Reaction of selenobenzophenones with olefins. Formation of 1H-2- benzoselenopyrans. Reaction of 1H-2-benzoselenopyrans with diazoalkanes

Article abstract of DOI:10.1021/jo991679w

Selenobenzophenone reacts as a diene with dimethyl acetylenedicarboxylate (DMAD) to lead to dimethyl 1H-1-diphenylmethyl-1- phenyl-2-benzoselenopyran-3,4-dicarboxylate (5c) in moderate yield; the initial [4 + 2] cycloaddition is followed by the addition of another 1 mol equiv of selenobenzophenone. The reaction might proceed through carbene insertion of the primary cycloadduct. On the other hand, 4,4'- dimethoxyselenobenzophenone combines as a diene with DMAD furnishing dimethyl 1H-1-p-methoxyphenyl-6-methoxy-2-benzoselenopyran-3,4-dicarboxylate (4a). The reaction of benzoselenopyran derivative (4) with diaryldiazomethanes afforded another type of carbene insertion product.

Full text of DOI:10.1021/jo991679w

2090
J . Org. Chem. 2000, 65, 2090-2095
Rea ction of Selen oben zop h en on es w ith Olefin s. F or m a tion of
1H-2-Ben zoselen op yr a n s. Rea ction of 1H-2-Ben zoselen op yr a n s
w ith Dia zoa lk a n es
Kentaro Okuma,* Yuji Koga, Kazuki Kojima, Kosei Shioji, Haruo Matsuyama,† and
Yoshinobu Yokomori‡
Department of Chemistry, Faculty of Science, Fukuoka University, J onan-ku, Fukuoka 814-0180, J apan,
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University,
Hachioji, Tokyo 192-0397, J apan, and Department of Chemistry, National Defense Academy,
Hashirimizu, Yokosuka 239-0811, J apan
Received October 26, 1999
Selenobenzophenone reacts as a diene with dimethyl acetylenedicarboxylate (DMAD) to lead to
dimethyl 1H-1-diphenylmethyl-1-phenyl-2-benzoselenopyran-3,4-dicarboxylate (5c) in moderate
yield; the initial [4 + 2] cycloaddition is followed by the addition of another 1 mol equiv of
selenobenzophenone. The reaction might proceed through carbene insertion of the primary
cycloadduct. On the other hand, 4,4′-dimethoxyselenobenzophenone combines as a diene with DMAD
furnishing dimethyl 1H-1-p-methoxyphenyl-6-methoxy-2-benzoselenopyran-3,4-dicarboxylate (4a ).
The reaction of benzoselenopyran derivative (4) with diaryldiazomethanes afforded another type
of carbene insertion product.
Sch em e 1
In tr od u ction
The reaction of selenocarbonyl compounds is of current
interest.1 In the past decades, the synthesis of many
stable selenocarbonyl compounds has been realized by
taking advantage of the steric protection afforded by
bulky substituents, and the chemistry of these com-
pounds has been extensively studied.2 Some electronically
stabilized selenocarbonyl compounds have been isolated
by taking advantage of the mesomeric effect due to
heteroatoms such as nitrogen and sulfur or coordination
to transition metals.3 We have also succeeded in the
isolation of selenobenzophenones (1).4 The reactivity of
selenobenzophenones is interesting because they act as
dienes or dienophiles toward olefins. Erker and co-
workers have also reported the unique stereochemistry
of the [4 + 2] cycloaddition of 1 with 2,4-hexadienes.5
Thiobenzophenone is well-known to react with DMAD to
afford the corresponding [4 + 2] cycloadduct (2).6 We have
reported that the reaction of selenobenzophenones with
DMAD gave benzoselenepin derivatives (3).7 However,
in the course of pursuing the reactivity of these deriva-
tives, some ambiguous results in the structure of 3 were
revealed (Scheme 1).
These results prompted us to investigate the precise
mechanism of this reaction. In this paper, we disclose
the full details of the reaction of 1 with olefins, correction
of structure 3, and X-ray crystallographic analysis of the
adducts.
† Tokyo Metropolitan University.
‡ National Defense Academy.
(1) For reviews, see (a) Guziec, J r., F. S. In Organoselenium
Chemistry; Liotta, D., Ed.; Wiley, New York, 1987; p 277. (b) Guziec,
F. S., J r.; Guziec, L. J . In Comprehensive Organic Functional Trans-
formations; Katritzky, A. R., M-Cohn, O., Rees, C. W., Pattenden, G.,
Eds.; Pergamon: Cambridge, 1995; Vol. 3, 3.09. For recent reports,
see (c) Fischer, H.; Kalbas, C.; Stumpf, R. Chem. Ber. 1996, 129, 1169.
(d) Shimada, K.; Yamaguchi, M.; Sasaki, T.; Ohnishi, K.; Takikawa,
Y. Bull. Chem. Soc. J pn. 1996, 69, 2235. (e) Murai, T.; Kakami, K.;
Itoh, N.; Kanda, T.; Kato, S. Tetrahedron 1996, 52, 2839. (f) Chesney,
A.; Bryce, M. R.; Batsanov, A. S.; Howard, J . A. K. Chem. Commun.
1997, 2293. (g) Zhou J .; Chen, R. Y. J . Chem. Soc., Perkin Trans. 1
1998, 2917. (h) Purseigle, F.; Dubreuil, D.; Marchand, A.; Pradere, J .
P.; Goli, M.; Toupet, L. Tetrahedron 1998, 54, 2545. (i) Back, T. G.;
Dyck, B. P.; Parvez, M. J . Org. Chem. 1995, 60, 4657. (j) Fischer, H.;
Treier, K.; Troll, C. Chem. Ber. 1995, 128, 1149. (k) Back, T. G.; Dyck,
B. P.; Parvez, M. J . Org. Chem. 1995, 60, 703. (l) Shimada, K.; Oikawa,
S.; Nakamura, H.; Takikawa, Y. Chem. Lett. 1995, 135. (m) Yong, D.
N.; Serguiski, P.; Detty, M. R. J . Org. Chem. 1998, 63, 5716.
(2) (a) Back, T. G.; Barton, D. H. R.; Britten-Kelly, M. R.; Guziec,
F. S., J r. J . Chem. Soc., Perkin Trans. 1 1976, 2079. (b) Okazaki, R.;
Kumon, N.; Inamoto, N. J . Am. Chem. Soc. 1989, 11, 5949. (c) Takeda,
N.; Tokitoh, N.; Okazaki, R. Tetrahedron 1997, 53, 12167.
(3) (a) Reid, D. H.; Webster, R. G.; Mckenzie, S. J . Chem. Soc., Perkin
Trans. 1 1979, 2334. (b) Michael, J . P.; Reid, D. H.; Rose, B. G.; Speirs,
R. A. J . Chem. Soc., Chem. Commun. 1988, 1494. (c) Fischer, H.;
Zeuner, S.; Riede, J . Angew. Chem., Int. Ed. Engl. 1984, 23, 726. (d)
Fischer, H.; Seuner, S.; Alt, H. G. J . Organomet. Chem. 1985, 289,
C21. (e) Fischer, H.; Zeuner, S.; Gerbing, U.; Riede, J .; Kreiter, C. G.
J . Organomet. Chem. 1989, 377, 105.
(4) (a) Okuma, K.; Kojima, K.; Kaneko, I.; Ohta, H. Chem. Lett. 1991,
1053. (b) Okuma, K.; Kojima, K.; Kaneko, I.; Tsujimoto, Y.; Ohta, H.;
Yokomori, Y. J . Chem. Soc., Perkin Trans. 1 1994, 2151.
Resu lts a n d Discu ssion
Selenocarbonyl compounds are generally difficult to
isolate, whereas 4,4′-dimethoxyselenobenzophenone (1a )
can be isolated as its monomeric form.4 We first tried the
reaction of 1a with DMAD. Treatment of 1a with DMAD
at room temperature in benzene gave colorless crystals
of dimethyl 1H-1-p-methoxyphenyl-6-methoxy-2-benzo-
selenopyran-3,4-dicarboxylate (4a ) in 66% yield (Scheme
2).
(5) Wilker S.; Erker, G. J . Am. Chem. Soc. 1995, 117, 10922.
(6) (a) Ohno, A.; Koizumi, T.; Ohnishi, Y. Bull. Chem. Soc., J pn.
1971, 44, 2511. (b) Gotthardt H.; Nieberl, S. Liebigs Ann. Chem. 1980,
867. (c) Rapp J .; Huisgen, R. Tetrahedron 1997, 53, 961.
(7) Okuma, K.; Kojima, K.; Kaneko, I.; Ohta, H. Tetrahedron Lett.
1992, 33, 1333.
10.1021/jo991679w CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/09/2000

Formation of 1H-2-Benzoselenopyrans
J . Org. Chem., Vol. 65, No. 7, 2000 2091
Sch em e 2
Sch em e 3
This result is similar to that of thiobenzophenone;6
selenobenzophenone acts as a diene toward DMAD. The
initial [4 + 2] cycloaddition is followed by 1,3-prototropy
to give 4a .
We then tried the reaction of 4,4′-dimethylselenoben-
zophenone (1b) with DMAD; 1b is relatively unstable and
is easily oxidized to give the corresponding benzophenone.
Thus, the reaction was carried out in a one-pot operation
of di-p-tolylmethylenetriphenylphosphorane with elemen-
tal selenium, followed by the addition of DMAD. Inter-
estingly, treatment of 4,4′-dimethylselenobenzophenone
(1b) with DMAD resulted in the formation of two differ-
ent adducts. One was the normal [4 + 2] cycloadduct (4b).
The other adduct was found not to be the normal [4 + 2]
cycloadduct but a 2:1 adduct by spectroscopic, MS, and
Sch em e 4
1
elemental analysis. H NMR of this adduct shows four
tolyl methyl (2.25, 2.26, 2.27, and 2.29 ppm), two methoxy
(3.73 and 3.75 ppm), one methine (5.02 ppm), and 15
aromatic protons. 13C NMR shows four tolyl methyl (20.9,
20.9, 21.0, and 21.1 ppm), two methoxy (52.6 and 52.7
ppm), one quaternary (58.9 ppm), one methine (59.4
ppm), and 19 olefinic and aromatic, and two ester
carbonyl (165.6 and 168.5 ppm) carbons. In our previous
communication, we have shown that this adduct may be
dimethyl 1,2-dihydro-1,2,2-tri-p-tolyl-3-benzoselenepin-
4,5-dicarboxylate (3b).7
Ta ble 1. Rea ction of Selen oben zop h en on es (1) w ith
DMAD
However, the structure of 3b was deemed incorrect for
the following two reasons. If the reaction proceeded
through a tetraarylethylene intermediate formed from
selenobenzophenone with phosphorus ylide, the tetra-
phenylethylene further reacts with selenium to give an
episelenide intermediate, which finally reacted with
DMAD to afford 3. However, the reaction of tetra-p-
tolylethylene with elemental selenium in the presence
of DMAD recovered the starting materials almost quan-
titatively. Krafft and Meinke reported the isolation of a
selenofluorenone dimer whose regioselectivity was con-
firmed by zinc dust reduction.8 We applied this method
to the reduction of 3b. Zinc dust reduction of 3b in acetic
acid led to the formation of 4b instead of a ring-opened
product, suggesting that the structure of this adduct
would not be 3b. Another possible structure of this adduct
would be dimethyl 1H-1-(4,4′-dimethyldiphenylmethyl)-
1-tolyl-2-benzoselenopyran-3,4-dicarboxylate (5b) (Scheme
3). The exact structure was finally confirmed by single-
crystal X-ray diffraction. An X-ray crystallographic struc-
ture of the adduct (3b or 5b ) has an exocyclic diaryl-
methyl group, thus confirming the structure to be 5b.9
We then carried out the reaction of selenobenzophe-
none (1c) with DMAD; 1c is relatively unstable and
easily dimerizes to give diselenetane. Thus, the reaction
was carried out by adding diphenylmethylenetriphen-
ylphosphorane with elemental selenium followed by
the addition of DMAD. Interestingly, only the colorless
crystals of the 2:1 cycloadduct (5c) were isolated in 71%
yield (Scheme 4). Other reactions were carried out in a
similar manner (Table 1).
Generally, electron-rich selenobenzophenones such as
1a and 1d gave the normal cycloadducts (entries 1 and
4). On the other hand, normal or electron-deficient
selenobenzophenones gave both cycloadducts (entries 3
and 5).
How do we account for the formation of 5? Compound
5 might be formed by the addition of 2 molar amounts of
1 with DMAD. Tokitoh et al. reported that the thermoly-
sis of triselenastannolane gave selenobenzophenone,
which reacted with DMAD to give only the normal
cycloadduct (4c).10
(8) Meinke, P. T.;. Krafft, G. A. J . Am. Chem. Soc. 1988, 110, 8679.
(9) The X-ray crystallographic analyses of 5b and 13 were carried
out by using Enraf-Nonius CAD4 diffractometer. Full details were
shown in Supporting Information.

2092 J . Org. Chem., Vol. 65, No. 7, 2000
Okuma et al.
Sch em e 5
Sch em e 7
Sch em e 8
Sch em e 6
Ta ble 2. Rea ction of 2 a n d 4 w ith Dia r yld ia zom eth a n ea
products (yields/%)
2 or
diaryl-
recovered
4b diazomethane catalyst
3 or 9
5 or 10 2 or 4b (%)
2
2
2
Ph2CdN2
Ph2CdN2
Ph2CdN2
none
9: 0
9: 10
9: 14
3b: 0
3b: 0
10: 0
10: 12
10: 8
5b: 0
5b: 0
5b: 1
2: 86
2: 32
2: 35
4b: 88
4b: 85
4b: 46
CuSO4
Rh2(OAc)4
none
CuSO4
Rh2(OAc)4 3b: 14
4b p-Tol2CdN2
4b p-Tol2CdN2
4b p-Tol2CdN2
a
All reactions were carried out in refluxing benzene.
Sch em e 9
When the reaction was carried out by using alkyl
propiolates instead of DMAD, the corresponding cyclo-
adducts (4f, 4g, 5f, and 5g) were obtained regioselectively
(Scheme 5). When propiolic acid was used as a substrate
in toluene for 2 h at 60 °C, compound 4h was obtained
in 81% yield. When isolated 4,4′-dimethylselenoben-
zophenone 1b was reacted with DMAD, 4b and 5b were
obtained in 11 and 32% yields, respectively, which
suggested that phosphorus ylide or elemental selenium
did not affect the formation of 5b. Noteworthy is that
the reaction of 1b with methyl propiolate in the presence
of 5 equiv of acetic acid led to the formation of 4f as the
sole product in 35% yield. Thus, acid would prevent the
formation of 5.
These results suggested that the cycloadduct 4 was
further attacked by a carbenoid produced from an ad-
ditional selenobenzophenone or its dimer. The produced
carbenoid might attack the selenium of 4 to give the
corresponding selenonium ylide, which abstracts the
R-hydrogen of the ylide to form another selenonium ylide.
Stevens rearrangement of the rearranged ylide finally
afforded the 2:1 adduct 5. The formation of a triplet
carbene is another possibility, which abstracts the R-hy-
drogen of 4 or γ-hydrogen of primary cycloadduct 4′ to
afford the radical intermediate, which finally recombines
to give 5 (Scheme 6).
tively.12 Thus, two types of carbene insertion might
proceed in this case (Scheme 7).
We applied this method to the reaction of 2 with
diaryldiazomethane. An attempted reaction of 2 with
diazomethane resulted in almost complete recovery of 2,
suggesting that the reactivity of 2 might be lower than
that of 6a . After several trials, we finally found that the
reaction of benzothiopyran 2 with diphenyldiazomethane
in the presence of CuSO4 afforded two adducts, which
were found to be benzothiepin derivative (9) and exo-
diphenylmethyl derivative (10) (Scheme 8).
If the same reaction occurs in the case of selenoben-
zophenone, carbene formation from selenobenzophenone
would be a good route to 5. An attempted reaction of 4b
with ditolyldiazomethane by using copper(II) sulfate
resulted in complete recovery of the starting 4b. By using
rhodium(II) acetate in place of copper sulfate, this
reaction provided the corresponding benzoselenepin (3b)
in 14% yield along with exo-benzhydrylbenzoselenopyran
(5b, 1%). Unreacted 4b was recovered in 46% yield (Table
2, Scheme 9). The structure of 3b was confirmed by
spectroscopic, MS, and elemental analysis.
Recently, we have isolated the thiobenzophenone-
benzyne adducts, one of which (6a ) was identical with
that of the product independently prepared by Benati et
al.11 They reported that 6a reacted with diphenyldi-
azomethane to afford benzothiepin (7) and exo-diphenyl-
methylbenzothiopyran (8) in 26 and 13% yields, respec-
(11) (a) Okuma, K.; Shirokawa, T.; Yamamoto, T.; Kitamura, T.;
Fujiwara, Y. Tetrahedron Lett. 1996, 37, 8883. (b) Benati, L.; Mon-
tevecchi, P. C.; Spagnolo, P.; Tundo, A. J . Chem. Soc., Perkin Trans. 1
1981, 1544.
(10) Tokitoh, N.; Matsuhashi, Y.; Okazaki, R. J . Chem. Soc., Chem.
Commun. 1993, 407.
(12) Benati, L.; Montevecchi, P. C.; Spagnolo P. J . Chem. Soc., Perkin
Trans. 1 1982, 917.

Formation of 1H-2-Benzoselenopyrans
J . Org. Chem., Vol. 65, No. 7, 2000 2093
Sch em e 10
Sch em e 12
lation afforded 11, which was further attacked by a
triplet carbenoid to give 12.
We also found that the reaction of 1c with norborna-
diene gave exclusively the 2:1 adduct. Treatment of 1c
with 2,5-norbornadiene at room-temperature resulted in
the formation of exo-methylbenzoselenopyran (13), a
similar product of 1c with DMAD (Scheme 12). The
structure of 13 was confirmed by 1H and 13C NMR
spectroscopy, elemental analysis, and X-ray crystal-
lographic analysis.9
In summary, we have succeeded in the cycloaddition
reaction of 1 with DMAD and 2,5-norbornadiene. The
formation of 1-diarylmethylene-1H-2-benzoselenopyrans
might proceed through diaryl carbenes as radical inter-
mediates.
Sch em e 11
Exp er im en ta l Section
Gen er a l. All chemicals were obtained from commercial
suppliers and used without further purification. Analytical
TLC was carried out on precoated plates (Merck silica gel 60,
F254), and flash column chromatography was performed with
silica (Merck, 70-230 mesh). NMR spectra (1H at 400 MHz;
13C at 100 MHz) were recorded in CDCl3 solvent, and chemical
shifts are expressed in ppm relative to internal TMS.
Ma ter ia l. 4,4′-Dimethoxyselenobenzophenone (1a ) and 4,4′-
dimethylselenobenzophenone (1b) were obtained by the reac-
tion of diarylmethylenetriphenylphosphoranes with elemental
selenium.4
Rea ction of 1a w ith DMAD. To a solution of 1a (0.090 g,
0.30 mmol) in toluene (10 mL) was added DMAD (0.184 mL,
1.5 mmol) in one portion. After being stirred for 10 h at room
temperature, the reaction mixture was concentrated to afford
a pale brown oil, which was chromatographed on silica gel
(elution with 4:1 hexane/ethyl acetate). Compound 4a was
isolated 0.089 g (66%). 4a : orange crystals: mp 45-46 °C. 1H
NMR (CDCl3) δ ) 3.77 (s, 3 H, OMe), 3.78 (s, 3 H, OMe), 3.81
(s, 3 H, OMe), 3.95 (s, 3 H, OMe), 5.25 (s, 1 H, CH with Se-H
satellite, J Se-H)20 Hz), 6.82 (d, 2 H, J ) 7 Hz, Ar), 6.92 (m, 1
H, Ar), 6.99 (m, 2 H, Ar), 7.13 (d, 2 H, J ) 7 Hz, Ar). 13C NMR
(CDCl3) δ ) 41.2 (CH), 52.9 (OMe), 53.0 (OMe), 55.3 (OMe),
55.5 (OMe), 113. 0, 114.1, 116.1, 124.6, 126.1, 128.3, 129.3,
132.4, 133.1, 138.7, 158.8, 159.0, 165.3 (COO), 168.5 (COO).
Anal. Calcd for C21H20O6Se: C, 56.38. H, 4.59%. Found: C,
56.43; H, 4.96%.
When copper(II) sulfate was used as a catalyst in the
reaction of 2 with diphenyldiazomethane, the product
ratio (9:10) was 5:6, whereas the ratio was changed to
7:4 by using rhodium(II) acetate as a catalyst, suggesting
that the cause of the product-ratio-deviation was depend-
ent on the carbenoid complex used. Considering these two
results, it is seen that singlet carbenoids play a main role
in the formation of 3 and 9. The reason only one product
5c is obtained in the reaction of 1c with DMAD would
be that the reaction proceeded through the triplet carbene
insertion of primary 4 + 2 adduct 4c′. Benati et al.
suggested a similar mechanism by the reaction of 1,2,3-
benzothiadiazole with diphenydiazomethane (Scheme
10).11
The reaction of 1a with 2,5-norbornadiene is further
confirmation of the carbene insertion mechanism. Treat-
ment of 1a and 2,5-norbornadiene in refluxing toluene
resulted in the formation of the demethylated cycloadduct
(11) and another type of 2:1 adduct (12) in 26 and 8%
yields, respectively (Scheme 11). The structure of 11 was
confirmed by spectroscopic, MS, and elemental analyses.
1H NMR of 12 shows three methoxy (3.74, 3.75, and 3.86
ppm), one methylene (1.40 and 1.69 ppm), seven methine
(1.86, 2.73, 2.75, 3.07, 3.42, 3.51, and 4.18 ppm), four
olefinic (5.60, 6.05, 6.17, and 7.01 ppm), and twelve
aromatic protons. 13C NMR of 12 shows one methylene
(42.7 ppm), seven methine, three methoxy (55 ppm
around), eighteen olefinic and aromatic, and one carbonyl
(201.6 ppm) carbons. Compound 12 would be a triplet
carbene insertion product; the initial formation of [4 +
2] cycloadduct followed by 1,3-prototropy and demethy-
Rea ction of 1b w ith DMAD. To a suspension of 4,4′-
dimethyldiphenylmethyltriphenylphosphonium tetrafluoro-
borate (1.09 g, 2.0 mmol) in toluene (50 mL) was added
butyllithium (1.5 mL in hexane, 10% w/v, 2.1 mmol) at room
temperature. After being stirred for 20 min, elemental sele-
nium (0.39 g, 6.0 mmol) was added to this red suspension in
one portion. After refluxing for 30 min, DMAD (0.55 mL, 4.5
mmol) was added to this bright green suspension. After
refluxing for 5 h, the reaction mixture was filtered and
concentrated to afford a pale brown oil, which was chromato-
graphed over silica gel by elution with hexanes-ethyl acetate
(4:1). Triphenylphosphine selenide (0.60 g, 1.7 mmol), colorless
oil of 4b (0.20 g, 0.48 mmol), and colorless crystals of 5b (0.33
g, 0.48 mmol) were obtained. Compound 5b; colorless crystals;
1
mp 173-175 °C. H NMR (CHCl3) δ ) 2.25 (s, 3H, Me), 2.25
(s, 3 H, Me), 2.27 (s, 3H, Me), 2.29 (s, 3 H, Me), 3.73 (s, 3 H,
OMe), 3.75 (s, 3 H, OMe), 5.02 (s, 1 H, CH), 6.50 (d, 2 H, J )
8 Hz, Ar), 6.86 (br, 4 H, Ar), 6.91 (d, 2 H, J ) 8 Hz, Ar), 6.97

2094 J . Org. Chem., Vol. 65, No. 7, 2000
Okuma et al.
(d, 2 H, J ) 8 Hz, Ar), 7.06 (d, 2H, J ) 8 Hz, Ar), 7.37 (d, 1 H,
J ) 8 Hz, Ar), 7.47 (d, 2 H, J ) 8 Hz, Ar). 13C NMR (CDCl3)
δ ) 20.90 (Me), 20.93 (Me), 20.99 (Me), 21.04 (Me), 52,65
(OMe), 52.73 (OMe), 58.79 (C), 59.36 (CH), 124.78, 127.83,
128,14, 128.32, 128.44, 128.65, 129.99, 130.23, 130.79, Å130.99,
133.04, 135.50, 136.06, 136.34, 136.50, 138.51, 138.82, 139.01,
139.34, 163.53 (CdO), 168.53 (CdO). HRMS: Found: m/z
610.1572. Calcd for C36H34O478Se (M+): m/z 610.1622. Anal.
Calcd for C36H34O4Se: C, 70.93; H, 5.62%. Found: C, 70.81;
H, 5.57%.
Zin c Du st Red u ction of 5b. To a solution of 5b (0.30 g,
0.5 mmol) in acetic acid (5 mL) was added zinc dust (0.13 g,
2.0 mmol) in one portion at room temperature. After refluxing
for 48 h, the suspension was filtered, poured into water (20
mL), and extracted with dichloromethane (10 mL × 3). The
combined extracts were washed with water, dried over anhy-
drous magnesium sulfate, and concentrated to give an orange
oil, which was subjected to silica gel chromatography by elution
with dichloromethane to give a orange oil of 4b (0.043 g, 0.10
mmol).
Rea ction of 1c w ith DMAD. To a solution of diphenyl-
methylenetriphenylphosphorane (0.436 g, 1 mmol) in benzene
(20 mL) was added elemental selenium (0.316 mg, 4 mmol) in
one portion. After refluxing for 30 min, DMAD (0.28 g, 2 mmol)
was added to this suspension. After being refluxed for 1 h, the
reaction mixture was filtered and concentrated to afford a pale
brown oil, which was chromatographed over silica gel by
elution of hexanes-ethyl acetate (4:1). Triphenylphosphine
selenide (0.26 g, 0.75 mmol) and colorless crystals of 5c (0.144
g, 0.26 mmol) were obtained.
Rea ction of 1b w ith Meth yl p r op iola te in th e P r esen ce
of Acetic Acid . To a solution of 4,4′-dimethyldiphenylmeth-
yltriphenylphosphonium tetrafluoroborate (2.72 g, 5.0 mmol)
in toluene (50 mL) was added butyllithium (3.4 mL in hexane,
15% w/v, 5.5 mmol) at room temperature. After being stirred
for 20 min, elemental selenium (1.58 g, 20 mmol) was added
in one portion to this red suspension. After refluxing for 30
min, the suspension turned to bright green. To this suspension,
acetic acid (1.50 g, 25 mmol) and methyl propiolate (0.84 g,10
mmol) was added. After being refluxed for 48 h, the reaction
mixture was filtered and concentrated to afford a pale brown
oil, which was chromatographed over silica gel by elution of
hexanes-ethyl acetate (4:1). Triphenylphosphine selenide
(1.20 g, 3.4 mmol) and colorless oil of 4f (0.97 g, 1.75 mmol)
were obtained. Compound 4f was identical with the authentic
sample.
1.0 mmol) and rhodium acetate (0.004 g, 0.05 mmol) in benzene
(10 mL) was added dropwise a solution of diphenyldiazo-
methane (0.29 g, 1.5 mmol) in benzene (5 mL). After refluxing
for 0.5 h, the reaction mixture was filtered and evaporated to
give pale brown oily crystals, which was subjected to column
chromatography by elution with hexane-dichloromethane
then dichloromethane-ethyl acetate to give diphenyl azine
(0.14 g, 0.38 mmol), 9 (0.07 g, 0.14 mmol), and 10 (0.037 g,
0.08 mmol). Starting 2 (0.11 g, 0.35 mmol) was recovered.
Separation of 9 and 10 is so difficult that all of 9 and 10 could
not be isolated.
Rea ction of 4b w ith Di-p-tolyld ia zom eth a n e in th e
P r esen ce of Rh 2(OAc)4. To a refluxing solution of 4b (0.179
g, 0.5 mmol) and rhodium acetate (0.004 g, 0.05 mmol) in
benzene (8 mL) was added dropwise a solution of ditolyl-
diazomethane (0.29 g, 1.5 mmol) in benzene (25 mL). After
being refluxed for 0.5 h, the reaction mixture was filtered and
evaporated to give pale brown oily crystals, which were
subjected to column chromatography by elution with hexane-
dichloromethane then dichloromethane-ethyl acetate to give
di-p-tolyl azine (0.357 g, 0.75 mmol), 3b (0.043 g, 0.075 mmol),
and 5b (0.003 g, 0.005 mmol). Starting 4b (0.082 g, 0.23 mmol)
was recovered. Compound 5b is identical with the authentic
sample. Compound 3b: pale yellow oil: 1H NMR (CHCl3) δ )
2.20 (s, 3 H, Me), 2.25 (s, 3 H, Me), 2.32 (s, 3 H, Me), 2.37 (s,
3 H, Me), 3.57 (s, 3 H, OMe), 3.87 (s, 3 H, OMe), 5.24 (s, 1 H,
CH), 6.74 (d, 2H, J ) 7 Hz, Ar), 6.86-7.05 (m, 8H, Ar), 7.31
(d, 2 H, J ) 7 Hz, Ar), 7.42 (d, 1 H, J ) 7 Hz, Ar). 13C NMR
(CDCl3) δ ) 20.99 (Me), 21.03 (Me), 21.14 (Me), 21.24 (Me),
52.63 (OMe), 52.96 (OMe), 54.61, 54.65 (CH), 127.53, 127.62,
127.97, 128.53, 129.10, 129.61, 130.50, 131.58, 131.75, 131.79,
135.56, 135.70, 136.44, 136.70, 136.98, 137.52, 140.63, 143.52,
166.41 (CdO), 167.19 (CdO). HRMS: Found: m/z 610.1709.
Calcd for C36H34O480Se (M+); m/z 610.1622. Anal. Calcd for
C
36H34O4Se: C, 70.93; H, 5.62%. Found: C, 70.53; H, 5.84%.
Rea ction of 1a w ith 2,5-Nor bor n a d ien e. To a solution
of 1a (0.154 g, 0.5 mmol) in toluene was added 2,5-norborna-
diene (0.18 g, 2.0 mmol) in one portion. After refluxing for 4
h, the reaction mixture was concentrated to afford pale brown
crystals, which was chromatographed over silica gel by elution
of hexanes-ethyl acetate (4:1). Yellow oil of 11 was obtained
in 26% yield (0.053 g, 0.13 mmol). 11: Yellow oil: 1H NMR
(CHCl3) δ ) 1.64 (br d, 1 H, J ) 9 Hz, CH2), 1.90 (dd, 1 H, J
) 8 and 10 Hz, CH), 2.36 (d, 1 H, J ) 9 Hz, CH2), 2.80 (br d,
1 H, J ) 16 Hz, CH), 2.90 (m, 2 H, CH2), 3.00 (d, 1H, J ) 8
Hz, CH2), 3.03 (br s, 1 H, CH2), 3.47 (dd, 1 H, J ) 2 and 8 Hz,
CH2), 3.84 (s, 3 H, OMe), 5.79 (d, 1 H, J ) 10 Hz, CHd), 6.11
(dd, 1 H, J ) 3 and 6 Hz, CHd), 6.23 (dd, 1 H, J ) 3 and 6 Hz,
CHd), 6.93 (d, 2 H, J ) 8 Hz, Ar), 7.06 (d, 1 H, J ) 10 Hz,
CHd), 7.42 (d, 2 H, J ) 8 Hz, Ar). 13C NMR (CDCl3) δ ) 40.45,
43.90, 45.56, 45.65, 47.20, 47.55, 50.35, 52.05, 55.26, 113.50,
122.16, 130.86, 131.27, 135.00, 135.64, 138.61, 141.71, 150.07,
160.08, 198.83 (CdO). HRMS: Found: m/z 385.0708. Calcd
for C21H21O280Se (M + 1+): 385.0706. Elemental analysis was
carried out by using its hydrazone. mp 230-232 °C. Found:
C, 57.16; H, 4.30; N, 9.65%. Calcd for C27H24N4O5Se: C, 57.55;
H, 4.29; N, 9.94%. Compound 12 was obtained in 8% yield
(0.012 g, 0.02 mmol). 12: Yellow crystals; mp 209-210 °C: 1H
NMR (CHCl3) δ ) 1.40 (d, 1 H, J ) 9 Hz, CHH), 1.69 (d, 1 H,
J ) 9 Hz, CHH), 1.86 (dd, 1 H, J ) 8 and 10 Hz, CH), 2.73 (br
s, 1 H, CH), 2.75 (d, 1 H, J ) 12 Hz, CH), 3.07 (br s, 1 H, CH),
3,42 (br d, 1 H, J ) 7 Hz, CH), 3.51 (d, 1 H, J ) 12 Hz, CH),
3.74 (s, 3 H, OMe), 3.75 (s, 3 H, OMe), 3.86 (s, 3 H, OMe),
4.18 (d, 1 H, J ) 12 Hz, CH), 5.60 (d, 1 H, J ) 10 Hz, CHd),
6.05 (dd, 1 H, J ) 3 and 6 Hz, CHd), 6.17 (dd, 1 H, J ) 3 and
6 Hz, CHd), 6.80 (d, 2 H, J ) 8 Hz, Ar), 6.83 (d, 2 H, J ) 8
Hz, Ar), 6.94 (d, 2 H, J ) 8 Hz, Ar), 7.01 (d, 1 H, J ) 10 Hz,
CHd), 7.22 (d, 2 H, J ) 8 Hz, Ar), 7.27 (d, 2 H, J ) 8 Hz, Ar),
7.47 (d, 2 H, J ) 8 Hz, Ar).). 13C NMR (CDCl3) δ ) 42.67 (CH2),
45.18 (CH), 46.76 (CH), 49.10 (CH), 50.49 (CH), 51.02 (CH),
54.97 (OMe), 55.10 (OMe), 55.25 (OMe), 55.31 (OMe), 55.81
(CH), 113.49, 113.56, 113.86, 121.28, 128.61, 128.71, 131.02,
131.42, 133.70, 134.33, 134.44, 135.92, 138.55, 139.95, 151.68,
157.75, 157.85, 160.23, 201.60 (CdO). HRMS: Found: m/z
Rea ction of 2 w ith Dip h en yld ia zom eth a n e in th e
P r esen ce of Cu SO4. To a boiling solution of 2 (0.46 g, 1.5
mmol) and CuSO4 (7 mg, 0.044 mmol) in benzene (10 mL) was
added diphenyldiazomethane (0.44 g, 2.3 mmol). After reflux-
ing for 12 h, excess benzene was distilled off and the residue
was chromatographed over silica gel by elution with hexanes-
ethyl acetate (4:1) afforded starting 2 (0.16 g, 0.48 mmol), 9
(0.075 g, 0.15 mmol), and 10 (0.09 g, 0.18 mmol). Separation
of 9 and 10 is so difficult that all of 9 and 10 could not be
isolated.
1
Compound 9: yellow oil. H NMR (CHCl3) δ ) 3.50 (s, 3 H,
OMe), 3.84 (s, 3 H, OMe), 5.34 (s, 1 H, CH), 6.82 (m, 3 H, Ar),
7.09-7.36 (m, 14 H, Ar), 7.51 (d, 2 H, J ) 7 Hz, Ar). 13C NMR
(CDCl3) δ ) 52.46 (OMe), 52.72 (OMe), 55.99 (CH), 79.31 (C),
125.92, 125.98, 126.14, 126.35, 126.85, 127.29, 127.49, 127.57,
127.76, 128.26, 129.55, 130.41, 130.65, 131.46, 135.12, 138.93,
140.96, 142.45, 145.27, 165.56 (CdO), 166.64 (CdO). HRMS:
Found: m/z 506.1537. Calcd for C32H26O4S (M+): m/z 506.1552.
1
Compound 10: yellow oil. H NMR (CHCl3) δ ) 3.72 (s, 3 H,
OMe), 3.80 (s, 3 H, OMe), 5.15 (1 H, s, CH), 6.62 (d, 3 H, J )
7 Hz, Ar), 7.02-7.31 (m, 14 H, Ar), 7.46 (d, 2 H, J ) 7 Hz, Ar,
7.68 (d, 2 H, J ) 7 Hz, Ar). 13C NMR (CDCl3) δ ) 52.69 (OMe),
52.97 (OMe), 59.25 (CH), 59.66, 125.80, 125.95, 126.40, 126.79,
126.98, 127.07, 127.12, 127.17, 127.66, 128.24, 128.50, 129.41,
130.88, 130.94, 131.35, 136.40, 136.89, 139.93, 141.06, 141.69,
164.30 (CdO), 167.60 (CdO). HRMS: Found: m/z 507.1605.
Calcd for C32H26O4S (M+1+): m/z 507.1606.
Rea ction of 2 w ith Dip h en yld ia zom eth a n e in th e
P r esen ce of Rh 2(OAc)4. To a refluxing solution of 2 (0.31 g,

Formation of 1H-2-Benzoselenopyrans
J . Org. Chem., Vol. 65, No. 7, 2000 2095
610.1613. Calcd for C36 H34O480Se (M+): m/z 610.1622. Anal.
Found: C, 70.58; H, 5.61%. Calcd for C36H34O4Se: C, 70.93;
H, 5.62%.
benzophenone (0.18 g, 1.0 mmol) were obtained. 13: colorless
crystals; mp 186-187 °C. H NMR (CHCl3) δ ) 1.28 (d, 1 H,
1
J ) 8 Hz, CHH),1.54 (br, 1 H, CH), 1.94 (d, 1 H, J ) 8 Hz,
CH), 2.60 (d, 1 H, J ) 7 Hz, CH), 2.67 (s, 1 H, CH), 3.14 (s, 1
H, CH), 5.08 (s, 1 H, CH), 5.97 (m, 1 H, CH), 6.22 (m, 1 H,
CH), 6.78-7.67 (m, 19 H, Ar). 13C NMR (CDCl3) δ ) 36.14,
40.55, 49.12, 53.18, 54.96, 61.69, 124.29, 125.97, 126.08,
126.22, 126.33, 127.05, 127.32, 127.49, 130.36, 130.76, 131.09,
131.38, 131.60, 135.09, 137.91, 142.17, 142.41, 143.09, 143.21,
146.12. Anal. Calcd for C33H28Se: C, 78.71; H, 5.60%. Found:
C, 78.86; H, 5.33%.
Rea ction of 1c w ith 2,5-Nor bor n a d ien e. To a suspension
of diphenylmethyltriphenylphosphonium bromide (2.55 g, 5.0
mmol) in toluene (50 mL) was added a solution of butyllithium
(3.5 mL, 10% w/v, 5.5 mmol) in hexane at room temperature.
After being stirred for 1 h, elemental selenium (1.18 g, 15
mmol) was added in one portion to this red suspension. After
refluxing for 5 min, the red suspension turned to a bright green
suspension of selenobenzophenone. 2,5-Norbornadiene (3.8 mL,
35 mmol) was added to this suspension and refluxed for 20 h.
The reaction mixture was filtered and evaporated to give
brown oily crystals, which were extracted with hexane three
times. The residue was recrystalized from methanol to afford
triphenylphosphine selenide (0.852 g, 2.5 mmol). The combined
extracts were chromatographed over silica gel by elution with
hexane-dichloromethane (9:1) to give triphenylphosphine
selenide (0.17 g, 0.5 mmol) and the adduct 13 (0.553 g, 1.1
mmol, 44%). Tetraphenylethylene (0.35 g, 1.05 mmol) and
Su p p or tin g In for m a tion Ava ila ble: Spectral data of
compounds 4b, 4d , 4e, 4f, 4g, 4h , 5c, 5e, 5f, and 5g; text giving
full details of the X-ray structure of 5b and 13 including the
tables of crystal sata, structure refinements, atomic coordina-
tion parameters, bond lengths, and bond angles. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O991679W