Studies on tellurium-containing heterocycles. Part 18. Preparation and structure of 2-benzotelluropyrylium salts and 2-benzoselenopyrylium salts

Article abstract of DOI:10.1039/b111045b

The regioselective and stereospecific intramolecular ring closure reactions of o-ethynylbenzyl tellurols 5A and o-ethynylbenzyl selenols 5B, which were readily generated by the reaction of the o-ethynylbenzyl bromides 4 with sodium hydrogen telluride (NaH

Full text of DOI:10.1039/b111045b

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Studies on tellurium-containing heterocycles. Part 18.1
Preparation and structure of 2-benzotelluropyrylium salts
and 2-benzoselenopyrylium salts
1
Haruki Sashida,*a Kazuo Ohyanagi,a Mao Minourab and Kin-ya Akibac
a Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi,
Kanazawa 920-1181, Japan. E-mail: h-sashida@hokuriku-u.ac.jp
b Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato,
Sagamihara, Kanagawa 228-8555, Japan
c Advanced Research Center for Science and Engineering, Waseda University, 3-4-1 Okubo,
Shinjuku-ku, Tokyo 169-8555, Japan
Received (in Cambridge, UK) 3rd December 2001, Accepted 18th January 2002
First published as an Advance Article on the web 8th February 2002
The regioselective and stereospecific intramolecular ring closure reactions of o-ethynylbenzyl tellurols 5A and
o-ethynylbenzyl selenols 5B, which were readily generated by the reaction of the o-ethynylbenzyl bromides 4 with
sodium hydrogen telluride (NaHTe) or sodium hydrogen selenide (NaHSe), produced the isotellurochromenes
6A and isoselenochromenes 6B together with (Z)-1-methylidene-2-telluraindans 7A and (Z)-1-methylidene-
2-selenaindans 7B, respectively. The obtained isochromenes 6A and 6B were transformed into the corresponding
2-benzotelluropyrylium tetrafluoroborates 9A and 2-benzoselenopyrylium tetrafluoroborates 9B by treatment
with triphenylcarbenium tetrafluoroborate (Ph3CϩBF4Ϫ) in excellent yields, respectively. An X-ray structural
analysis of the tert-butyl derivatives 9Ac and 9Bc is also described.
Introduction
The chemistry (syntheses, structure, physical properties,
and reactions) of six-membered sulfur-containing heterocycles,
thiopyrans,2 thiopyrylium salts3 and their benzo derivatives
has been widely investigated and well established. Recently,
extensive synthetic work on their tellurium2–4 and selenium2,3
analogs has been undertaken. The monocyclic pyrylium salts
and 1-benzo derivatives containing a selenium2 or tellurium
atom2,4 are known. However, no 2-benzotelluropyrylium salts,5a
a theoretically possible structural isomer of the latter, have been
prepared until now. With regard to the 2-benzoselenopyrylium
salts, the synthesis of only the unsubstituted derivative was
reported by Renson and Pirson more than 35 years ago.6
Recently, we focused on the synthesis of various tellurium- or
selenium-containing heterocycles7 based on the successive
intramolecular addition of the tellurols or selenols to an ethynyl
group. We have previously succeeded in the general and facile
two-step synthesis of the 1-benzotelluropyrylium salts8 and
1-benzoselenopyrylium salts9 from the corresponding telluro-
or seleno-chromen-4-ones7e and also examined their reactions10
with nucleophiles. As part of our continuing studies, we
describe herein an extension of our synthetic strategy for the
novel synthesis of the isotellurochromenes 6A and isoseleno-
chromenes 6B, and their transformation into the corresponding
title pyrylium salts 9.
Scheme 1 Reagents and conditions: i, PBr3, pyridine, CHCl3, 0 ЊC to
room temp., 6–10 h; ii, alkyne, PdCl2(Ph3P)2, CuI, benzene–piperidine,
room temp., 5–10 h; iii, K2CO3, MeOH, room temp., 1 h.
Results and discussion
path was eliminated because the ethynylation of 2 did not occur
and only the homo-coupling products of the alkynes were
obtained. o-Ethynylbenzyl alcohols 3 were easily prepared by
Sonogashira’s procedure.11 The palladium-catalyzed coupling
reaction of o-iodobenzyl alcohol 1 with 1-substituted alkynes
in a mixed solvent of benzene and piperidine gave the desired
ethynyl derivatives 3, which were readily brominated with
phosphorus tribromide to give the corresponding benzyl
bromides 4 in good yields. The trimethylsilyl (TMS) group on
Preparation of 2-benzotelluropyrylium and 2-benzoseleno-
pyrylium salts
There are two possible routes for the preparation of the key
starting o-ethynylbenzyl bromides 4 from o-iodobenzyl alcohol
1 as shown in Scheme 1. Route A through the o-iodobenzyl
bromide 2 is more effective than route B due to the use of 2 as
a mutual starting material for ethynylation. However, this
606
J. Chem. Soc., Perkin Trans. 1, 2002, 606–612
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b111045b

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Scheme 2 Reagents and conditions: i, NaHTe or NaHSe (1.2 equiv.), DMF, 0 ЊC room temp., 1 h; ii, EtOH, 90 ЊC, 1–3 h; iii, K3Fe(CN)6, H2O,
room temp., 10 min; iv, NaBH4, EtOH, room temp., 1 h; v, Ph3CϩBF4Ϫ (1.05 equiv.), MeNO2, room temp., 30 min.
the triple bond of the benzyl bromide 4e was easily removed
to give the o-ethynylbenzyl bromide 4f by treatment with
potassium carbonate in methanol at room temperature.
selectively cyclized to afford isoselenochromene 6Bf without
producing the 2-selenaindan 7Bf. In contrast, in the case of the
phenyl derivative 5Bd, only the 5-exo-dig reaction proceeded to
form the benzylidene-2-selenaindan 7Bd in 66% yield. Overall,
the 6-endo-dig ring closure was the preferential reaction during
the present intramolecular trans-addition of the tellurols or the
selenols to an acetylenic moiety except for the phenyl derivative
5d. These results are summarized in Table 1, and the 1H NMR
and MS spectral data for 6 and 7 are collected in Tables 2 and 3,
respectively. All the isotellurochromenes 6A and the isoseleno-
chromenes 6B except for the 3-unsubstituted isochromene 6Bf6
are hitherto unknown compounds.
Next, the transformation into the 2-benzotelluropyrylium
salts 9A and the 2-benzoselenopyrylium salts 9B was carried
out from the corresponding isochromenes 6A, 6B using the
substrates obtained, except for the phenyl derivative 6Bd. The
3-tert-butyl derivatives 6Ac, 6Bc and the 3-unsubstituted iso-
The syntheses of the 2-benzotelluropyrylium salts 9A and
2-benzoselenopyrylium salts 9B are shown in Scheme 2. In
order to obtain the isochromenes 6A and 6B, precursors for the
preparation of the title compounds, we examined the conver-
sion of the o-ethynylbenzyl bromides 4 into the o-ethynylbenzyl
tellurols 5A or o-ethynylbenzyl selenols 5B. The treatment
of the benzyl bromides 4 with sodium hydrogen telluride
(NaHTe),12 which was freshly prepared from tellurium dust
and sodium borohydride in DMF, followed by the addition of
ethanol, and then heating at 90 ЊC, resulted in the direct ring
closure to afford the desired isotellurochromenes 6A, together
with the five-membered compounds, the (Z)-1-methylidene-
2-telluraindans 7A, via the specific tellurol intermediates 5A.
The isotellurochromenes 6A were produced by the 6-endo-dig
ring closure of 5A at the sp carbon atom of the ethynyl group.
The 2-telluraindans 7A are the products of the 5-exo-dig reac-
tion. The formation of compounds 5A was characterized by the
isolation of the bis(o-ethynylbenzyl) ditellurides 8A, which were
obtained by the potassium ferricyanide oxidation13 of 5A
before heating in ethanol. The ditellurides 8A reverted back
to the tellurols 5A by treatment with sodium borohydride in
ethanol with reductive fission of the Te–Te bond. The trimeth-
ylsilylethynylbenzyl tellurol 5Ae also gave the 3-unsubstituted
isotellurochromene 6Af directly with reductive removal of the
TMS group under the reaction conditions, but in poor yield.
The cyclization of ethynylbenzyl tellurol 5Af proceeds to afford
6Af in a higher, good yield. In this case, the 1-methylidene-2-
telluraindan 7Af was not obtained. It is well known and estab-
lished that both intermolecular7a,14 and intramolecular7b–g
trans-additions of tellurols to a triple bond proceed stereo-
specifically to provide the anti Markovnikov-type products. The
phenyl derivative 5Ad gave the isotellurochromene 6Ad and the
chromenes 6Af, 6Bf were treated with triphenylcarbenium
tetrafluoroborate (Ph3CϩBF4
) in nitromethane at room
Ϫ
temperature to give the desired corresponding 2-benzotelluro-
pyrylium tetrafluoroborates 9Ac, 9Af and 2-benzoseleno-
pyrylium tetrafluoroborates 9Bc, 9Bf as yellow or pale green
prisms in high yields, respectively. These salts are quite stable
and can be stored for several months even at room temperature
under an argon atmosphere. However, they are instantaneously
decomposed upon contact with water or a protic solvent such
as an alcohol. In contrast, the 2-benzotelluropyrylium salts
9Aa, 9Ab and 2-benzoselenopyrylium salts 9Ba, 9Bb having
another alkyl substituted group (methyl and n-butyl) on the C-3
position could not be obtained in a stable crystalline state from
the corresponding isochromenes under the same conditions.
They are too unstable to be isolated, and decompose even in
solution in ca. 10–20 minutes. The reason why these pyrylium
salts are not stable compared to the 3-tert-butyl and 3-
unsubstituted derivatives might be the reaction shown in
Scheme 3. A β-hydrogen from the heteroatom of the pyrylium
salts 9 would be attacked and eliminated by the strong base, the
tetrafluoroborate (BF4Ϫ) anion, to form the o-quinonoid com-
pounds 10, which would be unstable due to the destruction of
the aromaticity of the benzene ring.
1
telluraindans 7Ad in 19 and 71% yields, respectively. In the H
NMR (400 MHz) spectra of the telluraindans 7A, a nuclear
Overhauser enhancement (NOE) was observed between the
exocyclic methyne proton (1Ј-H) and the aromatic 7-H. Thus,
the stereochemistry of the olefin moiety of 7A was found to be
the (Z)-form.
The isoselenochromenes 6B and the (Z)-1-methylidene-
2-selenaindans 7B were similarly obtained using sodium
hydrogen selenide (NaHSe). o-Ethynylbenzyl selenol 5Bf regio-
Similar β-hydrogen elimination behavior was observed in
the case of the 1-benzyl-2-benzotelluropyrylium salt; the (Z)-
1-benzylideneisotellurochromene5a was isolated. 3-Phenyl-2-
benzotelluropyrylium salt 9Ad was also moisture-sensitive
J. Chem. Soc., Perkin Trans. 1, 2002, 606–612
607

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Table 1 Isotellurochromenes 6A, isoselenochromenes 6B, (Z)-1-methylidene-2-telluraindans 7A and (Z)-1-methylidene-2-selenaindans 7B
6
7
M
R
Yield (%)a
Appearance
Mp/ЊC
Yield (%)a
Appearance
Mp/ЊC
Te
Te
Te
Te
Te
Se
Se
Se
Se
Se
Me
Bun
But
Ph
H
Me
Bun
But
Ph
H
66
66
84
19
64
48
49
60
0
Yellow prismsb
Yellow oil
59
—
63
51–52
66–67
43
—
69–71
—
25
20
0
71
0
33
22
14
66
0
Yellow prismsb
Pale yellow oil
—
73–74
—
—
98–99
—
61–63
—
—
77–80
—
Yellow prismsb
Yellow prismsd
Yellow prismsd
Pale yellow prismsb
Yellow oil
Yellow prismsc
—
Pale yellow prismsb
Yellow oil
Yellow oil
Colorless prismsc
—
Yellow prismsb
—
Yellow oil
56
—
a Isolated yields. b From n-hexane. c From benzene–n-hexane. d From acetone–n-hexane.
Table 2 Spectral data for the isotellurochromenes 6A and the isoselenochromenes 6B
δH (90 MHz, CDCl3)
Compd. no.
R
M
Formula
HRMS calcd (found) 1-H2
4-H
Ph-H
R-H
6Aa
6Ab
Me Te C10H10Te
Bun Te C13H13Te
259.9845 (259.9845)
302.0315 (302.0313)
3.90 (s) 6.59 (q, J 1.7)
3.86 (s) 6.59 (br s)
7.01–7.26 (4H, m) 2.40 (3H, d, J 1.7, Me)
7.02–7.23 (4H, m) 0.93, 1.19–1.62, 2.59 (3H, t, J 6.2,
4H, m, 2H, br t, J 7.0, Bun)
6Ac
6Ad
6Af
6Ba
6Bb
But Te C13H16Te
302.0315 (302.0313)
322.0002 (321.9996)
245.9689 (245.9693)
209.9948 (209.9943)
252.0418 (252.0425)
3.79 (s) 6.64 (s)
3.98 (s) 7.09 (s)
3.86 (s) 7.02 (d, J 10.3) 7.10–7.25 (4H, m) 7.22 (d, J 10.3, H)
3.85 (s) 6.63 (q, J 1.6)
3.85 (s) 6.71 (t, J 1.8)
7.10–7.26 (4H, m) 1.29 (9H, s, But)
7.17–7.64 (9H, m, Ph)
Ph
H
Te C15H12Te
Te C9H8Te
Me Se C10H10Se
6.92–7.30 (4H, m) 2.24 (3H, d, J 1.6, Me)
6.97–7.34 (4H, m) 0.95, 1.22–1.83, 2.52 (3H, t, J 6.0,
4H, m, 2H, dt, J 1.8, 7.0, Bun)
Bun Se C13H16Se
6Bc
6Bf
But Se C13H16Se
252.0418 (252.0414)
195.9791 (195.9791)
3.76 (s) 6.70 (s)
3.84 (s) 6.79 (d, J 9.9)
7.12–7.26 (4H, m) 1.29 (9H, s, But)
7.09–7.25 (4H, m) 6.95 (d, J 9.9, H)
H
Se C9H8Se
Table 3 Spectral data for (Z)-1-methylidene-2-telluraindans 7A and (Z)-1-methylidene-2-selenaindans 7B
δH (90 MHz, CDCl3)
Compd. no.
R
M
Formula
HRMS calcd (found) 1Ј-H
3-H2
Ph-H
R-H
7Aa
7Ab
Me Te C10H10Te
Bun Te C13H16Te
259.9845 (259.9850)
302.0315 (302.0312)
6.76 (q, J 6.2)
6.67 (t, J 6.6)
4.65 (s) 7.05–7.76 (4H, m) 1.85 (3H, d, J 6.2, Me)
4.62 (s) 7.05–7.71 (4H, m) 0.93, 1.26–1.62, 2.09 (3H, t, J 6.6,
4H, m, 2H, dt, J 6.6, 7.0, Bun)
7Ad
7Ba
7Bb
Ph
Te C15H12Te
322.0002 (322.0005)
209.9948 (209.9946)
252.0418 (252.0428)
7.86 (s)
6.44 (q, J 7.0)
6.36 (t, J 7.0)
4.66 (s)
7.15–7.84 (9H, m, Ph)
Me Se C10H10Se
4.38 (s) 7.03–7.70 (4H, m) 1.84 (3H, d, J 7.0, Me)
4.38 (s) 7.03–7.69 (4H, m) 0.94, 1.17–1.78, 2.16 (3H, t, J 6.6,
4H, m, 2H, dt, J 6.6, 7.0, Bun)
Bun Se C13H16Se
7Bc
7Bd
But Se C13H16Se
Ph
252.0418 (252.0417)
272.0105 (272.0104)
6.58 (s)
7.51 (s)
4.38 (s) 7.12–7.71 (4H, m) 1.26 (9H, s, But)
Se C15H12Se
4.50 (s)
7.23–7.79 (9H, m, Ph)
The 1H NMR spectral data for the monocyclic unsubsti-
tuted thiopyrylium,15 selenopyrylium15 and telluropyrylium
1
cations16 have been reported. However, no H NMR data for
the unsubstituted 2-benzothiopyrylium17 and 2-benzo-
selenopyrylium salts6 have been recorded in the literature,
although they have been prepared; the 2-benzotelluro-
pyrylium ring system was first constructed in this study. These
1H NMR data (Table 4) and those of the 3-benzoyl-2-benzo-
thiopyrylium cation reported by Shimizu and co-workers18
indicate a remarkable fact about their chemical shifts. The
chemical shifts of the aromatic protons of the pyrylium
salts 9A and 9B appear at lower fields, in particular, both
the proton signals of 1-H (δ 12.05–13.31) and those of 4-H
(δ 8.75–9.30) resonate at much lower fields compared to the
2-benzothiopyrylium salts.18 The chemical shift values of 1-H
in these three pyrylium nuclei decrease in the order 9A (Te) >
9B (Se) > thiopyrylium salt (S, δ 11.29).18 A similar tendency is
observed for the 2-H protons of the five-membered hetero-
cycles, the benzo[b]chalcogenophenes.7d In contrast, the proton
signals of 4-H of 9A and 9B appear at almost the same chem-
ical shifts (δ 8.75–9.30); that of the thiopyrylium salt is
Scheme 3
and immediately decomposed upon contact with air. Thus, the
deprotonation of these isochromenes by Ph3CϩBF4 to form
Ϫ
the corresponding pyrylium salts was carried out in CD3CN as
a solvent, and the formation of 9Aa, 9Ab, 9Ad, 9Ba and 9Bb
1
1
was then monitored by H NMR spectroscopy. The H NMR
spectral data of all the pyrylium salts 9A and 9B that have been
prepared in the present study are listed in Table 4. The
structures of these pyrylium salts 9 were elucidated from
their 1H and 13C NMR spectra and elemental analyses and also
from single-crystal X-ray studies in the case of the tert-butyl
derivatives 9Ac and 9Bc.
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J. Chem. Soc., Perkin Trans. 1, 2002, 606–612

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Table 4 1H NMR spectral data for 2-benzotelluropyrylium 9A salts and 2-benzoselenopyrylium salts 9B
δH (400 MHz, CD3CN)
Compd. no.
R
M
1-H
4-H
Ph-H
R-H
9Aaa
9Aba
9Ac
Me
Te 12.68 (br s)
8.75 (br s)
8.85 (br s)
9.12 (s)
7.80–8.43 (4H, m)
7.85–8.50 (4H, m)
7.81–8.53 (4H, m)
3.14 (3H, br s, Me)
Bun Te 12.96 (s)
0.98, 1.20–2.01, 3.54 (3H, t, J 7.6, 4H, m, 2H, t, J 7.9, Bun)
But
Ph
H
Te 13.25 (s)
Te 13.11 (s)
1.68 (9H, s, But)
7.77–8.55 (9H, m, Ph)
10.48 (dd, J 11.0, 2.9, H)
3.14 (3H, br s, Me)
9Ada
9Af
9.20 (s)
Te 13.31 (br d, J 2.9) 9.30 (d, J 11.0) 7.88–8.57 (4H, m)
9Baa
9Bba
Me
Se
11.82 (br s)
11.86 (s)
8.82 (br s)
8.85 (br s)
7.94–8.53 (4H, m)
7.98–8.55 (4H, m)
Bun Se
0.99, 1.20–2.07, 3.47 (3H, t, J 8.2, 4H, m, 2H, br t, J 8.6,
Bun)
9Bc
9Bf
But
H
Se
Se
11.96 (s)
12.05 (d, J 2.9)
9.06 (s)
9.15 (br s)
8.11–8.54 (4H, m)
8.08–8.64 (4H, m)
1.70 (9H, s, But)
9.87 (dd, J 9.5, 2.9, H)
a Not isolated.
Table 5 Selected bond lengths (Å) and angles (Њ) of 9Ac
Table 6 Selected bond lengths (Å) and angles (Њ) of 9Bc
Te(1)–C(1)
C(1)–C(9)
C(3)–C(8)
2.003(7)
1.392(7)
1.429(7)
Te(1)–C(2)
C(2)–C(3)
C(8)–C(9)
2.042(5)
1.374(8)
1.439(8)
Se(1)–C(1)
C(1)–C(9)
C(3)–C(8)
1.806(5)
1.394(7)
1.425(6)
Se(1)–C(2)
C(2)–C(3)
C(8)–C(9)
1.853(4)
1.363(6)
1.418(7)
C(1)–Te(1)–C(2)
Te(1)–C(2)–C(3)
C(3)–C(8)–C(9)
95.4(3)
120.5(5)
124.6(5)
Te(1)–C(1)–C(9)
C(2)–C(3)–C(8)
C(1)–C(9)–C(8)
125.2(4)
129.9(5)
124.4(5)
C(1)–Se(1)–C(2)
Se(1)–C(2)–C(3)
C(3)–C(8)–(9)
101.0(2)
120.3(3)
122.4(4)
Se(1)–C(1)–C(9)
C(2)–C(3)–C(8)
C(1)–C(9)–C(8)
124.8(3)
128.2(4)
123.2(4)
observed somewhat more downfield (δ 9.50) because it has
a benzoyl group as an electron-withdrawing substituent at the
C-3 position.
distance from tellurium to the nearest fluorine in the borate is
3.790(3) Å, which is longer than the sum of the van der Waals
radii (3.55 Å).20 It is noteworthy that the carbon (C-1)–
tellurium bond length (2.003 Å) in the telluropyrylium ring is
significantly shorter than the typical covalent bond length of
Te–C (2.12 Å). The shortness of the carbon–tellurium bond in
9Ac is rather comparable to the values of the carbon (sp2)–
tellurium double bond lengths that have been reported in the
range of 1.987–2.298 Å with an average of 2.06 Å.21 Although
the precise details of the resonance structures in the telluro-
pyrylium are not clear, it is likely that the localized double
bond that forms around the tellurium provides an important
contribution to the overall description.
X-Ray analysis
The structure of the 2-benzotelluropyrylium salt 9A, which is a
previously unknown heterocyclic ring system, was character-
ized by X-ray crystallographic analysis of a single crystal
obtained by recrystallization from dichloromethane.
Fig. 1 shows the molecular structure of the 3-tert-butyl
The structure of the corresponding 2-benzoselenopyrylium
9Bc was determined for comparison. The molecular structure
of 9Bc and selected bond lengths and angles are given in Fig. 2
and Table 6, respectively.
Fig. 1 ORTEP drawing of 9Ac with 50% probability level.
Fig. 2 ORTEP drawing of 9Bc with 50% probability level.
derivative 9Ac, and selected bond lengths and angles of 9Ac
are listed in Table 5. To our knowledge, this is the first
crystal structure of benzotelluropyrylium, although the struc-
ture of one monocyclic telluropyrylium has been reported.19
The benzopyrylium ring system in 9Ac is planar and the cation
and anion lie on mirror planes. The tellurium atom has no
significant interaction with the counter anion. The closest
The selenopyrylium 9Bc showed an isomorphous structure to
that of 9Ac and also has mirror planes through the cation and
anion. The C(1)–Se bond length [1.806(5) Å] is noticeably
shorter than those usually observed for carbon–selenium single
bond lengths (average 1.970 Å),22 being close to the C᎐Se
᎐
double bond lengths that have been observed in selenoketones
(1.774,23a and 1.790 Å23b).
J. Chem. Soc., Perkin Trans. 1, 2002, 606–612
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60 MHz) 1.36 (9H, s, But), 2.47 (1H, s, OH), 4.80 (2H, s,
Conclusion
Ph-CH2-OH), 7.2–7.5 (4H, m, Ph-H) (HRMS m/z: Mϩ calcd
In the present work, general preparations have been achieved
for the isotellurochromenes and isoselenochromenes together
with the (Z)-1-methylidene-2-indanes containing tellurium and
selenium atoms by an intramolecular cyclization reaction with
a triple bond. The isochromenes were transformed into the
corresponding novel 2-benzotelluropyrylium and 2-benzo-
selenopyrylium salts. The structure of these pyrylium salts has
been found to be quite flat based on the X-ray analyses of the
tert-butyl derivatives. Examination of the reactivities of these
pyrylium salts is in progress and will be reported in the near
future.
for C13H16O: 188.1201; found: 188.1197).
o-Phenylethynylbenzyl alcohol 3d. Yield 90%, pale yellow
prisms, mp 70–72 ЊC (from benzene–n-hexane); νmax (KBr)/cmϪ1
᎐
3264 (OH), 2240 (C᎐C); δ (CDCl , 60 MHz) 2.38 (1H, s, OH),
᎐
H
3
4.93 (2H, s, Ph-CH2-OH), 7.2–7.7 (9H, m, Ph-H) (HRMS
m/z: Mϩ calcd for C15H12O: 208.0888; found: 208.0888).
o-Trimethysilylethynylbenzyl alcohol 3e. Yield 92%, yellow
oil; νmax (neat)/cmϪ1 3352 (OH), 2156 (C᎐C); δ (CDCl3, 60
᎐
᎐
H
MHz) 0.28 (9H, s, TMS), 2.45 (1H, s, OH), 4.85 (2H, s,
Ph-CH2-OH), 7.2–7.6 (4H, m, Ph-H) (HRMS m/z: Mϩ calcd
for C12H16OSi: 204.0970; found: 204.0975).
Experimental
Melting points were measured on a Yanagimoto micro melting
point hot stage apparatus and are uncorrected. IR spectra were
recorded on a Hitachi 270-30 spectrometer. Mass spectra (MS)
and HRMS were recorded on a JEOL JMS-DX300 instrument.
1H NMR spectra were recorded on a JEOL PMX-60 SI (60
MHz), a JEOL EX-90A (90 MHz) or a JEOL JNM-GSX 400
(400 MHz) spectrometer in CDCl3 or CD3CN using tetrameth-
ylsilane as the internal standard; J values are given in Hz. 13C
NMR spectra and NOE spectra were measured on a JEOL
JNM-GSX 400 spectrometer. 125Te NMR spectra were recorded
on a JEOL EX-400 spectrometer at 126.1 MHz, and samples
were referenced to 125TeMe2 as an external standard. 77Se NMR
spectra were recorded on a JEOL EX-400 spectrometer at 76.2
MHz, and samples were referenced to Me2Se as an external
standard.
General procedure for the preparation of o-ethynylbenzyl
bromides 4a–e
To a stirred solution of o-ethynylbenzyl alcohol 3 (50 mmol)
and pyridine (5.14 g, 65 mmol) in chloroform (50 mL) at 0 ЊC
was slowly added phosphorus tribromide (14.9 g, 55 mmol).
The mixture was stirred at room temperature for 6–12 h, and
then poured into ice–water. The resulting aqueous mixture was
extracted with CH2Cl2 (200 mL × 3), and the combined organic
extract was washed with 5% H2SO4 (200 mL × 2), sat. NaHCO3
(200 mL × 2) and brine (200 mL × 2), and then dried (MgSO4).
After removal of the organic solvent in vacuo, the residual oil
was purified by silica gel chromatography using n-hexane as
eluent to give the pure benzyl bromide 4. The following
compounds were thus prepared.
General procedure for the preparation of o-ethynylbenzyl
alcohols 3a–e
o-Prop-1-ynylbenzyl bromide 4a. Yield 85%, colorless oil; νmax
(neat)/cmϪ1 2252, 2220 (C᎐C); δ (CDCl , 60 MHz) 2.12 (3H, s,
᎐
᎐
H
3
Me), 4.67 (2H, s, Ph-CH2-Br), 7.2–7.5 (4H, m, Ph-H) (HRMS
m/z: Mϩ calcd for C10H9Br: 207.9888, 209.9868; found:
207.9881, 209.9866).
To a mixture of alkyne (b: hex-1-yne, c: tert-butylacetylene, d:
phenylacetylene, e: trimethylsilylacetylene, 0.11 mol) and
o-iodobenzyl alcohol 1 (23.4 g, 0.1 mol)† in benzene (200 mL)
and piperidine (200 mL) were added PdCl2(Ph3P)2 (702 mg,
1 mmol) and CuI (400 mg, 2.1 mmol). The mixture was stirred
at room temperature under argon for 6–10 h. Cold water
(300 mL) was added to the mixture, and the resulting aqueous
mixture was extracted with benzene (200 mL × 3). The com-
bined organic extract was washed with water (200 mL × 4), 5%
H2SO4 (200 mL × 3), sat. NaHCO3 (200 mL × 2) and brine
(200 mL × 2), and then dried (MgSO4).
The benzene was removed in vacuo. The red residual oil was
purified by silica gel chromatography using n-hexane–CH2Cl2
(1 : 1) as eluent to give pure 3. In the case of 3a, a slow stream
of methylacetylene, which was prepared from 1,2-dibromo-
propane and KOH in refluxing n-BuOH, was immediately
passed through the reaction mixture without isolation.
o-n-Hex-1-ynylbenzyl bromide 4b. Yield 78%, colorless oil;
νmax (neat)/cmϪ1 2228 (C᎐C); δ (CDCl , 60 MHz) 0.97, 1.3–1.8,
᎐
᎐
H
3
2.49 (3H, t, J 6, 4H, m, 2H, t, J 7, Bun), 4.70 (2H, s, Ph-CH2-Br),
7.2–7.6 (4H, m, Ph-H) (HRMS m/z: Mϩ calcd for C13H15Br:
250.0357, 252.0338; found: 250.0329, 252.0337).
o-(3,3-Dimethybut-1-ynyl)benzyl bromide 4c. Yield 80%,
colorless oil; νmax (neat)/cmϪ1 2240 (C᎐C); δH (CDCl3, 60 MHz)
᎐
᎐
1.39 (9H, s, But), 4.67 (2H, s, Ph-CH2-Br), 7.2–7.5 (4H, m,
Ph-H) (HRMS m/z: Mϩ calcd for C13H15Br: 250.0357,
252.0338; found: 250.0350, 252.0347).
o-Phenylethynylbenzyl bromide 4d. Yield 94%, colorless oil;
νmax (neat)/cmϪ1 2216 (C᎐C); δ (CDCl3, 60 MHz) 4.72 (2H, s,
᎐
᎐
H
Ph-CH2-Br), 7.2–7.7 (9H, m, Ph-H) (HRMS m/z: Mϩ calcd for
o-Prop-1-ynylbenzyl alcohol 3a. Yield 88%, pale yellow
prisms, mp 71–72 ЊC (from benzene–n-hexane); νmax (KBr)/cmϪ1
C15H11Br: 270.0044, 272.0025; found: 270.0038, 272.0021).
᎐
3332 (OH), 2240 (C᎐C); δH (CDCl3, 60 MHz) 2.08 (3H, s, Me),
᎐
o-Trimethylsilylethynylbenzyl bromide 4e. Yield 76%, color-
2.35 (1H, s, OH), 4.80 (2H, s, Ph-CH2-OH), 7.2–7.5 (4H, m,
Ph-H) (HRMS m/z: Mϩ calcd for C10H10O: 146.0732; found:
146.0741).
less oil; νmax (neat)/cmϪ1 2160 (C᎐C); δH (CDCl3, 60 MHz) 0.30
᎐
᎐
(9H, s, TMS), 4.70 (2H, s, Ph-CH2-Br), 7.2–7.7 (4H, m, Ph-H)
(HRMS m/z: Mϩ calcd for C12H15BrSi: 266.0126, 268.0107;
found: 266.0121, 268.0114).
o-n-Hex-1-ynylbenzyl alcohol 3b. Yield 92%, yellow oil; νmax
(neat)/cmϪ1 3360 (OH), 2228 (C᎐C); δ (CDCl , 60 MHz): 0.96,
᎐
᎐
H
3
1.3–1.8, 2.46 (3H, t, J 6, 4H, m, 2H, t, J 7, Bun), 2.25 (1H, s,
OH), 4.82 (2H, s, Ph-CH2-OH), 7.2–7.6 (4H, m, Ph-H) (HRMS
m/z: Mϩ calcd for C13H16O: 188.1201; found: 188.1197).
o-Ethynylbenzyl bromide 4f. To a stirred solution of o-
trimethylsilylethynylbenzyl bromide 4e (8.01 g, 30 mmol) in
methanol (60 mL) at room temperature was added K2CO3
(0.35 g). After the reaction mixture had been stirred for 1 h, it
was poured into ice–water. The resulting aqueous mixture was
extracted with with CH2Cl2 (100 mL × 3), and the combined
organic extract was washed with brine (100 mL × 2) and dried
(MgSO4). The organic solvent was evaporated in vacuo to give
almost pure o-ethynylbenzyl bromide 4f (5.21 g, 89%) as a
o-(3,3-Dimethylbut-1-ynyl)benzyl alcohol 3c. Yield 88%,
yellow oil; νmax (neat)/cmϪ1 3368 (OH), 2236 (C᎐C); δH (CDCl3,
᎐
᎐
† This compound 1 is commercially available, but easily obtained quan-
titatively by diborane reduction of o-iodobenzoic acid on a large scale.
610
J. Chem. Soc., Perkin Trans. 1, 2002, 606–612

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colorless oil; νmax (neat)/cmϪ1 2108 (C᎐C); δH (CDCl3, 60 MHz)
133.4 (d), 133.5 (d), 136.6 (s), 138.4 (d), 140.7 (s), 141.7 (d),
145.4 (d), 184.0 (d) (Anal. calcd for C9H7BF4Se: C, 38.48;
H, 2.51. Found: C, 38.53; H, 2.32%).
᎐
᎐
᎐
3.48 (1H, s, C᎐CH ), 4.74 (2H, s, Ph-CH -Br), 7.3–7.7 (4H, m,
᎐
2
Ph-H) (HRMS m/z: Mϩ calcd for C9H7Br: 193.9731, 195.9711;
found: 193.9733, 195.9712).
X-Ray data collection for 9Ac and 9Bc‡
General procedure for the treatment of the benzyl bromides 4
with NaHTe: formation of isotellurochromenes 6Aa–f and
1-methylidene-2-telluraindan 7Aa–f
Single crystals suitable for X-ray diffraction study of 9Ac and
9Bc were obtained from a dichloromethane solution of the
compound at room temperature.
A solution of o-ethynylbenzyl bromide 4 (10 mmol) in DMF
(10 mL) was slowly added to a solution of NaHTe (12 mmol),
which was freshly prepared from tellurium dust (1.53 g) and
NaBH4 (0.54 g) in DMF (40 mL) at 0 ЊC under an argon
atmosphere. The reaction mixture was stirred under the con-
ditions for 1 h. EtOH (40 mL) was added to the reaction
mixture, and then the whole mixture was heated at 90 ЊC with
stirring for 1–3 h. After addition of water (200 mL), the
aqueous mixture was extracted with benzene (100 mL × 3). The
organic extract was washed with water (200 mL × 3) and
brine (200 mL × 3), dried (MgSO4), and concentrated in vacuo.
The resulting residue was purified by silica gel chromatography
using n-hexane as eluent to give pure 6A and 7A. The results
and spectral data are given in Tables 1–3.
Crystal data for 9Ac. C13H15BF4Te, M = 385.67, ortho-
rhombic, Pnma, a = 14.2630(5), b = 6.7450(2), c = 14.3100(5) Å,
V = 1376.68(7) Å3, Z = 4, ρcalcd = 1.861 g cmϪ3. Rw = 0.060
(R = 0.100) and GOF = 1.356 for 1572 observed reflections
[109 parameters, I > 3.00σ(I )].
Crystal data for 9Bc. C13H15BF4Se, M = 337.03, ortho-
rhombic, Pnma, a = 13.8420(4), b = 6.7860(1), c = 14.2960(5) Å,
V = 1342.85(5) Å3, Z = 4, ρcalcd = 1.667 g cmϪ3. R = 0.060 (Rw =
0.108) and GOF = 1.475 for 1528 observed reflections [109
parameters, I > 3.00σ(I )]. All data were collected at 190 K
on a MAC Science DIP2030 imaging plate with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). The
structure was solved using the teXsan (Rigaku) system and
all nonhydrogen atoms were refined anisotropically. The hydro-
gen atoms were included at calculated positions but not refined.
Atomic coordinates, bond lengths and angles, and other
important parameters have been deposited at the Cambridge
Crystallographic Data Centre.‡
General procedure for the treatment of benzyl bromides 4 with
NaHSe: formation of isoselenochromenes 6Ba–f and 1-methyl-
idene-2-selenaindan 7Ba–f
A solution of 3 (10 mmol) in DMF (10 mL) was treated with
sodium hydrogen selenide (12 mmol), prepared from selenium
dust (0.96 g) and sodium borohydride (0.54 g), and worked up
to give 6B and 7B. The results and spectral data are given in
Tables 1–3.
Acknowledgements
Part of this work was supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Science,
Sports and Culture, Japan. The authors wish to thank to
Dr S. Yasuike (Hokuriku University) for the 13C NMR
measurements.
General procedure for the preparation of 2-benzotelluropyrylium
tetrafluoroborates 9A and 2-benzoselenopyrylium
tetrafluoroborates 9B
Ϫ
Ph3CϩBF4 (1.88 g, 5.5 mmol) was added to a stirred solution
of the isochromenes 6 (1.51 g, 5 mmol) in dry MeNO2 (10 mL)
and the mixture was stirred at room temperature for 30 min. To
the reaction mixture was added dry Et2O to precipitate the
pyrylium salts 9. The following compounds were thus obtained.
(1H NMR spectral data are listed in Table 4.)
‡ CCDC reference numbers 175478 and 175479. See http://
www.rsc.org/suppdata/p1/b1/b111045b/ for crystallographic files in .cif
or other electronic format.
References
3-tert-Butyl-2-benzotelluropyrylium tetrafluoroborate 9Ac.
Yield 89%, pale green prisms (CH2Cl2–CHCl3), mp 101 ЊC
(decomp.); νmax (KBr)/cmϪ1 1054 (BF4Ϫ); δC (CD3CN, 100
MHz) 33.3 (q), 43.8 (s), 131.4 (d), 132.1 (d), 135.40 (d), 137.8
(d), 139.6 (d), 139.9 (s), 143.7 (s), 182.9 (s), 188.8 (d); δTe
(CD3CN) 1257.5 (Anal. calcd for C13H15BF4Te: C, 40.49; H,
3.92. Found: C, 40.35; H, 3.75%).
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3-tert-Butyl-2-benzoselenopyrylium tetrafluoroborate 9Bc.
Yield 89%, pale green prisms (CH2Cl2–CHCl3), mp 182–184 ЊC
(decomp.); νmax (KBr)/cmϪ1 1056 (BF4Ϫ); δC (CD3CN, 100
MHz) 32.3 (q), 42.4 (s), 132.4 (d), 132.8 (d), 133.5 (d), 134.4 (d),
135.3 (s), 141.6 (d), 142.2 (s), 177.8 (s), 181.2 (d); δSe (CD3CN)
890.0 (Anal. calcd for C13H15BF4Se: C, 46.33; H, 4.49. Found:
C, 46.21; H, 4.46%).
2-Benzoselenopyrylium tetrafluoroborate 9Bf. Yield 85%, pale
green prisms (CH2Cl2–CHCl3), mp 127 ЊC (decomp.); νmax
(KBr)/cmϪ1 1052 (BF4Ϫ); δC (CD3CN, 100 MHz) 133.1 (d),
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