C for 1 d. Flash column chromato-

graphy (silica gel using 1:1 ethyl acetate/hexanes as eluent;

R_f¼0.42) followed by precipitation from acetone/hexanes

afforded the desired product (0.780 g, ,72% yield) which

was taken directly onto the oxidation step.¹⁷0.300 g

(0.662 mmol) of this compound was dissolved in THF

(10 mL). Acetonitrile (90 mL) and water (3 mL) were

placed in a plastic bottle and cooled to 2458C. A 20%

mixture of F₂in He was bubbled through at 60 cc/min for

2.5 h. Helium was then bubbled through for 20 min at

60 cc/min. Added the THF solution and stirred for 2.5 min.

The reaction mixture was then poured into NaHCO₃(aq)

and extracted with CH₂Cl₂. Column chromatography (silica

gel using 2:1 CH₂Cl₂/hexanes as eluent; R_f¼0.46) afforded

the desired tetranitro product (0.180 g, 45% over 2 steps).

¹H NMR (400 MHz, CDCl₃) d 8.66 (s, 1H), 8.58 (s, 1H),

8.04 (s, 1H), 7.84 (s, 1H), 7.65 (m, 2H), 7.43 (m, 3H).

HRMS calcd for C₂₀H₉BrN₄O₈: 511.960396. Found:

511.959296 (Error¼2.1 ppm).

5.4.31. 4-Iodo-2-nitro-phenylamine (34).³²2-Nitroaniline

(30.0 g, 217 mmol), sodium acetate (18.7 g, 228 mmol) and

acetic acid (150 mL) were added to a 500 mL round bottom

ﬂask with a stir bar. To this ﬂask was added a solution of

iodine monochloride (37.0 g, 228 mmol) in acetic acid

(100 mL) and the resulting solution was heated at 808C for

30 min. The solution was immediately poured into water

(600 mL) and allowed to stand for 3 h. The orange solid was

ﬁltered to give the desired product (54.5 g, 95%): mp 121–

1248C (lit²⁰: mp 121–1238C). ¹H NMR (400 MHz, CDCl₃)

d 8.40 (d, J¼2.1 Hz, 1H), 7.54 (dd, J¼8.8, 2.1 Hz, 1H), 6.59

(d, J¼8.8 Hz, 1H), 6.09 (br s, 2H).

salt was ﬁltered and washed with cold Et₂O to afford 10.92 g

of solid. To a 500 mL round bottom ﬂask was added

acetonitrile (125 mL), NaI (9.92 g, 66.2 mmol) and I₂

(8.4 g, 33.1 mmol). The diazonium salt was then slowly

added to this solution over 15 min. The solution was washed

with Na₂S₂O₃(aq) and extracted with CH₂Cl₂to afford the

desired product which needed no further puriﬁcation

(9.78 g, 85% yield): mp 114–1168C. IR (KBr) 3078.2,

3047.5, 2211.9, 1522.2, 1439.3, 1351.6, 1014.3, 891.6,

1

824.3, 755.0, 686.0 cm²¹. H NMR (400 MHz, CDCl₃) d

8.00 (d, J¼8.2 Hz, 1H), 7.96 (d, J¼1.9 Hz, 1H), 7.52 (m,

2H), 7.36 (m, 4H). ¹³C NMR (100 MHz, CDCl₃) d 142.3,

136.0, 132.2, 129.7, 129.0, 128.4, 125.4, 122.4, 93.7, 86.6,

85.9. HRMS calcd for C₁₄H₈NO₂I: 348.959973. Found:

348.959869 (Error¼0.30 ppm).

5.4.34. Trimethyl-(4-tributylstannanyl-phenylethynyl)-

silane (37). To a 500 mL round-bottom ﬂask was

added (4-bromo-phenylethynyl)-trimethyl-silane²¹(3.63 g,

14.3 mmol) and a stir bar. Air was removed and N₂

backﬁlled (3£). THF (50 mL) was added and the solution

cooled to 788C. Next, n-BuLi (6.22 mL of a 2.53 M

solution) was added dropwise over 15 min. The solution

was stirred for 10 min. Tributyltin chloride (4.46 mL,

16.4 mmol) in THF (10 mL) was then added over 15 min.

The reaction was allowed to warm to room temperature

overnight before washing with NaCl (aq) and CH₂Cl₂.

Column chromatography (silica gel using hexanes as eluent;

R_f¼0.65) followed by Kugelrohr distillation (1508C at

1.5 mm Hg) removed the impurities and left the desired

1

product as an oil (4.53 g, 68% yield). H NMR (400 MHz,

CDCl₃) d 7.37 (m, 4H), 1.50 (m, 6H), 1.29 (m, 6H), 1.03 (m,

6H), 0.86 (m, 9H), 0.22 (s, 9H). ¹³C NMR (100 MHz,

CDCl₃) d 143.9, 136.7, 136.6, 136.4, 131.6, 131.4, 131.2,

122.9, 105.9, 94.5, 29.6, 29.4, 29.3, 28.0, 27.7, 27.5, 14.1,

11.7, 11.6, 10.0, 8.4, 8.3, 0.4.

5.4.32. 2-Nitro-4-phenylethynyl-phenylamine (35). 4-

Iodo-2-nitro-phenylamine (34) (10.0 g, 37.9 mmol), bis(tri-

5.4.35. Trimethyl-(2⁰-nitro-4⁰-phenylethynyl-biphenyl-4-

ylethynyl)-silane (39). 1-Iodo-2-nitro-4-phenylethynyl-

benzene (36) (3.41 g, 9.78 mmol), bis(dibenzylideneaceto-

ne)palladium(0) (0.112 g, 0.200 mmol), and triphenylarsine

(0.122 g, 0.400 mmol) were placed in a screw cap tube.²²

Air was removed and N₂backﬁlled (3£). Trimethyl-(4-

phenylphosphine)palladium(II)

dichloride

(0.266 g,

0.379 mmol), copper(I) iodide (0.144 g, 0.758 mmol),

DIEA (19.8 mL, 114 mmol), THF (35 mL) and phenyl-

acetylene (4.6 mL, 37.9 mmol) were used following the

general procedure for couplings. The tube was capped and

the solution was stirred at RT for 2.5 h. Precipitation from

CH₂Cl₂/hexanes followed by extraction with Et₂O and

water afforded the desired product (7.93 g, 88% yield): mp

162–1638C. IR (KBr) 3470.7, 3342.1, 1641.5, 1598.7,

1552.2, 1516.3, 1411.5, 1340.5, 1234.8, 1142.8, 833.7,

756.2, 687.6 cm²¹. ¹H NMR (400 MHz, CDCl₃) d 8.35 (d,

J¼2.0 Hz, 1H), 7.52 (m, 3H), 7.38 (m, 3H), 6.81 (dd, J¼8.6,

0.4 Hz, 1H), 6.24 (br s, 2H). ¹³C NMR (100 MHz, CDCl₃) d

144.6, 138.7, 132.2, 131.9, 129.9, 128.8, 128.7, 123.4,

119.3, 112.5, 89.1, 88.0. HRMS calcd for C₁₄H₁₀N₂O₂:

238.074228. Found: 238.074109 (Error¼0.50 ppm).

tributylstannanyl-phenylethynyl)-silane

(38)

(3.41 g,

9.78 mmol) and THF (35 mL) were then added. The tube

was capped and placed in a 808C oil bath for 19 h. The

mixture was washed with NaCl (aq) and diethyl ether.

Column chromatography (silica gel using 3:1 hexanes/CH₂-

Cl₂as eluent; R_f¼0.50) afforded the desired product (2.59 g,

67% yield): mp 107–1108C. IR (KBr) 3062.5, 2962.5,

2157.0, 1533.1, 1492.8, 1355.6, 1248.3, 855.1, 829.0, 762.8,

694.6 cm²^{1 1}H NMR (400 MHz, CDCl₃) d 7.99 (d,

.

J¼1.6 Hz, 1H), 7.71 (dd, J¼8.0, 1.6 Hz, 1H), 7.55 (m,

2H), 7.51 (dt, J¼8.3, 1.8 Hz, 2H), 7.37 (m, 4H), 7.25 (dt,

J¼8.3, 1.7 Hz, 2H), 0.26 (s, 9H). ¹³C NMR (100 MHz,

CDCl₃) d 149.4, 137.3, 135.4, 135.4, 132.7, 132.2, 129.5,

128.9, 128.2, 127.5, 124.6, 123.9, 122.6, 104.8, 96.3, 92.9,

87.1, 0.3. HRMS calcd for C₂₅H₂₁SiNO₂: 395.134158.

Found: 395.134321 (Error¼0.41 ppm).

5.4.33. 1-Iodo-2-nitro-4-phenylethynyl-benzene (36). To

a 500 mL round bottom ﬂask (cooled to 220 to 2308C) was

added BF₃·OEt₂(16.8 mL, 132 mmol) followed by 2-nitro-

4-phenylethynyl-phenyamine (35) (7.89 g, 33.1 mmol) in

THF (55 mL) over 15 min. Next, t-BuONO (13.8 mL,

115.9 mmol) in THF (45 mL) was added over 20 min. The

solution was allowed to warm to 08C over 25 min and Et₂O

was added to effect precipitation of the diazonium salt. The

5.4.36. 4⁰-Ethynyl-2-nitro-4-phenylethynyl-biphenyl

(40).

ylethynyl)-silane (39) (2.52 g, 6.37 mmol), potassium

Trimethyl-(2⁰-nitro-4⁰-phenylethynyl-biphenyl-4-

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3151

carbonate (2.64 g, 19.1 mmol), methanol (25 mL), and

CH₂Cl₂(25 mL) were used following the general

deprotection method to afford the product (2.03 g, 99%

After 30 min (1 h total time), the reaction was complete by

TLC. The mixture was washed with water and CH₂Cl₂.

Column chromatography (silica gel using CH₂Cl₂as eluent;

R_f¼0.84) afforded the product (0.348 g, 73% yield): 180–

1908C (decomp.). IR (KBr) 3052.6, 2121.2, 1540.9, 1523.3,

1501.1, 1348.1, 999.2, 834.2, 760.2, 692.7, 538.3 cm²¹. ¹H

NMR (400 MHz, CDCl₃) d 8.01 (d, J¼1.4 Hz, 1H), 7.73

(dd, J¼8.0, 1.8 Hz, 1H), 7.56 (m, 6H), 7.41 (d, J¼8.2 Hz,

1H), 7.37 (m, 5H), 7.31 (dt, J¼8.5, 1.9 Hz, 2H). ¹³C NMR

(100 MHz, CDCl₃) d 166.3, 149.4, 137.7, 135.4, 135.3,

133.1, 132.5, 132.2, 129.6, 129.0, 128.4, 127.6, 126.9,

126.4, 125.0, 124.8, 123.2, 122.6, 93.0, 92.0, 89.4, 87.0.

HRMS calcd for C₂₉H₁₆N₂O₂: 424.121178. Found:

424.121021 (Error¼0.37 ppm).

1

yield). H NMR (400 MHz, CDCl₃) d 8.00 (d, J¼1.7 Hz,

1H), 7.72 (dd, J¼8.0, 1.7 Hz, 1H), 7.56–7.52 (m, 4H),

7.40–7.36 (m, 4H), 7.27 (dt, J¼8.5, 1.8 Hz, 2H), 3.13 (s,

1H).

5.4.37. Thioacetic acid S-[4-(2⁰-nitro-4⁰-phenylethynyl-

biphenyl-4-ylethynyl)-phenyl] ester (41). 4⁰-Ethynyl-2-

nitro-4-phenylethynyl-biphenyl (40) (1.00 g, 3.09 mmol),

bis(dibenzylideneacetone)palladium(0) (0.089 g, 0.155

mmol), copper(I) iodide (0.059 g, 0.31 mmol), triphenyl-

phosphine (0.162 g, 0.620 mmol), THF (15 mL), DIEA

(2.15 mL, 12.4 mmol), and 4-(thioacetyl)iodobenzene (7)²⁶

(0.859 g, 3.09 mmol) were used following the general

procedure for couplings. The tube was capped and the

solution was stirred at ambient temperature for 16 h. Flash

column chromatography (silica gel using 1:1 hexanes/CH₂-

Cl₂as eluent; R_f¼0.47) followed by precipitation from

CH₂Cl₂/hexanes afforded the desired product as a yellow

solid (0.982 g, 67% yield): mp 134–1368C. IR (KBr)

3057.4, 2202.1, 1707.2, 1527.3, 1494.8, 1350.1, 1111.0,

1085.5, 1003.7, 953.9, 829.3, 758.0, 688.8, 606.1,

5.4.40. 4-Bromo-5,5⁰-dinitro-4⁰-trimethylsilanylethynyl-

biphenyl-2,2⁰-diamine.

4,4⁰-Dibromo-5,5⁰-dinitro-bi-

phenyl-2,2⁰-diamine (27) (2.49 g, 5.76 mmol) was coupled

with TMSA (1.06 mL, 7.49 mmol) following the Pd/Cu

protocol

using

bis(triphenylphosphine)palladium(II)

dichloride (0.202 g, 0.288 mmol), copper(I) iodide

(0.110 g, 0.576 mmol), THF (75 mL), and DIEA (4.0 mL,

23.04 mmol). The tube was capped and the solution was

heated in a 458C oil bath for 3 h. Flash column

chromatography (silica gel using 1:1 hexanes/ethyl acetate

as eluent; R_f¼0.65) afforded the impure desired product

(1.44 g, ,80% pure) which was taken directly onto the next

step. ¹H NMR (400 MHz, acetone-d₆) d 7.98 (d, J¼1.1 Hz,

1H), 7.95 (d, J¼1.1 Hz, 1H), 7.25 (m, 1H), 7.09 (m, 1H),

5.98 (br s, 2H), 5.94 (br s, 2H), 0.20 (s, 9H).

545.5 cm²^{1 1}H NMR (400 MHz, CDCl₃) d 8.01 (d,

.

J¼1.6 Hz, 1H), 7.73 (dd, J¼8.0, 1.6 Hz, 1H), 7.55 (m,

6H), 7.39 (m, 6H), 7.37 (m, 4H), 7.31 (dt, J¼8.3, 1.7 Hz,

2H), 2.43 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) d 193.9,

149.4, 137.3, 135.4, 134.7, 132.7, 132.5, 132.2, 129.6,

129.0, 128.7, 128.4, 127.6, 124.7, 124.6, 123.7, 122.6, 93.0,

90.9, 90.4, 87.1, 30.8.

5.4.41. 5,5⁰-Dinitro-4-phenylethynyl-4⁰-trimethylsilanyl-

ethynyl-biphenyl-2,2⁰-diamine (44). Crude 4-br₀omo-5,5⁰-

dinitro-4⁰-trimethylsilanylethynyl-biphenyl-2,2 -diamine

(from the previous reaction; 1.44 g, ,2.56 mmol) was

coupled with phenylacetylene (0.46 mL, 4.16 mmol) fol-

lowing the Pd/Cu protocol using bis(triphenylphosphine)-

palladium(II) dichloride (0.112 g, 0.160 mmol), copper(I)

iodide (0.061 g, 0.320 mmol), THF (30 mL), and DIEA

(2.2 mL, 12.8 mmol). The tube was capped and the solution

was heated in a 508C oil bath for 16 h. Flash column

chromatography (silica gel using 1:1 hexanes/ethyl acetate

as eluent; R_f¼0.59) afforded the desired product (0.937 g,

35% yield over 2 steps). IR (KBr) 3457.2, 3366.9, 1621.2,

5.4.38. N-[4-(2⁰-Nitro-4⁰-phenylethynyl-biphenyl-4-

ylethynyl)-phenyl]-formamide (42). 4⁰-Ethynyl-2-nitro-4-

phenylethynyl-biphenyl (40) (1.01 g, 3.12 mmol) was

coupled with N-(4-iodo-phenyl)-formamide (9)³⁰(0.771 g,

3.12 mmol) following the Pd/Cu protocol using bis(di-

benzylideneacetone)palladium(0) (0.090 g, 0.156 mmol),

copper(I) iodide (0.059 g, 0.31 mmol), triphenylphosphine

(0.162 g, 0.62 mmol), DIEA (2.2 mL, 12.5 mmol), and THF

(15 mL). After stirring at room temperature for 18 h, the

reaction mixture was washed with NH₄Cl (aq) and CH₂Cl₂.

Column chromatography (silica gel using CH₂Cl₂followed

by 1:1 CH₂Cl₂/ethyl acetate as eluent; R_f¼0.66) afforded the

desired compound (1.28 g, 93% yield): mp 190–2008C

(decomp.). IR (KBr) 1687.6, 1603.4, 1522.4, 1352.5,

1541.7, 1504.0, 1311.1, 1252.7, 845.6, 755.8 cm²^{1 1}H

.

NMR (200 MHz, acetone-d₆) d 8.04 (s, 1H), 8.00 (s, 1H),

7.61 (m, 2H), 7.47 (m, 3H), 7.16 (s, 1H), 7.09 (s, 1H), 5.96

(br s, 2H), 5.94 (br s, 2H), 0.27 (s, 9H). ¹³C NMR (100 MHz,

acetone-d₆) d 151.6, 151.5, 139.0, 138.7, 132.1, 129.7,

129.6, 129.5, 129.1, 123.2, 120.9, 120.6, 120.4, 120.3,

119.6, 101.7, 101.4, 95.5, 86.6, 20.7. HRMS calcd for

C₂₅H₂₂N₄O₄Si: 470.141034. Found: 470.141303

(Error¼0.57 ppm).

1298.0, 838.4, 756.6, 691.9 cm²^{1 1}H NMR (400 MHz,

.

CDCl₃) d 8.74 (d, J¼11.4 Hz, 0.4H), 8.39 (d, J¼1.6 Hz,

0.6H), 8.00 (m, 1H), 7.72 (m, 1H), 7.54 (m, 7H), 7.48 (br s,

0.22H), 7.45 (br s, 0.22H), 7.42 (d, J¼7.9 Hz, 1H), 7.38 (m,

3H), 7.30 (m, 2H), 7.15 (br s, 0.6H), 7.05 (m, 0.82H).

HRMS calcd for C₂₉H₁₈N₂O₃: 442.131742. Found:

442.132230 (Error¼1.1 ppm).

5.4.39. 4⁰-(4-Isocyano-phenylethynyl)-2-nitro-4-phenyl-

ethynyl-biphenyl (43)₀. To a 50 mL round bottom ﬂask

was added N-[4-(2 -nitro-4⁰-phenylethynyl-biphenyl-4-

ylethynyl)-phenyl]-formamide (42) (0.500 g, 1.13 mmol).

Air was removed and N₂backﬁlled (3£). CH₂Cl₂(25 mL)

and triethylamine (5 mL) were added and the tube was

cooled to 08C. Triphosgene (0.152 g, 0.570 mmol) was then

added. After 30 min starting material remained by TLC. An

additional 0.076 g (0.285 mmol) of triphosgene was added.

5.4.42. 4⁰-Ethynyl-5,5⁰-dinitr₀o-4-phenylethynyl-bi-

phenyl-2,2⁰-diamine (45). 5,5 -Dinit₀ro-4-phenylethynyl-

4⁰-trimethylsilanylethynyl-biphenyl-2,2 -diamine

(44)

(1.38 g, 2.93 mmol), potassium carbonate (1.62 g,

11.7 mmol), methanol (100 mL), CH₂Cl₂(50 mL), and

THF (50 mL) were used following the general deprotection

method described earlier. A short silica plug (using 1:1

hexanes/ethyl acetate; R_f¼0.42) afforded the desired

product (0.934 g, 80% yield). ¹H NMR (200 MHz,

3152

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

acetone-d₆) d 8.05 (s, 1H), 8.01 (s, 1H), 7.61 (m, 2H), 7.47

(m, 3H), 7.16 (s, 1H), 7.13 (s, 1H), 5.98 (br s, 4H), 4.08 (s,

1H).

solution was stirred at room temperature for 1 d. More

TMSA was added (0.76 mL, 5.4 mmol) and the tube was

placed in a 558C oil bath for 15 h. Flash column

chromatography (silica gel using 3:1 hexanes/CH₂Cl₂as

eluent; R_f¼0.51) afforded the desired product (0.709 g, 65%

yield): mp 221–2248C. IR (KBr) 3077.9, 3052.3, 2959.7,

2898.7, 2150.8, 1517.0, 1449.8, 1356.2, 1248.3, 980.3,

5.4.43. Thioacetic acid S-[4-(2,2-diamino-5,5-dinitro-4-

p₀henylethynyl-biphenyl-4-ylethynyl)-phenyl] ester ₀(46).

4 -Ethynyl-5,5⁰-dinitro-4-phenylethynyl-biphenyl-2,2 -dia-

mine (45) (0.934 g, 2.34 mmol), bis(dibenzylidene-

acetone)palladium(0) (0.067 g, 0.117 mmol), copper(I)

iodide (0.045 g, 0.234 mmol), triphenylphosphine

(0.123 g, 0.468 mmol), THF (20 mL), DIEA (1.63 mL,

9.36 mmol), and 4-(thioacetyl)iodobenzene (7) (0.716 g,

2.57 mmol) were used following the general procedure for

couplings. The tube was placed in a 508C oil bath for 15 h.

Column chromatography (silica gel using 1:1 hexanes/ethyl

acetate; R_f¼0.45) followed by precipitation from acetone/

hexanes and CH₂Cl₂/hexanes afforded the desired product

as a yellow-green solid (0.460 g, 36% yield): mp 200–

2088C (decomp.). IR (KBr) 3463.1, 3360.6, 3237.0, 3047.5,

2207.7, 1690.5, 1622.6, 1602.0, 1538.1, 1504.7, 1302.8,

1

938.1, 842.2, 759.3, 701.1, 655.4, 424.8 cm²¹. H NMR

(400 MHz, CDCl₃) d 7.96 (m, 2H), 7.77 (d, J¼1.4 Hz, 1H),

7.64 (m, 1H), 7.47 (m, 1H), 3.90 (s, 2H), 0.262 (s, 9H),

0.258 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) d 147.0, 145.2,

144.8, 137.3, 134.1, 132.6, 131.7, 128.6, 127.2, 125.1,

124.1, 122.7, 105.3, 103.0, 98.1, 96.7, 37.0, 0.3, 0.2. HRMS

calcd for C₂₃H₂₅NO₂Si₂: 403.142387. Found: 403.142344

(Error¼0.11 ppm).

5.4.47. 2,7-Diethynyl-4-nitro-9H-ﬂuorene (50). 4-Nitro-

2,7-bis-trimethylsilanylethynyl-9H-ﬂuorene (49) (0.700 g,

1.73 mmol), potassium carbonate (0.954 g, 6.90 mmol),

methanol (50 mL), and CH₂Cl₂(50 mL) were used follow-

ing the general deprotection method described earlier to

1

1254.8, 1096.4, 819.9, 743.1 cm²¹. H NMR (400 MHz,

1

acetone-d₆) d 8.08 (s, 1H), 8.07 (s, 1H), 7.68 (dt, J¼8.3,

1.8 Hz, 2H), 7.62 (m, 2H), 7.53 (dt, J¼8.4, 1.8 Hz, 2H), 7.47

(m, 3H), 7.19 (s, 1H), 7.18 (s, 1H), 5.98 (br d, J¼8.8 Hz,

4H), 2.46 (s, 3H). ¹³C NMR (100 MHz, acetone-d₆) d 192.5,

151.7, 151.6, 138.7, 138.7, 134.9, 132.6, 132.1, 130.1,

129.8, 129.7, 129.6, 129.1, 124.2, 123.2, 120.9, 120.5,

120.5, 120.3, 119.8, 119.7, 95.5, 94.5, 88.1, 86.6, 29.8.

afford the desired product (0.418 g, 92% yield). H NMR

(400 MHz, CDCl₃) d 8.00 (m, 2H), 7.82 (m, 1H), 7.69 (m,

1H), 7.52 (m, 1H), 3.96 (s, 2H), 3.22 (s, 1H), 3.17 (s, 1H).

5.4.48. Thioacetic acid S-{4-[7-(4-acetylsulfanyl-phenyl-

ethynyl)-5-nitro-9H-ﬂuoren-2-ylethynyl]-phenyl} ester

(51). 2,7-Diethynyl-4-nitro-9H-ﬂuorene (50) (0.418 g,

1.60 mmol),

bis(dibenzylideneacetone)palladium(0)

5.4.44. 2,7-Dibromo-9H-ﬂuorene (47).²³To a 1 L round-

bottom ﬂask, wrapped in aluminum foil, was added ﬂuorene

(50.0 g, 300.8 mmol) and CHCl₃(450 mL). The solution

was cooled to 08C and ferric chloride (0.716 g, 4.5 mmol)

was added. Bromine (32.6 mL, 632 mmol) was added

slowly over 15 min at which point the ice bath was removed

and the solution allowed to warm slowly over 3 h. The

mixture was washed with Na₂S₂O₃(aq) and extracted with

CHCl₃followed by drying with MgSO₄to afford the desired

product (98.1 g, 100% yield): mp 161–1648C (lit. mp

163.5–165.58C³³). ¹H NMR (400 MHz, CDCl₃) d 7.62 (m,

2H), 7.55 (d, J¼8.1 Hz, 2H), 7.47 (m, 2H), 3.81 (s, 2H).

5.4.45. 2,7-Dibromo-4-nitro-9H-ﬂuorene (48).²⁴To a

250 mL round-bottom ﬂask was added 2,7-dibromo-9H-

ﬂuorene (47) (10.0 g, 30.7 mmol) and glacial acetic acid

(125 mL). The solution was heated to 358C and a solution of

HNO₃(7 mL) and H₂SO₄(7 mL) was added slowly over

20 min. The mixture was stirred for 5 min and then heated to

708C for 15 min. After cooling to room temperature, a

yellow solid was ﬁltered and washed with water. Recrys-

tallization from ethanol/toluene afforded the desired product

as yellow crystals (7.15 g, 63% yield): mp 192–1938C (lit²⁴

mp 194.5–195.58C). ¹H NMR (400 MHz, CDCl₃) d 8.04 (d,

J¼1.4 Hz, 1H), 7.92 (d, J¼8.6 Hz, 1H), 7.87 (br s, 1H), 7.71

(br s, 1H), 7.53 (m, 1H), 3.96 (s, 2H).

(0.046 g, 0.080 mmol), copper(I) iodide (0.030 g,

0.160 mmol), triphenylphosphine (0.084 g, 0.320 mmol),

THF (65 mL), DIEA (1.1 mL, 6.4 mmol), and 4-(thio-

acetyl)iodobenzene (7) (0.934 g, 3.36 mmol) were used

following the general procedure for couplings. The tube was

placed in a 558C oil bath for 17 h. Column chromatography

(silica gel using 5:1 CH₂Cl₂/hexanes; R_f¼0.61) followed by

precipitation from CH₂Cl₂/hexanes afforded the desired

product as a yellow solid (0.402 g, 45% yield): mp 197–

2008C. IR (KBr) 1708.2, 1526.7, 1488.8, 1354.1, 1287.8,

1119.0, 946.4, 829.2, 608.0 cm²^{1 1}H NMR (400 MHz,

.

CDCl₃) d 8.02 (m, 2H), 7.83 (d, J¼1.4 Hz, 1H), 7.69 (m,

1H), 7.54 (m, 5H), 7.39 (m, 4H), 3.95 (s, 2H), 2.43 (s, 3H),

2.42 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) d 193.8, 193.6,

147.2, 145.3, 145.0, 137.3, 134.7, 134.7, 134.2, 132.7,

132.6, 132.3, 131.5, 129.4, 128.8, 128.3, 126.9, 125.3,

124.6, 123.9, 123.3, 122.5, 91.7, 91.4, 90.9, 89.3, 37.1, 30.8,

30.7. HRMS calcd for C₃₃H₂₁NO₄S₂: 559.091203. Found:

559.091932 (Error¼1.3 ppm).

5.4.49. 2-Ethynyl-4-nitro-7-phenylethynyl-9H-ﬂuorene

(52). 2,7-Dibromo-4-nitro-9H-ﬂuorene (48) (1.00 g,

2.70 mmol) was coupled with TMSA (0.42 mL, 3.0 mmol)

following the Pd/Cu protocol using bis(triphenylphos-

phine)palladium(II) dichloride (0.095 g, 0.135 mmol),

copper(I) iodide (0.051 g, 0.270 mmol), THF (30 mL), and

DIEA (1.90 mL, 10.8 mmol) (the tube was cooled to 08C

before addition of TMSA). The reaction was allowed to

warm to room temperature and stirred for 1 d. Flash column

chromatography (silica gel using 3:1 hexanes/CH₂Cl₂as

eluent; R_f¼0.45) afforded the impure intermediate (0.849 g,

,57% by NMR) that was taken onto the next coupling

following the Pd/Cu protocol. Bis(triphenylphosphine)-

palladium(II) dichloride (0.077 g, 0.110 mmol), copper(I)

5.4.46. 4-Nitro-2,7-bis-trimethylsilanylethynyl-9H-ﬂuor-

ene (49). 2,7-Dibromo-4-nitro-9H-ﬂuorene (48) (1.00 g,

2.70 mmol) was coupled with TMSA (0.42 mL, 3.0 mmol)

following the Pd/Cu protocol using bis(triphenylphos-

phine)palladium(II) dichloride (0.095 g, 0.135 mmol),

copper(I) iodide (0.051 g, 0.270 mmol), THF (20 mL), and

DIEA (1.9 mL, 10.8 mmol). The tube was capped and the

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3153

iodide (0.042 g, 0.219 mmol), THF (30 mL), and DIEA

(1.53 mL, 8.76 mmol) and phenylacetylene (0.48 mL,

4.4 mL) were used with the crude material. The reaction

was placed in a 558C oil bath and stirred for 1 d. Flash

column chromatography (silica gel using 3:1 hexanes/CH₂-

Cl₂as eluent; R_f¼0.40) afforded the impure intermediate

(0.453 g, ,90% by NMR) that was taken onto the step.

Potassium carbonate (0.611 g, 4.42 mmol), methanol

(50 mL), and CH₂Cl₂(50 mL) were added following the

general deprotection method described earlier to afford the

slightly impure (,95 % purity by NMR) product (0.373 g,

7.87 (m, 1H), 7.69 (m, 1H), 7.54 (m, 3H), 7.37 (m, 3H), 3.98

(s, 2H), 3.18 (s, 1H).

5.4.52. Thioacetic acid S-[4-(5-nitro-7-phenylethynyl-

9H-ﬂuoren-2-ylethynyl)-phenyl] ester (55). 7-Ethynyl-4-

nitro-2-phenylethynyl-9H-ﬂuorene (54) (0.875 g, 2.59

mmol), bis(dibenzylideneacetone)palladium(0) (0.074 g,

0.13 mmol), copper(I) iodide (0.049 g, 0.26 mmol), tri-

phenylphosphine (0.136 g, 0.520 mmol), THF (35 mL),

DIEA (1.80 mL, 10.4 mmol), and 4-(thioacetyl)iodo-

benzene (7) (0.792 g, 2.85 mmol) were used following the

general procedure for couplings. The tube was placed in a

558C oil bath for 3 h. Column chromatography (silica gel

using 2:1 CH₂Cl₂/hexanes as eluent; R_f¼0.60) followed by

precipitation from CH₂Cl₂/hexanes afforded the desired

product as a yellow solid [0.841 g, ,67% yield (25% over 4

steps)]: mp 192–1958C. IR (KBr) 3042.1, 2202.1, 1705.1,

1520.1, 1491.6, 1350.2, 1287.1, 1111.7, 944.4, 827.4, 757.8,

691.6, 614.6 cm²¹. ¹H NMR (400 MHz, CDCl₃) d 8.05 (m,

2H), 7.86 (m, 1H), 7.72 (m, 1H), 7.55 (m, 5H), 7.37 (m, 5H),

3.98 (s, 2H), 2.43 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) d

193.8, 147.2, 145.4, 145.0, 137.5, 134.7, 133.9, 132.6,

132.2, 132.2, 131.5, 129.4, 128.9, 128.7, 128.3, 126.9,

125.3, 124.7, 123.9, 122.9, 122.8, 92.6, 91.5, 90.8, 87.8,

37.1, 30.7. HRMS calcd for C₃₁H₁₉NO₃S: 485.108566.

Found: 485.108470 (Error¼0.20 ppm).

1

,41% yield over 3 steps). H NMR (400 MHz, CDCl₃) d

7.99 (m, 2H), 7.77 (d, J¼1.0 Hz, 1H), 7.67 (m, 1H), 7.52 (m,

4H), 7.34 (m, 4H), 3.91 (s, 2H), 3.21 (s, 1H).

5.4.50. Thioacetic acid S-[4-(4-nitro-7-phenylethynyl-

9H-ﬂuoren-2-ylethynyl)-phenyl] ester (53). 2-Ethynyl-4-

nitro-7-phenylethynyl-9H-ﬂuorene (52) (0.373 g, 1.11

mmol), bis(dibenzylideneacetone)palladium(0) (0.032 g,

0.055 mmol), copper(I) iodide (0.021 g, 0.111 mmol),

triphenylphosphine (0.058 g, 0.220 mmol), THF (20 mL),

DIEA (0.77 mL, 4.42 mmol), and 4-(thioacetyl)iodo-

benzene (7) (0.338 g, 1.22 mmol) were used following the

general procedure for couplings. The tube was placed in a

558C oil bath for 3 h. Column chromatography (silica gel

using 1:1 CH₂Cl₂/hexanes) followed by precipitation from

CH₂Cl₂/hexanes afforded the desired product as a yellow

solid [0.297 g, ,55% yield (23% over 4 steps)]: mp 180–

1838C. IR (KBr) 1713.9, 1544.6, 1516.6, 1490.7, 1346.4,

1289.3, 1117.0, 944.8, 824.0, 752.5, 689.8, 609.1,

5.4.53. N-[4-(5-Nitro-7-phenylethynyl-9H-ﬂuoren-2-

ylethynyl)-phenyl]-formamide (56). 7-Ethynyl-4-nitro-2-

phenylethynyl-9H-ﬂuorene (54) (0.875 g, ,2.59 mmol)

was coupled with N-(4-iodo-phenyl)-formamide (9)

(0.704 g, 2.85 mmol) following the Pd/Cu protocol using

1

537.5 cm²¹. H NMR (400 MHz, CDCl₃) d 8.05 (m, 2H),

7.87 (d, J¼0.90 Hz, 1H), 7.73 (s, 1H), 7.56 (m, 5H), 7.42

(m, 2H), 7.37 (m, 3H), 4.00 (s, 2H), 2.43 (s, 3H). ¹³C NMR

(100 MHz, CDCl₃) d 193.6, 147.2, 145.3, 145.0, 137.1,

134.7, 134.3, 132.7, 132.3, 132.1, 131.4, 129.4, 129.0,

128.8, 128.2, 126.9, 125.3, 124.4, 124.0, 123.4, 122.4, 91.7,

91.6, 89.8, 89.4, 37.1, 30.8. HRMS calcd for C₃₁H₁₉NO₃S:

485.108566. Found: 485.108900 (Error¼0.69 ppm).

bis(dibenzylideneacetone)

palladium(0)

(0.074 g,

0.129 mmol), copper(I) iodide (0.049 g, 0.26 mmol), tri-

phenylphosphine (0.136 g, 0.518 mmol), DIEA (1.80 mL,

10.3 mmol), and THF (35 mL). The tube was placed in a

558C oil bath for 3 h. Column chromatography (silica gel

using 3:1 CH₂Cl₂/ethyl acetate; R_f¼0.35) afforded the

impure product (1.07 g) which was taken directly onto the

next step. ¹H NMR (400 MHz, DMSO-d₆) d 10.42 (s, 0.9H),

10.35 (d, J¼10.7 Hz, 0.3H), 8.90 (d, J¼10.8 Hz, 0.3H), 8.32

(d, J¼1.5 Hz, 1H), 8.11 (s, 1H), 8.07 (s, 1H), 7.86–7.81 (m,

2.3H), 7.73–7.45 (m, 13H), 7.26 (d, J¼8.4 Hz, 0.7H).

5.4.51. 7-Ethynyl-4-nitro-2-phenylethynyl-9H-ﬂuorene

(54). 2,7-Dibromo-4-nitro-9H-ﬂuorene (48) (5.00 g,

13.5 mmol) was coupled with phenylacetylene (1.56 mL,

14.2 mmol) following the Pd/Cu protocol using bis(tri-

phenylphosphine)palladium(II)

dichloride

(0.190 g,

0.27 mmol), copper(I) iodide (0.103 g, 0.54 mmol), THF

(70 mL), and DIEA (9.4 mL, 54 mmol). The reaction was

stirred at room temperature for 14 h at which point TMSA

(2.86 mL, 20.2 mmol) was added. The tube was placed in a

558C oil bath for 6 h. After workup, the reaction was

found not to be complete. Therefore, the crude material

was reacted with bis(triphenylphosphine)palladium(II)

dichloride (0.095 g, 0.135 mmol), copper(I) iodide

(0.051 g, 0.27 mmol), THF (70 mL), and DIEA (9.4 mL,

54 mmol). The tube was placed in a 608C oil bath for 1 d.

Flash column chromatography (silica gel using 3:1

hexanes/CH₂Cl₂as eluent; R_f¼0.43) afforded the impure

intermediate (2.25 g, ,94% by NMR) that was taken onto

the next step. Potassium carbonate (3.04 g, 22 mmol),

methanol (100 mL), and CH₂Cl₂(100 mL) were added

following the general deprotection method described earlier

to afford the slightly impure (,93 % purity by NMR)

product (1.75 g, ,41% yield over 2 steps). ¹H NMR

(400 MHz, CDCl₃) d 8.04 (m, 1H), 8.02 (d, J¼8.3 Hz, 1H),

5.4.54. 7-(4-Isocyano-phenylethynyl)-4-nitro-2-phenyl-

ethynyl-9H-ﬂuorene (57). To a 500 mL round bottom

ﬂask was added N-[4-(5-nitro-7-phenylethynyl-9H-ﬂuoren-

2-ylethynyl)-phenyl]-formamide (56) (1.07 g, ,2.30

mmol). Air was removed and N₂backﬁlled (3£). CH₂Cl₂

(250 mL) and triethylamine (50 mL) was added and the

ﬂask was cooled to 08C. Triphosgene (0.434 g, 1.61 mmol)

was then added. After 3 h the solution was at room

temperature and starting material remained by TLC. An

additional 0.124 g (0.46 mmol) of triphosgene was added.

After 15 min (3.25 h total time), the reaction was complete

by TLC. The mixture was washed with water and CH₂Cl₂.

Column chromatography (silica gel using 1:1 hexanes/CH₂-

Cl₂as eluent; R_f¼0.39) followed by precipitation from

CH₂Cl₂/hexanes afforded the product (0.356 g, 31% yield

over 2 steps): mp 210–2258C (decomp.). IR (KBr) 3068.0,

2119.2, 1519.9, 1504.2, 1360.8, 1287.6, 838.3, 752.8,

1

686.8 cm²¹. H NMR (400 MHz, CDCl₃) d 8.03 (m, 2H),

7.83 (s, 1H), 7.68 (s, 1H), 7.53 (m, 5H), 7.36 (m, 5H), 3.96

3154

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

(s, 2H). ¹³C NMR (100 MHz, CDCl₃) d 166.4, 147.2, 145.4,

145.0, 137.7, 133.7, 133.0, 132.2, 132.2, 131.5, 129.4,

128.9, 128.3, 126.9, 126.9, 125.3, 124.9, 123.31, 123.11,

122.73, 92.67, 92.56, 89.79, 87.74, 37.07. HRMS calcd for

C₃₀H₁₆N₂O₂: 436.121178. Found: 436.121833 (Error¼1.5

ppm).

CH₂Cl₂as eluent; R_f¼0.47) afforded the desired product as

a yellow solid (0.370 g, 56% yield): mp 239–2418C. IR

(KBr) 1725.8, 1702.5, 1600.3, 1490.4, 1101.9, 957.3, 829.8,

1

785.3, 618.8, 526.4 cm²¹. H NMR (400 MHz, CDCl₃) d

7.79 (d, J¼0.8 Hz, 2H), 7.65 (dd, J¼7.9, 1.4 Hz, 2H), 7.53

(m, 6H), 7.40 (d, J¼8.4 Hz, 2H), 2.43 (s, 6H). ¹³C NMR

(100 MHz, CDCl₃) d 193.7, 192.5, 143.8, 138.3, 134.9,

134.7, 132.6, 129.0, 127.9, 124.6, 124.4, 121.1, 91.1, 90.5,

30.7. HRMS calcd for C₃₃H₂₀O₃S₂: 528.085390. Found:

528.085952 (Error¼1.1 ppm).

5.4.59. 2,7-Dibromo-4-nitro-ﬂuoren-9-one (62).²⁴2,7-

Dibromo-4-nitro-9H-ﬂuorene (48) (1.00 g, 2.70 mmol) and

CH₂Cl₂(60 mL) were added to a 100 mL round bottom

ﬂask equipped with a stir bar. Chromium(III) oxide

(0.013 g, 0.135 mmol) and t-butyl hydroperoxide

(1.80 mL, 18.9 mmol) were then added and the solution

was stirred at ambient temperature for 1 d (red solution).

The solution was then heated to reﬂux for 19 h (yellow

solution). After cooling to ambient temperature, the mixture

was ﬁltered through alumina. Column chromatography

(silica gel using 1:1 CH₂Cl₂/hexanes as eluent; R_f¼0.51)

afforded the desired product as a yellow solid (0.637 g,

,95% pure). ¹H NMR (400 MHz, CDCl₃) d 8.20 (d,

J¼1.8 Hz, 1H), 8.02 (d, J¼1.9 Hz, 1H), 7.91 (d, J¼8.3 Hz,

1H), 7.88 (d, J¼2.0 Hz, 1H), 7.71 (dd, J¼8.3, 2.0 Hz, 1H).

5.4.55. 2,7-Dibromo-ﬂuoren-9-one (58).²⁶2,7-Dibromo-

ﬂuorene (47) (10.0 g, 30.7 mmol) was added to a 500 mL

round bottom ﬂask equipped with a stir bar along with

CH₂Cl₂(400 mL). t-Butyl hydroperoxide (20.6 mL,

215 mmol) and catalytic chromium(III) oxide (0.153 g,

1.53 mmol) were then added. The solution was stirred at

ambient temperature for 1 d, at which point starting material

remained. The solution was then heated to reﬂux for 19 h.

After cooling to ambient temperature, the solution was

1

ﬁltered through alumina. H NMR showed approximately

50% conversion. The mixture was re-subjected to

the reaction conditions with 0.306 g (3.07 mmol) of

chromium(III) oxide and heated to reﬂux for 20 h. The

material was ﬁltered through alumina (¹H NMR showed

approximately 90% product). The product was then

recrystallized from ethanol/toluene to afford the pure

product (8.65 g, 83% yield): mp 205–2098C (lit. mp 205–

2078C).^{34 1}H NMR (400 MHz, CDCl₃) d 7.75 (d, J¼1.8 Hz,

2H), 7.61 (dd, J¼7.9, 1.9 Hz, 2H), 7.37 (d, J¼7.9 Hz, 2H).

5.4.56. 2,7-Bis-trimethylsilanylethynyl-ﬂuoren-9-one

(59).²⁷

5.4.60. 4-Nitro-2,7-bis-trimethylsilanylethynyl-ﬂuoren-

9-one (63). 2,7-Dibromo-4-nitro-ﬂuorenone (62) (0.637 g,

1.65 mmol) was coupled with TMSA (0.51 mL, 3.6 mmol)

following the Pd/Cu protocol using bis(triphenylphos-

phine)palladium(II) dichloride (0.058 g, 0.083 mmol),

copper(I) iodide (0.031 g, 0.165 mmol), THF (25 mL), and

triethylamine (5 mL). The tube was capped and stirred at

ambient temperature for 5 h. Flash column chromatography

(silica gel using 2:1 hexanes/CH₂Cl₂as eluent; R_f¼0.61)

afforded the desired product (0.475 g, 42% yield over 2

steps): mp 234–2358C. IR (KBr) 2958.1, 2903.8, 2156.0,

1732.1, 1557.9, 1531.4, 1453.2, 1356.3, 1249.2, 845.2,

2,7-Dibromo-9-oxo-ﬂuorene

(58)

(0.753 g,

2.21 mmol) was coupled with TMSA (0.69 mL, 4.9 mmol)

following the Pd/Cu protocol using bis(triphenylphos-

phine)palladium(II) dichloride (0.078 g, 0.110 mmol),

copper(I) iodide (0.042 g, 0.22 mmol), THF (20 mL), and

DIEA (2.30 mL, 13.3 mmol). The tube was capped and

stirred at 508C for 15 h. Flash column chromatography

(silica gel using 2:1 hexanes/CH₂Cl₂as eluent; R_f¼0.47)

afforded the desired product (0.480 g, 58% yield): mp 164–

1688C. IR (KBr) 2958.4, 2898.7, 2154.6, 1715.0, 1603.5,

1

1463.6, 1249.5, 859.1, 758.7, 644.7, 535.7 cm²¹. H NMR

(400 MHz, CDCl₃) d 7.71 (dd, J¼1.5, 0.7 Hz, 2H), 7.56 (dd,

J¼7.7, 1.5 Hz, 2H), 7.43 (dd, J¼7.7, 0.7 Hz, 2H), 0.24 (s,

18H). ¹³C NMR (100 MHz, CDCl₃) d 192.5, 143.8, 138.6,

134.7, 128.3, 124.8, 120.9, 104.3, 97.1, 0.3.

767.5 cm²^{1 1}H NMR (400 MHz, CDCl₃) d 8.08 (d,

.

J¼1.5 Hz, 1H), 7.93 (m, 2H), 7.81 (d, J¼1.6 Hz, 1H),

7.62 (dd, J¼8.1, 1.7 Hz, 1H), 0.26 (s, 9), 0.25 (s, 9H). ¹³C

NMR (100 MHz, CDCl₃) d 190.0, 144.8, 139.6, 139.2,

137.1, 136.0, 134.9, 133.3, 131.6, 128.4, 126.8, 126.4,

126.0, 103.6, 101.6, 100.8, 99.2, 0.2, 0.1. HRMS calcd for

5.4.57. 2,7-Diethynyl-ﬂuoren-9-one (60).²⁷2,7-Bis-tri-

methylsilanylethynyl-ﬂuoren-9-one (59) (0.480 g, 1.28

mmol), potassium carbonate (0.709 g, 5.13 mmol), metha-

nol (50 mL), and CH₂Cl₂(50 mL) were used following the

general deprotection method described earlier to afford the

C₂₃H₂₃NO₃Si₂:

(Error¼0.42 ppm).

417.121651.

Found:

417.121826

5.4.61. 2,7-Diethynyl-4-nitro-ﬂuoren-9-one (64). 4-Nitro-

2,7-bis-trimethylsilanylethynyl-ﬂuoren-9-one (63) (0.450 g,

1.07 mmol), potassium carbonate (0.887 g, 6.42 mmol),

methanol (50 mL), and CH₂Cl₂(50 mL) were used follow-

ing the general deprotection method described earlier to

afford the desired product (0.290 g) which was taken

directly onto the next step with no further puriﬁcation.

1

desired product (0.285 g, 97% yield). H NMR (400 MHz,

CDCl₃) d 7.76 (m, 2H), 7.61 (dd, J¼7.7, 1.5 Hz, 2H), 7.48

(d, J¼7.8 Hz, 2H), 3.17 (s, 2H).

5.4.58. Thioacetic acid S-{4-[7-(4-acetylsulfanyl-phenyl-

ethynyl)-9-oxo-9H-ﬂuoren-2-ylethynyl]-phenyl} ester

(61). 2,7-Diethynyl-ﬂuorenone (60) (0.285 g, 1.24 mmol),

bis(dibenzylideneacetone)palladium(0) (0.036 g, 0.062

mmol), copper(I) iodide (0.024 g, 0.124 mmol), triphenyl-

phosphine (0.065 g, 0.248 mmol), THF (25 mL), DIEA

(1.30 mL, 7.44 mmol), and 4-(thioacetyl)iodobenzene (7)

(0.690 g, 2.48 mmol) were used following the general

procedure for couplings. The tube was placed in a 508C

oil bath for 4 h. Column chromatography (silica gel using

5.4.62. Thioacetic acid S-{4-[7-(4-acetylsulfanyl-pheny-

lethynyl)-5-nitro-9-oxo-9H-ﬂuoren-2ylethynyl]-phenyl}

ester (65). 2,7-Diethynyl-4-nitro-ﬂuorenone (64) (0.290 g,

1.05 mmol),bis(dibenzylideneacetone)palladium(0)(0.030 g,

0.053 mmol), copper(I) iodide (0.020 g, 0.105 mmol),

triphenylphosphine (0.055 g, 0.21 mmol), THF (25 mL),

DIEA (1.1 mL, 6.3 mmol), and 4-(thioacetyl)iodobenzene

D. W. Price, Jr., J. M. Tour / Tetrahedron 59 (2003) 3131–3156

3155

(7) (0.613 g, 2.21 mmol) were used following the general

Acknowledgements

procedure for couplings. The tube was placed in a 558C oil

bath for 18 h. Column chromatography (silica gel using

CH₂Cl₂as eluent; R_f¼0.63), followed by precipitation form

CH₂Cl₂/hexanes (to remove dba) afforded the desired

product as an orange solid (0.372 g, 60% yield over 2

steps): mp 234–2368C. IR (KBr) 2202.1, 1724.8, 1557.4,

1528.2, 1492.1, 1454.4, 1354.4, 1235.5, 1113.1, 1090.7,

We thank the Defense Advanced Research Projects Agency

(DARPA) administered by the Ofﬁce of Naval Research

(ONR), and the Air Force Ofﬁce of Scientiﬁc Research

(AFOSR F49620-01-1-0364) for ﬁnancial support of this

work. We thank Dr I. Chester of FAR Research Inc. for

trimethylsilylacetylene and Jake Ciszek for obtaining the

crystal of 53 and the X-ray analysis.

1

937.0, 822.0, 602.8 cm²¹. H NMR (400 MHz, CDCl₃) d

8.13 (d, J¼1.5 Hz, 1H), 7.97 (m, 2H), 7.84 (d, J¼1.2 Hz,

1H), 7.67 (dd, J¼8.1, 1.6 Hz, 1H), 7.55–7.52 (m, 4H),

7.42–7.38 (m, 4H), 2.43 (s, 3H), 2.42 (s, 3H).HHH ¹³C

NMR (100 MHz, CDCl₃) d 193.6, 193.4, 189.9, 144.9,

139.6, 138.9, 137.2, 135.1, 134.7, 134.7, 133.0, 132.8,

132.7, 131.2, 130.0, 129.5, 128.0, 126.6, 126.6, 125.8,

123.9, 123.3, 93.8, 92.8, 89.9, 88.1, 30.8, 30.8. HRMS calcd

for C₃₃H₁₉NO₅S₂: 573.070468. Found: 573.071403

(Error¼1.6 ppm).

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Article Doi

Biphenyl- and fluorenyl-based potential molecular electronic devices

DOI: 10.1016/S0040-4020(03)00334-X

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