Studies on tellurium-containing heterocycles. Part 20. Reactions of 2-benzoselenopyrylium salts and 2-benzotelluropyrylium salts with nucleophiles: Formation of 1-functionalized 1H-isoselenochromenes and 1H-isotellurochromenes

Article abstract of DOI:10.1248/cpb.52.57

The reactions of the 2-benzoselenopyrylium (1A) and 2-benzotelluropyrylium cations (1B) with a variety of nucleophiles have been investigated. LiAlH ₄, sodium alkoxide (NaOMe, NaOi-Pr and NaOt-Bu), diethylamine, n-butylamine and acetone reacted with 1 to give the 1H-isochromenes (2) and the corresponding 1-substituted products (4-9) under mild conditions in almost good to high yields. The 1-alkyl(phenyl)isoselenochromenes (10-13) and 1-benzylisochromenes (18A, 18B), which were produced by the reaction of the salts 1 with Grignard reagents, were converted to the corresponding 1,3-disubstituted 2-benzopyrylium salts (14-17, 19) by treatment with triphenylcarbenium tetrafluoroborate (Ph₃C⁺ BF₄ ^-), respectively. The 1-benzylselenopyrylium salts (19A) and 1-benzyltelluropyrylium salts (19B) exist in the solvent as an equilibrium mixture of the salts (19) and the corresponding (Z)-benzylidene compounds (20).

Full text of DOI:10.1248/cpb.52.57

January 2004
Chem. Pharm. Bull. 52(1) 57—62 (2004)
57
Studies on Tellurium-Containing Heterocycles. Part 20.1) Reactions of
2-Benzoselenopyrylium Salts and 2-Benzotelluropyrylium Salts with
Nucleophiles: Formation of 1-Functionalized 1H-Isoselenochromenes and
1H-Isotellurochromenes
*
Haruki SASHIDA and Kazuo OHYANAGI
Faculty of Pharmaceutical Sciences, Hokuriku University; Kanagawa-machi, Kanazawa 920–1181, Japan.
Received September 2, 2003; accepted October 23, 2003
The reactions of the 2-benzoselenopyrylium (1A) and 2-benzotelluropyrylium cations (1B) with a variety of
nucleophiles have been investigated. LiAlH4, sodium alkoxide (NaOMe, NaOi-Pr and NaOt-Bu), diethylamine, n-
butylamine and acetone reacted with 1 to give the 1H-isochromenes (2) and the corresponding 1-substituted
products (4—9) under mild conditions in almost good to high yields. The 1-alkyl(phenyl)isoselenochromenes
(10—13) and 1-benzylisochromenes (18A, 18B), which were produced by the reaction of the salts 1 with Grig-
nard reagents, were converted to the corresponding 1,3-disubstituted 2-benzopyrylium salts (14—17, 19) by
treatment with triphenylcarbenium tetrafluoroborate (Ph3C؉ BF؊4 ), respectively. The 1-benzylselenopyrylium
salts (19A) and 1-benzyltelluropyrylium salts (19B) exist in the solvent as an equilibrium mixture of the salts (19)
and the corresponding (Z)-benzylidene compounds (20).
Key words 2-benzoselenopyrylium salt; 2-benzotelluropyrylium salt; isoselenochromene; isotellurochromene; nucleophile
Recently, the chemistry of the selenopyrylium2—4) and tel-
duction of 1A and 1B with LiAlH4 in diethyl ether at 0 °C af-
forded the 1H-isoselenochromenes (2A) and 1H-isotelluro-
choromenes (2B) in moderate yields as the sole products, re-
spectively. The use of THF as a solvent almost gave similar
results. The pyrylium salts (1) were also reduced by DIBAL-
H to give the 1H-isochromenes (2) in quantitative yields.
These compounds (2) were identical with the authentic sam-
ples,16) which were the precursors for the synthesis of the
corresponding pyrylium salts (1A) and (1B). The 3-tert-
butyl-2-benzopyrylium salts (1Aa) and (1Ba) reacted with
excess zinc dust in acetonitrile at 0 °C under an argon atmos-
phere to give 1,1Ј-bis(tert-butylisochromenyl) (3Aa) and
(3Ba) in 18 and 15% yield as the sole characterized products,
respectively. The MS spectrum of compound 3Aa suggested
the diselenide molecular formula of C26H30Se2 as it measured
a molecular ion at m/zϭ502 (80Se) and the expected isotope
pattern for Se2. The base peak was m/zϭ251, which was a
half of the molecular ion. In addition the HR-MS of 3Aa
showed the exact molecular formula. There was no character-
istic absorption in the IR spectrum. 3Aa and 3Ba were also
obtained by the catalytic hydrogenation of 1a using 5% Pd–C
in THF in ca. 25% yields. These bisisochromenyl com-
pounds (3) would be produced by the homo-coupling of the
radical intermediates.24—26)
Reaction of Pyrylium Salts with Nucleophiles We
have recently found that both the 1-benzotelluropyrylium11)
and 1-benzoselenopyrylium salts14) were attacked by a
methoxide ion in MeOH to form the corresponding 4-
methoxy-4H-chromenes as the major products in high yields.
Although the telluropyrylium salts did not react with a sec-
ondary or tertiary alkoxide in the corresponding alcohol to
give any characterizable products, the unsubstituted 1-ben-
zoselenopyrylium salts14) reacted with NaOi-Pr and KOt-Bu
to afford the corresponding the 2-alkoxy-2H-seleno-
chromenes in good yields. Furthermore, the NaOi-Pr ion at-
tacked the C-4 position of the 2-substituted selenopyrylium
salts to give the 4-isopropoxy-4H-selenochromenes.14) Thus,
luropyrylium salts,2—5) six-membered cationic heteroaromat-
ics containing a selenium or tellurium atom, in both fields of
organic synthesis and the chemical transformation of organ-
otellurium and organoselenium compounds, has attracted
considerable attention. Both of the monocyclic pyrylium6,7)
and 1-benzopyrylium salts8—10) containing these atoms have
been prepared, and the chemistry of these compounds has
been reviewed. We have also previously reported the practi-
cal and facile preparation11—13) and the reactions11,14,15) of
these 1-benzopyrylium salts. More recently, we succeeded in
preparing16) the stable 2-benzotelluropyrylium17) and 2-ben-
zoselenopyrylium salts,18) structural isomers of them; the for-
mer is a previously unknown heterocyclic ring system.
Therefore, this paper deals with the results of the examina-
tion of the reactivity of these novel 2-benzopyryliun salts
with various nucleophiles using the stable compounds, 3-
tert-butyl and (or) 3-unsubstituted derivatives as easily avail-
able pyrylium salts. The differences in the reactivity of these
pyrylium salts containing a tellurium or selenium atom have
received most of our attention thus far.
Results and Discussion
Reduction of Pyrylium Salts The reductions of the
monocyclic chalcogenopyrylium ions by hydride donors such
22)
as LiAlH4,19,20) NaBH4,21) LiBH4 and diisobutylaluminum
hydride (DIBAL-H)23) were reported. In all cases, the major
products are 4H-pyrans. The one-electron reduction of them
when treated with zinc dust24—26) in a degassed aprotic sol-
vent gives the bichalcogenopyran derivatives via the pyranyl
radical intermediates. We have previously described that the
LiAlH4 reduction of the 1-benzotelluropyrylium salts11) and
1-benzoselenopyrylium salts,14) the regioisomers of the title
compounds, afforded a mixture of the corresponding 2H- and
4H-chromenes, respectively; the latter was the major product.
In order to compare these behaviors, we first examined the
hydride reduction of the 2-benzopyrylium salts (1). The re-
To whom correspondence should be addressed. e-mail: h-sashida@hokuriku-u.ac.jp
© 2004 Pharmaceutical Society of Japan

58
Vol. 52, No. 1
Reagents and conditions: i, LiAlH4, Et2O, 0 °C, ii, DIBAL-H, THF, Ϫ20 °C, iii, Zn dust, MeCN, 0 °C to room temp., iv, H2, Pd–C, THF, room temp., v, NaOMe, MeOH, room
temp., vi, NaOi-Pr, i-PrOH, room temp., vii, NaOt-Bu, t-BuOH, room temp., viii, NHEt2, benzene, room temp., ix, NH2 n-Bu, benzene, room temp., x, MeCOMe, room temp.
Chart 1
Table 1. 1-Functionalized 1H-Isoselenochromenes and 1H-Isotelluro-
chromenes (4—9)
we examined the reactivities of the 2-benzoselenopyrylium
(1A) and 2-benzotelluropyrylium salts (1B) towards primary,
secondary and tertiary alkoxide ions. The reaction of the
salts 1 with NaOMe in MeOH at room temperature resulted
in the nucleophilic addition at the C-1 position on the hetero
cation ring to give the desired 1-methoxy-1H-isochromenes
(4Aa, 4Ab, 4Ba) in very high yields as the sole products ex-
cept for the unsubstituted telluropyrylium salt (1Bb). The
treatment of 1 with NaOi-Pr also produced the 1-isopropoxy-
1H-isochromenes (5) in almost quantitative yields. Moreover,
the nucleophilic attack of the tertiary butoxide ion at the
same position was carried out to yield only the 1-tert-butoxy-
1H-isoselenochromenes (6Aa, 6Ab) in 33 and 10% yields,
respectively. These facts suggest that the C-1 position on the
2-benzoseleno- and 2-benzotelluropyrylium cation ring has a
higher reactivity than that of the C-4 position of the 1-ben-
zopyrylium ring as might have been expected. For the reac-
tion with alkoxide anions, the 3-unsubstituted telluropy-
rylium salt (1Bb) decomposed to give a complex mixture,
probably due to the thermal instability of the products.
Compd.
No.
Yield
(%)
Appearance
mp/°C
M
R
X
4Aa
4Ab
4Ba
Se
Se
Te
t-Bu
H
t-Bu
OMe
OMe
OMe
98
93
94
Pale yellow oil
Yellow oil
Yellow prisms
mp 56—58
5Aa
Se
t-Bu
Oi-Pr
99
Colorless prisms
mp 67—68
5Ab
5Ba
Se
Te
H
t-Bu
Oi-Pr
Oi-Pr
90
96
Yellow oil
Pale yellow prisms
mp 70—71
6Aa
Se
t-Bu
Ot-Bu
33
Pale yellow prisms
mp 187—190
Yellow oil
Pale yellow prisms
mp 57—58
6Ab
7Aa
Se
Se
H
t-Bu
Ot-Bu
NEt2
10
98
7Ab
Se
H
NEt2
84
Yellow prisms
mp 36—38
7Ba
8Aa
8Ab
9Aa
9Ab
9Ba
Te
Se
Se
Se
Se
Te
t-Bu
t-Bu
H
t-Bu
H
NEt2
NH n-Bu
NH n-Bu
CH2COCH3
CH2COCH3
CH2COCH3
95
96
84
97
11
27
Yellow oil
Yellow oil
Yellow oil
Yellow oil
Yellow oil
Pale yellow oil
When 1 were treated with an aliphatic secondary amine,
diethylamine in benzene at room temperature, the reaction
mixtures immediately became yellow or orange, and the
starting materials had disappeared. The corresponding 1-di-
ethylamino-1H-isochoromenes (7) were obtained in high
yields. n-Butylamine, a primary amine, reacted with the 2-
benzoselenopyrylium salts (1A) to afford the desired 1-n-
t-Bu
All the 1-functionalized isoselenochromenes (3A—9A)
butylaminoisoselenochromenes (8A) in high yields. In con- and isotellurochromenes (3B—9B) thus obtained in this way
trast, the reaction of the 3-tert-butyl-telluropyrylium salt are the novel compounds except for the isochromenes (2A,
(1Ba) gave the complex mixture including unknown prod- 2B) were mainly characterized on the basis of HR-MS and
ucts.
1H-NMR spectral analyses. These results and the spectral
Previously, we observed that both the 1-benzotelluropy- data of the products are summarized in Tables 1 and 2. Gen-
rylium11) and selenopyrylium salts14) easily reacted with ace- erally, the isoselenochromenes are more stable than the
tone in the absence of a base catalyst to afford the corre- isotellurochromenes, and the yields of the products are
sponding 1-acetonyl-1H-isochromene derivatives. It was also higher. The 3-unsubstituted isotellurochromenes are not very
reported27) that the 2-benzothiopyrylium salt having a ben- stable, consequently, the 3-tert-butylisoselenochromenes are
zoyl group as a strong electron-withdrawing group at the C-3 the most stable.
position easily reacted with acetone under similar conditions
Introduction of a Carbon Functional Group at C-1 Po-
to form 1-acetonyl-3-benzoyl-1H-isothiochromene. These re- sition For the purpose to introduce a normal carbon func-
sults prompted us to examine the reaction of 1 with acetone. tional group into the hetero ring of the salts (1), Grignard
The addition of the salts (1) to dry acetone at room tempera- reagents are employed as the nucleophiles. The treatment of
ture gave the 1-acetonyl-1H-isocheromenes (9). However, the the 2-benzoselenopyrylium salts (1A) with Grignard
yield of the products was very low except for the 1-acetonyl- reagents, such as methyl-, ethyl- and phenyl-magnesium bro-
3-tert-butyl-1H-isoselenocheromenes (9Aa).
mide (iodide) in ether or THF at 0 °C resulted in carbon–car-

January 2004
59
Table 2. Spectral Data for the 1-Functionalized 1H-Isoselenochromenes and 1H-Isotellurochromenes (4—9)
1H-NMR (90 MHz, CDCl3, JϭHz)
Formula HR-MS
Calcd (Found)
Compd.
No.
M
R
X
1-H
4-H
Ar-H
R-H
X-H
4Aa
4Ab
4Ba
5Aa
Se t-Bu
OMe
OMe
OMe
Oi-Pr
C14H18OSe
282.0523
(282.0525)
C10H10OSe
225.9897
(225.9902)
C14H18OTe
332.0421
(332.0412)
C16H22OSe
310.0836
5.76
(s)
6.90
(s)
7.2—7.3
(4H, m)
1.32
(9H, s, t-Bu)
3.31
(3H, s, OMe)
Se
H
5.77
(d, Jϭ2)
7.16
(d, Jϭ10)
7.2—7.4
(4H, m) (1H, dd, Jϭ10, 2, 3-H)
6.88
3.33
(3H, s, OMe)
Te t-Bu
Se t-Bu
5.99
(s)
6.85
(s)
7.2—7.4
(4H, m)
1.30
(9H, s, t-Bu)
3.26
(3H, s, OMe)
5.84
(s)
6.90
(s)
7.2—7.3
(4H, m)
1.31
(9H, s, t-Bu)
1.10, 1.23
(each 3H, d, Jϭ6, OCH(CH3)2),
4.10
(310.0837)
(1H, dq, Jϭ6, 6, OCH(CH3)2)
1.11, 1.20
(each 3H, d, Jϭ6, OCH(CH3)2),
4.05
(1H, dq, Jϭ6, 6, OCH(CH3)2)
1.12, 1.24
(each 3H, d, Jϭ6, OCH(CH3)2),
3.92
5Ab
5Ba
Se
H
Oi-Pr
Oi-Pr
C12H14OSe
254.0210
(254.0202)
5.86
(d, Jϭ2)
7.13
(d, Jϭ10)
7.0—7.6
(4H, m) (1H, dd, Jϭ10, 2, 3-H)
6.83
Te t-Bu
Se t-Bu
C16H22OTe
360.0734
(360.0752)
6.07
(s)
6.82
(s)
7.1—7.4
(4H, m)
1.29
(9H, s, t-Bu)
(1H, dq, Jϭ6, 6, OCH(CH3)2)
1.30
6Aa
6Ab
7Aa
7Ab
7Ba
8Aa
8Ab
9Aa
9Ab
9Ba
Ot-Bu
Ot-Bu
NEt2
C17H24OSe
324.0993
(324.0998)
C13H16OSe
268.0367
(268.0369)
C17H25NSe
323.1153
(323.1152)
C13H17NSe
267.0527
(267.0522)
C17H25NTe
373.1050
(373.1041)
C17H25NSe
323.1153
(323.1147)
C13H17NSe
267.0527
6.04
(s)
6.83
(s)
7.2—7.3
(4H, m)
1.33
(9H, s, t-Bu)
(9H, s, Ot-Bu)
Se
H
6.10
(d, Jϭ1)
7.09
(d, Jϭ10)
7.2—7.4
(4H, m) (1H, dd, Jϭ10, 1, 3-H)
6.92
1.34
(9H, s, Ot-Bu)
Se t-Bu
5.75
(s)
6.71
(s)
7.1—7.3
(4H, m)
1.32
(9H, s, t-Bu)
1.00, 2.1—2.7
(6H, t, Jϭ7, 4H, m, NEt2)
Se
H
NEt2
5.81
(br s)
6.98
(d, Jϭ10)
7.0—7.3
(4H, m)
6.86
0.99, 2.1—2.8
(6H, t, Jϭ7, 4H, m, NEt2)
(1H, d, Jϭ10, 3-H)
Te t-Bu
Se t-Bu
NEt2
5.96
(s)
6.69
(s)
7.1—7.4
(4H, m)
1.31
(9H, s, t-Bu)
1.04, 2.1—2.7
(6H, t, Jϭ7, 4H, m, NEt2)
NH n-Bu
NH n-Bu
5.16
(s)
6.87
(s)
7.1—7.3
(4H, m)
1.30
(9H, s, t-Bu)
0.89, 1.2—1.4, 2.4—3.0
(3H, t, Jϭ7, 4H, m, 2H, m, N n-Bu),
1.6 (1H, br, NH)
Se
H
5.19
(d, Jϭ2)
7.03
(d, Jϭ7)
7.1—7.4
(4H, m)
6.82
0.89, 1.2—1.6, 2.4—2.9
(1H, dd, Jϭ7, 2, 3-H) (3H, t, Jϭ7, 4H, m, 2H, m, N n-Bu),
(267.0523)
1.6 (1H, br, NH)
Se t-Bu CH2COCH3 C16H20OSe
4.40
(dd, Jϭ9, 6)
6.75
(s)
7.1—7.2
(4H, m)
1.28
(9H, s, t-Bu)
2.03 (3H, s, CH2COCH3)
2.80, 3.17 (1H, dd, Jϭ17, 6, 1H, dd,
Jϭ17, 9, CH2COCH3)
308.0680
(308.0684)
Se
H
CH2COCH3 C12H12OSe
4.39
6.99
7.1—7.4
6.71
2.05 (3H, s, CH2COCH3)
(4H, m) (1H, dd, Jϭ10, 2, 3-H) 2.85, 3.35 (1H, dd, Jϭ17, 5, 1H, dd,
Jϭ17, 9, CH2COCH3)
252.0054 (ddd, Jϭ9, 5, 2) (d, Jϭ10)
(252.0049)
Te t-Bu CH2COCH3 C16H20OTe
4.30
(dd, Jϭ8, 7)
6.72
(s)
7.1—7.3
(4H, m)
1.27
(9H, s, t-Bu)
2.01 (3H, s, CH2COCH3)
3.13, 3.38 (1H, dd, Jϭ17, 7, 1H, dd,
Jϭ17, 8, CH2COCH3)
358.0577
(358.0582)
bon bond formation at the C-1 position to afford the desired duced via a free radical mechanism. This result evidently
corresponding 1-substituted 1H-isoselenochromenes (10— supports the present formation of the dimer (3B) proceeding
13) in good yields. In contrast, the reaction of the telluropy- via a similar radical mechanism. 3B were also obtained by
rylium salt (1Ba) with Grignard reagents gave 1,1Ј-bis(tert- the reaction of 1B with zinc powder or catalytic hydrogena-
butylisotellurochromenyl) (3B), which was a self-coupling tion as already described.
product at the C-1 position of the parent pyrylium salt (1Ba)
Next, we planned the preparation of the 1,3-disubstituted
in ca. 10% yield as the sole characterized product; the nor- 2-benzoselenopyrylium salts by the reaction of the obtained
mal coupling products were not obtained. It is already well products with triphenylcarbenium tetrafluoroborate (Ph3Cϩ
known28) that the treatment of telluraxanthylium salts with BFϪ4 ). The treatment of the 1,3-disubstituted isochromenes
reducing agents (e.g., zinc powder) or nucleophiles (e.g., am- (10—13) with a small excess of Ph3Cϩ BF4ϩ in MeNO2 re-
monium chloride) gives the telluraxanthyl ditellurides, pro- sulted in the dehydrogenation to afford the corresponding

60
Vol. 52, No. 1
Chart 3
1.29) were observed in the ratio of 2 : 3 indicating the pres-
ence of the salt (19Ba) and the benzylidene derivative
(20Bb).17) The ratio of the unsubstituted selenopyrylium salt
(19Ab) and the benzylidene compound (20Ab) was similar
at ca. 1 : 1 in the NMR spectrum.
The fact, that 20 could be isolated clearly indicated that
BFϪ4 , the counter anion of the salts (19), abstracted the b-hy-
drogen of the methylene carbon of the benzyl group at the C-
1 on the pyrylium cation ring (19) to form the olefin. In the
case of the 2-benzoselenopyrylium salts (14—16) having an
alkyl group at the C-1 position except a benzyl group, the b-
hydrogen elimination did not occur forming any 1-methyl-
ideneisoselenochromenes.
Chart 2
stable 2-benzoselenopyrylium tetafluoroborates (14—17) as
yellow or green prisms in good to high yields. The unsubsti-
tuted29) and 3-substituted 2-benzoselenopyrylium salts16)
have been prepared before, while these selenopyrylium salts
(14—17) having two carbon functional groups at the C-1 and
C-3 positions are hitherto unknown compounds.
Reaction of Pyrylium Salts with Benzylmagnesium
Bromide The 2-benzoselenopyrylium salts (1A) also re-
acted with benzylmagnesium bromide to afford the 1-benzyl-
1H-isoselenochromenes (18A), as normal coupling products
in ca. 60% yields. It has already been found11) that the 4-ben-
zyl-4H-tellurochromenes are produced from the 2-substituted
1-benzotelluropyrylium salts using benzylmagnesium bro-
mide as a Grignard reagent without forming dimeric-type
compounds. This finding on the reaction of the pyrylium
salts containing a selenium or tellurium atom with benzyl-
magnesium bromide suggests that the 1-benzyl-1H-isotel-
lurochromenes could be obtained from the 2-benzotelluropy-
rylium salts (1B). Both the tert-butyl-1-benzotelluropyrylium
salt (1Ba) and the unsubstituted telluropyrylium salt (1Bb)
were coupled with benzylmagnesium bromide to give the de-
sired 1-benzyl derivatives (18Ba, 18Bb) as the sole product
in 48 and 11% yields, respectively. The reaction of the 1-ben-
zylisochromenes (18A, 18B) with Ph3Cϩ BF4Ϫ afforded the
desired 1-benzyl-2-benzopyrylium salts (19) as stable yellow
prisms in ca. 60% yields except for the 3-unsubstituted 2-
benzotelluropyrylium salts (19Bb), which were perhaps ther-
Conculusion
In the present study, the reactivity of the 2-benzoseleno-
and 2-benzotelluro-pyrylium salts towards several nucleo-
philes including the reducing and Grignard reagents was ex-
amined, the latter pyrylium cation is a novel heterocyclic ring
system. Various 1-functionalized isoselenochromenes and
isotellurochoromenes were obtained as a result, and then
transformed into several 2-benzoselenopyrylium salts and 2-
benzotelluropyrylium salts having two carbon functional
groups at the C-1 and C-3 positions. It has become certain by
the isolation of the benzylidene compounds that the b-hydro-
gen of the methylene carbon of the pyrylium cation ring was
eliminated by BFϪ4 , the counter anion of the salt. Further re-
actions and applications of the 2-benzopyrylium salts con-
taining a selenium or tellurium atom are now under investi-
gation.
1
Experimental
mally unstable. Surprisingly, the H-NMR spectrum of the
Melting points were measured on a Yanagimoto micro melting point hot
stage apparatus and are uncorrected. IR spectra were determined with a Hi-
tachi 270-30 spectrometer. Mass spectra (MS) and HRMS were recorded on
a JEOL JMS-DX300 instrument. NMR spectra were determined with a
JEOL EX-90A (90 MHz) or a JEOL JNM-GSX 400 (400 MHz) spectrome-
ter in CDCl3 or CD3CN using tetramethylsilane as internal standard and J
values are given in Hz. Microanalyses were performed in the Microanalyti-
cal Laboratory in this Faculty.
crude isolated 1-benzyl-3-tert-butyl-selenopyrylium salt
(19Aa) in CD3CN appeared as two tert-butyl signals at d
1.59 and 1.25 in a ratio of 4 : 3. This result indicates the pres-
ence of the salt (19Aa) and benzylidene compound (20Aa).
Actually, the treatment of the salt (19Aa) by base or alumina
column chromatography eluted with methylene chloride
afforded (Z)-1-benzylidene-3-tert-butylisoselenochromene
(20Aa)17) in almost quantitative yield. For the 1-benzyltel-
LiAlH4 Reduction of Pyrylium Salts (1) LiAlH4 (16 mg, 0.33 mmol)
was added in a small portion to a suspended mixture of 1 (0.3 mmol) in Et2O
luropyrylium salt (19Ba), two tert-butyl signals (d 1.59 and (6 ml) at 0 °C under an argon atmosphere. The reaction mixture was stirred

January 2004
61
at room temperature for 30 min, and then quenched by the addition of satu- selenopyrylium salt (1A) was treated with n-butylamine instead of diethyl-
lated aqueous Na2CO3 solution (5 drops). The resulting solution was dried amine and worked up as described for the preparation of 7 to give 8.
(MgSO4) and evaporated in vacuo. The resulting residue was chro-
1-n-Butyl-3-tert-butyl-1H-isoselenochromene (8Aa): IR (neat) cmϪ1
:
matographed on silica gel eluted with n-hexane to give the isochromene (2). 3340 (NH).
The products were identical with authentic samples.16)
3-tert-Butyl-1H-isoselenochromene (2Aa): Yield 59%.
1H-Isoselenochromene (2Ab): Yield 59%.
3-tert-Butyl-1H-isotellurochromene (2Ba): Yield 58%.
1H-Isotellurochromene (2Bb): Yield 56%.
1-n-Butyl-1H-isoselenochromene (8Ab): IR (neat) cmϪ1: 3340 (NH).
Treatment of Pyrylium Salts (1) with Acetone The pyrylium salt (1)
(0.3 mmol) was disolved in dry acetone (6 ml) at 0 °C under an argon atmos-
phere. The reaction mixture was stirred at room temperature for 30 min, and
then extracted with CH2Cl2 (20 mlϫ3). The organic layers were washed with
DIBAL-H Reduction of Pyrylium Salts (1) DIBAL-H hexane solution brine (30 mlϫ2) and dried (MgSO4) and evaporated in vacuo. The resulting
(0.95 mol/l, 1.58 ml, 1.5 mmol) was added dropwise with stirring to a solu- residue was chromatographed on silica gel eluted with n-hexane–CH2Cl2
tion of the pyrylium salt (1) (1 mmol) in dry THF (20 ml) under an argon at-
mosphere at Ϫ20 °C. The mixture was stirred for 1 h, diluted with water
(1 : 1) to give 9 as a pale yellow or yellow oil.
1-Acetonyl-3-tert-butyl-1H-isoselenochromene (9Aa): IR (neat) cmϪ1
:
(20 ml), and then extracted with CH2Cl2 (30 mlϫ3). The organic layers were 1722 (CϭO).
washed with 5% HCl (30 mlϫ2) and saturated aqueous NaHCO3 (30 mlϫ2),
dried (MgSO4) and evaporated in vacuo. The residue was chromatographed
on silica gel using n-hexane as eluent to give 2.
2Aa: Yield 98%.
2Ab: Yield 92%.
1-Acetonyl-1H-isoselenochromene (9Ab): IR (neat) cmϪ1: 1716 (CϭO).
1-Acetonyl-3-tert-butyl-1H-isotellurochromene (9Ba): IR (neat) cmϪ1
1718 (CϭO).
:
Reaction of 2-Benzoselenopyrylium Salts 1A with Grignard Reagent.
3-tert-Butyl-1-methyl-1H-isoselenochromene (10) MeMgI (4 mmol) in
ether solution (4 ml) was slowly added to a suspended mixture of the
pyrylium salt (1Aa) (3 mmol) in ether (20 ml) at 0 °C under an argon atmos-
2Ba: Yield 92%.
2Bb: Yield 89%.
Reaction of Pyrylium Salts (1) with Zn Dust Zn dust (80 mg) was phere. The resulting mixture was stirred under the conditions for 30 min, and
added to a stirred solution of the pyrylium salt (1) (1 mmol) in dry MeCN quenched by the addition of saturated aqueous NH4Cl solution (10 ml). The
(5 ml) under an argon atmosphere at 0 °C for 3 h. After removal of Zn dust, resulting mixture was extracted with Et2O (30 mlϫ3). The organic layers
the mixture was evaporated in vacuo. The resulting residue was chro- were washed with brine (30 mlϫ2) and dried (MgSO4) and evaporated in
matographed on silica gel, with n-hexane–CH2Cl2 (5 : 1) as eluent to give 3.
vacuo. The resulting residue was chromatographed on silica gel eluted with
1,1Ј-Bis(tert-butylisoselenochromenyl) (3Aa): Yield 18%, pale yellow n-hexane–CH2Cl2 (20 : 1) to give 10 (76%), pale yellow oil. 1H-NMR
prisms (acetone–n-hexane), mp 271—273 °C. MS m/z: 502 (Mϩ, 2), 500 (2),
(90 MHz, CDCl3) d: 1.28 (9H, s, t-Bu), 1.60 (3H, d, Jϭ7 Hz, 1-Me), 4.02
1
251 (100), 249 (50). H-NMR (90 MHz, CDCl3) d: 1.33 (18H, s, t-Buϫ2), (1H, q, Jϭ7 Hz, 1-H), 6.72 (1H, s, 4-H), 7.1—7.3 (4H, m, Ph-H). HR-MS
3.91 (2H, s, 1- and 1Ј-H), 6.88 (2H, s, 4- and 4Ј-H), 7.2—7.3 (8H, m, Ph- m/z Mϩ Calcd for C14H18Se: 266.0574. Found: 266.0576.
Hϫ2). HR-MS m/z Mϩ Calcd for C26H30Se2: 502.0683. Found: 502.0691.
3-tert-Butyl-1-ethyl-1H-isoselenochromene (11) The pyrylium salt
1,1Ј-Bis(tert-butylisotellurochromenyl) (3Ba): Yield 15%, yellow (1Aa) was treated with EtMgBr instead of MeMgI and worked up as de-
1
prisms (acetone–n-hexane), mp 235—236 °C. MS m/z: 602 (Mϩ, 5), 600
scribed for the preparation of 10 to give 11 (69%), colorless oil. H-NMR
1
(10), 598 (12), 596 (8), 301 (100), 299 (90), 297 (60). H-NMR (90 MHz, (90 MHz, CDCl3) d: 0.89 (3H, t, Jϭ7 Hz, CH2CH3), 1.28 (9H, s, t-Bu), 1.78
CDCl3) d: 1.33 (18H, s, t-Buϫ2), 3.97 (2H, s, 1- and 1Ј-H), 6.88 (2H, s, 4- (dq, Jϭ7, 7 Hz, CH2CH3), 3.68 (1H, t, Jϭ7 Hz, 1-H), 6.69 (1H, s, 4-H),
and 4Ј-H), 7.1—7.3 (8H, m, Ph-Hϫ2). HR-MS m/z Mϩ Calcd for 7.1—7.2 (4H, m, Ph-H). HR-MS m/z Mϩ Calcd for C15H20Se: 280.0731.
C26H30Te2: 602.0476. Found: 602.0472.
Found: 280.0724.
Hydrogenation of Pyrylium Salts (1) with Pd–C A solution of 1
1-n-Butyl-3-tert-butyl-1H-isoselenochromene (12) The pyrylium salt
(1 mmol) in dry THF (40 ml) was hydrogenated with 5% Pd–C (50 mg) with 1Aa was treated with n-BuMgCl instead of MeMgI and worked up as de-
stirring under atmospheric pressure of H2 at room temperature. The reaction scribed for the preparation of 10 to give 12 (71%), pale yellow oil. 1H-NMR
mixture subjected to filtration and the filtrate was evaporated in vacuo. The (90 MHz, CDCl3) d: 0.85 (3H, t, Jϭ7 Hz, CH2CH2CH2CH3), 1.1—1.4 (4H,
resulting residue was chromatographed on silica gel, with n-hexane–CH2Cl2
(5 : 1) as eluent to give 3.
3Aa: Yield 26%.
m, CH2CH2CH2CH3), 1.27 (9H, s, t-Bu), 1.6—1.8 (2H, m, CH2CH2CH2CH3),
3.75 (1H, t, Jϭ7 Hz, 1-H), 6.70 (1H, s, 4-H), 7.1—7.2 (4H, m, Ph-H). HR-
MS m/z Mϩ Calcd for C17H24Se: 308.1044. Found: 308.1043.
3Ba: Yield 20%.
3-tert-Butyl-1-phenyl-1H-isoselenochromene (13) The pyrylium salt
Treatment of Pyrylium Salts (1) with NaOMe in MeOH NaOMe (1Aa) was treated with PhMgBr instead of MeMgI and worked up as de-
(28% solution in MeOH, 1 ml) was added to a solution of the pyrylium salt scribed for the preparation of 10 to give 13 (74%), yellow prisms (n-
1
(1) (0.5 mmol) in MeOH (10 ml) under an argon atmosphere. The resulting hexane), mp 43—44 °C. H-NMR (90 MHz, CDCl3) d: 1.16 (9H, s, t-Bu),
solution was stirred for 30 min and extracted with CH2Cl2 (20 mlϫ3). The 5.24 (1H, s, 1-H), 6.78 (1H, s, 4-H), 6.9—7.2 (9H, m, Ph-H). HR-MS m/z
organic layers were washed with brine (30 mlϫ2), dried (MgSO4), and evap- Mϩ Calcd for C19H20Se: 328.0731. Found: 328.0732.
orated in vacuo to give the 1-methoxy-1H-isochromene (4). Products were
1,1؅-Bis(tert-butylisotellurochromenyl) (3B) This compound was ob-
obtained in a nearly pure form, and decomposed during the attempted purifi- tained in ca. 10% yield by the reaction of 1B with the Grignarn reagents
cation by silica gel chromatography. Crystalline products were recrystallized (e.g., MeMgI, EtMgBr, n-BuMgCl, PhMgBr).
from n-hexane.
Treatment of Isochromenes (10—13) with Ph3C؉ BF؊4 : Formation of
Treatment of Selenopyrylium Salts (1) with NaOi-Pr in i-PrOH 2-Benzoselelopyrylium Tetrafluoroborate (14—17) Ph3CϩBFϪ4 (187 mg,
NaOi-Pr (30% solution in i-PrOH, prepared from Na and i-PrOH, 1 ml) was 0.55 mmol) was added to a stirred solution of the isoselenochromene (10)
added to a solution of the pyrylium salt (1) (0.5 mmol) in i-PrOH (10 ml) (0.5 mmol) in dry MeNO2 (2 ml) and the mixture was stirred at room tem-
under an argon atmosphere. The resulting reaction mixture was worked up perature for 2 h. To the reaction mixture was added dry Et2O (25 ml) to pre-
as described for the preparation of 4 to give the 1-isopropoxy-1H- cipitate the pyrylium salts.
isochromene (5).
Treatment of Selenopyrylium Salts (1A) with KOt-Bu in t-BuOH Yield 86%, pale yellow prisms (CHCl3), mp 200—202 °C (decomp.). IR
KOt-Bu (200 mg) was added to a solution of the selenopyrylium salt (1A)
3-tert-Butyl-1-methyl-2-benzoselelopyrylium Tetrafluoroborate (14):
(KBr) cmϪ1 1062 (BFϪ4 ). 1H-NMR (90 MHz, CD3CN) d: 1.67 (9H, s, t-Bu),
(0.5 mmol) in t-BuOH (10 ml) under an argon atmosphere. The resulting re- 3.53 (3H, s, 1-Me), 8.3—8.7 (4H, m, Ph-H), 8.88 (1H, s, 4-H). Anal. Calcd
action mixture was worked up as described for the preparation of 4 to give for C14H17BF4Se: C, 47.90; H, 4.88. Found: C, 47.89, H, 4.85.
the 1-tert-butoxy-1H-isoselenochromene (6A).
3-tert-Butyl-1-ethyl-2-benzoselelopyrylium Tetrafluoroborate (15):
Treatment of Pyrylium Salts (1) with Diethylamine Diethylamine Yield 74%, yellow prisms (CHCl3), mp 146—148 °C (decomp.). IR (KBr)
1
(0.6 ml) was added slowly to a suspended mixture of 1 (0.3 mmol) in ben- cmϪ1 1060 (BF4Ϫ). H-NMR (90 MHz, CD3CN) d: 1.67 (9H, s, t-Bu), 1.70
zene (6 ml) at room temperature under an argon atmosphere. The reaction (3H, t, Jϭ8 Hz, CH2CH3), 4.01 (2H, q, Jϭ8 Hz, CH2CH3), 8.1—8.5 (4H, m,
mixture was stirred at room temperature for 30 min, and then extracted with Ph-H), 8.86 (1H, s, 4-H). Anal. Calcd for C15H19BF4Se: C, 49.35; H, 5.25.
benzene (20 mlϫ3). Benzene layer was washed with brine (30 mlϫ2) and
dried (MgSO4), and evaporated in vacuo to give the 1-diethylamino-1H-
Found: C, 49.28; H, 5.20.
1-n-Butyl-3-tert-butyl-2-benzoselelopyrylium Tetrafluoroborate (16):
isochromene (7). All products (7) were obtained in nearly pure states. Thus, Yield 72%, yellow prisms (CHCl3), mp 100—102 °C (decomp.). IR (KBr)
1
crystalline products were recrystallized from n-hexane.
Treatment of Selenopyrylium Salts (1A) with n-Butylthylamine The (3H, t, Jϭ7 Hz, CH2CH2CH2CH3), 1.4—1.8 (4H, m,, CH2CH2CH2CH3),
cmϪ1 1055 (BFϪ4 ). H-NMR (90 MHz, CD3CN) d: 1.67 (9H, s, t-Bu), 1.13

62
Vol. 52, No. 1
1H-NMR (400 MHz, CDCl3) d: 1.24 (9H, s, t-Bu), 6.86 (1H, s, 4-H), 7.18—
7.44 (8H, m, Ph-H), 7.48 (1H, s, 1Ј-H), 7.53 (1H, br d, Jϭ7.8 Hz, 8-H). HR-
MS m/z Mϩ Calcd for C20H20Te: 390.0628. Found: 390.0627.
3.99 (2H, t, Jϭ8 Hz, CH2CH2CH2CH3), 8.4—8.8 (4H, m, Ph-H), 8.87 (1H,
s, 4-H). Anal. Calcd for C17H23BF4Se: C, 51.94; H, 5.90. Found: C, 51.84;
H, 6.00.
3-tert-Butyl-1-phenyl-2-benzoselelopyrylium Tetrafluoroborate (17):
Yield 77%, yellow prisms (CHCl3), mp 70—72 °C (decomp.). IR (KBr)
cmϪ1 1057 (BFϪ4 ). 1H-NMR (90 MHz, CD3CN) d: 1.71 (9H, s, t-Bu), 7.8
(5H, br s, 1-Ph), 8.0—8.5 (4H, m, Ph-H), 9.01 (1H, s, 4-H). Anal. Calcd for
C19H19BF4Se: C, 55.24; H, 4.64. Found: C, 55.24; H, 4.86.
Reaction of Pyrylium Salts (1) with PhCH2MgBr The pyrylium salt
(1) was treated with PhCH2MgBr instead of MeMgI and worked up as de-
scribed for the preparation of 13 to give 18.
Acknowledgements A part of his work was supported by a Grant-in-
Aid for Scientific Research from The Ministry of Education, Culture,
Sports, Science and Technology of Japan, and The Specific Research Fund
of Hokuriku University. The authors wish to express to Mr. H. Satoh for his
technical assistance.
References and Notes
1) For part 19; ref. 13.
1-Benzyl-3-tert-butyl-1H-isoselenochromene (18Aa): Yield 59%, yel-
low prisms (n-hexane), mp 52—53 °C. H-NMR (90 MHz, CDCl3) d: 1.32
(9H, s, t-Bu), 3.05 (2H, d, Jϭ8 Hz, CH2Ph), 3.99 (1H, t, Jϭ8 Hz, 1-H), 6.80
(1H, s, 4-H), 6.9—7.3 (9H, m, Ph-H). HR-MS m/z Mϩ Calcd for C22H22Se:
342.0888. Found: 342.0888.
1-Benzyl-1H-isoselenochromene (18Ab): Yield 31%, pale yellow prisms
(n-hexane), mp 49—52 °C. 1H-NMR (90 MHz, CDCl3) d: 3.12 (2H, d,
Jϭ8 Hz, CH2Ph), 3.95 (1H, dd, Jϭ8, 1 Hz, 1-H), 6.74 (1H, dd, Jϭ10, 1 Hz,
3-H), 7.04 (1H, d, Jϭ10 Hz, 4-H), 6.8—7.3 (9H, m, Ph-H). HR-MS m/z Mϩ
Calcd for C16H14Se: 286.0261. Found: 286.0258.
1
2) Kuthan J., Sebek P., Bohm S., “Advances in Heterocyclic Chemistry:
Developments in the Chemistry of Thiopyrans, Selenopyrans, and Tel-
luropyrans,” Vol. 59, Academic Press, London, 1994, pp. 179—244.
3) Doddi G., Ercolani G., “Advances in Heterocyclic Chemistry: Thiopy-
rylium, Selenopyrylium, and Telluropyrylium Salts,” Vol. 60, Acade-
mic Press, London, 1994, pp. 65—195.
4) Sadekov I. D., Minkin V., “Advances in Heterocyclic Chemistry: Six-
Membered heterocycles with a Tellurium Atom,” Vol. 63, Academic
Press, London, 1994, pp. 1—60.
5) Detty M. R., O’regan M. B., “The Chemistry of Heterocyclic Com-
pounds: Telluropyrylium Compounds,” Vol. 53, ed. by Taylor E. C.,
John Wiley & Sons, New York, 1994, pp. 219—291.
1-Benzyl-3-tert-butyl-1H-isotellurochromene (18Ba): Yield 48%, yel-
low oil. 1H-NMR (90 MHz, CDCl3) d: 1.31 (9H, s, t-Bu), 3.21 (2H, d,
Jϭ7 Hz, CH2Ph), 3.96 (1H, t, Jϭ7 Hz, 1-H), 6.78 (1H, s, 4-H), 6.9—7.3
(9H, m, Ph-H). HR-MS m/z Mϩ Calcd for C20H22Te: 392.0785. Found:
392.0781.
6) Detty M. R., Murray B. J., J. Org. Chem., 47, 5235—5239 (1982).
7) Detty M. R., Luss H. R., Organometallics, 11, 2157—2162 (1992).
8) Ladatko A. A., Nivorozhkin V. L., Sadekov I. D., Khim. Geterotsikl.
Soedin., 1986, 1571—1572, [Chem. Abstr., 107, 58818s (1987)].
9) Detty M. R., Murray B. J., J. Am. Chem. Soc., 105, 883—890 (1983).
10) Detty M. R., Luss H. R., Organometallics, 5, 2250—2256 (1986).
11) Sashida H., Minamida H., J. Chem. Soc., Perkin Trans. 1, 1999,
1665—1670.
12) Sashida H., Minamida H., J. Chem. Res. (S), 2000, 569—571.
13) Sashida H., Yoshida M., Heterocycles, 57, 649—656 (2002).
14) Sashida H., Minamida H., Yamamoto K., J. Chem. Res. (S), 2000,
572—575.
15) Sashida H., Yoshida M., Minamida H. Teranishi M., J. Heterocyclic
Chem., 39, 405—409 (2002).
16) Sashida H., Ohyanagi K., Minoura M., Akiba K.-Y., J. Chem. Soc.,
Perkin Trans. 1, 2002, 606—612.
17) A part of this work has been published in a preliminary communica-
tion: Sashida H., Ohyanagi K., J. Chem. Soc., Perkin Trans. 1, 1998,
2123—2124.
1-Benzyl-1H-isotellurochromene (18Bb): Yield 11%, yellow oil. 1H-
NMR (90 MHz, CDCl3) d: 3.28 (2H, d, Jϭ7 Hz, CH2Ph), 3.95 (1H, t,
Jϭ7 Hz, 1-H), 6.8—7.4 (11H, m, 3-, 4- and Ph-H). HR-MS m/z Mϩ Calcd
for C16H14Te: 336.0159. Found: 336.0151.
Treatment of Isochromenes (18) with Ph3C؉ BF4؊: Formation of 1-
Benzyl-2-benzopyrylium Tetrafluoroborate (19) The isoselenochromene
(18) was treated with Ph3Cϩ BF4Ϫ and worked up as described for the prepa-
ration of 14 to give 19.
1-Benzyl-3-tert-butyl-2-benzoselelopyrylium
Tetrafluoroborate
(19Aa): Yield 61%, yellow prisms (CHCl3), mp 120—123 °C (decomp.). IR
(KBr) cmϪ1 1064 (BFϪ4 ). 1H-NMR (90 MHz, CD3CN) d: 1.59 (9H, s, t-Bu),
5.25 (2H, s, CH2Ph), 7.3—7.5 (9H, m, Ph-H), 8.86 (1H, s, 4-H). Anal. Calcd
for C20H21BF4Se: C, 56.24; H, 4.96. Found: C, 56.22; H, 4.88.
1-Benzyl-2-benzoselelopyrylium Tetrafluoroborate (19Ab): Yield 60%,
yellow prisms (CHCl3), mp 106—108 °C (decomp.). IR (KBr) cmϪ1 1056
1
(BFϪ4 ). H-NMR (90 MHz, CD3CN) d: 5.25 (2H, s, CH2Ph), 7.3—7.5 (9H,
m, Ph-H), 8.96 (1H, d, Jϭ9 Hz, 4-H), 9.57 (1H, d, Jϭ9 Hz, 3-H). Anal.
18) A part of this work has been published in a preliminary communica-
tion: Sashida H., Ohyanagi K., Heterocycles, 51, 17—20 (1999).
19) Suld G., Price C. C., J. Am. Chem. Soc., 84, 2090—2094 (1962).
20) Hortmann A. G., Harris R. L., Miles J. A., J. Am. Chem. Soc., 96,
6119—6132 (1974).
21) Doddi G., Ercolani G., J. Org. Chem., 56, 1674—1675 (1991).
22) Desbene P.-L., Cherton J.-C., Tetrahedron, 40, 3539—3548 (1984).
23) Detty M. R., Organometallics, 7, 1122—1126 (1988).
24) Yoshida Z., Yoneda S., Sugimoto T., Kikukawa O., Tetrahedron Lett.,
1971, 3999—4002.
Calcd for C16H13BF4Se: C, 51.79; H, 3.53. Found: C, 51.57; H, 3.43.
1-Benzyl-3-tert-butyl-2-benzotelluropyrylium
Tetrafluoroborate
(19Ba): Yield 60%, pale green prisms (CHCl3), mp 106—108 °C (decomp.).
1
IR (KBr) cmϪ1 1052 (BF4Ϫ). H-NMR (90 MHz, CD3CN) d: 1.55 (9H, s, t-
Bu), 4.82 (2H, s, CH2Ph), 7.2—7.6 (9H, m, Ph-H), 8.92 (1H, s, 4-H). Anal.
Calcd for C20H21BF4Te: C, 50.49; H, 4.45. Found: C, 50.64; H, 4.47.
Treatment of 1-Benzylpyrylium Salts (19) with Basic Alumina A so-
lution of 19 (ca. 0.1 mmol) in MeCN–CHCl3 (1 : 5) was passed through a
basic alumina column. The eluent was evaporated in vacuo and residue was
recrystallized from n-hexane to give 20 quantitatively.
25) Es-Seddiki S., Le Coudtumer G., Mollier Y., Devaud M., Tetrahedron
Lett., 1981, 2771—2772.
26) Niinuma S., Sato N., Kawata H., Suzuki Y., Toda T., Kokubun H.,
Bull. Chem. Soc. Jpn., 58, 2600—2607 (1985).
(Z)-1-Benzylidene-3-tert-butyisoselenochromene (20Aa): Yellow prisms
1
(acetone–n-hexane), mp 118—120 °C. H-NMR (400 MHz, CDCl3) d: 1.28
(9H, s, t-Bu), 6.74 (1H, s, 4-H), 7.15—7.54 (9H, m, Ph-H), 7.41 (1H, s, 1Ј-
H). HR-MS m/z Mϩ Calcd for C20H20Se: 340.0731. Found: 340.0734.
27) Shimizu H., Miyazaki S., Kataoka T., Hori M., Muraoka O., J. Chem.
Soc., Perkin Trans. 1, 1994, 3129—3140.
28) Bumber A. A., Ivakhnenko E. P., Ladatko A. A., Arutyunyants A. A.,
Sadekov I. D., Okhlobistin O. Yu., Khim. Geterotsikl. Soedin., 1988,
1196—1200, [Chem. Abstr., 111, 38699h (1989)].
(Z)-1-Benzylideneisoselenochromene
(20Ab):
Yellow
prisms
1
(acetone–n-hexane), mp 119—121 °C. H-NMR (400 MHz, CDCl3) d: 6.79
(1H, br d, Jϭ9.9 Hz, 3-H), 7.02 (1H, d, Jϭ9.9 Hz, 4-H), 7.15—7.52 (9H, m,
Ph-H), 7.40 (1H, s, 1Ј-H). HR-MS m/z Mϩ Calcd for C16H12Se: 284.0105.
Found: 284.0103.
29) Renson P., Pirson P., Bull. Soc. Chim. Belges, 75, 456—464 (1966).
(Z)-1-Benzylidene-3-tert-butyisotellurochromene (20Ba): Yellow oil.