1,3-Diethynylbicyclo[1.1.1]pentane, a useful molecular building block

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DOI: 10.1002/ejoc.201200351

1,3-Diethynylbicyclo[1.1.1]pentane, a Useful Molecular Building Block

[a][‡]

[a,b]

and Ctibor Mazal*^[a]

ˇ

Jirí Kaleta,

Marek Necas,

Dedicated to Professor Jaroslav Jonas on the occasion of his 75th birthday

Keywords: Alkynes / Cross coupling / Umpolung / Small ring systems / Rod-like molecules

1,3-Diethynylbicyclo[1.1.1]pentane (DEBCP) has been found

to be a valuable molecular building block mostly for the syn-

thesis of extended, rigid, rod-like molecules. With its

straightforward linear geometry, DEBCP can be used as a

nonconjugated alternative to more frequently used π-conju-

gated, rod-like building blocks. Examples of reactions that

introduce DEBCP into larger structures are (1) the reaction of

DEBCP lithium acetylides with electrophiles such as TMSCl,

CO₂, and Ph₂PCl, (2) Sonogashira–Hagihara cross-coupling

reactions with aryl or heteroaryl iodides or bromides, and

(3) umpolung reactions that afford the corresponding di-

bromo and diiodo derivatives of DEBCP, which then success-

fully react with tert-C-cuprates derived from p- and m-di-

carbadodecaboranes or bicyclopentanes. These umpolung

reactions afforded a new class of molecular rods that com-

bine carborane or bicyclo[1.1.1]pentane cages with ethyn-

ylene linkers. Many of the DEBCP derivatives were studied

by single-crystal X-ray diffraction. They form well-organized

arrays of molecular rotors, the DEBCP units, and so can be

considered as examples of artificial molecular-size machines.

building blocks that help to tailor the required properties of

miscellaneous target substances. In addition to the entirely

newly developed structures, there are some old ones, the

synthetic potential and scope of which deserve further

Introduction

Various rigid, rod-like molecules are attracting increasing

attention for a number of reasons, as addressed in the excel-

lent review published by Schwab et al.^[1]The most impor-

tant of them are (1) the long-distance interaction phenom-

ena such as electron and energy transfer and the magnetic

coupling of transition-metal atoms, and (2) the molecular

rods and connectors can be used for the construction of

supramolecular assemblies and giant molecules for various

purposes. Both of these factors play important roles in the

design and preparation of functional devices on a molecular

level, the straight rigid molecules being used as axles, wheel

shafts, draw bars as well as conducting or insulating con-

necting rods. The rod-like molecules can also be useful in

the construction of new functional materials by the so-

called “bottom-up” approach in which one can take advan-

tage of their defined geometry and stiffness in creating the

void space in meso- and nanoporous materials. This is why

there is a constant demand for new rigid, rod-like molecular

investigation.

The

1,3-diethynylbicyclo[1.1.1]pentane

(DEBCP, 1) is an example. Since its preparation by Bunz

and Szeimies,^[2]who studied 1 as an interesting relay for π/

σ conjugation,^[3]it has attracted the attention of theoreti-

cians.^[4]However, it took a decade to find a significant syn-

thetic application. Then Schwab et al. used DEBCP as a

rod-like molecular building block for the preparation of ex-

tended trigonal and tetragonal connectors for a molecular

construction set.^[5]Only recently did we use DEBCP as a

“line segment” in the construction of a molecular triangle.^[6]

We found this building block very interesting and decided

to investigate its synthetic scope and limitations more thor-

oughly. We report our results herein.

Results and Discussion

The diyne 1 is relatively easily accessible from cheap pen-

taerythritol (2). Its synthesis follows the pathway shown in

Scheme 1 and exploits already known procedures, the indi-

vidual steps of which are well described in recent litera-

ture.^[5–7]The crucial intermediates, the tetrahalide 3 and the

diketone 4, are stable enough to be stored in a refrigerator

for a long time without change. (Note, both provided crys-

tals suitable for X-ray diffraction.) Contrary to the origi-

nally used procedure,^[7]we modified the first two steps of

the synthesis, the preparation of the methallyl dichloride 5,

[a] Department of Chemistry, Faculty of Science, Masaryk University,

Kotlárˇská 2, 61137 Brno, Czech Republic

Fax: +420-549492443

E-mail: mazal@chemi.muni.cz

Homepage: http://ww w .muni.cz/sci/people/Ctibor.Mazal

[b] CEITEC – Central European Institute of Technology, Masaryk

University Brno,

Kamenice 5, 62500 Brno-Bohunice, Czech Republic

[‡] Present address: Institute of Organic Chemistry and

Biochemistry, Academy of Sciences of the Czech Republic,

Flemingovo nám. 2, 16610 Praha 6, Czech Republic

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejoc.201200351.

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which is the precursor of 3. Our approach combined the Table 1. Reactions of lithium acetylides of 1 and 8 with electro-

preparation of the cyclic sulfite 6^[8]with its vacuum flash

philes.

pyrolysis,^[9]thus avoiding a disagreeable oxidation with con-

centrated nitric acid, which can be a potential source of

danger. The method suits preparations of 5 on the

multigram scale, and so we were able to prepare a satisfac-

tory amount of 1 in high purity. Fortunately, some of the

concerns about the explosiveness of 1 conveyed by others

did not come true^[5]and we were able to sublime 1 and

obtain a single crystal suitable for XRD analysis. Neverthe-

less, some caution in the handling of 1 is advisable as the

diyne represents a kinetically stable, yet very strained mole-

cule. In fact, the strain and resulting tendency of the bi-

cyclopentane cage to rearrange were also the reasons why

we decided to investigate carefully the scope and reactivity

of 1.

Entry

1

Starting

compd.

Electrophile

“E”

Product

Y

No.

R

No.

X

Yield [%]^[a]

1

H

TMSCl^[b]

7

8

9

TMS TMS

TMS

CO₂H CO₂H

35

45

H

2

3

4

5

1

8

H

TMS

CO₂

PPh₂Cl

CO₂

72^[c]

40

10 PPh₂PPh₂

11 TMS CO₂H

12 TMS PPh₂

78^[d]

63^[e]

PPh₂Cl

[a] Yields are given for the isolated and purified materials. [b]

1.25 equiv. of nBuLi and 1.5 equiv. of TMSCl were used in the

reaction (see ref.^[6]). [c] Reaction with an excess of ethereal diazo-

methane afforded the corresponding diester 13 (as 9, X = Y =

CO₂Me) in almost quantitative yield. [d] The product was isolated

as the methyl ester 14 (as 11, X = TMS, Y = CO₂Me) after reaction

with an excess of diazomethane in diethyl ether. [e] Desilylation of

12 was carried out by reaction with TBAF in THF at 25 °C to yield

92% of 15.

DEBCP unit, were prepared also in good yields (Table 1,

Entries 4 and 5). For better purification and/or crystalliz-

ation, the carboxylic acids 9 and 11 were methylated to their

esters 13 and 14 by reaction with diazomethane to give ex-

cellent yields, 96 and 97%, respectively. The diester 13 then

provided crystals suitable for XRD analysis.

Scheme 1. Synthesis of the diyne 1 from pentaerythritol (2). Rea-

gents and conditions: (a) SOCl₂, Py, 0–60 °C, 77%;^[8](b) 500 °C,

1 Torr, 65%;^[9](c) HCBr₃, KOH, 40 °C;^[7](d) (1) MeLi, diethyl

ether, –40 to 0 °C, (2) biacetyl, hν, 0 °C;^[7](e) (1) hexachloroethane,

PPh₃, 100 °C, (2) NaNH₂, liq. NH₃.^[5,6]

The phosphane 12 was desilylated by a standard pro-

cedure with TBAF in THF to yield phosphane 15. The lat-

ter as well as the bis(phosphane) 10 were easily oxidized

with 10% H₂O₂to afford almost quantitative yields of the

corresponding phosphane oxides 16 and 17 (Scheme 2). A

two-phase reaction system (CH₂Cl₂/aqueous H₂O₂) in com-

bination with a relatively short reaction time (ca. 40 min)

prevented the formation of side-products and notably sim-

plified the isolation of the desired compounds. These were

obtained in high purity simply by evaporation of CH₂Cl₂

from the organic phase. The oxidation reaction modifies the

coordination properties of the phosphanes, and the re-

sulting phosphane oxides can be used to further extend the

range of rod-like ligands for use in coordination polymers.

Our reinvestigation of the reactivity of 1 first focused on

simple modifications of the diyne termini in reactions of its

lithium acetylides with electrophiles (Table 1). Recently, we

have already performed one such reaction, silylation.^[6]In

addition to the disilylated derivative 7, we were also able

to prepare monosilylated 8, which is of obvious synthetic

importance (Table 1, Entry 1). Moreover, we have proven

that 7 can be recycled to 1 in a deprotection reaction with

aqueous ammonium fluoride in diethyl ether, if necessary.

It increases the efficiency of the diyne exploitation remarka-

bly. The less volatile disilyl derivative 7 can be stored (con-

trary to diyne 1) in a refrigerator for months without any

visible decomposition and then used as a convenient source

of 1.

Other electrophiles, carbon dioxide and chlorodiphenyl-

phosphane, were chosen with a view to a possible coordina-

tion polymer investigation. A dilithium diacetylide of 1,

which was quantitatively formed by the addition of 2 equiv.

of nBuLi (Table 1, Entries 2 and 3), afforded the dicarboxy-

lic acid 9 and the bis(phosphane) 10, respectively, in reason-

able yields. When the monoprotected diyne 8 was used with

1 equiv. of nBuLi in similar reactions, the derivatives 11 and

12, with different substituents at each terminus of the Scheme 2. Oxidation of phosphanes to phosphane oxides.

2

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1,3-Diethynylbicyclo[1.1.1]pentane

The ability of the diyne 1 to undergo Sonogashira–Hagi- minal alkynes. Only an obvious incompatibility of the ester

hara cross-coupling reactions has already been proven un- group with the TBAF deprotection procedure reduced the

der standard^[6]or copper-free^[5]reaction conditions. Analo- yield of the terminal alkyne formed from the methyl ester

gous reactivity has also been found in the case of its lat- 14 to 69%.

erally substituted derivative.^[10]In this study we synthesized

a group of molecular rods 18–26, mostly in high isolated

Table 3. Sonogashira cross-coupling reactions of the diyne 8.

yields (Table 2). The esters 23–25 are precursors of free ac-

ids with potential in the preparation of new metal–organic

frameworks (MOFs).

Table 2. Sonogashira–Hagihara cross-coupling reactions of the di-

yne 1.

[a] Yields are given for isolated and purified material. [b] See ref.^[6]

The synthetic applicability of terminal alkynes can be ex-

tended by their umpolung to 1-haloalkynes.^[11]It is well

Sonogashira–Hagihara cross-coupling reactions of the known from carborane chemistry that 1-bromoalkynes cou-

monoprotected diyne 8 (Table 3) afforded acceptable yields ple with C-cuprates derived from p-carboranes without any

of the rods 27 and 28, which contain one DEBCP unit, catalyst in high yields.^[12]To prove the synthetic potential

the straight and V-shaped molecules 29 and 30 contain two of 1 in similar reactions, we also tried its umpolung. The

DEBCP units, and the star-shaped molecule 31 has three dibromodiyne 32 was prepared in high yield from 1 by

DEBCP units in its structure. Desilylation of 27–31 can using NBS in the presence of AgNO₃in dry acetone^[13]

yield terminal alkyne derivatives that are useful molecular (Scheme 3a). The umpoled dibromodiyne 32 was found to

building blocks for the construction of larger covalent, be light-sensitive and highly reactive. The diiododiyne 33

“giant” molecules by suitable alkyne coupling reactions. was also synthesized. In this case, however, we started from

Deprotection by a standard TBAF procedure was success- the disilyl derivative 7 applying the procedure used probably

fully demonstrated for compounds 12, 27, and 31, which for the first time by Jacobson and Carothers^[14]and recently

afforded good yields (92–95%) of the corresponding ter- by others,^[15]who treated the starting alkynes with potas-

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sium hydroxide and iodine in methanol. We used 7 in that in their structures. The terminal carborane units offer op-

procedure to accomplish the deprotection and subsequent portunities for further modifications. As an example, the

iodination in a one-pot reaction (Scheme 3b). The intended trihexylsilyl groups of 35 were removed by using TBAF in

advantage of such an approach, the use of cheap and heavy- THF to yield 38, and an even longer extended rod-like di-

metal-free reagents as well as 7 instead of the more volatile carboxylic acid 39 was prepared by lithiation and carboxyl-

1, was, however, paid by the rather low yield of 33 (ca. ation (Scheme 4). It was interesting to compare the solubil-

50%).

ity of 39 with that of the dicarboxylic acid obtained by hy-

drolysis of the diester 23, which has almost the same length.

Although the latter, which has two p-phenylene groups in

its structure, showed only negligible solubility, the two p-

carborane units in molecule 39 led to a significant increase

in solubility in common polar organic solvents.

Scheme 3. Diyne umpolung: Synthesis of 1-haloalkynes 32 (a) and

33 (b).

The stability and reactivity of the dibromodiyne 32 under

cross-coupling reaction conditions were tested in the reac-

tion with a cuprate derived from 1-(trihexylsilyl)-1,12-di-

carba-closo-dodecaborane (34; Table 4, Entry 1). An unop-

timized coupling reaction gave a very encouraging 38% iso-

lated yield of 35. NMR analysis of the reaction mixture

showed that the coupling reaction actually afforded more

than 90% of 35, but its unwillingness to crystallize together

with further difficulties in separation, mostly due to the

presence of two lipophilic trihexylsilyl groups, lowered the

isolated amount of pure 35 to only 38%. These problems

were eliminated in the next reaction, in which an excess of

m-carborane 36 was used in place of 34. No protecting

groups were necessary, and the product 37 was isolated in

89% yield (Table 4, Entry 2). Together with the compounds

prepared earlier,^[16]35 and 37 extend the family of molecu-

lar rods that combine carborane and bicyclopentane cages

Scheme 4. Preparation of the dicarboxylic acid 39.

To the best of our knowledge, no successful C(sp³)–C(sp)

cross-coupling between the tertiary bridgehead carbon

atom of a bicyclo[1.1.1]pentane cage and terminal alkynes

has been published to date. The main reason for this is

probably the insufficient reactivity of bicyclopentyl bridge-

head halides in the crucial step of the coupling catalytic

cycle, the oxidative addition of a transition-metal complex

to a C–X bond at the bridgehead position due to the quite

disadvantageous geometry of the reaction center, and the

high strength of the C–X bond. It is therefore clear that

for a successful coupling, an opposite arrangement, which

would combine a suitable bridgehead organometal com-

pound with a haloalkyne, could be more advantageous. Sev-

eral unsuccessful attempts^[17]indicated, however, that the

choice of an appropriate metal at the bridgehead position

would be of great importance. For example, the reaction

of (3-butylbicyclo[1.1.1]pentyl)zinc chloride with 1-iodo-2-

(trimethylsilyl)ethyne under [PdCl₂(dppf)] catalysis led only

to an almost quantitative yield of a metal/halogen exchange

product, the 1-butyl-3-iodobicyclo[1.1.1]pentane. Because

the bicyclopentane bridgeheads have a geometry resembling

that of the closo-carborane bridgehead carbon atoms, we

were interested in whether the bicyclopentane bridgehead

cuprates would be an appropriate choice for the cross-cou-

pling reactions with haloalkynes such as 32 and 33. Indeed,

the reactions of the cuprates derived from 1-(chloromethyl)-

6-iodotricyclo[3.2.0.0^2,6]heptane (40)^[16,18]and 1-iodo-3-

methylbicyclo[1.1.1]pentane (41)^[17,19]with the dibromo-

diyne 32 were accomplished under the same reaction condi-

tions as those used for the carboranes (Table 4, Entries 3

and 4). Even though the reactions gave rather low yields of

42 and 43, it is the first time that molecular rods have been

prepared that contain two bicyclopentane cages linked by

an ethynylene bridge. The molecular structure of 42 was

also confirmed by XRD analysis (Figure 1).

Table 4. Reactions of dibromodiyne 32 with cuprates.^[a]

[a] 1 equiv. of nBuLi in hexanes and 2 equiv. of tBuLi in pentane

were used for lithiation of the carboranes and the iodo derivatives,

respectively. [b]

ؠ

= BH. [c] Yields are given for isolated and purified

material.

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1,3-Diethynylbicyclo[1.1.1]pentane

Table 5. Selected interatomic distances [Å] in terminally substituted

DEBCPs.

Figure 1. ORTEP representation of the molecular structure of the

three-cage derivative 42.

One of the common applications of terminal alkyne

functionalities is in the formation of 1,2,3-triazole-1,4-diyl

linkages by the Sharpless–Huisgen click reaction,^[20]the 1,3-

dipolar cycloaddition with organic azides. Clearly, we were

interested in whether the alkyne 1 could take part in such

click chemistry. However, our attempts to accomplish a

model cycloaddition reaction of 1 with benzyl azide failed

with or without a Cu catalyst. A poorly soluble white poly-

mer was obtained instead, probably as a result of bicy-

clopentane cage opening, because no signals specific to the

[a] The upper value is for the molecule involved in a C–H···π inter-

action.

1

protons of the cage were detected by H NMR analysis of

the crude products. It has been proven several times that

whenever in the course of a reaction a reactive site, such as

an anion, cation, radical, or carbene, emerges at the atom

next to the strained bicyclopentane cage, the cage tends to

rearrange.^[21]This might also be the reason for the re-

arrangement in this particular case.^[22]Further investi-

gations of cycloaddition reactions in the close proximity of

the bicyclopentane cage should respect this fact in general

and prospective reaction partners need to be carefully cho-

sen to avoid the problem. We continue our investigations in

this area.

The molecules of all three compounds are arranged in par-

quet-like ordered layers (Figure 2), but the mutual orienta-

tion of the parquet-like patterns in the neighboring layers

is different. Although the “parquets” in the neighboring

layers of 1 are more or less collinear, the ones in 32 and 33

are crossed. Because the C–H···π distance in 1 is much

shorter than that of C–X···π, the molecules of 1 in the par-

quet layers are more tightly packed and thus leave less space

for the lateral accommodation of the bulky bicyclopentane

cages of the neighboring layers. They then favor the parallel

arrangement. The longer C–X···π distance together with the

bulkiness of the halogen atoms leave more space for the

bicyclopentane cages. The crossed orientation then suits a

close-packing of the neighboring layers much better.

Crystal Structure Analyses

The structures of many of the compounds presented in

In addition to the crystals of 1, the packing forces in the

this paper were also determined by X-ray structure analysis. crystals of two other compounds, the phosphorus deriva-

The corresponding CIF files have been deposited with the tives 10 and 17, bring their CϵC triple bonds into close

CCDC, and images of anisotropically refined structures can contact with C–H bonds, which suggests weak C–H···π in-

be found in the Supporting Information. Selected in- teractions. The hydrogen atoms in the phenyl rings of the

teratomic distances of the rod-like derivatives are presented phosphane or phosphane oxide moieties of these com-

in Table 5. Measurements of the DEBCP core, such as the pounds, respectively, are involved. Particularly in the case

intercage bridgehead-to-bridgehead distance (ICD), the of the phosphane oxide 17, the packing is much closer due

length of the bridgehead exocyclic C–C bonds (D_ex), and to additional C–H···O=P interactions and results in a C(sp)···

the triple bond (D_CϵC), which may play an important role H–C distance significantly shorter than the corresponding

in the propagation of various long-range interactions sum of the van der Waals radii of the atoms involved (Fig-

through the DEBCP building block, are reported along ure 3).

with the “rod length” D, which is given as the distance of

the two most distant non-hydrogen atoms located along the in the crystals of p-carborane derivative 38, which was suc-

longitudinal axis of the molecule. cessfully crystallized from toluene. The tabular crystals were

A different example of a C–H···π interaction was found

An interesting analogy was found between the crystal- stable in solution but collapsed upon drying or even after a

packing characteristics of the diyne 1 and its bromo and few hours of standing at ambient temperature. Clearly, the

iodo analogues 32 and 33. The C–H···π interaction ob- solvent molecules are incorporated into the crystal lattice.

served in crystals of 1 directs a “zig-zag” arrangement of Indeed, the bulky rods of 38 are arranged in columns sur-

the molecules. Similar “zig-zag” motifs were found in the rounded by molecules of toluene. Some of the molecules of

haloalkynes 32 and 33. These were directed, however, by C– 38 are involved in the C–H···π interactions of their carbor-

Br···π and C–I···π intermolecular interactions, respectively. ane C–H bonds with toluene molecules, which are located

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towards the ends of each of them and oriented almost per-

pendicular to their longitudinal axis at a distance of

2.356 Å, measured to the center of the toluene ring (Fig-

ure 4). Such a C–H···π interaction corresponds to the pre-

viously published examples found in crystals of o-carborane

derivatives.^[23]Interestingly, the packing forces slightly re-

duce the lengths of the rods in the interactions compared

with the others (Table 5).

Figure 4. (a) Columnar organizations of the rod-like molecules in

crystals of 38. (b) C–H···π interactions between 38 and two mole-

cules of toluene. The C–H···π distances, measured to the center of

the phenyl ring and drawn as dotted lines, are 2.356(3) Å.

Figure 2. Comparison of the molecular packing in crystals of

(a) the diyne 1 and (b) its bromo and (c) iodo analogues 32 and 33,

respectively. An arrangement of molecules in one layer is shown for

each compound. The C–H···π and C–X···π interactions are shown

as dashed lines (the H···CϵC, Br···CϵC, and I···CϵC distances are

2.710, 3.201, and 3.337 Å, respectively, measured to the center of

the triple bond), the in-layer halogen···halogen contacts are slightly

larger than the sum of the van der Waals radii (Br···Br and I···I

distances are 3.953(4) and 4.096(1) Å, respectively). Space-filling

models show different orientations of the parquet-like layers in 1

and its halo analogues 32 and 33.

Well-organized arrays of molecular rotors are nowadays

of great interest in materials science and nanotechnology

research as well as being studied as examples of artificial

molecular-sized machines.^[24]From this point of view, the

crystal structures of the DEBCP derivatives represent an

interesting set of compounds in which one rotor, the bicy-

clo[1.1.1]pentane cage, is located in various kinds of crystal

lattice environments. They differ not only in shape and im-

mediate environment of the rotors, but also in the mutual

orientation of their rotational axes in the crystal lattice,

both given by the corresponding molecular crystal-packing

patterns. It has already been shown that the parent diyne 1

and its halo analogues 32 and 33 prefer zig-zag arrange-

ments of their molecules in their crystal lattices, although

with different orientations of the parquet-ordered layers.

Similarly, zig-zag motifs with cross-like oriented rotational

axes of the bicyclopentane rotors were found in crystals of

the diester 13 and the diphenyl derivative 18 (Figure 5a,b).

In contrast, a more or less collinear, parallel orientation of

the rotors was found in crystals of the diketone 4, the disilyl

derivative 7, the bis(phosphane) 10, the phosphane oxide

17, and the “three-cage derivative” 42 (Figure 5c–g). In ad-

dition, “multidirectional” arrangements were found in crys-

tals of the p-carborane derivative 38 (Figure 4) and diphos-

phane dioxide 16 (Figure 5h).

Figure 3. Crystal structures of (a) diphosphane 10 and (b) phos-

phane oxide 17. The C–H···π distances depicted as dotted lines are

2.777(1) and 2.731(2) Å in 10 and 17, respectively. The C–H···O=P

distances drawn as dotted lines in the structure of 17 are 2.322(2)

and 2.379(2) Å.

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1,3-Diethynylbicyclo[1.1.1]pentane

Conclusions

The linear DEBCP molecular rods can be considered as

nonconjugated alternatives to more frequently used π-con-

jugated, rod-like molecular building blocks. Their acetylene

termini are readily lithiated and react with electrophiles,

such as TMSCl, CO₂, and Ph₂PCl, to afford rigid rod-like

extended ligands. In addition to the simultaneous function-

alization of both termini, the reaction of only one terminus

or successive reactions of both termini with different rea-

gents were possible when trimethylsilyl-protected DEBCP 8

was used. Sonogashira–Hagihara coupling reactions of

DEBCP (1) with aryl or heteroaryl iodides or bromides af-

forded new extended molecules of rod-like or star-shape ge-

ometry. DEBCP (1) was successfully umpoled to its 1-iodo-

and 1-bromoalkyne derivatives. Reactions of the latter with

tert-C-cuprates, such as those derived from p- and m-dicar-

badodecaboranes or bicyclopentanes, afforded a new class

of molecular rods that combine carborane or bicyclo[1.1.1]-

pentane cages with ethynylene bridges.

As a part of the synthetic procedures presented herein,

we have developed a simple method for the recovery of the

parent DEBCP (1) from its bis(trimethylsilyl) derivative 7,

which remarkably increased the effectiveness of the prepa-

ration of monosilylated diyne 8, in which 7 was formed as

the main byproduct.

Crystals of some of the DEBCP derivatives were pre-

pared and studied by single-crystal X-ray diffraction. In ad-

dition to multidirectional arrangements, parallel or zig-zag

ordering of the DEBCP units was observed in the crystal

lattices. The different molecular arrangements, the partici-

pation of molecules, particularly of their possibly rotating

parts, in various crystal-packing interactions, and the ef-

fects of these interactions on the degree of rotational free-

dom of the DEBCP structural unit, as an example of a rigid

molecular-size rotor, are our current interest.

Experimental Section

General: All reactions were carried out under argon with dry sol-

vents, freshly distilled under anhydrous conditions unless otherwise

noted. Standard Schlenk and vacuum techniques were used for all

manipulations of air- or moisture-sensitive compounds. Yields refer

to isolated chromatographically and spectroscopically homogen-

eous materials unless otherwise stated. [1.1.1]Propellane,^[7]1,3-di-

ethynylbicyclo[1.1.1]pentane (1),^[3,5]1,3-bis(trimethylsilylethynyl)bi-

cyclo[1.1.1]pentane (7),^[6][(3-ethynylbicyclo[1.1.1]pentyl)ethynyl]-

trimethylsilane (8),^[6]1-iodo-3-methylbicyclo[1.1.1]pentane (41),^[17]

1-(chloromethyl)-6-iodotricyclo[3.2.0.0^2,6]heptane (40),^[16,18]and an

ethereal solution of diazomethane^[25]were prepared according to

previously published procedures. 1,12-Dicarba-closo-dodecabor-

ane, 1,7-dicarba-closo-dodecaborane (36), CuBr, CuI, 1,4-diiodo-

benzene, 4,4Ј-diiodobiphenyl, 3,6-diiodopyridazine, chlorodiphen-

ylphosphane, chlorotrihexylsilane, iodobenzene, iodomethane, 1-

iodonaphthalene, methyl 4-bromobenzoate, methyl 2-bromobenzo-

ate, [(4-bromophenyl)ethynyl]trimethylsilane, dimethyl 5-bromo-

isophthalate, [Pd(PPh₃)₄], TBAF in THF, and 1,3,5-tribromobenz-

ene were purchased and used without further purification. Triethyl-

amine was distilled from CaH₂under argon immediately prior to

use. Acetone was dried with CaCl₂and distilled from P₄O₁₀prior

Figure 5. Molecular packing in crystals of the derivatives prepared.

(a), (b) Cross-like orientation of the rotational axes of the BCP ro-

tors in crystal lattices of the diester 13 and the diphenyl derivative

18, respectively. (c)–(g) Parallel orientation of rotational axes of the

rotors in molecules of (c) diketone 4, (d) disilyl derivative 7, (e) bis-

(phosphane) 10, (f) phosphane oxide 17, and (g) the three-cage de-

rivative 42. (h) In the diphosphane dioxide 16, the rotational axes

are oriented in three different directions. Hydrogen atoms have

been omitted for clarity.

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J. Kaleta, M. Necˇas, C. Mazal

FULL PAPER

to use. NBS was recrystallized from water and dried under vacuum

(1.97 mL, 11.0 mmol) was then added, and the reaction mixture

turned yellow immediately. Cooling was interrupted after 40 min,

and the yellow reaction mixture was stirred at room temperature

for 10 h. A white precipitate slowly dissolved during this time leav-

ing a clear yellow solution. The reaction mixture was diluted with

diethyl ether (80 mL), washed with concentrated aqueous NH₄Cl

(2ϫ40 mL) and water (1ϫ30 mL), and the yellow organic phase

1

prior to use. H, ¹³C, ¹¹B, and ³¹P NMR spectra were acquired at

25 °C with 300, 400, and 500 MHz spectrometers. ¹H and ¹³C

NMR spectra are referenced to residual solvent peaks. GC–MS

was performed with an instrument equipped with a fused silica

capillary column (cross-linked 5% phenyl methyl silicone). Diffrac-

tion data were collected with a KUMA KM-4 κ-axis CCD dif-

fractometer with Mo-K_αradiation (λ = 0.71073 Å). The structures was dried with Na₂SO₄. Volatiles were removed under reduced

were solved by direct methods and refined by standard methods pressure to leave a yellow oil. Column chromatography on silica

using SHELXTL.^[26]CCDC-871802 (for 1), -871803 (for 3), gel (hexane/CH₂Cl₂, 2:1) yielded 10 as a white crystalline solid

-871804 (for 4), -871805 (for 7), -871806 (for 10), -871807 (for 13),

-871808 (for 16), -871809 (for 17), -871810 (for 18), -871811 (for 32),

-871812 (for 33), -871813 (for 38), -871814 (for 41), and -871815

(for 42) contain the supplementary crystallographic data for this

paper. These data can be obtained free of charge from The Cam-

bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/

data_request/cif.

(824 mg, 40%). M.p. 128.9–132.4 °C. ¹H NMR (300 MHz, CDCl₃):

δ = 2.52 (s, 6 H, CH₂), 7.38–7.40 (m, 12 H, Ar-H), 7.62–7.67 (m,

8 H, Ar-H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 31.0, 59.2, 76.6,

107.3 (J = 2.61 Hz), 128.5 (J = 7.56 Hz), 129.0, 132.5 (J =

21.00 Hz), 136.1 (J = 6.38 Hz) ppm. ³¹P NMR (121 MHz, CDCl₃):

δ = –31.77 ppm. IR (KBr): ν = 3049, 2988, 2963, 2914, 2874, 2166,

˜

1584, 1478, 1433, 1237, 1096, 1070, 1026, 998, 745, 695 cm^–1. MS:

m/z (%) = 485 (45) [M]⁺, 484 (39) [M]⁺, 409 (27), 407 (100) [M –

Ph]⁺, 377 (30), 375 (86), 300 (13), 299 (65) [M – PPh₂]⁺, 297 (10),

283 (13), 265 (18), 252 (11), 233 (10), 221 (22), 220 (21), 207 (12),

189 (8), 183 (50) [PPh₂]⁺, 178 (10), 170 (8), 165 (18), 152 (11), 133

(12), 115 (19), 109 (20), 108 (47), 107 (69), 91 (21), 77 (58) [Ph]⁺,

1,3-Diethynylbicyclo[1.1.1]pentane (1):^[2,5,6]A solution of ammo-

nium fluoride (900 mg, 24.3 mmol) in water (10 mL) was added to

a solution of the disilyl derivative 7 (520 mg, 2 mmol) in diethyl

ether (7 mL), and the resulting mixture was stirred at room tem-

perature for 2 h. The ethereal layer was then separated and the

aqueous layer extracted with diethyl ether (3ϫ10 mL). The com-

bined organic layers were dried with Na₂SO₄, filtered, and carefully

concentrated at atmospheric pressure and 50 °C. The residue was

sublimed by Kugelrohr distillation (50 °C, 400 Torr) into a flask

cooled with liquid nitrogen. The diyne 1 was obtained as long white

needles (212 mg, 91%). M.p. 63–65 °C (ref.^[2]65–67 °C).

65 (12), 57 (12), 51 (41). HRMS (APCI): calcd. for [C₃₃H₂₆P₂

+

H]⁺485.1583; found 485.1574.

({3-[(Trimethylsilyl)ethynyl]bicyclo[1.1.1]pentyl}ethynyl)diphenyl-

phosphane (12): A solution of nBuLi in hexane (2.5 m, 720 μL,

1.8 mmol) was added dropwise to a solution of silane 8 (310 mg,

1.6 mmol) in THF (12 mL) at –78 °C. The colorless reaction mix-

ture was stirred at this temperature for 30 min, then at 0 °C for

10 min, and finally cooled back to –78 °C. Subsequently, Ph₂PCl

(359 μL, 2.0 mmol) was added to the reaction mixture, which

turned yellow immediately. Cooling was interrupted after 1 h, and

the yellow reaction mixture was stirred at room temperature for an

additional 10 h. The solution was diluted with diethyl ether

(40 mL) and washed with concentrated aq. NH₄Cl (2ϫ20 mL) and

water (1ϫ20 mL). The yellow organic phase was dried with

Na₂SO₄. The solvents were removed under reduced pressure, and

column chromatography on silica gel (hexane/CH₂Cl₂, 2:1) yielded

12 as white crystals (388 mg, 63%). M.p. 141.1–143.2 °C. ¹H NMR

(300 MHz, CDCl₃): δ = 0.22 (s, 9 H, CH₃), 2.44 (s, 6 H, CH₂),

7.32–7.42 (m, 6 H, Ar-H), 7.59–7.65 (m, 4 H, Ar-H) ppm. ¹³C

NMR (75 MHz, CDCl₃): δ = 0.02, 30.7, 59.1, 76.3 (J = 7.32 Hz),

84.8, 104.4, 107.5 (J = 2.72 Hz), 128.5 (J = 7.60 Hz), 128.9, 132.5

(J = 21.01 Hz), 136.1 (J = 6.48 Hz) ppm. ³¹P NMR (121 MHz,

3,3Ј-(Bicyclo[1.1.1]pentane-1,3-diyl)diprop-2-ynoic Acid (9): A solu-

tion of nBuLi in hexane (2.5 m, 4.00 mL, 10.000 mmol) was added

dropwise to a stirred solution of freshly sublimed diyne 1 (550 mg,

4.735 mmol) in THF (25 mL) at –78 °C. A white dense precipitate

formed immediately. The suspension was stirred at –78 °C for

40 min, heated to room temperature, and then cooled back to

–78 °C. Gaseous CO₂was bubbled into the solution through a

PTFE cannula at –78 °C for 20 min and at room temperature for

15 min. The white suspension was dissolved in 30% aqueous

NaHCO₃(50 mL) and the basic water phase was washed with di-

ethyl ether (3ϫ50 mL). The colorless water phase was then acidi-

fied with concentrated aqueous HCl (pH ≈ 1). The product was

salted out with NaCl, extracted with diethyl ether (4ϫ50 mL), and

the combined organic phases were dried with Na₂SO₄. Solvents

were removed under reduced pressure, and the remaining impuri-

ties were washed out from the resulting yellowish solid on a frit

with ice-cold CHCl₃(30 mL) and pentane (20 mL). Diacid 9 was

isolated as a snow-white crystalline solid (700 mg, 72%). M.p.

CDCl ): δ = –31.73 ppm. IR (KBr): ν = 3063, 2989, 2962, 2913,

˜

3

2877, 2167, 1477, 1434, 1247, 1115, 847, 763, 744, 721, 695 cm^–1.

GC–MS: m/z (%) = 371 (23) [M]⁺, 357 (7) [M – CH₃]⁺, 343 (1),

299 (18), 283 (5), 265 (8), 247 (4), 233 (7), 221 (22), 191 (4), 183

(15), 165 (5), 135 (30), 107 (13), 97 (6), 73 (100) [TMS]⁺, 59 (14), 45

(8). HRMS (APCI): calcd. for [C₂₄H₂₅PSi + H]⁺373.1536; found

373.1530.

1

243 °C (dec.). H NMR (300 MHz, [D₆]acetone): δ = 2.51 (s, 6 H,

CH₂), 10.75 (br. s, 2 H, OH) ppm. ¹³C NMR (75 MHz, [D₆]ace-

tone): δ = 30.6, 59.9, 74.1, 85.8, 154.9 ppm. IR (KBr): ν = 3065,

˜

3004, 2977, 2925, 2886, 2606, 2518, 2238, 1676, 1509, 1408, 1283,

1223, 1131, 914, 859, 755, 657, 602 cm^–1. MS: m/z (%) = 203 (Ͻ1)

[M]⁺, 159 (5) [M – COOH]⁺, 143 (6), 131 (13), 116 (10), 115 (100),

113 (6), 103 (27), 102 (10), 90 (8), 89 (21), 78 (17), 77 (25), 74 (6),

66 (6), 65 (15), 63 (27), 62 (13), 51 (39), 50 (33), 49 (8), 45 (10), 44

(62). HRMS (ESI): calcd. for [C₁₁H₇O₄]^–203.0350; found 203.0350.

[(3-Ethynylbicyclo[1.1.1]pentyl)ethynyl]diphenylphosphane (15):

A

solution of TBAF in THF (1.0 m, 1.00 mL, 1.0 mmol) was slowly

added to a solution of silyl–phosphane 12 (240 mg, 0.6 mmol) in

THF (5 mL) at room temperature, and the reddish reaction mixture

was stirred for 50 min, then diluted with diethyl ether (50 mL),

P,PЈ-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)bis(diphenylphos- washed with water (3ϫ20 mL), and dried with Na₂SO₄. Solvents

phane) (10): Freshly distilled diyne 1 (500 mg, 4.304 mmol) was dis-

solved in THF (25 mL), and the colorless solution was cooled to

–78 °C. Subsequently, a solution of nBuLi in hexane (2.5 m,

4.00 mL, 10.0 mmol) was added, and a dense white precipitate

formed. The suspension was stirred at –78 °C for 40 min, at room

temperature for 10 min, and then cooled back to –78 °C. Ph₂PCl

were removed under reduced pressure, and the resulting reddish

oil was purified by column chromatography on silica gel (hexane/

CH₂Cl₂, 2:1) to yield the pure product 15 as a white crystalline

solid (178 mg, 92%). M.p. 94.1–95.8 °C. ¹H NMR (300 MHz,

CDCl₃): δ = 2.14 (s, 1 H, ϵCH), 2.45 (s, 6 H, CH₂), 7.34–7.42 (m,

6 H, Ar-H), 7.59–7.66 (m, 4 H, Ar-H) ppm. ¹³C NMR (75 MHz,

8

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1,3-Diethynylbicyclo[1.1.1]pentane

CDCl₃): δ = 29.9, 30.8, 58.8, 68.4, 76.4 (J = 7.34 Hz), 82.3, 107.1

CDCl₃): δ = 2.07 (s, 1 H, ϵCH), 2.37 (s, 6 H, CH₂), 3.73 (s, 3 H,

(J = 2.98 Hz), 128.5 (J = 7.65 Hz), 128.9, 132.4 (J = 21.00 Hz), CH₃) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 29.1, 30.4, 52.7, 58.4,

136.0 (J = 6.29 Hz) ppm. ³¹P NMR (121 MHz, CDCl₃): δ =

–31.83 ppm. IR (KBr): ν = 3275, 3056, 2991, 2967, 2913, 2877, 2918, 2880, 2851, 2231, 1709, 1436, 1334, 1259, 1218, 1101, 1022,

68.6, 71.5, 81.6, 85.7, 153.7 ppm. IR (KBr): ν = 3271, 2996, 2963,

˜

2156, 1476, 1432, 1311, 1291, 1234, 1087, 1023, 913, 740, 693,

803, 747, 682 cm^–1. GC–MS: m/z (%) = 173 (2) [M]⁺, 159 (4) [M –

653 cm^–1. GC–MS: m/z (%) = 299 (17) [M]⁺, 283 (9), 265 (8), 252 CH₃]⁺, 143 (13) [M – OCH₃]⁺, 131 (9), 128 (4), 115 (100) [M –

(12), 233 (5), 221 (18), 207 (13), 191 (100), 178 (34), 165 (21), 133

(8), 107 (28), 91 (11), 77 (14) [Ph]⁺, 65 (6), 51 (13). HRMS (APCI):

calcd. for [C₂₁H₁₇P + H]⁺301.1141; found 301.1141.

COOCH₃]⁼, 103 (34), 89 (36), 77 (44), 75 (9), 63 (33), 51 (29).

HRMS (EI): calcd. for [C₁₁H₉O₂]⁺173.0603; found 173.0604.

P,PЈ-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)bis(diphenylphos-

phane oxide) (16): A solution of bis(phosphane) 10 (500 mg,

1.0 mmol) in CH₂Cl₂(15 mL) was mixed with 10% aqueous H₂O₂

(20 mL), and the resulting two-phase system was rapidly stirred at

room temperature for 45 min. Subsequently, an additional portion

of CH₂Cl₂(80 mL) was added, and the aqueous phase was sepa-

rated. The colorless organic phase was washed with water

(3ϫ30 mL) and dried with Na₂SO₄. Complete evaporation of

CH₂Cl₂provided the pure product 16 as white crystals (525 mg,

98%). M.p. 233.8–235.1 °C. ¹H NMR (300 MHz, CDCl₃): δ = 2.53

(s, 6 H, CH₂), 7.45–7.50 (m, 8 H, Ar-H), 7.53–7.57 (m, 4 H, Ar-

H), 7.76–7.81 (m, 8 H, Ar-H) ppm. ¹³C NMR (75 MHz, CDCl₃):

δ = 30.2 (J = 3.35 Hz), 58.7, 74.8 (J = 165.75 Hz), 103.9 (J =

28.39 Hz), 128.4 (J = 13.44 Hz), 130.7 (J = 11.19 Hz), 132.1 (J =

Dimethyl 3,3Ј-(Bicyclo[1.1.1]pentane-1,3-diyl)diprop-2-ynoate (13):

An ethereal solution of CH₂N₂was added dropwise to a solution

of diacid 9 (41 mg, 0.2 mmol) in diethyl ether (4 mL) at room tem-

perature until the reaction mixture turned yellow. The solution was

stirred for 10 min, and then the volatiles were removed under re-

duced pressure. Column chromatography on silica gel (hexane/ethyl

acetate, 2:1) yielded 13 as white crystals (45 mg, 96%). M.p. 165.3–

166.9 °C. ¹H NMR (300 MHz, CDCl₃): δ = 2.44 (s, 6 H, CH₂),

3.74 (s, 6 H, OCH₃) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 29.8,

52.7, 58.4, 71.9, 84.9, 153.6 ppm. IR (KBr): ν = 3008, 2963, 2922,

˜

2886, 2235, 1710, 1436, 1283, 1218, 1121, 967, 855, 753 cm^–1. GC–

MS: m/z (%) = 232 (69) [M]⁺, 217 (100) [M – CH₃]⁺, 201 (41) [M –

2CH₃]⁺, 189 (22), 173 (67) [M – CO₂CH₃]⁺, 157 (28) [M – CO₂CH₃

+ CH₃]⁺, 145 (73), 129 (24), 117 (15), 115 (94), 102 (42), 88 (37),

75 (18), 63 (43), 59 (40), 43 (21). HRMS (EI): calcd. for

[C₁₃H₁₁O₄]⁺231.0657; found 231.0659.

2.30 Hz), 132.4 (J

=

122.04 Hz) ppm. ³¹P NMR (121 MHz,

CDCl ): δ = 9.05 ppm. IR (KBr): ν = 3052, 3000, 2919, 2882, 2184,

˜

3

1482, 1439, 1233, 1202, 1121, 1070, 997, 751, 726, 697 cm^–1. MS:

m/z (%) = 517 (46), 515 (100) [M]⁺, 488 (9), 487 (19), 440 (9), 439

(32) [M – Ph]⁺, 425 (8), 411 (9), 391 (8), 331 (19), 315 (14) [M –

POPh₂]⁺, 265 (10), 202 (10), 201 (39) [POPh₂]⁺, 189 (7), 185 (7),

183 (33), 78 (15), 77 (74) [Ph]⁺, 65 (7), 51 (55), 50 (15), 47 (49).

HRMS (APCI): calcd. for [C₃₃H₂₆O₂P₂+ H]⁺517.1481; found

517.1472. C₃₃H₂₆O₂P₂+ H₂O: calcd. C 74.15, H 5.28, P 11.59;

found C 74.43, H 5.11, P 11.73.

Methyl

3-{3-[(Trimethylsilyl)ethynyl]bicyclo[1.1.1]pentyl}prop-2-

ynoate (14): A flame-dried Schlenk flask was charged with a solu-

tion of monosilylated diyne 8 (411 mg, 2.2 mmol) in dry THF

(15 mL), and nBuLi (2.5 m, 920 μL, 2.3 mmol) was added at

–78 °C. The colorless solution was stirred at –78 °C for 60 min,

then heated to 0 °C and cooled back to –78 °C. Gaseous CO₂was

bubbled into the solution through a PTFE cannula at –78 °C for

15 min and at room temperature for an additional 15 min. A white

solid precipitated during this time. The reaction mixture was di-

luted with water (30 mL) and washed with CHCl₃(2ϫ20 mL). The

water phase was acidified with concentrated HCl (pH ≈ 1), and the

product was salted out with NaCl and extracted with diethyl ether

(4ϫ20 mL). The combined ethereal phases were dried with

Na₂SO₄. Evaporation of the solvents under reduced pressure pro-

vided crude 11 as a white solid (475 mg), which was dissolved in

diethyl ether (10 mL). An ethereal solution of diazomethane was

then added at room temperature, and the yellow solution was

stirred for an additional 10 min. The volatiles were removed under

reduced pressure. Column chromatography on silica gel (hexane/

CHCl₃, 1:1) afforded the product 14 as white needles (421 mg,

78%). M.p. 90.3–91.9 °C. ¹H NMR (300 MHz, CDCl₃): δ = 0.13

(s, 9 H, CH₃), 2.37 (s, 6 H, CH₂), 3.74 (s, 3 H, OCH₃) ppm. ¹³C

NMR (75 MHz, CDCl₃): δ = –0.2, 28.9, 31.1, 52.5, 58.6, 71.5, 85.1,

[(3-Ethynylbicyclo[1.1.1]pentyl)ethynyl]diphenylphosphane

Oxide

(17): Oxidation of the phosphane 15 (155 mg, 0.5 mmol) according

to the previous procedure afforded the pure product 17 as a color-

less oil that slowly crystallized (161 mg, 98%). M.p. 156.3–

157.9 °C. ¹H NMR (300 MHz, CDCl₃): δ = 2.06 (s, 1 H, ϵCH),

2.36 (s, 6 H, CH₂), 7.37–7.46 (m, 6 H, Ar-H), 7.71–7.78 (m, 4 H,

Ar-H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 29.5 (J = 3.56 Hz),

30.3, 58.5, 68.7, 74.2 (J = 167.61 Hz), 81.4, 104.7 (J = 28.86 Hz),

128.4 (J = 13.42 Hz), 130.6 (J = 11.35 Hz), 132.0 (J = 2.94 Hz),

132.6 (J = 121.85 Hz) ppm. ³¹P NMR (121 MHz, CDCl₃): δ =

8.89 ppm. IR (KBr): ν = 3273, 3070, 3003, 2972, 2920, 2885, 2172,

˜

1437, 1230, 1196, 1117, 924, 775, 750, 723, 692, 648 cm^–1. GC–MS:

m/z (%) = 316 (98) [M]⁺, 287 (23), 271 (11), 253 (26), 239 (33), 220

(12), 201 (42), 191 (97), 183 (74), 165 (60), 152 (35), 127 (31), 115

(52), 107 (22), 91 (33), 77 (100) [Ph]⁺, 63 (23), 51 (54). HRMS

(APCI): calcd. for [C₂₁H₁₇OP + H]⁺317.1090; found 317.1085.

General Procedure for the Sonogashira–Hagihara Cross-Coupling

Reaction (GP): A flame-dried Schlenk flask was charged with a

haloarene (3 equiv.), [Pd(PPh₃)₄] (8 mol-%), and CuI (6 mol-%).

After three successive vacuum/argon cycles, dry and degassed THF

(2.50 mL) and triethylamine (2.50 mL) were added through a sy-

ringe. Finally, a solution of freshly sublimed diyne 1 (1 equiv.) in

THF (2.50 mL) was added to the reaction mixture. The yellow

solution was stirred at room temperature (in the case of iodoarenes)

or at 55 °C (in the case of bromoarenes) for 16 h. A white solid

precipitated. The yellow reaction mixture was cooled to room tem-

perature, diluted with diethyl ether or CH₂Cl₂(100–150 mL), and

washed with saturated aqueous NH₄Cl (3ϫ30 mL) and water

(1ϫ20 mL). The yellow organic phase was dried with Na₂SO₄. Af-

ter evaporation of the volatiles, the pure products were isolated by

column chromatography on silica gel or recrystallized.

85.8, 103.5, 153.5 ppm. IR (KBr): ν = 2995, 2960, 2916, 2881, 2229,

˜

2162, 1712, 1437, 1336, 1259, 1213, 1115, 980, 849, 758, 719 cm^–1.

GC–MS: m/z (%) = 245 (2) [M]⁺, 231 (41) [M – CH₃]⁺, 215 (13),

201 (35), 187 (12) [M – COOCH₃]⁺, 173 (48) [M – TMS]⁺, 157

(18), 145 (59), 129 (30), 115 (18), 107 (21), 97 (26), 89 (89), 73 (78)

[TMS]⁺, 59 (100), 43 (35). HRMS (EI): calcd. for [C₁₄H₁₈O₂Si +

Na]⁺269.0968; found 269.0968.

Methyl 3-(3-Ethynylbicyclo[1.1.1]pentyl)prop-2-ynoate: The ester 14

(180 mg, 0.73 mmol) was desilylated in THF (8 mL) according to

the procedure previously used for 15; however, only a small excess

of TBAF solution in THF (1.0 m, 850 μL, 0.85 mmol) and a lower

temperature (–15 °C) were used. Column chromatography on silica

gel (hexane/CH₂Cl₂, 1:1) afforded the pure product as a white crys-

talline solid (88 mg, 69%). M.p. 84.4–85.5 °C. ¹H NMR (300 MHz,

Eur. J. Org. Chem. 0000, 0–0

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FULL PAPER

1,3-Bis(phenylethynyl)bicyclo[1.1.1]pentane (18): Compound 18 was

79.6, 91.1, 127.6, 129.4, 129.5, 131.7, 166.5 ppm. IR (KBr): ν =

˜

prepared according to the GP from iodobenzene (1.282 g,

2991, 2947, 2914, 2877, 2848, 2225, 1716, 1603, 1437, 1404, 1281,

6.3 mmol, 703 μL) and the diyne 1 (243 mg, 2.1 mmol). Pure 18 1194, 1173, 1111, 1014, 964, 854, 769 cm^–1. MS: m/z (%) = 384 (33)

(485 mg, 86%) was isolated as a white solid by column chromatog-

raphy on silica gel (hexane/CH₂Cl₂, 4:1). M.p. 173.4–174.8 °C. H

NMR (500 MHz, CDCl₃): δ = 2.49 (s, 6 H, CH₂), 7.29–7.30 (m, 6

H, Ar-H), 7.42–7.44 (m, 4 H, Ar-H) ppm. ¹³C NMR (125 MHz,

CDCl₃): δ = 30.8, 59.0, 80.1, 88.2, 122.9, 128.1, 128.2, 131.8 ppm.

[M]⁺, 369 (3) [M – CH₃]⁺, 353 (12) [M – OCH₃]⁺, 325 (27) [M –

CO₂CH₃]⁺, 310 (7) [M – CO₂CH₃– CH₃]⁺, 293 (9), 265 (100) [M –

2CO₂CH₃]⁺, 239 (8), 189 (9), 185 (8), 161 (16), 139 (15), 126 (20),

115 (11), 97 (9), 83 (13), 69 (11), 59 (34) [CO₂CH₃]⁺. HRMS

(APCI): calcd. for [C₂₅H₂₀O₄+ H]⁺385.1434; found 385.1434.

1

IR (KBr): ν = 3080, 3060, 3049, 3033, 2993, 2983, 2963, 2910, 2874,

˜

4,4Ј-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)dibenzoic Acid: The

diester 23 (60 mg, 0.16 mmol) was suspended in a solution of KOH

(330 mg, 5.88 mmol) in MeOH (15 mL) and water (10 mL). The

suspension was stirred at 60 °C for 14 h. During this time, the sus-

pension slowly disappeared leaving a clear solution. The reaction

mixture was cooled to room temperature and acidified with concen-

trated HCl (pH ≈ 1). A white precipitate was filtered off and

washed with water (2ϫ10 mL), CHCl₃(2ϫ15 mL), and diethyl

ether (2ϫ10 mL). The diacid was isolated as grayish crystals

(36 mg, 64%). M.p. Ͼ260 °C (dec.). ¹H and ¹³C NMR spectra were

not recorded due to the poor solubility of in common solvents. IR

2230, 1597, 1571, 1490, 1442, 1302, 1205, 1177, 1070, 1027, 914,

841, 755, 691 cm^–1. MS: m/z (%) = 268 (49) [M]⁺, 267 (52), 265

(50), 253 (38), 252 (100), 239 (17), 226 (12), 215 (9), 202 (5), 189

(21), 176 (4), 165 (18), 152 (11), 139 (14), 127 (30), 115 (19), 101

(7), 89 (6), 77 (20), 63 (8), 51 (9). HRMS (EI): calcd. for

[C₂₁H₁₆]⁺268.1252; found 268.1249. C₂₁H₁₆(268.36): calcd. C

93.99, H 6.01; found C 93.90, H 5.84.

1,3-Bis(1-naphthylethynyl)bicyclo[1.1.1]pentane (19): Compound 19

was prepared from 1-iodonaphthalene (283 μL, 1.9 mmol) and the

diyne 1 (90 mg, 0.8 mmol) according to the GP. The reaction mix-

ture was stirred at 45 °C for 6 h. Column chromatography on silica

gel (hexane/CH₂Cl₂, 4:1) provided the hydrocarbon 19 as a white

solid (252 mg, 88%). M.p. 185.4–186.8 °C (dec.). ¹H NMR

(400 MHz, CDCl₃): δ = 2.68 (s, 6 H, CH₂), 7.43 (dd, J₁= 7.21, J₂=

8.21 Hz, 2 H, Ar-H), 7.54 (ddd, J₁= 1.25, J₂= 6.89, J₃= 8.06 Hz, 2

H, Ar-H), 7.61 (ddd, J₁= 1.32, J₂= 6.86, J₃= 8.30 Hz, 2 H, Ar-

H), 7.70 (dd, J₁= 1.07, J₂= 7.14 Hz, 2 H, Ar-H), 7.83 (dd, J₁=

1.79, J₂= 8.29 Hz, 2 H, Ar-H), 7.86 (ddd, J₁= 0.82, J₂= 2.07, J₃=

8.06 Hz, 2 H, Ar-H), 8.34 (ddd, J₁= 1.02, J₂= 1.85, J₃= 8.46 Hz, 2

H, Ar-H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 31.2, 59.4, 78.3,

93.2, 120.6, 125.2, 126.1, 126.3, 126.7, 128.3, 128.6, 130.6, 133.2,

(KBr): ν = 3072, 2987, 2910, 2879, 2818, 2669, 2549, 2224, 1684,

˜

1603, 1556, 1421, 1313, 1290, 1174, 1109, 1014, 858, 768 cm^–1. MS:

m/z (%) = 356 (43) [M]⁺, 311 (40) [M – COOH]⁺, 265 (100) [M –

2COOH]⁺, 252 (67), 239 (11), 189 (18), 165 (18), 152 (8), 127 (12),

115 (11), 77 (9). HRMS (EI): calcd. for [C₂₃H₁₆O₄]⁺356.1049;

found 356.1052.

Tetramethyl 5,5Ј-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)diiso-

phthalate (24): Compound 24 was prepared from dimethyl 5-bro-

moisophthalate (487 mg, 1.8 mmol) and the diyne 1 (90 mg,

0.8 mmol) according to the GP. Column chromatography of the

crude product on silica gel (CH₂Cl₂) provided the tetraester 24 as

a white solid (346 mg, 89%). M.p. Ͼ170 °C (dec.). ¹H NMR

(400 MHz, CDCl₃): δ = 2.50 (s, 6 H, CH₂), 3.94 (s, 12 H, OCH₃),

8.25 (dd, J₁= 0.61, J₂= 1.61 Hz, 4 H, Ar-H), 8.58 (dt, J₁= 0.82,

J₂= 1.60 Hz, 2 H, Ar-H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

30.7, 52.5, 58.9, 78.4, 90.0, 123.9, 130.0, 130.8, 136.6, 165.5 ppm.

133.5 ppm. IR (KBr): ν = 3086, 3055, 3045, 2990, 2967, 2914, 2876,

˜

2214, 1585, 1532, 1505, 1480, 1460, 1435, 1397, 1375, 1334, 1297,

1253, 1219, 1178, 1156, 1119, 1017, 949, 902, 861, 796, 771, 745,

696, 633, 610, 567, 543, 457 cm^–1. MS: m/z (%) = 368.2 (14) [M]⁺,

352.1 (11), 339.1 (8), 326.1 (5), 277.1 (72), 262.1 (100), 239.1 (4),

215.1 (6), 199.0 (13), 183.0 (67), 152.1 (16), 141.0 (7), 108.0 (21),

77.0 (11), 51.0 (9). HRMS (EI): calcd. for [C₂₉H₂₀]⁺368.1565;

found 368.1563. C₂₉H₂₀(368.48): calcd. C 94.53, H 5.47; found C

94.20, H 5.46.

IR (KBr): ν = 3098, 3074, 2998, 2979, 2953, 2919, 2879, 2850, 2227,

˜

1722, 1597, 1454, 1444, 1434, 1343, 1306, 1264, 1248, 1206, 1127,

1108, 1086, 1004, 977, 957, 921, 875, 784, 757, 722, 676, 564 cm^–1.

MS, (ESI): m/z (%) = 501 (10) [M + H]⁺, 523 (100) [M + Na]⁺.

HRMS (ESI): calcd. for [C₂₉H₂₄O₈+ H]⁺501.15439; found

501.15411. C₂₉H₂₄O₈(500.50): calcd. C 69.59, H 4.83; found C

69.68, H 4.71.

1,3-Bis[(4-iodophenyl)ethynyl]bicyclo[1.1.1]pentane (20): Compound

20 was prepared from 1,4-diiodobenzene (7.100 g, 21.5 mmol) and

the diyne 1 (500 mg, 4.3 mmol) according to the GP. Recrystalli-

zation from CHCl₃yielded pure 20 as white crystals (1.648 g, 74%).

Dimethyl 2,2Ј-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)dibenzoate

(25): Compound 25 was prepared from methyl 2-bromobenzoate

(465 μL, 3.3 mmol) and the diyne 1 (150 mg, 1.3 mmol) according

to the GP. The reaction mixture was stirred at 55 °C for 18 h. Col-

umn chromatography of the crude product on silica gel (CH₂Cl₂)

provided the diester 25 as a white solid (322 mg, 65%). M.p. 134.6–

135.8 °C. ¹H NMR (400 MHz, CDCl₃): δ = 2.53 (s, 6 H, CH₂),

3.92 (s, 6 H, OCH₃), 7.34 (ddd, J₁= 1.38, J₂= 7.70, J₃= 7.65 Hz,

2 H, Ar-H), 7.43 (ddd, J₁= 1.42, J₂= 7.58, J₃= 7.70 Hz, 2 H, Ar-

H), 7.53 (dd, J₁= 0.97, J₂= 7.75 Hz, 2 H, Ar-H), 7.91 (dd, J₁=

1.03, J₂= 7.86 Hz, 2 H, Ar-H) ppm. ¹³C NMR (100 MHz, CDCl₃):

δ = 31.2, 52.0, 59.1, 78.8, 93.4, 123.4, 127.8, 130.3, 131.5, 132.3,

1

M.p. Ͼ235 °C (dec.). H NMR (300 MHz, CDCl₃): δ = 2.46 (s, 6

H, CH₂), 7.10–7.14 (m, 4 H, Ar-H), 7.60–7.65 (m, 4 H, Ar-H) ppm.

¹³C NMR (75 MHz, CDCl₃): δ = 30.8, 58.9, 79.3, 89.6, 94.0, 122.4,

133.3, 137.4 ppm. IR (KBr): ν = 2989, 2910, 2873, 1900, 1479,

˜

1387, 1296, 1107, 1055, 1003, 818, 779, 700 cm^–1. MS: m/z (%) =

520 (20) [M]⁺, 393 (4) [M – I]⁺, 265 (98) [M – 2I]⁺, 239 (9), 213

(6), 169 (14), 139 (15), 126 (41) [I]⁺, 112 (14), 97 (21), 83 (26), 72

(67), 59 (100). HRMS (APCI): calcd. for [C₂₁H₁₄I₂+ H]⁺520.9258;

found 520.9253.

Dimethyl 4,4Ј-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)dibenzoate

(23): Compound 23 was prepared from methyl 4-bromobenzoate

(2.777 g, 12.9 mmol) and the diyne 1 (500 mg, 4.3 mmol) according

to the GP. The reaction mixture was stirred at 55 °C for 18 h. After

general workup, column chromatography on silica gel (hexane/

CH₂Cl₂, 1:20) followed by recrystallization from CHCl₃provided

the diester 23 as a white solid (1.126 g, 68%). M.p. 244.9–246.8 °C.

¹H NMR (300 MHz, CDCl₃): δ = 2.50 (s, 6 H, CH₂), 3.91 (s, 6 H,

OCH₃), 7.46 (d, J = 8.27 Hz, 4 H, Ar-H), 7.96 (d, J = 8.28 Hz, 4

134.3, 166.7 ppm. IR (KBr): ν = 3069, 3030, 2990, 2967, 2931,

˜

2876, 2841, 2228, 1736, 1717, 1595, 1567, 1485, 1445, 1434, 1425,

1294, 1271, 1253, 1193, 1164, 1134, 1079, 1058, 1043, 961, 830,

800, 780, 760, 705, 664 cm^–1. MS: m/z (%) = 384 (8) [M]⁺, 369 (55)

[M – CH₃]⁺, 354 (14) [M – OCH₃]⁺, 337 (100) [M – OCH₃

–

CH₃]⁺, 325 (9) [M – CO₂CH₃]⁺, 309 (31) [M – CO₂CH₃– CH₃]⁺,

293 (13), 281 (34), 265 (23) [M – 2CO₂CH₃]⁺, 252 (37), 239 (11),

H, Ar-H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 30.9, 52.2, 59.0, 226 (6), 209 (5), 165 (7), 126 (6), 114 (9). HRMS (EI): calcd. for

10

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1,3-Diethynylbicyclo[1.1.1]pentane

[C₂₅H₂₀O₄]⁺384.1362; found 384.1363. C₂₅H₂₀O₄(384.43): calcd.

C 78.11, H 5.24; found C 77.86, H 5.18.

3033, 2990, 2968, 2914, 2878, 2223, 2112, 1619, 1585, 1570, 1505,

1447, 1400, 1334, 1325, 1292, 1266, 1247, 1217, 1170, 1158, 1105,

1019, 969, 955, 865, 799, 775, 740, 662, 652, 603, 564, 540, 505,

463, 451, 428 cm^–1. MS: m/z (%) = 242.1 (36) [M]⁺, 241.1 (100)

[M – H]⁺, 239.1 (87), 226.1 (70), 215.1 (23), 202.1 (11), 189.1 (12),

176.1 (69), 165.1 (16), 151.1 (29), 126.0 (8), 119.5 (7), 101.4 (4),

1,3-Bis({4-[(trimethylsilyl)ethynyl]phenyl}ethynyl)bicyclo[1.1.1]-

pentane (26): Compound 26 was prepared from [(4-bromophenyl)-

ethynyl]trimethylsilane (633 mg, 2.5 mmol) and the diyne 1

(112 mg, 1.0 mmol) according to the GP. The reaction mixture was

stirred at 55 °C for 18 h. The product precipitated from the reaction

mixture. Consecutive washing with saturated aqueous NH₄Cl

(2ϫ15 mL), water (2ϫ20 mL), diethyl ether (3ϫ10 mL), and hex-

87.0 (5), 75.0 (5), 63.0 (6), 51.0 (5). HRMS (EI): calcd. for

+

[C₁₉H₁₄

]

242.1096; found 242.1084. C₁₉H₁₄(242.32): calcd. C

94.18, H 5.82; found C 93.94, H 5.96.

ane (3ϫ10 mL) and drying in vacuo afforded 26 in satisfactory ({3-[(4Ј-Iodobiphenyl-4-yl)ethynyl]bicyclo[1.1.1]pentyl}ethynyl)tri-

purity as a white solid (310 mg, 70%). M.p. Ͼ265 °C (dec.). ¹H

NMR (400 MHz, CDCl₃): δ = 0.24 (s, 18 H, CH₃), 2.46 (s, 6 H,

CH₂), 7.33 (d, J = 8.58 Hz, 4 H, Ar-H), 7.38 (d, J = 8.57 Hz, 4 H,

Ar-H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = –0.1, 30.9, 59.0,

methylsilane (28): Compound 28 was prepared from 4,4Ј-diiodobi-

phenyl (2.910 g, 7.2 mmol) and the monosilylated diyne 8 (450 mg,

2.4 mmol) according to the GP. Slow-elution column chromatog-

raphy on silica gel (hexane/CHCl₃, 4:1) provided the iodo derivative

1

79.9, 90.1, 96.2, 104.6, 122.8, 123.0, 131.5, 131.8 ppm. IR (KBr): ν

28 as a white solid (531 mg, 48%). M.p. 257.2–258.1 °C (dec.). H

˜

= 3087, 3047, 2985, 2960, 2908, 2873, 2223, 2154, 1602, 1507, 1497,

1412, 1405, 1298, 1254, 1245, 1224, 1175, 1103, 1014, 865, 847,

835, 760, 699, 641, 551 cm^–1. MS: m/z (%) = 460 (100) [M]⁺, 445

NMR (400 MHz, CDCl₃): δ = 0.16 (s, 9 H, CH₃), 2.41 (s, 6 H,

CH₂), 7.29–7.31 (m, 2 H, Ar-H), 7.45–7.46 (m, 4 H, Ar-H), 7.75–

7.76 (m, 2 H, Ar-H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 0.01,

(49) [M – CH₃]⁺, 387 (9) [M – TMS]⁺, 371 (13), 357 (27), 215 (18), 30.6, 30.8, 59.1, 79.7, 84.8, 89.3, 93.4, 104.6, 122.3, 126.6, 128.8,

2 0 7 ( 1 6 ) , 7 3 ( 4 9 ) [ T M S ] ⁺. H R M S ( E I ) : c a l c d . f o r

[C₃₁H₃₂Si₂]⁺460.2043; found 460.2050. C₃₁H₃₂Si₂(460.77): calcd.

C 80.81, H 7.00; found C 80.56, H 6.89.

132.3, 137.9, 139.6, 139.8 ppm. IR (KBr): ν = 3038, 2988, 2963,

˜

2912, 2876, 2221, 2163, 1585, 1557, 1518, 1480, 1448, 1411, 1387,

1307, 1263, 1250, 1213, 1191, 1120, 1102, 1085, 1064, 1000, 920,

861, 852, 843, 814, 761, 728, 718, 701, 623, 558, 519, 507, 497 cm^–1.

MS: m/z (%) = 466.1 (42) [M]⁺, 451.0 (72) [M – CH₃]⁺, 435.0 (15),

423.0 (12), 407.0 (11), 393.0 (13) [M – TMS]⁺, 361.0 (13), 339.2

(17) [M – I]⁺, 324.1 (11), 309.1 (23), 279.1 (11), 265.1 (23), 239.1

(10), 215.1 (12), 200.1 (24), 189.1 (14), 127.9 (34) [I]⁺, 97.0 (15),

73.0 (100) [TMS]⁺, 59.0 (18), 44.0 (11). HRMS (EI): calcd. for

[C₂₄H₂₃ISi]⁺466.0614; found 466.0606. UV/Vis (CH₂Cl₂): λ_max(ε)

= 290 (44.7ϫ10³m^–1cm^–1) nm. C₂₄H₂₃ISi (466.44): calcd. C 61.80,

H 4.97; found C 61.59, H 4.93.

Trimethyl{[3-(1-naphthylethynyl)bicyclo[1.1.1]pentyl]ethynyl}silane

(27): Compound 27 was prepared from 1-iodonaphthalene (263 μL,

1.8 mmol) and the monosilylated diyne 8 (320 mg, 1.7 mmol) ac-

cording to the GP. Column chromatography of the crude product

on silica gel (hexane/CH₂Cl₂, 4:1) provided the silyl derivative 27

as a white crystalline solid (358 mg, 67%). M.p. 128.3–129.7 °C. ¹H

NMR (400 MHz, CDCl₃): δ = 0.20 (s, 9 H, CH₃), 2.51 (s, 6 H,

CH₂), 7.40 (dd, J₁= 7.20, J₂= 8.24 Hz, 1 H, Ar-H), 7.51 (ddd, J₁

= 1.33, J₂= 6.88, J₃= 8.09 Hz, 1 H, Ar-H), 7.58 (ddd, J₁= 1.40,

J₂= 6.86, J₃= 8.32 Hz, 1 H, Ar-H), 7.65 (dd, J₁= 1.16, J₂

=

3,6-Bis({3-[(trimethylsilyl)ethynyl]bicyclo[1.1.1]pentyl}ethynyl)pyrid-

azine (29): Compound 29 was prepared from 3,6-diiodopyridazine

(111 mg, 0.335 mmol) and the monosilylated diyne 8 (140 mg,

0.7 mmol) according to the GP. Column chromatography on silica

gel (CH₂Cl₂) provided the pyridazine derivative 29 as a white crys-

talline solid (99 mg, 0.219 mmol, 65%). M.p. Ͼ160 °C (dec.). ¹H

NMR (500 MHz, CDCl₃): δ = 0.15 (s, 18 H, CH₃), 2.43 (s, 12 H,

CH₂), 7.40 (s, 2 H, Ar-H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ =

–0.1, 30.0, 31.2, 58.9, 76.7, 85.2, 94.7, 104.0, 128.7, 145.5 ppm. IR

7.16 Hz, 1 H, Ar-H), 7.83 (ddd, J₁= 4.51, J₂= 7.68, J₃= 14.70 Hz,

2 H, Ar-H), 8.29 (ddd, J₁= 1.12, J₂= 2.19, J₃= 8.28 Hz, 1 H, Ar-

H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 0.04, 30.7, 30.8, 59.2,

78.0, 84.8, 93.2, 104.6, 120.5, 125.1, 126.1, 126.3, 126.7, 128.2,

128.5, 130.5, 133.1, 133.4 ppm. IR (KBr): ν = 3088, 3059, 3047,

˜

2986, 2963, 2913, 2877, 2163, 1633, 1586, 1507, 1461, 1448, 1401,

1334, 1270, 1250, 1218, 1173, 1157, 1142, 1116, 1010, 966, 950,

918, 863, 847, 796, 772, 760, 724, 712, 700, 623, 601, 567, 514, 458,

437, 421 cm^–1. MS: m/z (%) = 314.1 (59) [M]⁺, 299.1 (63) [M – (KBr): ν = 2991, 2965, 2915, 2900, 2879, 2229, 2165, 1570, 1557,

˜

CH₃]⁺, 283.1 (33), 269.1 (21), 255.1 (20), 239.1 (92), 226.1 (30),

215.1 (36), 202.1 (24), 189.1 (29), 176.1 (58), 165.1 (21), 151.1 (23),

1531, 1507, 1486, 1449, 1408, 1336, 1269, 1251, 1120, 1101, 920,

857, 846, 760, 720, 701, 621 cm^–1. MS: m/z (%) = 452.2 (31) [M]⁺,

121.0 (6), 107.0 (11), 97.0 (16), 83.0 (12), 73.0 (100) [TMS]⁺, 59.0 437.2 (100) [M – CH₃]⁺, 421.2 (42), 407.1 (9), 379.2 (29) [M –

(20), 43.0 (8). HRMS (EI): calcd. for [C₂₂H₂₂Si]⁺314.1491; found

314.1484. C₂₂H₂₂Si (314.50): calcd. C 84.02, H 7.05; found C 83.81,

H 7.13.

TMS]⁺, 363.1 (38), 349.1 (53), 337.1 (10), 307.1 (14), 277.1 (13),

255.1 (7), 240.1 (8), 226.1 (9), 202.1 (5), 189.1 (6), 138.1 (3), 123.1

(11). HRMS (EI): calcd. for [C₂₈H₃₂N₂Si₂]⁺452.2104; found

452.2099. C₂₈H₃₂N₂Si₂(452.75): calcd. C 74.28, H 7.12, N 6.19;

found C 74.46, H 7.38, N 6.11.

1-Ethynyl-3-(1-naphthylethynyl)bicyclo[1.1.1]pentane: The silyl de-

rivative 27 (159 mg, 0.5 mmol) was desilylated according to the pro-

cedure previously used for compound 15 with TBAF in THF

(1.0 m, 800 μL, 0.8 mmol) at room temperature. Column

chromatography on silica gel (hexane/CH₂Cl₂, 4:1) afforded the

pure product as a white solid (116 mg, 95%). M.p. 85.6–87.0 °C.

1,3,5-Tris({3-[(trimethylsilyl)ethynyl]bicyclo[1.1.1]pentyl}ethynyl)-

benzene (31): A flame-dried Schlenk flask was charged with the

silyldiyne 8 (130 mg, 0.690 mmol), 1,3,5-tribromobenzene (72 mg,

0.215 mmol), [Pd(PPh₃)₄] (32 mg, 0.028 mmol, 4 mol-%), and CuI

¹H NMR (400 MHz, CDCl₃): δ = 2.15 (s, 1 H, ϵCH), 2.52 (s, 6 (4 mg, 0.021 mmol, 3 mol-%). After three successive vacuum/argon

H, CH₂), 7.40 (dd, J₁= 7.38, J₂= 8.06 Hz, 1 H, Ar-H), 7.52 (ddd,

cycles, dry and degassed THF (4 mL) and triethylamine (2 mL)

were added through syringe. The dark solution was stirred at 55 °C

for 96 h. A white solid precipitated. The reaction mixture was co-

oled to room temperature, diluted with toluene (50 mL), and

washed with water (3ϫ20 mL). The dark organic phase was dried

with Na₂SO₄. After evaporation of the volatiles, the pure product

31 was isolated by column chromatography on silica gel (hexane/

CHCl₃, 2:1) as white crystals (53 mg, 37%). M.p. Ͼ230 °C (dec.).

J₁= 1.19, J₂= 6.87, J₃= 7.98 Hz, 1 H, Ar-H), 7.58 (ddd, J₁

=

1.27, J₂= 6.90, J₃= 8.29 Hz, 1 H, Ar-H), 7.65 (dd, J₁= 0.77, J₂=

7.11 Hz, 1 H, Ar-H), 7.82 (ddd, J₁= 4.55, J₂= 7.23, J₃= 8.19 Hz, 2

H, Ar-H), 8.28 (ddd, J₁= 0.75, J₂= 1.66, J₃= 8.32 Hz, 1 H, Ar-

H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 30.1, 30.9, 58.9, 68.2,

78.1, 82.6, 92.9, 120.5, 125.1, 126.1, 126.3, 126.7, 128.2, 128.6,

130.5, 133.1, 133.4 ppm. IR (KBr): ν = 3286, 3088, 3059, 3045,

˜

Eur. J. Org. Chem. 0000, 0–0

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J. Kaleta, M. Necˇas, C. Mazal

FULL PAPER

¹H NMR (300 MHz, CDCl₃): δ = 0.15 (s, 27 H, CH₃), 2.35 (s, 18 1443, 1230, 1097, 802 cm^–1. GC–MS: m/z (%) = 368 (1) [M]⁺, 241

H, CH₂), 7.32 (s, 3 H, Ar-H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ (11) [M – I]⁺, 177 (7), 165 (3), 127 (4) [I]⁺, 114 (100), 88 (24), 74

= 0.01, 30.3, 30.8, 59.0, 78.5, 84.8, 89.3, 104.4, 123.4, 134.3 ppm.

(6), 63 (16), 50 (23). HRMS (EI): calcd. for [C₉H₆I₂]⁺367.8559;

found 367.8560.

IR (KBr): ν = 2987, 2964, 2916, 2879, 2164, 1583, 1417, 1252, 1095,

˜

856, 760, 723 cm^–1. MS: m/z (%) = 636 (1) [M]⁺, 621 (1) [M –

CH₃]⁺, 563 (Ͻ1) [M – TMS]⁺, 547 (Ͻ1) [M – TMS – CH₃]⁺, 533

(1), 517 (1), 503 (1), 490 (1) [M – 2TMS]⁺, 473 (2), 459 (3), 449 (1),

431 (2), 417 (2) [M – 3TMS]⁺, 401 (2), 357 (1), 303 (Ͻ1), 155 (2),

97 (8), 73 (100) [TMS]⁺, 59 (4). HRMS (EI): calcd. for

[C₄₂H₄₈Si₃]⁺636.3064; found 636.3077.

1,3-Bis{[12-(trihexylsilyl)-1,12-dicarba-closo-dodecaboran-1-yl]eth-

ynyl}bicyclo[1.1.1]pentane (35): A flame-dried Schlenk flask was

charged with trihexylsilyl-p-carborane 34 (970 mg, 2.3 mmol) in

dry THF (10 mL). The solution was cooled to –78 °C, and a solu-

tion of nBuLi in hexane (2.5 m, 940 μL, 2.350 mmol) was added

dropwise. After 15 min, the cooling was interrupted, and the reac-

tion mixture was heated to room temperature and stirred for

60 min. The colorless solution was cooled to –78 °C, and CuBr

(344 mg, 2.4 mmol) was added. The reaction mixture was stirred at

that temperature for 15 min, then heated up to room temperature

and vigorously stirred for an additional 90 min. The reaction mix-

ture turned from bright to dark green during this time. A solution

of dibromodiyne 32 (301 mg, 1.1 mmol) in dry THF (5 mL) was

added, and the mixture was stirred at 45 °C for 60 h. The crude

reaction mixture was cooled to room temperature, diluted with

CH₂Cl₂(150 mL), washed with water (3ϫ40 mL), and the clear

green organic phase was dried with Na₂SO₄. Solvents were evapo-

rated under reduced pressure, and most of the impurities were re-

moved by repeated (3ϫ) column chromatography on silica gel (hex-

ane). The crude product obtained as colorless oil was dissolved in

THF and precipitated by MeOH to yield pure 35 as a white crystal-

line solid (406 mg, 38 %). M.p. 154.2–155.8 °C. ¹H NMR

(300 MHz, CDCl₃): δ = 0.45–0.56 (m, 12 H, CH₂), 0.91 (t, J =

6.25 Hz, 18 H, CH₃), 1.12–1.41 (m, 48 H, CH₂), 2.06 (s, 6 H, CH₂),

1.30–3.10 (m, 20 H, BH) ppm. ¹³C NMR (75 MHz, CDCl₃): δ =

12.8, 14.1, 22.6, 23.4, 29.7, 31.4, 33.4, 58.4, 70.3, 72.7, 76.4,

77.9 ppm. ¹¹B NMR (96 MHz, CDCl₃): δ = –10.4 (d, J = 182 Hz),

1,3,5-Tris[(3-ethynylbicyclo[1.1.1]pentyl)ethynyl]benzene:

Com-

pound 31a was prepared from trisilylated derivative 31 (38 mg,

0.06 mmol) in THF (3.50 mL) and a solution of TBAF in THF

(1.0 m, 240 μL, 0.24 mmol) according to the procedure described

for compound 27a. Column chromatography on silica gel (hexane/

CHCl₃, 2:1) afforded the product as white crystals (23 mg, 92%).

1

M.p. Ͼ202 °C (dec.). H NMR (300 MHz, CDCl₃): δ = 2.09 (s, 3

H, ϵCH), 2.36 (s, 18 H, CH₂), 7.33 (s, 3 H, Ar-H) ppm. ¹³C NMR

(75 MHz, CDCl₃): δ = 30.0, 30.5, 58.7, 68.3, 78.4, 82.4, 89.0, 123.4,

134.3 ppm. IR (KBr): ν = 3300, 2987, 2914, 2877, 2224, 2112, 1583,

˜

1450, 1417, 1246, 877, 758 cm^–1. MS: m/z (%) = 415 (14) [M –

2H₂]⁺, 401 (72), 387 (100), 374 (57), 363 (59), 350 (84), 337 (99),

324 (48), 313 (57), 300 (63), 287 (56), 274 (29), 263 (27), 261 (26),

250 (26), 237 (24), 224 (16), 211 (10), 200 (13), 187 (19), 175 (12),

162 (12), 150 (13), 115 (14), 89 (9), 65 (12), 51 (25). HRMS (APCI):

calcd. for [C₃₃H₂₄+ H]⁺421.1951; found 421.1943.

1,3-Bis(bromoethynyl)bicyclo[1.1.1]pentane (32): Freshly recrys-

tallized NBS (1.388 g, 7.8 mmol) and AgNO₃(340 mg, 2.0 mmol)

were added to a solution of freshly sublimed diyne 1 (405 mg,

3.5 mmol) in acetone (10 mL). The yellowish solution was stirred

at room temperature in the dark for 2.5 h. A white solid precipi-

tated. The reaction mixture was diluted with CH₂Cl₂(25 mL) and

washed with water (2ϫ20 mL). The clear colorless organic phase

was dried with Na₂SO₄. Solvents were removed under reduced

pressure, and the residue was purified by flash column chromatog-

raphy on silica gel (hexane/CH₂Cl₂, 3:1) to give 32 as white crystals

(778 mg, 81%). M.p. 118 °C (subl.), 182 °C (dec.). ¹H NMR

(300 MHz, CDCl₃): δ = 2.31 (s, 6 H, CH₂) ppm. ¹³C NMR

–13.2 (d, J = 176 Hz) ppm. IR (KBr): ν = 2956, 2926, 2856, 2613,

˜

1693, 1626, 1464, 1408, 1298, 1188, 1090, 993, 962, 870, 768,

737 cm^–1. MS (MALDI-TOF): m/z (center of isotope cluster) =

968.4 [M + H]⁺, 685.7 [M – SiHex₃+ H]⁺. HRMS (APCI): calcd.

for [C₄₉H₁₀₄B₂₀Si₂+ H]⁺969.9610; found 969.9652.

1,3-Bis[(1,7-dicarba-closo-dodecaboran-1-yl)ethynyl]bicyclo[1.1.1]-

pentane (37): A flame-dried Schlenk flask was charged with m-carb-

orane 36 (548 mg, 3.8 mmol) in THF (15 mL), and a solution of

nBuLi in cyclohexane (2.0 m, 950 μL, 1.9 mmol) was added to the

colorless solution at –78 °C. After 15 min, cooling was interrupted,

and the yellowish reaction mixture was stirred at room temperature

for 60 min, then cooled to –78 °C, and CuBr (287 mg, 2.0 mmol)

was added. The yellow-green reaction mixture was stirred at this

temperature for 15 min, then heated up to room temperature, and

vigorously stirred for an additional 90 min. The reaction mixture

turned from bright to dark green during this time. A solution of

dibromodiyne 32 (130 mg, 1.1 mmol) in dry THF (5 mL) was

added, and the mixture was stirred at 45 °C for 24 h. The crude

reaction mixture was cooled to room temperature, diluted with di-

ethyl ether (150 mL), washed with saturated aqueous NH₄Cl

(3 ϫ40 mL) and water (1ϫ40 mL), and the clear green organic

phase was dried with MgSO₄. Solvents were removed under re-

duced pressure, and the unreacted starting carborane 36 (330 mg,

2.3 mmol) was sublimed off from the crude reaction mixture by

Kugelrohr distillation (115 °C, 500 mTorr). Column chromatog-

raphy on silica gel (hexane) afforded the carborane 37 as a white

crystalline solid (170 mg, 0.424 mmol, 89%). M.p. 235 °C (subl.),

272–274 °C (dec.). ¹H NMR (400 MHz, CDCl₃): δ = 1.40–3.70 (br.

s, 20 H, BH), 2.20 (s, 6 H, CH₂), 2.93 (br. s, 2 H, CH) ppm. ¹H{¹¹B}

NMR (400 MHz, CDCl₃): δ = 2.10 (br. s, 4 H, BH), 2.17 (br. s, 6

H, BH), 2.20 (s, 6 H, CH₂), 2.40 (br. s, 4 H, BH), 2.52 (br. s, 2 H,

BH), 2.86 (br. s, 4 H, BH), 2.93 (br. s, 2 H, CH) ppm. ¹³C NMR

(75 MHz, CDCl ): δ = 30.7, 39.9, 58.6, 78.5 ppm. IR (KBr): ν =

˜

3

2993, 2970, 2914, 2877, 2557, 2198, 1506, 1446, 1236, 1119,

719 cm^–1. GC–MS: m/z (%) = 273 (1) [M]⁺, 193 (3) [M – Br]⁺, 167

(1), 143 (1), 129 (4), 114 (100), 88 (16), 74 (4), 63 (15), 50 (21).

HRMS (EI): calcd. for [C₉H₅Br₂]⁺270.8758; found 270.8769.

C₉H₆Br₂(273.95): calcd. C 39.46, H 2.21, Br 58.33; found C 39.60,

H 2.25, Br 58.11.

1,3-Bis(iodoethynyl)bicyclo[1.1.1]pentane (33): A solution of KOH

(337 mg, 6.0 mmol) in water (1.50 mL) was added to a suspension

of the silylated diyne 7 (150 mg, 0.6 mmol) in a mixture of MeOH

(5 mL) and THF (2 mL) at room temperature. Freshly sublimed I₂

(584 mg, 2.3 mmol) was added to the cloudy reaction mixture after

15 min. The yellowish solution was stirred at room temperature for

2.5 h, and a dense white precipitate formed. The reaction mixture

was then diluted with water (25 mL) and extracted with CH₂Cl₂

(2ϫ25 mL). The combined organic phases were dried with

Na₂SO₄. Solvents were removed under reduced pressure, and the

product was isolated by column chromatography on silica gel (pent-

ane) in a purity of around 95%. The remaining impurities were

sublimed by Kugelrohr distillation (100 °C, 360 mTorr). The de-

sired diiododiyne 33 was obtained as a white crystalline solid

1

(102 mg, 48%). M.p. 196 °C (dec.). H NMR (300 MHz, CDCl₃):

δ = 2.32 (s, 6 H, CH₂) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = –3.8,

31.3, 59.2, 92.7 ppm. IR (KBr): ν = 2989, 2962, 2910, 2873, 1502,

˜

12

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Pages: 15

1,3-Diethynylbicyclo[1.1.1]pentane

(100 MHz, CDCl₃): δ = 29.6, 54.8, 58.5, 61.1, 75.2, 76.3 ppm.

green solution was stirred at the same temperature for 15 min, then

¹¹B{¹H} NMR (128 MHz, CDCl₃): δ = –3.17 (br. s, 2 B), –8.30 (br. slowly warmed to room temperature and cooled again to –78 °C.

s, 2 B), –9.85 (br. s, 4 B), –11.01 (br. s, 4 B), –13.86 (br. s, 4 B),

A solution of dibromodiyne 32 (210 mg, 0.8 mmol) in THF (5 mL)

was added to the dark solution of cuprate at –78 °C. The cooling

source was then removed, and the solution was stirred at room

temperature for 24 h and at 45 °C for an additional 24 h. The reac-

–14.59 (br. s, 4 B) ppm. IR (KBr): ν = 3071, 2991, 2973, 2916,

˜

2880, 2608, 2253, 1449, 1306, 1209, 1135, 1081, 1052, 1008, 994,

971, 922, 906, 824, 783, 728 cm^–1. MS: m/z (center of isotope clus-

ter) (%) = 399.4 (100) [M]⁺, 384.4 (46), 365.3 (7), 257.2 (72) [M – tion mixture was diluted with CHCl₃(75 mL), washed with concen-

C₂H₁₁B₁₀]⁺, 195.2 (31). HRMS (EI): calcd. for [C₁₃H₂₈¹⁰B₂B₁₈]⁺

402.4125; found 402.4138. C₁₃H₂₈B₂₀(400.56): calcd. C 38.98, H

7.05; found C 39.25, H 7.06.

trated aqueous NH₄Cl (2ϫ20 mL) and water (1ϫ20 mL), and the

brownish organic phase was dried with Na₂SO₄. Evaporation of

the solvents provided the crude product 42, which was purified by

column chromatography on silica gel (hexane/CHCl₃, 3:1) and ob-

tained as a white crystalline solid (75 mg, 25 %). M.p. Ͼ255 °C

(dec.). ¹H NMR (300 MHz, CDCl₃): δ = 1.66–1.83 (m, 8 H, CH₂),

2.18 (s, 4 H, CH₂), 2.21 (s, 6 H, CH₂), 2.73 (s, 4 H, CH), 3.35 (s,

4 H, CH₂Cl) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 25.2, 30.1,

11

1,3-Bis[(1,12-dicarba-closo-dodecaboran-1-yl)ethynyl]bicyclo[1.1.1]-

pentane (38): A solution of TBAF in THF (1.0 m, 4.50 mL,

4.500 mmol) was added to a stirred solution of silylated carborane

35 (200 mg, 0.2 mmol) in THF (5 mL) at room temperature. The

yellowish reaction mixture was stirred at this temperature for 2 h.

The mixture was then diluted with diethyl ether (60 mL), washed

with water (3 ϫ 20 mL), and the organic phase was dried with

Na₂SO₄. Solvents were removed under reduced pressure, and col-

umn chromatography on silica gel (hexane) afforded the pure carb-

orane 38 as white crystals (76 mg, 91 %). M.p. 164 °C (subl.),

Ͼ272 °C (dec.). ¹H NMR (300 MHz, CDCl₃): δ = 1.20–3.40 (m,

20 H, BH), 2.08 (s, 6 H, CH₂), 2.61 (br. s, 2 H, CH) ppm. ¹³C

NMR (75 MHz, CDCl₃): δ = 29.6, 58.4, 59.7, 69.3, 76.3, 77.9 ppm.

¹¹B NMR (96 MHz, CDCl₃): δ = –11.7 (d, J = 172 Hz), –15.4 (d,

34.0, 41.0, 44.5, 45.4, 58.9, 65.9, 76.2, 80.7 ppm. IR (KBr): ν =

˜

2964, 2908, 2870, 1460, 1437, 1306, 1282, 1259, 1227, 1142, 1074,

1016, 804, 715 cm^–1. MS: m/z (%) = 395 (Ͻ1) [M]⁺, 345 (Ͻ1), 333

(2), 305 (3), 281 (13), 269 (20), 255 (23), 243 (16), 229 (30), 215

(39), 203 (50), 191 (29), 179 (33), 165 (45), 153 (23), 141 (24), 129

(25), 115 (37), 103 (8), 91 (24), 79 (100), 67 (8), 59 (8). HRMS

(APCI): calcd. for [C₂₅H₂₆Cl₂+ H]⁺397.1484; found 397.1475.

1,3-Bis[(3-methylbicyclo[1.1.1]pentyl)ethynyl]bicyclo[1.1.1]pentane

(43): Compound 43 was prepared according to the previous general

procedure used for compound 42 from 1-iodo-3-methylbicy-

clo[1.1.1]pentane (41; 687 mg, 3.3 mmol), tBuLi in pentane (1.7 m,

3.88 mL, 6.6 mmol), CuBr (488 mg, 3.4 mmol), and dibromodiyne

32 (380 mg, 1.387 mmol) in THF (14 mL). Product 43 was purified

by column chromatography on silica gel (hexane/CH₂Cl₂, 3:1, then

hexane/CH₂Cl₂, 4:1) and isolated as a white crystalline solid

J = 169 Hz) ppm. IR (KBr): ν = 3064, 2989, 2916, 2879, 2613,

˜

2247, 1304, 1207, 1144, 1084, 1045, 1005, 939, 820, 731 cm^–1. GC–

MS: m/z (center of isotope clusters) (%) = 400 (100) [M]⁺, 385 (62),

368 (6), 353 (3), 342 (2), 257 (77), 231 (8), 217 (2), 196 (5), 180 (2),

167 (3). HRMS (APCI): calcd. for [C₁₃H₂₈B₂₀+ H]⁺405.4125;

found 405.4119.

1

(47 mg, 12%). M.p. 143.8–145.0 °C. H NMR (300 MHz, CDCl₃):

12,12Ј-(Bicyclo[1.1.1]pentane-1,3-diyldiethynediyl)bis(1,12-dicarba-

closo-dodecaborane-1-carboxylic acid) (39): A solution of nBuLi in

hexane (2.5 m, 140 μL, 0.35 mmol) was added to a solution of car-

borane 38 (60 mg, 0.15 mmol) in THF (8 mL) at 0 °C. The clear,

slightly yellowish reaction mixture was stirred at room temperature

for 60 min. Subsequently, gaseous CO₂was bubbled into the reac-

tion mixture through a PTFE cannula for 30 min. A dense white

precipitate was formed during this time. The reaction mixture was

diluted with 20% aqueous NaHCO₃(30 mL), then washed with

CH₂Cl₂(2ϫ20 mL), and finally acidified with concentrated HCl

(pH ≈ 1). The product was salted out with NaCl and extracted with

diethyl ether (4ϫ20 mL). The combined colorless organic phases

were dried with Na₂SO₄. Solvents were removed under reduced

pressure, and impurities were washed off with ice-cold CH₂Cl₂. The

pure diacid 39 was obtained as white crystals (64 mg, 0.131 mmol,

87%). M.p. Ͼ280 °C (dec.). ¹H NMR (300 MHz, [D₆]acetone): δ

= 1.50–3.40 (m, 20 H, BH), 2.15 (s, 6 H, CH₂), 9.41 (br. s, 2 H,

COOH) ppm. ¹³C NMR (75 MHz, [D₆]acetone): δ = 31.1, 59.8,

69.7, 77.2, 78.7, 81.6, 163.9 ppm. ¹¹B NMR (96 MHz, [D₆]acetone):

δ = 1.10 (s, 6 H, CH₃), 1.87 (s, 12 H, CH₂), 2.23 (s, 6 H, CH₂) ppm.

¹³C NMR (75 MHz, CDCl₃): δ = 17.7, 27.9, 30.1, 38.8, 56.4, 58.9,

78.1, 79.4 ppm. IR (KBr): ν = 2966, 2910, 2870, 1444, 1377, 1342,

˜

1277, 1134, 1051, 806 cm^–1. MS: m/z (%) = 277 (Ͻ1) [M]⁺, 259 (2),

245 (7), 231 (18), 217 (25), 203 (48), 191 (47), 178 (53), 165 (100),

152 (40), 141 (37), 128 (53), 115 (68), 105 (20), 91 (55), 77 (50), 65

(26), 55 (37). HRMS (APCI): calcd. for [C₂₁H₂₄+ H]⁺277.1951;

found 277.1946.

Supporting Information (see footnote on the first page of this arti-

cle): ¹H, ¹¹B, and ¹³C NMR spectra of all new compounds and

ORTEP diagrams of anisotropically refined structures of the com-

pounds studied by XRD.

Acknowledgments

This work was supported by the Ministry of Education, Youth and

Sports of the Czech Republic (grant no. MSM0021622410) and by

the European Community’s Seventh Framework Program

(CZ.1.05/1.1.00/02.0068) of the European Regional Development

Fund. J. K. greatly acknowledges financial support from Synthon

s.r.o., CZ.

δ = –12.2 (d, J = 162 Hz), –13.9 (d, J = 164 Hz) ppm. IR (KBr): ν

˜

= 3500, 3421, 3373, 3238, 2993, 2918, 2881, 2621, 2249, 1724, 1616,

1412, 1275, 1128, 987, 906, 791, 731 cm^–1. MS (MALDI-TOF): m/z

(center of isotope cluster) = 489.7 [M + H]⁺, 444.6 [M – COO +

H]⁺. HRMS (EI): calcd. for [C₁₅H₂₈B₂₀O₄]⁺492.3849; found

492.3837.

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FULL PAPER

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Received: March 20, 2012

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Published Online: ᭿

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Job/Unit: O20351

/KAP1

Date: 17-07-12 10:33:51

Pages: 15

1,3-Diethynylbicyclo[1.1.1]pentane

Rod-Like Building Blocks

ˇ

J. Kaleta, M. Necas, C. Mazal* ..... 1–15

1,3-Diethynylbicyclo[1.1.1]pentane, a Use-

ful Molecular Building Block

1,3-Diethynylbicyclo[1.1.1]pentane

been investigated to prove its usefulness as

versatile rod-like molecular building

block that can be considered a nonconju-

gated analogue of the more frequently used

has

diethynylarylenes. Standard terminal alk- Keywords: Alkynes / Cross coupling / Um-

yne chemistry worked well, including um-

polung reaction to 1-haloalkynes and sub-

sequent cross-coupling with carboranyl or

bicyclopentyl bridgehead cuprates.

polung / Small ring systems / Rod-like mo-

lecules

a

Eur. J. Org. Chem. 0000, 0–0

www.eurjoc.org

15

Article Doi

1,3-Diethynylbicyclo[1.1.1]pentane, a useful molecular building block

DOI: 10.1002/ejoc.201200351

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Article abstract of DOI:10.1002/ejoc.201200351

Full text of DOI:10.1002/ejoc.201200351

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