Synthesis of buta-1,3-diyne-bridged macrocycles with (Z)-1,4-diethynyl-1,4-dimethoxycyclohexa-2,5-diene as the building block

Article abstract of DOI:10.1002/ejoc.200390106

(Z)-1,4-Diethynyl-1,4-dimethoxycyclohexa-2,5-diene has been used as a building block for the synthesis of two novel macrocycles containing buta-1,3-diyne units as bridges. The tetrayne derivative 5c has been structurally characterized by single crystal X-ray crystallographic data. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200390106

FULL PAPER
Synthesis of Buta-1,3-diyne-Bridged Macrocycles with (Z)-1,4-Diethynyl-
1,4-dimethoxycyclohexa-2,5-diene as the Building Block
Manivannan Srinivasan,[a] Sethuraman Sankararaman,*[a] Henning Hopf,*[b] and
Babu Varghese[c]
Keywords: Macrocycles / Cyclophanes / Alkynes / CϪC coupling
(Z)-1,4-Diethynyl-1,4-dimethoxycyclohexa-2,5-diene
has
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
been used as a building block for the synthesis of two novel Germany, 2003)
macrocycles containing buta-1,3-diyne units as bridges. The
tetrayne derivative 5c has been structurally characterized by
single crystal X-ray crystallographic data.
Introduction
reported spectroscopic evidence for the formation of
[12.12]paracyclophane dodecayne.[6] The hexakis(octayne)-
bridged all-carbon cage compound C60 with Ci point group
symmetry, proposed by Rubin, is the ultimate goal of the
cyclophyne series.[7]
The oxidative dimerization of a terminal acetylene to the
corresponding diacetylene Ϫ the Glaser coupling[1] Ϫ is a
very powerful tool for the synthesis of a variety of molecu-
lar frameworks containing acetylenic units. The recent past
has witnessed the synthesis of several novel acetylenic build-
ing blocks which are potentially useful for molecular scaf-
folding for the synthesis of n-cyclocarbons, dehydroannul-
enes, pericyclynes, graphyne subunits, and cyclophynes, to
name but a few.[2] Cyclophynes are an interesting class of
compounds in which the aromatic units are connected by
acetylenic bridges. The simplest cyclophyne is [2.2]paracy-
clophyne, a hydrocarbon in which one ethano bridge has
been replaced by a triple bond. This compound was gener-
ated as a highly reactive intermediate as early as 1982 and
the term cyclophyne was also introduced for the first time.[3]
Oda has reported the synthesis of a highly strained
[2.2.2]metacyclophane-1,9,17-triyne in which the sp bond
angles are 158.6°.[4] Haley has recently reported the syn-
thesis of an octacobalt complex of [8.8]paracyclophane oc-
tayne.[5] However, the parent hydrocarbon of this cobalt
complex has eluded isolation, presumably due to the strain-
induced high reactivity of the tetrayne bridges. Tobe has
Although dehydrobenzannulenes 1[8] and 2[9] have been
reported, the corresponding para isomers, cyclophynes 3
and 4, are unknown in the literature (Scheme 1). [26]- and
[28]Paracyclophane hexayne and octayne, respectively, have
been reported by Oda.[10] These are belt-shaped molecules
in which the paraphenylene units are connected by a single
acetylenic unit.
[a]
Department of Chemistry,
Indian Institute of Technology Madras, Chennai 600036, India
Fax: (internat.) ϩ 91-44/2570545
Scheme 1. A selection of cyclophynes containing diacetylenic
bridges
E-mail: sanka@iitm.ac.in
[b]
Institut für Organische Chemie, Technische Universität
Braunschweig,
Hagenring 30, 38106 Braunschweig, Germany
Fax: (internat.) ϩ 49-(0)531/3915388
E-mail: h.hopf@tu-bs.de
Regional Sophisticated Instrumentation Centre, Indian
Institute of Technology Madras,
Chennai 600036, India
As a part of our ongoing efforts to synthesize cyclo-
phanes and related macrocycles bearing polyyne bridges,[11]
we have devised a new methodology for the synthesis of
novel macrocycles bearing 1,4-cyclohexadiene units instead
of aromatic rings. The 1,4-hexadiene-based macrocycles are
worthwhile targets because they could serve as potential
[c]
660
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/03/0204Ϫ0660 $ 20.00ϩ.50/0 Eur. J. Org. Chem. 2003, 660Ϫ665

Buta-1,3-diyne Bridged Macrocycles
FULL PAPER
precursors for the synthesis of paracyclophynes, as shown
in the retrosynthetic analysis (Scheme 2). Because of its lin-
ear geometry 1,4-diethynylbenzene is an unsuitable starting
material for the synthesis of 3 and 4 using Glaser-coupling
conditions. In the literature two methodologies are com-
monly used to ‘‘bend’’ the otherwise linear buta-1,3-diyne
unit in order to construct macrocycles bearing polyyne
bridges. The first one involves the formation of an η2-dico-
balt hexacarbonyl derivative of the alkyne by the reaction
Results and Discussion
Addition of two equivalents of lithium trimethylsilylace-
tylide in THF to p-benzoquinone (8) furnished the diol 6a
as a mixture of Z- and E-diastereomers in a 1:2 ratio, re-
spectively (Scheme 3). It is interesting to note that the addi-
tion of lithium trimethylsilylacetylide stopped at the mono-
addition stage to yield the dienone 9 as the only product in
nearly quantitative yield when the reaction was carried out
of the alkyne with dicobalt octacarbonyl. After the con- at Ϫ78 °C. It was necessary to warm the reaction mixture
struction of the macrocycle the alkyne is regenerated by ox- to above Ϫ40 °C in order for the second addition to take
idative demetallation of the cobalt complex.[12] The second
approach involves the use of cyclobutene-based precursors
which serve as masked alkynes. In this method the alkyne
is restored by a photochemical [2ϩ2] cycloreversion.[6] In
the Z-isomer of the diol 7a the two terminal acetylenic
groups point at an angle of 128° from the nearly planar
cyclohexadiene unit.[13] The disposition of the two acetyl-
enic groups at this angle makes 7a and its derivatives amen-
able for the synthesis of macrocycles bearing buta-1,3-diyne
bridges by a Glaser coupling reaction. Although diol 7a
was reported by Ried in 1957,[14] it has not been used as a
building block for the synthesis of macrocyclic structures.
The crucial step in Scheme 2 is the conversion of 5 by a
reductive 1,4-elimination of X groups to the aromatic sys-
tem 3. To carry out this conversion it would be desirable to
have X as a good leaving group such as halide or acetate.
Herein we report the synthesis and characterization of two
new macrocycles 5c and 12 using (Z)-1,4-diethynyl-1,4-di-
methoxycyclohexa-2,5-diene as the building block. We de-
scribe our attempts to synthesize 5a؊b and 5d from the
corresponding precursors 7a؊b and 7d, respectively. We
also report the calculated energy minimized structures of
the hypothetical cyclophynes 3 and 4 along with their
strain energies.
place to yield 6a. The diastereomers of 6a were separated
by column chromatography. The E-isomer was also ob-
tained in pure form by fractional crystallization of the
crude product from a mixture of CH2Cl2 and pentane, leav-
ing behind a mother liquor that was enriched in the Z-iso-
mer. The structure of the E-isomer was established by
single-crystal X-ray crystallographic data.[15] Since the E-
isomer is not useful for the synthetic route presented in
Scheme 2, further transformations of the diol 6 were per-
formed only with the Z-isomer. Deprotection of the TMS
groups proceeded smoothly when the diol 6a was treated
with K2CO3 in methanol. Although the synthesis of diol 7
has been reported in 30Ϫ45% yield,[14,16] the two-step strat-
egy presented here gives the diol in 85Ϫ90% overall yield
starting from p-benzoquinone.
Scheme 3. The ethynylation of p-benzoquinone (8)
The Z-diol 6a was converted into the corresponding di-
acetate Z-6b and dimethyl ether Z-6c using standard pro-
cedures in high yields. The silyl protecting groups were then
removed with K2CO3 in methanol to yield the desired ter-
minal acetylene derivatives Z-7b and Z-7c, respectively, in
good yields (Scheme 4). Attempts to synthesize the dichloro
derivative Z-6d from Z-6a and Z-7d from Z-7a, respectively,
by using SOCl2 and pyridine were unsuccessful due to the
propensity of the diols 6a and 7a to undergo aromatization
under strong acidic conditions.
Initially our attention was focused on the synthesis of the
tetraacetate derivative 5b because the acetate functions
could be made to undergo reductive 1,4-elimination to yield
the target cyclophyne 3. The idea that the 1,4-elimination
of these groups could be performed gained support from a
serendipitous observation. The fact that propargylic acet-
ates undergo (SN2Ј) substitution, with propargylic re-
Scheme 2. Cyclophane-tetrayne 3: retrosynthesis
Eur. J. Org. Chem. 2003, 660Ϫ665
661

M. Srinivasan, S. Sankararaman, H. Hopf, B. Varghese
FULL PAPER
observations were made when the diol Z-7a was subjected
to GlaserϪEglinton coupling conditions. In sharp contrast,
however, the dimethoxy derivative Z-7c, when subjected to
an Eglinton coupling reaction in the presence of Cu(OAc)2
and pyridine, gave a crude product which was completely
soluble in common organic solvents such as CHCl3,
CH2Cl2, and diethyl ether (Scheme 6). Careful chromato-
graphic separation yielded 5c and 12 in 2.5% and 9.1%
yields, respectively. In spite of the low yields, compounds 5c
and 12 were isolated and purified by column chromato-
graphy and repeated crystallization and were thoroughly
characterized by spectroscopic and analytical data (see
Exp. Sect.).
Scheme 4. Preparation of the building blocks 7; Reagents and con-
ditions: a. K2CO3, MeOH, room temp., 1 h, 95Ϫ100%; b. Ac2O,
Py, 60 °C, 4 h, 74%; c. NaH, THF, MeI, Ϫ30 °C to room temp.,
overnight, 94%
Scheme 6. Preparation of the macrocyclic polyynes 5c and 12
Additionally, the structure of 5c was confirmed by single-
crystal X-ray crystallographic data (Figure 1). In each of
the cyclohexadiene rings the sp2 carbon atoms form an al-
3
˚
most ideal plane and the sp carbons lie 0.304 A above the
plane towards the cavity of the macrocycle. The distance
˚
between the centers of the cyclohexadiene rings is 7.27 A
Scheme 5. Reaction of (Z)-6b with R2CuLi
and the distance between the centers of the two acetylenic
arrangement to give allenes, when reacted with dialkylcup-
rates[17] under appropriate conditions led us to an inde-
pendent investigation of the reactions of the diacetate 6b
with dialkylcuprates for the synthesis of extended quinodi-
methides, as shown in Scheme 5.
Treatment of the diacetate 6b with either lithium di-
methylcuprate or lithium di-n-butylcuprate at Ϫ78 °C did
not yield the expected compound 10. Instead, a very clean
reductive elimination of the acetate groups was observed
leading to the formation of 1,4-bis(trimethylsilylethynyl)-
benzene 11 as the sole product in 78% yield. This observa-
tion encouraged us to investigate the synthesis of 5b from
Z-7b. The diacetate Z-7b was subjected to
a
GlaserϪEglinton coupling reaction under a variety of con-
ditions.[11a] None of these reactions gave any tractable mat-
erial. In all the cases along with major amounts of insoluble
polymeric materials, aromatic compounds were obtained in
small amounts which were not fully characterized. Similar Figure 1. Structure of 5c in the crystal
662 Eur. J. Org. Chem. 2003, 660Ϫ665

Buta-1,3-diyne Bridged Macrocycles
FULL PAPER
˚
bridges is 3.70 A. The acetylenic bridges are bow shaped.
Conclusion
The average sp angles are 176 and 170° for the sp carbon
atoms at the center of the bridge C(1)ϪC(2)ϪC(3)Ј and the
sp carbon atoms connected to the sp3 carbon of the cyclo-
hexadiene ring C(2)ϪC(1)ϪC(8), respectively (Figure 1). In
comparison with the sp bond angle of 158.6° reported by
Oda[4] for [2.2.2]metacyclophane-1,9,17-triyne, the macro-
cycle 5c is relatively strain free. Recently Fallis[18] has re-
ported sp bond angles of 163° and 153.4° in highly strained
cyclophane polyyne systems.
The synthesis of two new macrocycles 5c and 12 with
buta-1,3-diyne bridges derived from (Z)-1,4-diethynyl-1,4-
dimethoxycyclohexa-2,5-diene (Z-7c) as the building block
has been accomplished. Macrocycle 5c has been structurally
characterized by single-crystal X-ray crystallographic data.
The derivatives of 5c and 12 are promising candidates for
the synthesis of cyclophynes by the methodology outlined
in Scheme 2; this work is currently in progress.
Energy-Minimized Structures of 3 and 4 Based on
Semiempirical Calculations
Experimental Section
The energy-minimization calculations on the structures
of the hypothetical cyclophynes 3 and 4 were carried out
by semiempirical AM1 and PM3 methods.[19] The energy-
minimized structures A and B are shown in Figure 2, from
1
General Remarks: H and 13C NMR spectroscopy: Jeol GSX-400
at 400 MHz and 100 MHz or Bruker AM-200 at 200 MHz and
50 MHz, respectively; in CDCl3 solution unless otherwise stated,
TMS as internal standard. All reactions were carried out under
which it is clear that cyclophynes 3 and 4 are belt-shaped nitrogen unless indicated otherwise. Column chromatography: sil-
ica gel (60Ϫ120 or 240Ϫ400 mesh) with various mixtures of diethyl
ether (Et2O), ethyl acetate (EtOAc), and hexane. TLC:
MachereyϪNagel polygram sil G/UV254 plates. Melting points are
uncorrected. THF was distilled from calcium hydride.
molecules. According to these calculations 3 possesses D2h
symmetry while 4 prefers D3h symmetry. The average sp
angle in 3 is approximately 155°; that in 4 is 163°. As ex-
pected, the aromatic rings are not planar. In the case of
structure 3, carbon atoms 1 and 4 of the aromatic rings are
19° above the plane containing the rest of the ring carbons,
whereas in 4 this deviation amounts to 12°. The strain ener-
gies of 3 and 4 based on AM1 (PM3) calculations are 106
(93) and 69 (60) kcal·molϪ1, respectively.
(Z)-1,4-Bis(trimethylsilylethynyl)cyclohexa-2,5-dien-1,4-diol (Z-6a):
nBuLi (0.25 mol, 156 mL of a 1.6  solution in hexane) was added
at Ϫ78 °C to a stirred solution of trimethylsilylacetylene (35 mL,
0.25 mol) in anhydrous THF (300 mL). The resulting pale yellow
solution was stirred for 45 min at the same temperature before it
was added dropwise through a stainless steel needle to a stirred
yellow viscous suspension of p-benzoquinone (10.8 g, 0.1 mol) in
anhydrous THF (500 mL) at Ϫ78 °C. The mixture initially turned
dark blue and then became dark brown. The reaction was allowed
to reach ϩ10 °C (ca. 16 h) and was cooled to 0 °C before it was
quenched with aqueous saturated NH4Cl solution (600 mL). The
organic layer was separated and the aqueous layer was extracted
with CH2Cl2 (3 ϫ 100 mL). The combined organic extract was
washed with ice-cold water (200 mL) and once with ice-cold satur-
ated brine solution (200 mL). After drying with MgSO4, the solvent
was removed and the resulting tan colored solid was used for the
1
next step. The H NMR spectrum of the crude product indicated
a mixture of Z and E diastereomers of 6a in a 1:2 ratio (29.1 g,
96%). The mixture (5.0 g) was separated by silica-gel column chro-
matography with diethyl ether/hexane (20:80, v/v) to yield the pure
E-isomer (2.6 g) and the Z-isomer (1.9 g). The synthesis and spec-
troscopic characterization of the E-diastereomer has been reported
1
earlier.[16] Z-6a: m.p. 152Ϫ154 °C. H NMR: δ ϭ 0.00 ppm (s, 18
H), 3.17 (br. s, 2 H), 5.79 (s, 4 H). 13C NMR: δ ϭ Ϫ0.3 ppm (CH3),
61.1 (Cq), 90.1 (Cq), 104.3 (Cq), 129.3 (CH). IR: ν˜ ϭ 3328 cmϪ1
,
2160, 1248. MS (EI): m/z ϭ (%) ϭ 304 [Mϩ] (12), 286 (22), 271
(78), 255 (98), 73 (100). HRMS: calcd. 304.1315; found 304.1304.
(Z)-1,4-Dimethoxy-1,4-bis(trimethylsilylethynyl)cyclohexa-2,5-diene
(Z-6c): The crude diol 6a containing a mixture of the Z- and E-
isomers (29.0 g, 0.095 mol) in anhydrous THF (300 mL) was added
to a stirred suspension of NaH (6.0 g, 0.24 mol) in anhydrous THF
(300 mL) at Ϫ78 °C. The yellow suspension was stirred for 30 min
at the same temperature. Methyl iodide (68.1 g, 30 mL, 0.48 mol)
was added dropwise slowly with a syringe and the mixture was
allowed to warm to room temp. overnight (18 h). The reaction mix-
ture was poured into ice-cold saturated NH4Cl solution (500 mL).
The organic layer was separated and the aqueous portion was re-
peatedly extracted with diethyl ether (3 ϫ 200 mL). The combined
Figure 2. Calculated energy-minimized structures of 3 (A) and 4
(B) in different perspective views
Eur. J. Org. Chem. 2003, 660Ϫ665
663

M. Srinivasan, S. Sankararaman, H. Hopf, B. Varghese
FULL PAPER
organic extract was washed thoroughly with water (2 ϫ 200 mL)
and finally with saturated brine solution (200 mL). After drying
with MgSO4, the solvent was removed in vacuo to give a pale yel-
low solid (29.7 g, 94%). The 1H NMR spectrum of the crude prod-
uct indicated a mixture of Z- and E-diastereomers of 6c in a 1:2
mol) in anhydrous THF (50 mL). The resulting pale yellow solution
was stirred for 45 min at the same temperature before it was added
to a yellow viscous solution of p-benzoquinone (2.2 g, 0.02 mol) in
anhydrous THF (50 mL) at Ϫ78 °C. The mixture was stirred for
45 min and quenched with aqueous saturated NH4Cl solution
ratio. The diastereomers were separated and purified by silica-gel (300 mL). The organic layer was separated and the aqueous layer
column chromatography with diethyl ether/hexane (1:19, v/v) to
yield the E-isomer (13.6 g) and the Z-isomer (8.6 g) of 6c. Z-6c:
Low-melting solid. 1H NMR: δ ϭ 0.00 ppm (s, 18 H), 3.10 (s, 6
was extracted with CH2Cl2 (3 ϫ 100 mL). The combined organic
extracts were washed with water (200 mL) and once with saturated
brine solution (200 mL). After drying with MgSO4, the solvent was
H), 5.85 (s, 4 H). 13C NMR: δ ϭ Ϫ0.2 ppm (CH3), 51.5 (OCH3), removed in vacuo to furnish a colorless solid; yield: 3.8 g (0.02 mol,
66.7 (Cq), 90.8 (Cq), 102.9 (Cq), 129.3 (CH). IR: ν˜ ϭ 2242 cmϪ1
,
93%), m.p. 98Ϫ100 °C. H NMR: δ ϭ 0.00 ppm (s, 9 H), 3.36 (br.
1
2146. MS (EI): m/z ϭ (%) ϭ 332 [Mϩ] (12), 301 (18), 270 (18), 255 s, 1 H), 6.73 and 5.99 (AAЈBBЈ-q, J ϭ 10.04 Hz, 4 H). 13C NMR:
(70), 213 (42), 73 (100). E-6c: pale yellow solid; m.p. 102Ϫ104 °C.
δ ϭ Ϫ0.5 ppm (CH3), 62.4 (Cq), 91.9 (Cq), 100.4 (Cq), 126.8 (CH),
1
IR: ν˜ ϭ 2176 cmϪ1. H NMR: δ ϭ 0.00 ppm (s, 18 H), 3.07 (s, 6 147.2 (CH), 185.1 (Cq) ppm. IR ν˜ ϭ 3281 cmϪ1, 1665. MS (EI):
H), 5.89 (s, 4 H). 13C NMR: δ ϭ Ϫ0.3 ppm (CH3), 51.2 (OCH3), m/z ϭ (%) ϭ 206 [Mϩ] (10), 190 (12), 175 (50), 73 (100).
66.8 (Cq), 90.7 (Cq), 103.0 (Cq), 130.1 (CH). MS (EI): m/z ϭ (%) ϭ
332 [Mϩ] (80), 317 (15), 301 (100), 270 (10), 255 (70), 213 (62),
73 (85).
Glaser؊Eglinton Coupling of Z-7c; Synthesis of Macrocycles 5c and
12: Cu (OAc)2·H2O (1.86 g, 0.01 mol) was added to a degassed
mixture of CH3CN and pyridine (4:1, v/v 100 mL), and the mixture
stirred at room temp. for 30 min. A solution of Z-7c (0.7 g, 0.004
mol) in CH3CN (5 mL) was added slowly to the suspension and
the mixture stirred for another 3 h at room temp. The color of
the solution changed from deep blue to brown within 10 min. The
reaction was monitored by TLC. After 3 h the mixture was poured
slowly into an ice-cold 5% HCl solution (500 mL) with constant
stirring, then extracted repeatedly with diethyl ether (3 ϫ 100 mL).
The combined organic extracts were washed with ice-cold 5% HCl
solution (2 ϫ 100 mL), followed by saturated NaHCO3 (200 mL),
water (200 mL), and finally with saturated brine solution (100 mL).
The organic layer was dried with anhydrous Na2SO4, filtered, and
the solvent was removed in vacuo. The crude product was chroma-
tographed on silica gel and eluted with hexane/ethyl acetate (8:2 v/
v) to afford a mixture of 5c, 12, and some higher oligomers. This
was rechromatographed on silica gel with hexane/ethyl acetate (9:1
v/v) to yield pure fractions of 5c and 12. Repeated crystallization
from a diethyl ether/hexane mixture gave pure 5c and 12 as color-
less crystalline solids.
(Z)-1,4-Diethynyl-1,4-dimethoxycyclohexa-2,5-diene (Z-7c): Col-
umn purified Z-6c (6.6 g, 0.02 mol) was dissolved in degassed
MeOH (100 mL). K2CO3 (6.9 g, 0.05 mol) was added and the mix-
ture stirred under argon at room temp. for 1 h. The reaction mix-
ture was poured into a large excess of ice-cold water (700 mL) and
extracted with diethyl ether (3 ϫ 100 mL). The combined organic
extracts were again washed thoroughly with water (2 ϫ 100 mL),
followed by a saturated brine solution (200 mL). After drying with
anhydrous Na2SO4, the solvent was removed to obtain Z-7c as a
colorless crystalline solid, which was used for the next step without
further purification. Yield: 3.7 g (0.02 mol, 100%); m.p. 94Ϫ96 °C.
1H NMR: δ ϭ 2.62 ppm (s, 2 H), 3.32 (s, 6 H), 6.08 (s, 4 H). 13C
NMR: δ ϭ 51.6 ppm (OCH3), 66.0 (Cq), 74.2 (Cq), 81.8 (CH),
129.1 (CH). IR: ν˜ ϭ 2113 cmϪ1. MS (EI): m/z ϭ (%) ϭ 188 [Mϩ]
(Ͻ 5) 173 (10), 157 (52), 142 (40), 127 (100), 114 (50).
(Z)-1,4-Diacetoxy-1,4-bis(trimethylsilylethynyl)cyclohexa-2,5-diene
(Z-6b): A mixture of diol Z-6a (1.54 g, 0.005 mol), acetic anhydride
(5 mL, 0.05 mol) and pyridine (1.5 mL) was stirred at room temp.
overnight and at 60Ϫ70 °C for 4 h. The progress of the reaction
was monitored by TLC. The reaction mixture was cooled to Ϫ5
°C, quenched with aqueous ammonia solution (28% 20 mL) and
extracted with diethyl ether (3 ϫ 100 mL). The combined organic
phases were washed with 1  HCl (2 ϫ 100 mL), followed by satur-
ated NaHCO3 (200 mL), water (200 mL), and once with saturated
brine solution (100 mL). After drying with anhydrous Na2SO4, the
solvent was removed to yield a colorless solid, which was used for
the next step without further purification. Z-6b: colorless solid,
1,6,9,14-Tetramethoxytricyclo[12.2.2.26,9]icosa-7,5,17,19-tetraene-
2,4,10,12-tetrayne (5c): Yield 0.02 g (2.5%); colorless crystalline
1
solid, m.p. 205 °C (decomp.). H NMR: δ ϭ 3.36 ppm (s, 12 H),
6.15 (s, 8 H). 13C NMR: δ ϭ 52.4 ppm (OCH3), 68.9 (Cq), 69.6
(Cq), 130.6 (CH). IR: ν˜ ϭ 2240 cmϪ1, 2136. MS (EI): m/z ϭ (%) ϭ
372 [Mϩ] (5), 357 (10), 341 (10), 327 (30). HRMS calcd. 372.1362;
found 372.1358. C24H20O4 (372.1): calcd. C 77.39, H 5.42; found
C 77.27, H 5.45.
1,6,9,14,17,22-Hexamethoxytetracyclo[20.2.2.26,9.214,17]triaconta-
7,15,23,25,27,29-hexaene-2,4,10,12,18,20-hexayne (12): Yield 0.06 g
1
m.p.118Ϫ120 °C. H NMR: δ ϭ 0.00 ppm (s, 18 H), 1.89 (s, 6 H),
1
(9.1%); colorless solid, m.p. 180 °C (decomp.). H NMR: δ ϭ 3.22
6.12 (s, 4 H). 13C NMR: δ ϭ Ϫ0.4 ppm (CH3), 21.7 (CH3), 67.0
(Cq), 92.4 (Cq), 101.0 (Cq), 128.0 (CH), 168.7 (Cq). MS(EI): m/
z ϭ (%) ϭ 329 [Mϩ Ϫ 59], (80), 286 (100), 271 (90), 255 (92),
73 (65).
ppm (s, 18 H), 5.93 (s, 12 H). 13C NMR: δ ϭ 51.9 ppm (OCH3),
66.6 (Cq), 70.2 (Cq), 77.6 (Cq), 128.3 (CH). IR: ν˜ ϭ 2251 cmϪ1
.
MS (EI): m/z ϭ (%) ϭ 558 [Mϩ] (2), 527 (30), 497 (10), 481 (15).
HRMS calcd. 558.2042; found 558.2048.
(Z)-1,4-Diacetoxy-1,4-diethynylcyclohexa-2,5-diene (Z-7b): Depro-
tection of Z-6b by the standard procedure with K2CO3 in degassed
methanol gave Z-7b in quantitative yield as a pale yellow solid. H
NMR: δ ϭ 2.07 ppm (s, 6 H), 2.70 (s, 2 H), 6.36 (s, 4 H). Com-
pound Z-7b was found to be unstable in the solid state and in
solution (CDCl3) and decomposed to yield an aromatic compound
which has been tentatively identified as 2-acetoxy-1,4-diethynylben-
zene.
X-ray Crystallographic Data for Compound 5c: Data were collected
with an EnrafϪNonius CAD4 diffractometer by using Cu-Kα radi-
1
˚
ation (λ ϭ 1.54180 A) at 293 K. Crystal data: monoclinic, space
˚
group P21/n, a ϭ 9.6894 (17), b ϭ 5.8296 (13), c ϭ 17.343 (4) A,
3
˚
V ϭ 979.2 (4) A , Z ϭ 2. Data collection: a crystal of ca. 0.3 ϫ
0.3 ϫ 0.4 mm was used to record 1768 intensities, 2θmax ϭ 67.75°,
completeness to θ ϭ 67.75 was 99.9%. Structure refinement: the
structure was refined anisotropically by full-matrix least-squares on
F2 to wR2 ϭ 0.0922, R1 ϭ 0.0347 for 144 parameters and zero
restraints. CCDC-193339 contains the supplementary crystallo-
4-Hydroxy-4-trimethylsilylethynylcyclohexa-2,5-dienone (9): nBuLi
(26.5 mL, 0.03 mol of a 1.6  solution in hexane) was added at
Ϫ78 °C to a stirred solution of trimethylsilylacetylene (6.0 mL, 0.04 graphic data for this paper. These data can be obtained free of
664 Eur. J. Org. Chem. 2003, 660Ϫ665

Buta-1,3-diyne Bridged Macrocycles
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Calculations were performed using PC Spartan Pro Version
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Received September 27, 2002
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