Generation of 1,3-chalcogenaza-1,3-butadienes by thermal cycloreversion of 2,4,6-trisubstituted 6H-1,3,5-oxachalcogenazines

Article abstract of DOI:10.1246/bcsj.74.511

1,3-Thiaza- and 1,3-selenaza- 1,3-butadienes bearing several substituents at the C-2 and C-4 positions were generated through thermal cycloreversion of 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines, respectively, and the heterodienes were efficiently trapped by using acetylenic dienophiles. When 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines were heated in the presence of nucleophiles, such as alcohols or thiols, the corresponding 1,4-adducts of the heterodienes with the nucleophiles were obtained in good yields. On the other hand, heating of 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines in the absence of trapping agents afforded several products which originated from the in situ generated 1,3-chalcogenaza-1,3-butadienes; also the heterodienes were not isolated or observed directly as the monomeric forms at all.

Full text of DOI:10.1246/bcsj.74.511

© 2001 The Chemical Society of Japan
511
Bull. Chem. Soc. Jpn., 74, 511–525 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes by Thermal
Cycloreversion of 2,4,6-Trisubstituted 6H-1,3,5-Oxachalcogenazines
Kazuaki Shimada, Kei Aikawa, Takuji Fujita, Masanobu Sato, Kurara Goto, Shigenobu Aoyagi,
Yuji Takikawa,* and Chizuko Kabuto†
Department of Chemical Engineering, Faculty of Engineering, Iwate University, Morioka, Iwate 020-8551
†Instrumental Analytical Center for Chemistry, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578
(Received September 8, 2000)
1,3-Thiaza- and 1,3-selenaza-1,3-butadienes bearing several substituents at the C-2 and C-4 positions were generat-
ed through thermal cycloreversion of 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines, respectively, and the hetero-
dienes were efficiently trapped by using acetylenic dienophiles. When 6H-1,3,5-oxathiazines or 6H-1,3,5-oxaselenazines
were heated in the presence of nucleophiles, such as alcohols or thiols, the corresponding 1,4-adducts of the heterodienes
with the nucleophiles were obtained in good yields. On the other hand, heating of 6H-1,3,5-oxathiazines or 6H-1,3,5-ox-
aselenazines in the absence of trapping agents afforded several products which originated from the in situ generated 1,3-
chalcogenaza-1,3-butadienes; also the heterodienes were not isolated or observed directly as the monomeric forms at all.
Recently, interest concerning the generation and trapping of
reactive chalcogenocarbonyl compounds has concentrated on
an extension to highly reactive analogues possessing higher π-
conjugation systems. However, among various aza-1,3-diene
derivatives, the generation of 1,3-chalcogenaza-1,3-butadienes
-
B(X = S, Se) has less been studied in spite of their synthetic po
Scheme 1.
tentiality as novel and versatile building blocks of chalcogen-
and nitrogen-containing various heterocycles. Actually, studies
on the generation and trapping of 1,3-thiaza- and 1,3-selenaza-
1,3-butadienes B(X = S, Se) bearing some substituents at the
C-2 and C-4 positions have been achieved by several
groups.1–19 However, these studies never resulted in the isola-
tion or detection of the reactive species, except for some elec-
tronically-stabilized N-thioacyl- and N-selenoacylamidine de-
rivatives.20–34 In most cases, these species were converted into
various heterocyclic compounds by [4+2]-type cycloaddition
with dienophiles, by [4+2] type dimerization, or by 1,4-addi-
tion of H2S, H2Se, or their synthetic equivalents.
During our attempts to generate various reactive species
bearing a chalcogenocarbonyl functionality by using the ring
cleavage of suitable cyclic precursors possessing heteroacetal-
type substructures,35–39 it was strongly expected that hetero-
dienes B would be efficiently generated by thermally- or Lewis
acid-induced retro-[4+2] type cycloreversion of 6H-1,3,5-ox-
ing attempts to isolate or detect heterodienes B are also men-
tioned in this paper.
Results and Discussion
Preparation of 6H-1,3,5-Oxathiazines (5) and 6H-1,3,5-
Oxaselenazines (6). 6H-1,3,5-Oxathiazines 5 and 6H-1,3,5-
oxaselenazines 6 bearing substituents at the C-2, C-4, and C-6
positions were at first prepared by treating a dichloromethane
solution of arenecarbochalcogenoamides (1, 2), such as
thiobenzamide (1a),41,42 p-chlorobenzothioamide (1c),41 sele-
nobenzamide (2a),43 or p-chlorobenzoselenoamide (2c),43 with
2,4,6-trimethyl-1,3,5-trioxane (paraldehyde, 3) or pivalalde-
hyde (4) and Et2O•BF3 at room temperature according to re-
ported methods.7,44 In all cases, the physical data of the prod-
1
ucts, including the MS, IR, H NMR, and 13C NMR spectra,
were fully consistent with the structures of 5a–d and 6a–d. Es-
pecially, the physical data of 6a and 6b were identical in all re-
spects with those of the reported data.44 The relative stere-
ochemistry of these products was confirmed to be cis in all cas-
es by NMR measurements based on the NOE experiments.44
All results concerning the preparation of 5a–d and 6a–d are
given in Table 1. However, a similar treatment of a dichlo-
romethane solution of selenobenzamide (2a) with benzalde-
hyde and Et2O•BF3 only afforded the recovery of substrates,
-
achalcogenazines A(X = S, Se), as shown in Scheme 1. Ac
cording to such an expectation, we previously reported the gen-
eration and trapping of 1,3-selenaza-1,3-butadienes B(X =
Se).40 In this paper, we would like to give a full account on the
-
generation of heterodienes B(X = S, Se) by thermal cyclorever
sion of A(X = S, Se) and trapping of such reactive species by
using various dienophiles and nucleophiles. Results concern-

512 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
and the vinyl protons at the C-6 position of these compounds
with small coupling constants (10a: J = ~0 Hz, 12a: J = ~1.5
Hz, 12c: J = ~0 Hz). The NMR experiments of these com-
pounds also revealed no NOE between the methine protons and
the vinyl protons of these products. These results clearly
showed that the methoxycarbonyl group of 10a, 12a, or 12c
was located at the C-5 position.
Table 1. Preparation of 6H-1,3,5-Oxathiazines 5 and 6H-
1,3,5-Oxaselenazines 6
The formation of cycloadducts of these heterodienes, 7 and
8 (Chart 1), with highly reactive acetylenic dienophiles must be
explained by the usual [4+2]-type cycloaddition, including the
reaction of heterodienes (7, 8) as novel 4π systems. The regi-
oselectivity of the cycloaddition of the heterodienes with meth-
yl propiolate was also fully consistent with the expectation
from FMO theory that predicted the favored orbital interac-
tions between the HOMO of the heterodienes and the LUMO
of methyl propiolate. However, an alternative ionic stepwise
mechanism including the nucleophilic attack of the sulfur or
selenium atom of the heterodienes to the dienophiles followed
by the ring-closure remained as a possible route to afford these
[4+2]-type cycloadducts.
Substrate
R1
X 1, 2 (mol amt.)
Reagent (3, 4) Producta)
Yield
R2 5, 6
/%
C6H5
C6H5
p-ClC6H4
p-ClC6H4
C6H5
C6H5
p-ClC6H4 Se 2c
p-ClC6H4 Se 2c
S
S
S
S
1a
1a
1c
1c
3 (0.8)
4 (2.4)
3 (0.8)
4 (2.4)
3 (0.8)
4 (2.4)
3 (0.8)
4 (2.4)
CH3 5a
t-C4H9 5b
CH3 5c
t-C4H9 5d
CH3 6a
t-C4H9 6b
CH3 6c
t-C4H9 6d
95
43
38
32
56
32
53
44
Se 2a
Se 2a
a) Single stereoisomers. The relative stereochemistry of the prod-
ucts was determined to be cis by NOE experiments between the
C-4 and C-6 protons of 5a and 6a.
and attempts starting from selenoacetamide or propaneselenoa-
mide and 2,4,6-trimethyl-1,3,5-trioxane (3) in a similar manner
only gave complicated results; further, the preparation of the
target compounds 6 bearing an alkyl substituent at the C-2 po-
sition was not successful at all.
Heating of 6H-1,3,5-Oxathiazines (5) or 6H-1,3,5-Oxase-
lenazines (6) in the Presence of an Acetylenic Dienophile, p-
Chart 1. Structures of 1,3-Chalcogenaza-1,3-butadienes
7 and 8.
Benzoquinone, or Diethyl Azodicarboxylate (DEAD).
A
benzene or a toluene solution of 6H-1,3,5-oxathiazines 5 or
6H-1,3,5-oxaselenazines 6 was treated with a 10 molar amount
of dimethyl acetylenedicarboxylate (DMAD), and the reaction
mixture was heated for several hours at refluxing temperature
under an Ar atmosphere. The crude reaction mixture was sub-
jected to chromatographic separation to obtain 4H-1,3-thiazine
9 or 4H-1,3-selenazines 11 as the cycloadducts of 1,3-thiaza-
1,3-butadienes 7 or 1,3-selenaza-1,3-butadienes 8 in high
yields. Furthermore, the treatment of 5a, 6a, or 6c with methyl
propiolate in a similar manner also afforded the corresponding
cycloadducts 10a, 12a, or 12c, respectively, as sole regioiso-
mers. The 1H NMR spectra of 10a, 12a, and 12c revealed long-
range coupling between the methine protons at the C-4 position
A similar treatment of 6a with p-benzoquinone or diethyl
azodicarboxylate (DEAD) also afforded 13a or 14a, respec-
tively, in modest yields. It was naturally assumed that 13a was
afforded by cycloaddition of the in situ generated 1,3-selenaza-
1,3-butadiene 8a with p-benzoquinone, followed by dehydro-
genation through aerobic oxidation during the usual workup
(Scheme 2). Burger has already reported on the cycloaddition
of 4-trifluoromethyl-1,3-thiaza-1,3-butadiene with the cyano
group of TCNE.13 However, in our case, the treatment of 6a
with TCNE only gave a complex mixture. All results concern-
ing the reactions are given in Table 2.
Heating of 6H-1,3,5-Oxathiazines (5) or 6H-1,3,5-Oxase-
Scheme 2.

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 513
Table 2. Heating of 6H-1,3,5-Oxathiazines 5 or 6H-1,3,5-Oxaselenazines 6 in the Presence of Acetylenic Dienophiles
Substrate
R2
Dienophile
R3 R4
Solvent Time Product Yielda)
R1
X 5, 6
/h 9–12
/%
C6H5
C6H5
C6H5
C6H5
C6H5
CH3
t-C4H9
CH3
S
S
S
5a CO2Me CO2Me Toluene
5b CO2Me CO2Me Toluene
1
4
3
9a
9b
10a
85
71
42
78
53
46
76
33
5a CO2Me
H
Toluene
CH3 Se 6a CO2Me CO2Me Benzene 2.5 11a
t-C4H9 Se 6b CO2Me CO2Me Benzene 2.5 11bb)
p-ClC6H4 CH3 Se 6c CO2Me CO2Me Benzene 2.5 11c
C6H5
p-ClC6H4 CH3 Se 6c CO2Me
CH3 Se 6a CO2Me
H
H
Benzene 2.5 12ac)
Benzene 2.5 12cc)
a) Isolated yields. b) Obtained as a conjugated enolic form. c) Single regioisomer.
lenazines (6) in the Presence of a Nucleophilic Reagent.
Heating an ethanolic solution of 6H-1,3,5-oxathiazine 5a at re-
fluxing temperature for a prolonged time afforded the recovery
of 5a. However, a similar heating of a toluene solution of 5a in
the presence of a 10 molar amount of ethanol or 2-propanol at
refluxing temperature gave 15a or 15b, respectively, in high
yields. On the other hand, when 6H-1,3,5-oxaselenazines 6
were heated in a methanolic or an ethanolic media under an Ar
atmosphere, the 1,4-adducts (17, 18) of 1,3-selenaza-1,3-buta-
dienes 8 with the alcohols were obtained in good yields in all
cases. These results indicated that a higher reaction tempera-
ture was required for the thermal cycloreversion of 6H-1,3,5-
oxathiazines 5 than those cases starting from the selenium ana-
logues 6. The treatment of a benzene solution of 6a with a 10
molar amount of benzenethiol or phenylmethanethiol at reflux-
ing temperature also gave the corresponding 1,4-adducts, 19a
or 20a, respectively, in good yields. All results of the reactions
are given in Table 3.
In contrast, the treatment of a benzene solution of 6a with a
10 molar amount of propylamine in a similar manner at reflux-
ing temperature only afforded N-propylselenobenzamide in
56% yield, and a treatment of 6b with propylamine, even at
room temperature, also gave a similar result. It was supposed
that N-propylselenobenzamide was given through a route in-
cluding the formation of heterodiene 8a followed by nucleo-
philic 1,4-addition of propylamine to 8a, an intramolecular nu-
Table 3. Heating of 6H-1,3,5-Oxathiazines 5 or 6H-1,3,5-oxaselenazines 6 in the Presence of Nucleophilic Reagents
Substrate
R2
Nucleophile
Solvent Time Product Yielda)
R1
X 5, 6 /Nu H (excess)
/h 15 20
/%
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
CH3
t-C4H9
CH3
CH3 Se 6a
CH3 Se 6a
t-C4H9 Se 6b
S
S
S
5a
5b
C2H5OH
C2H5OH
Toluene
Toluene
CH3OH
C2H5OH
C2H5OH
CH3OH
C2H5OH
Benzene
4
15ab)
15b
16a
17a
18a
18b
17c
18c
19a
20a
—
0
99
95
62
66
53
92
85
85
82
C2H5OHc)
4
4
4
4
4
4
4
4
4
4
5a i-C3H7OHc)
CH3OH
C2H5OH
C2H5OH
CH3OH
C2H5OH
C6H5SHc)
p-ClC6H4 CH3 Se 6c
p-ClC6H4 CH3 Se 6c
C6H5
C6H5
C6H5
CH3 Se 6a
CH3 Se 6a C6H5CH2SHc) Benzene
CH3 Se 6a
C3H7NH2
Benzene
0e)
d)
a) Isolated yields. b) 5a was recovered in quantitative yield. c) 10 Molar amount of
alcohol or thiol was treated for the reactions. d) 10 Molar amount of propylamine was
treated with 6a for the reaction. e) N-Propylbenzenecarboselenoamide was obtained
in 56% yield.

514 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
cleophilic attack of the nitrogen atom of the newly-introduced
propylamino group to the C-2 carbon of the 1,4-adduct, and a
final elimination of aldimine from the intermediate.
Heating of 6H-1,3,5-Oxathiazine (5) in the Absence of
Trapping Agents. Heating of a toluene solution of 5a or 5c
at refluxing temperature mainly afforded four products (5,6-di-
hydro-4H-1,3,5-thiadiazines 21, 5,6-dihydro-4H-1,3-thiazines
22, 3H-1,2,4-dithiazoles 23) and the starting arenecarbothioa-
mides 1 in all cases.
formed through the double-bond isomerization of 7a or 7c, re-
spectively.16,30 Compounds 22 were assumed to be afforded
through the 1,4-addition of 25 to the C-3 positions of hetero-
dienes 7 (Table 4).
On the other hand, heating of a toluene solution of 5b bear-
ing a t-butyl group at the C-4 position at refluxing temperature
in a similar manner gave a diastereomeric mixture of 26b
(about 5:3 ratio estimated by the integration of their 1H NMR
spectra for each case) and 23b along with unidentified several
products; neither the dimeric products nor the monomeric het-
erodiene 7b were not found at all in the reaction mixture.
The formation of thioamides 1 during a thermal reaction
might be explained by a hydrolytic cleavage of the starting ma-
terials 5 or heterodienes 7 caused by a trace amount of water
contained in the solvent or in the atmosphere or the solvent.
Heating of 6H-1,3,5-Oxathiazine (5) in the Presence of a
Thioamide. When a toluene solution of 6H-1,3,5-oxathiaz-
ine 5a was treated with 1.0 molar amount of thiobenzamide
(1a) at refluxing temperature for 5 h, 6H-1,3,5-thiadiazine 24a
was obtained in low yields along with an inseparable epimeric
mixture of 4H-1,3-thiazines 22a; the treatment of a toluene so-
lution of 5a with thiobenzamide (1a) in the presence of 1.0 mo-
lar amount of Et2O•BF3 at refluxing temperature also gave the
same products in a similar product-composition. A similar
heating of 5b in the presence of 1a gave 3H-1,2,4-dithiazoles
23 and an epimeric mixture of 26 in low yields; also actually,
heating a toluene solution of 5b in the presence of an excess
amount of thioacetamide at refluxing temperature for 3 h gave
26b (49%, major-26b:minor-26b = 5:3) and 23b (14%) in
much higher yields (Table 5). This result strongly suggests that
both 26b and 23b were formed by the reaction of heterodienes
7b with thioamides. Thioacetamide has been widely regarded
and used as a sulfur nucleophile, which is a stable synthetic
equivalent of H2S.45 Thus, the formation mechanisms of all
products by the heating of 5 in the presence of thioamides were
explained by the nucleophilic 1,4-addition of heterodienes 7
with in situ generated thiobenzamide (1a) followed by a ther-
mal elimination of benzonitrile from the adducts to form inter-
mediary thiol species, which might give 22 and 23 through a
further 1,4-addition of heterodienes 7 or through aerobic oxi-
dation, respectively.
The structures of 21a and 21c were determined to be insepa-
rable epimeric mixtures of the [4+2]-type dimers (major-
21a:minor-21a = 4:1, major-21c:minor-21c = 2:1) of 1,3-thi-
aza-1,3-butadienes (7a, 7c) from their spectral data.12 The
1H NMR and 13C NMR spectra of 21a and 21c measured in
CDCl3 at 27 °C showed rather complicated patterns with the
broadening signals. However, the 1H NMR spectra of 21a mea-
sured at –30 °C revealed sharpened and simplified signal pat-
terns including the pairs of doublets of the methyl groups of the
C-4 and the C-6 positions of 21a at δ = 1.77 and 1.98 ppm for
the major isomer and at δ = 1.71 and 1.90 ppm for the minor
isomer, respectively. The pairs of quartets of the methine pro-
1
tons of the C-4 and the C-6 positions of 21a in the H NMR
spectra of 21a were also observed at δ = 5.60 and 7.08 ppm for
the major isomer and at δ = 5.88 and 7.35 ppm for the minor
isomer, respectively. The 13C NMR spectra of 21a measured at
–30 °C showed a couple of thiocarbonyl carbon signals at δ =
198.2 and 201.3 ppm along with the doublet signals at δ = 52.9,
70.0, and 71.1 ppm, assigned to the methine carbons at the C-4
and the C-6 positions of the major and minor isomers of 21a,
respectively. The 13C NMR spectrum of 21c measured at –30
°C also showed similar spectral features to those of 21a. It was
strongly suggested that the temperature-dependent spectral
patterns of 21 in 1H NMR and 13C NMR spectra showed a con-
formational change of the 21, including a rotation of the C-N
bond of the thioamide moiety at above –30 °C. However, the
major conformation of 21 at low temperature was not clarified
from these spectral data.
The physical data including MS, IR, 1H NMR, and
13C NMR spectra also showed that both 22a and 22c were in-
separable epimeric mixtures (about 1:1 in both cases) of the
[4+2]-type dimers of 1,3-thiaza-1,3-butadienes, 7a or 7c, with
N-vinylthioamides, 25a or 25c, which were assumed to be
Generation of 1,3-Thiaza-1,3-butadienes (7a) by Ther-
Table 4. Thermal Reaction of 6H-1,3,5-Oxathiazines 5
Substrate
R2
Solvent Temp Time
/h 21 (major : minor)b) 22 (isomeric ratio)b)
Yields/%a)
R1
5
23
26
C6H5
CH3 5a Toluene Reflux
3
5
5
73 (21a, 4 : 1)
0
49 (21c, 4 : 1)
22 (22a, 1 : 1)
—
19 (22c, 1 : 1)
trace (23a)
0 (26a)
C6H5 t-C4H9 5b Toluene Reflux
p-ClC6H4 CH3 5c Toluene Reflux
trace (23b) trace (26b)c)
trace (23c)
0 (26c)
a) Isolated yields. b) Estimated by integration of the 1H NMR spectrum. c) The ratio of major-26b : minor-26b was estimated to be
5 : 3 by integration of the 1H NMR spectrum of the diastereomeric mixture.

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 515
Table 5. Thermal Reaction of 6H-1,3,5-Oxathiazines 5 in the Presence of Thioamide
Substrate
Thioamide
R3
Additive
Solvent Temp Time
/h 22 (isomeric ratio)b)
Yields/%a)
R1
R2
5
(mol amt.)
23
24
26
C6H5 CH3 5a
C6H5 CH3 5a
C6H5 t-C4H9 5b C6H5
C6H5
C6H5
—
Toluene Reflux
5
5
9
3
22 (22a, 1 : 1)
44 (22a, 1 : 1)
trace (23a)
11 (24a)
5 (24a)
0 (24b)
0 (24b)
0
0
BF3•OEt2 (1.0) Toluene Reflux
17 (23a)
22 (23b)
14 (23b)
—
—
Toluene Reflux
Toluene Reflux
—
—
trace (26b)
C6H5 t-C4H9 5b CH3
49 (26b)c)
a) Isolated yields. b) Estimated by integration of the 1H NMR spectrum. c) The ratio of major-26b : minor-26b was estimated to be 5 : 3 by
integration of the 1H NMR spectrum of the diastereomeric mixture.
mal Cycloreversion of 2H-1,3,5-Thiadiazines (21).
When
selenoamides 30 were obtained as the products. Even if 6 was
subjected to heating in the presence of an excess amount of re-
active dienophiles, such as cyclohexene, phenylacetylene, ma-
leic anhydride, or p-tolunitrile, the same products (27, 28, 29,
and 30) in all cases were obtained in similar ratios to those ob-
tained from the reaction in the absence of trapping agents. Ac-
tually, the expected 1,3-selenaza-1,3-butadienes 8 were not
found or detected at all as monomeric forms in the reaction
mixture, and the expected dimeric products 32 were not found
in the crude reaction mixture. On the other hand, heating a ben-
zene solution of 6a in a similar manner in the presence of a 2
molar amount of Et2O•BF3 only caused ring cleavage to give
selenobenzamide 2a in modest yield through the reverse-reac-
tion of formation of 6a. Thus, it was clear that Lewis acids pro-
moted the hydrolytic ring cleavage of the cyclic chalco-
genoaminoacetal- and chalcogenoimidate-moieties of 6a.
The structures of products 28 were confirmed by their phys-
ical data, including the MS, IR, 1H NMR, and 13C NMR spec-
tra, and their elemental analysis data were also consistent with
their structures. Especially, the 1H NMR and 13C NMR spectral
patterns of 28 were similar to those of the sulfur analogues and
the reported selenium derivatives. It was naturally supposed
that 28 were originated from 1,4-addition of the in situ generat-
a toluene solution of cycloadduct 21a was heated at refluxing
temperature for 12 h, only a small amount of epimeric mixture
of 22a (16% combined yield) was afforded along with the re-
covery of 21a (73%). Heating a toluene solution of 21a in the
presence of 10 molar amount of DMAD at refluxing tempera-
ture for 12 h afforded the cycloadduct 9a in only 20% yield
along with the recovery of 21a (78%); a similar heating of 21a
in 2-propanol at refluxing temperature for 8 h also gave the cor-
responding 1,4-adduct 16a in 34% yield along with the recov-
ery of 21a (58%), as shown in Scheme 3. These results indicat-
ed that 21 should be recognized as new stable precursors of
1,3-thiaza-1,3-butadienes 7 and that the retro [4+2]-type ther-
mal cycloreversion of 21 requires a higher temperature than the
thermal cycloreversion of 5 mentioned above.
Thermal Reaction of 6H-1,3,5-Oxaselenazines (6) in the
Absence of Trapping Agents or in the Presence of a Dieno-
phile. Heating of a benzene solution of 6H-1,3,5-oxaselena-
zines 6 at refluxing temperature under an Ar atmosphere in the
absence of trapping agents gave different results from those of
the thermal reaction of 6H-1,3,5-oxathiadines 5; in all cases
6H-1,3,5-selenadiazines 27, 3H-1,2,4-diselenazoles 28, an
epimeric mixture of 2H-1,3-imidazolines 29, and unexpected
Scheme 3.

516 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
ed selenoamides to the C-4 position of 1,3-selenaza-1,3-buta-
dienes 8 followed by the extrusion of arylonitriles and aerobic
oxidation of the resulting adducts according to the analogous
formation of 23 from 5 in the sulfur series.
1,3-selenaza-1,3-butadienes 8 with in situ generated nitrile.14
However, when a benzene solution of 6a was heated in the
presence of p-tolunitrile, the product compositions of the re-
sulting reaction mixtures were essentially similar to those of
the heating of 6a in the absence of such additives, and no prod-
ucts, 27–30, bearing p-tolyl substituents were found in the re-
action mixture (Table 6). Thus, the plausible structure of D for
27 was also excluded. The structure of 27a was finally deter-
mined by an X-ray crystallographic analysis, by which 27a
were shown to possess an unexpected 1,3,5-selenadiazine ring
C, as shown below.
On the other hand, the spectral data showed that the ring sys-
tem of 29 was different from that of the [4+2]-type dimers (21),
which were obtained by thermal reaction of 5 in the sulfur se-
ries. The mass spectra of 29 in each cases revealed the typical
set of parent ion peaks with a significant isotope distribution
pattern of the molecule containing one selenium atom, and
1H NMR and 13C NMR also showed that 29 were isolated as
epimeric mixtures (about 1:1 ratio estimated from the integra-
1
tion of the H NMR spectra) possessing one selenocarbonyl
functionality. It was strongly suggested that 29 originated from
the [4+2]-type dimers of the in situ generated 1,3-selenaza-1,3-
butadienes 8 as the similar formation route from 7 to 21. The
1
structures of 30 were determined from their H NMR and
Chart 2. Possible Structures for 27.
All results are given in Table 6.
13C NMR spectral data and, especially, the structure of 30a was
confirmed by selective conversion into the corresponding
amide (2-amino-N-benzoylpropiophenone (31a))46–48 in 63%
yield by treating with a 1.2 molar amount of mCPBA (Scheme
4).49,50
X-ray Crystallographic Study of 27a. Pale-yellow crys-
tals of 27a were obtained on recrystallization from hexane-
chloroform at room temperature; also, a single-crystal X-ray
analysis demonstrated that 27a possessed the 6H-1,3,5-selena-
diazine ring bearing two phenyl groups at the C-2 and C-4 po-
sitions. In the crystal, there are mixed two isomers with two po-
sitions (equatorial and axial) in the methyl group at the C-6 po-
sition. The occupancy ratio is about 65:35 for two isomers
with equatorial:axial positions. An ORTEP drawing of 27a
bearing an equatorial methyl group at the C-6 position is shown
in Fig. 1, and the selected bond lengths and bond angles of 27a
are given in Tables 7 and 8.
These data show that the molecule of 27a possessed, as a
whole, a planar conformation and that the core six-membered
ring possessed a distorted boat form in which C(1), N(1), C(2),
and N(2) were almost planar and the Se(1) and C(3) atoms de-
viated by 0.318 Å and –0.635 Å, respectively. Two phenyl
rings, [C(5)–C(10)] and [C(11)–C(16)], were shown to rotate
by 20.2° and 15.1° from the central ring plane. All bond lengths
and angles for the chemical structure of 27a exhibited values
within the normal range of common compounds. There is no
Scheme 4.
The structures of 27 were not fully defined only from their
spectral data. The elemental-analysis data supported the mo-
lecular formula of C16H14N2Se for 27a, and three plausible
structures, 6H-1,3,5-selenadiazine C, 4H-1,2,5-selenadiazine
D, and 4H-1,3,5-selenadiazine E, were proposed for 27a
(Chart 2). 4H-1,3,5-Selenadiazine ring system E was excluded
out for the structure of 27a by the 1H NMR and 13C NMR spec-
tra because 27a possessed non-equivalent two phenyl groups in
the molecule. At first, 27a was supposed to possess the 4H-
1,2,5-selenadiazine ring system (D). It was rationalized that
such products would be formed through the cycloaddition of
Table 6. Thermal Reaction of 6H-1,3,5-Oxaselenazines 6
Substrate
R2
Additive
(mol amt.)
—
Solvent Temp Time
/◦C /h
Yields/%a)
29 (major : minor)b)
R1
6
27
28
30
2
C6H5
C6H5
C6H5
C6H5
CH3 6a
Benzene Reflux 5
23 (27a) 29 (28a) 37 (29a, 2 : 1)
13 (27a) 37 (28a) 33 (29a, 2 : 1)
trace (27a) 8 (28a) 79 (29a, 2 : 1)
58 (27a) 18 (28a) 22 (29a, 2 : 1)
10 (27b) 43 (28b) 0 (29b)
11 (30a)
trace (30a)
trace (30a)
trace (30a)
42 (30b)
0
0
0
0
0
0
CH3 6a phenylacetylene (10) Benzene Reflux 2.5
CH3 6a p-tolunitrile (10) Benzene Reflux 3
CH3 6a
Se (1.1)
—
—
Benzene Reflux 2.5
Benzene Reflux 5
Benzene Reflux 5
C6H5 t-C4H9 6b
p-ClC6H4 CH3 6c
28 (27c) 24 (28c) 30 (29c, 2 : 1)
18 (30c)
C6H5
CH3 6a
BF3•OEt2 (1.0)
CH2Cl2 R.T. 2.5 trace (27a) 7 (28a) 0 (29b)
0 (30b) 26 (2a)c)
a) Isolated yields. b) Estimated by integration of the 1H NMR spectrum. c) 6a was recovered in 46% yield.

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 517
an epimeric mixture of the [4+2]-type dimers of 7, and com-
pounds 22 were the epimeric mixture of the another [4+2]-type
dimers of 7, i.e. the cycloadducts of heterodienes 7 with the in
situ generated double-bond isomers 25. These results clearly
showed that the double-bond isomerization of 1,3-thiaza-1,3-
butadienes 7 bearing a methyl group at the C-4 positions might
compete with the Diels–Alder dimerization of 7 under the ther-
mal-reaction condition mentioned above. However, an alterna-
tive ionic stepwise dimerization mechanism initiated by the
Michael-type nucleophilic attack of the sulfur atom of hetero-
diene 7 to afford 21 was not excluded at this time. A similar
heating of 5 in the presence of thioacetamide or thiobenzamide
(1) afforded 23 and 24 and, especially in such a case, 23 were
obtained in much higher yields than the usual cases of thermal
reactions of 5 in the absence of thioamides. These results indi-
cated that 23 were assumed to have originated by the 1,4-addi-
tion of thioamides 1 to heterodienes 7; also the formation of 24
is explained by a mechanism that includes a nucleophilic attack
of the sulfur atom of thioamides at the C-4 position of hetero-
dienes 7 and a subsequent ring closure accompanying the ex-
trusion of H2S. On the other hand, in all cases of thermal reac-
tions starting from 5 bearing bulky and non-isomerizable t-bu-
tyl groups at the C-4 and C-6 positions, we only obtained com-
plicated mixtures including a trace amount of 23 and 26, and
the 1H NMR monitoring experiments of the thermal reaction of
5 in an NMR tube only gave unsuccessful results for the detec-
tion of heterodiene 7b in the reaction mixture at all. However,
when a solution of 5b was heated in the presence of thioaceta-
mide or thiobenzamide, 26b was afforded in much higher
yield. This result also suggested the nucleophilic addition of
thioamides to the C-4 position of heterodiene 7b followed by
the thermal extrusion of nitriles from F to afford thiol-type in-
Figure 1. An ORTEP Drawing of 27a.
short contact in the crystal structure.
Plausible Reaction Pathway of Thermal Reaction of
6H-1,3,5-Oxathiazines (5) and 6H-1,3,5-Oxaselenazines
(6). 6H-1,3,5-Oxathiazines 5 and 6H-1,3,5-oxaselenazines 6
are known to cause retro-[4+2]-type thermal cycloreversion to
generate 1,3-thiaza-1,3-butadienes 7 or 1,3-selenaza-1,3-buta-
dienes 8, respectively, bearing some electron-deficient or elec-
tron-donating groups at the C-4 positions of the heterodienes as
stabilizing substituents. Our attempts were concentrated on the
generation, isolation, or detection of such reactive species 7
lacking a factor of electronic stabilization; we obtained com-
pounds 21, 22, and 23 by the thermal reaction of 5 bearing me-
thyl groups at the C-4 and C-6 positions. Compounds 21 were
Table 7. Selected Bond Lengths (Å) for 27a.a)
Atom Atom Distance Atom Atom Distance Atom Atom Distance Atom Atom Distance
Se(1) C(1)
Se(1) C(3)
N(1) C(1)
N(1) C(2)
N(2) C(2)
N(2) C(3)
1.904(5) C(1) C(5)
1.987(7) C(2) C(11)
1.288(6) C(3) C(4)
1.402(6) C(3) C(4ꢀ)
1.273(6) C(4) C(4ꢀ)
1.452(8) C(5) C(6)
1.472(7) C(5) C(10)
1.487(6) C(6) C(7)
1.397(7) C(11) C(16) 1.383(6)
1.373(8) C(12) C(13) 1.388(7)
1.384(8) C(13) C(14) 1.376(8)
1.352(9) C(14) C(15) 1.363(8)
1.374(8) C(15) C(16) 1.385(7)
1.40(1)
1.29(2)
1.59(2)
C(7) C(8)
C(8) C(9)
C(9) C(10)
1.382(7) C(11) C(12) 1.377(7)
a) Distances are in Angstroms. Estimated standard deviations in the least significant figure are given in parentheses.
Table 8. Selected Bond Angles (deg) for 27aa)
Atom Atom Atom
Angle
Atom Atom Atom
Angle
Atom Atom Atom
Angle
C(1) Se(1) C(3)
C(1) N(1) C(2)
C(2) N(2) C(3)
Se(1) C(1) N(1)
Se(1) C(1) N(5)
N(1) C(1) C(5)
N(1) C(2) N(2)
N(1) C(2) C(11)
N(2) C(2) C(11)
Se(1) C(3) N(2)
Se(1) C(3) C(4)
90.3(3)
122.1(5)
118.9(5)
122.3(4)
117.5(4)
120.2(5)
127.7(5)
113.8(5)
118.5(5)
110.1(5)
116.5(7)
Se(1) C(3) C(4ꢀ)
N(2) C(3) C(4)
N(2) C(3) C(4ꢀ)
C(4) C(3) C(4ꢀ)
C(3) C(4) C(4ꢀ)
C(3) C(4ꢀ) C(4)
C(1) C(5) C(6)
C(1) C(5) C(10)
C(6) C(5) C(10)
C(5) C(6) C(7)
C(6) C(7) C(8)
116(1)
113.4(7)
123(1)
73(1)
50.6(8)
57(1)
119.6(5)
122.3(5)
118.0(5)
120.8(6)
120.1(6)
C(7) C(8) C(9)
119.8(6)
120.8(6)
120.5(6)
120.5(5)
120.6(5)
118.9(5)
120.7(5)
119.6(5)
120.1(5)
120.3(5)
120.4(5)
C(8) C(9) C(10)
C(5) C(10) C(9)
C(2) C(11) C(12)
C(2) C(11) C(16)
C(12) C(11) C(16)
C(11) C(12) C(13)
C(12) C(13) C(14)
C(13) C(14) C(15)
C(14) C(15) C(16)
C(11) C(16) C(15)
a) Angles are in degrees. Estimated standard deviations in the least significant figure are given in parentheses.

518 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
termediates G. It was assumed that any further oxidative ring
closure of G just gave 23, and the further nucleophilic addition
of G to another heterodiene 7b also resulted in the formation of
26. Thus, the formation of all products, 21, 22, 23, 24, and 26,
obtained by the thermal reactions of 5 was fully rationalized by
the in situ generation of 1,3-thiaza-1,3-butadienes 7.
a trace amount of water in the solvent or the atmosphere. The
reaction of heterodienes 8 with selenoamides 2 might give the
1,4-addition products F in the primary stage, and F might un-
dergo a thermal elimination of arylonitrile to give the interme-
diates G; also further oxidative ring closure of G in a similar
route of the formation of 23 from 5 in the sulfur series finally
gave 28. The formation mechanism of 27 was also explained
by the 1,4-addition of selenoamides 2 to heterodienes 8 as in an
analogous course of formation of 24 from 7. Interestingly, in
contrast with the formation of 21 and 22 in the sulfur series,
analogous [4+2]-type dimers of 8 were not found at all in the
reaction mixture, and we just obtained unexpected products, 29
and 30, besides 27 and 28. The formation of [4+2]-type dimers
21 in the sulfur series strongly suggested that in situ generated
heterodienes 8 also caused facile [4+2]-type dimerization to
give 32 under the condition of the thermal reaction of 6.12 Thus,
it was assumed that 29 were afforded through the thermal or
oxidative selenium extrusion of dimers 32. Selenoamides 30
were also suggested to be afforded by further hydrolytic ring
cleavage of 29. However, the 1H NMR monitoring experiments
of the thermal reaction of 6 in an NMR tube only gave discou-
rageous results for the detection of 8 or 32 in the reaction mix-
ture.
The heating of 6H-1,3,5-oxaselenazines 6 in the absence of
trapping agents afforded 27, 28, 29, and 30 along with a small
amount of selenoamides 2. The heating of 6a in the presence of
an excess amount of p-tolunitrile, cyclohexene, phenylacety-
lene, maleic anhydride, or 2,3-dimethyl-1,3-butadiene also
gave resulting reaction mixtures whose product composition
was similar to that of the heating of 6a in the absence of such
additives; neither the [4+2]-cycloadducts of 1,3-selenaza-1,3-
butadienes 8 with p-tolunitrile,13 products 27–29 bearing p-
tolyl substituents in place of a phenyl group, nor the [4+2]-cy-
cloadducts of 8 with the alkene or alkyne were obtained. In ad-
dition, no cycloadducts of selenoaldehydes, generated through
an alternative retro-[2+2+2]-type cycloreversion of 6, with 2,3-
dimethyl-1,3-butadiene were found at all in the crude products.
A slight improvement in the yield of 28a was achieved by heat-
ing 6a in the presence of a selenating agent,10 i.e. (Me3Si)2Se-
Et2O•BF3;37 in this case small amounts of 27a, 29a, 30a, and
the unidentified compounds were also obtained along with 28a.
These results suggested that compounds 28 were afforded from
8 and selenating agents, i.e. selenoamides 2,10,11 which might
be generated through a hydrolytic cleavage of 6 or 8 caused by
The plausible reaction paths for the formation of the prod-
ucts by thermal reactions of 6H-1,3,5-oxathiazines 5 and 6H-
1,3,5-oxaselenazines 6 in the absence of trapping agents are
summarized in Scheme 5. However, to date, all attempts to de-
Scheme 5.

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 519
mmol) or pivalaldehyde (4, 2.06 g, 24.0 mmol) and Et2O•BF3 (2.84
g, 20.0 mmol) at 0 °C, and the reaction mixture was stirred for 3 h
at room temperature. The reaction was then quenched with an
aqueous NaHCO3 solution, and extracted with dichloromethane.
The organic layer was washed with water, and then dried over an-
hydrous Na2SO4 powder. After removing the solvent in vacuo, the
crude product was purified using column chromatography on silica
gel to afford 2,6-dialkyl-4-aryl-6H-1,3,5-oxathiazine (5) or 2,6-di-
alkyl-4-aryl-6H-1,3,5-oxaselenazine (6), respectively, in good
yields. Purification of solidified products 6b and 6d was achieved
by recrystallization using hexane-dichloromethane.
tect or isolate heterodienes, 7 or 8, or the intermediates, F or G,
were not successful at all.
Conclusion. In conclusion, we found the generation of
heterodienes, 1,3-thiaza-1,3-butadienes 7 and 1,3-selenaza-
1,3-butadienes 8, by retro-[4+2]-type thermal cycloreversion
of 2,4,6-trisubstituted 6H-1,3,5-oxathiazines 5 or 6H-1,3,5-ox-
aselenazines 6, respectively. Various applications of hetero-
dienes 7 and 8 for the syntheses of chalcogen-containing het-
erocycles are in progress in our laboratory.
Experimental
5a (R1 = C6H5, R2 = CH3): Pale yellow oil; MS m/z (%) 207
(M+; 17), 165 (21), 39 (bp); IR (neat) 2985, 1614, 1447, 1373,
1323, 1231, 1161, 1114, 961, 766, 692 cm–1; 1H NMR (CDCl3) δ
1.60 (3H, d, J = 6.1 Hz), 1.61 (3H, d, J = 6.2 Hz), 5.28 (1H, q, J =
6.2 Hz), 5.35 (1H, q, J = 6.1 Hz), 7.35–7.43 (3H, m), 7.78–7.80
(2H, m); 13C NMR (CDCl3) δ 22.2 (q), 22.5 (q), 75.6 (s), 87.4 (d),
126.2 (d), 128.3 (d), 130.7 (d), 138.5 (s), 157.0 (s). Found: C,
63.05; H, 6.54; N, 6.37%. Calcd for C11H13NOS: C, 63.74; H, 6.32;
N, 6.76%.
Instruments. The melting points were determined with a
1
Büchi 535 micro-melting-point apparatus. H NMR spectra were
recorded on a Bruker AC-400P (400 MHz) spectrometer, and the
chemical shifts of the 1H NMR spectra are given in δ relative to in-
ternal tetramethylsilane (TMS). 13C NMR spectra were recorded
on a Bruker AC-400P (100 MHz). 77Se NMR spectra were record-
ed on a BrukerAC-400P (76 MHz). Mass spectra were recorded on
a Hitachi M-2000 mass spectrometer with electron-impact ioniza-
tion at 20 or 70 eV using a direct inlet system. IR spectra were re-
corded for thin film (neat) or KBr disks on a JASCO FT/IR-7300
spectrometer. Elemental analyses were performed using a
Yanagimoto CHN corder MT-5.
Materials. Column chromatography was performed using sil-
ica gel (Merck, Cat. No. 7734 or 9385) without pretreatment.
Dichloromethane and chloroform were dried over P4O10 and were
freshly distilled before use. Benzene, toluene, and hexane were
dried over CaH2 and were freshly distilled before use. Methanol,
ethanol, and 2-propanol were dried over MgO and were freshly dis-
tilled before use. All substrates and reagents including benzoni-
trile, p-chlorobenzonitrile, p-tolunitrile, thiobenzamide (1a), thio-
acetamide, 2,4,6-trimethyl-1,3,5-trioxane (paraldehyde, 3), pivala-
ldehyde (4), benzaldehyde, dimethyl acetylenedicarboxylate
(DMAD), methyl propiolate, maleic anhydride, p-benzoquinone,
diethyl azodicarboxylate (DEAD), tetracyanoethylene (TCNE),
cyclohexene, phenylacetylene, 2,3-dimethyl-1,3-butadiene, ben-
zenethiol, phenylmethanethiol, propylamine, boron trifluoride di-
ethyl ether complex (Et2O•BF3), m-chloroperbenzoic acid (mCP-
BA), elemental selenium, and sodium tetrahydroborate (NaBH4)
were commercially available reagent grade and were used without
any pretreatment.
5b (R1 = C6H5, R2 = t-C4H9): Colorless plates, mp 95.4–96.0
°C; MS m/z (%) 291 (M+; 22), 41 (bp); IR (KBr) 2954, 2866, 1611,
1479, 1361, 1229, 1063, 767, 691 cm–1; 1H NMR (CDCl3) δ 1.05
(9H, s), 1.06 (9H, s), 4.84 (1H, s), 4.98 (1H, s), 7.38–7.43 (3H, m),
7.84–7.87 (2H, m); 13C NMR (CDCl3) δ 25.1 (q), 25.3 (q), 36.0 (s),
36.8 (s), 88.6 (d), 96.8 (d), 126.3 (d), 128.1 (d), 130.6 (d), 139.2 (s),
157.5 (s). Found: C, 69.83; H, 8.66; N, 4.97%. Calcd for
C17H25NOS: C, 70.06; H, 8.65; N, 4.81%.
5c (R1 = p-ClC6H4, R2 = CH3):
Colorless needles, mp
101.9–102.5 °C (dec.); MS m/z (%) 197 (M+ – CH3CHO; 17), 58
(bp); IR (KBr) 2979, 1606, 1489, 1398, 1311, 1238, 1230, 1162,
1089, 965, 846, 838, 827 cm–1; 1H NMR (CDCl3) δ 1.61 (3H, d, J =
6.3 Hz), 1.64 (3H, d, J = 6.3 Hz), 5.30 (1H, q, J = 6.3 Hz), 5.36 (1H,
q, J = 6.3 Hz), 7.37 (2H, d, J = 8.9 Hz), 7.74 (2H, d, J = 8.9 Hz);
13C NMR (CDCl3) δ 22.2 (q), 22.5 (q), 75.8 (d), 87.5 (d), 127.6 (s),
128.6 (d), 136.9 (s), 137.0 (s), 156.0 (s). Found: C, 54.73; H, 4.97;
N, 5.75%. Calcd for C11H12ClNOS: C, 54.66; H, 5.00; N, 5.79%.
5d (R1 = p-ClC6H4, R2 = t-C4H9):
Colorless crystals, mp
95.4–96.0 °C (dec.); MS m/z (%) 325 (M+; 2), 268 (M+ – t-C4H9; 2),
239 (M+ – t-C4H9CHO; 17), 41 (bp); IR (KBr) 2954, 2866, 1611,
1479, 1229, 1063, 767, 691 cm–1; 1H NMR (CDCl3) δ 1.05 (9H, s),
1.06 (9H, s), 4.81 (1H, s), 4.96 (1H, s), 7.35 (2H, d, J = 8.6 Hz),
7.79 (2H, d, J = 8.6 Hz); 13C NMR (CDCl3) δ 25.1 (q), 25.3 (q),
36.0 (s), 36.8 (s), 88.7 (d), 96.8 (d), 127.5 (d), 128.3 (d), 136.6 (s),
137.5 (s), 156.3 (s). Found: C, 62.39; H, 7.29; N, 4.49%. Calcd for
C17H24ClNOS: C, 62.65; H, 7.42; N, 4.30%.
General Procedure for the Preparation of Arenecarbosele-
noamides (2). A dichloromethane solution of arylonitrile was
treated with (Me3Si)2Se (1.1 mol amt.) and Et2O•BF3 (2.2 mol
amt.)43 under anAr atmosphere, and the reaction mixture was heat-
ed to 60 °C for 8 h in a sealed tube. The reaction mixture was then
quenched with an aqueous NaHCO3 solution, and extracted with
dichloromethane. The organic layer was washed with water, and
then dried over anhydrous Na2SO4 powder. After removing the sol-
vent in vacuo, the crude product was purified using column chro-
matography on silica gel to afford the corresponding arenecarbose-
lenoamides (2a, 2c) in 70–80% yields.
6a (R1 = C6H5, R2 = CH3):44 Orange oil; MS m/z (%) 257
(M+; 50, 80Se), 213 (bp); IR (neat) 3059, 2982, 2923, 1602, 1533,
1447, 1314, 1223, 1116, 951, 764, 691 cm–1; 1H NMR (CDCl3) δ
1.63 (3H, d, J = 6.2 Hz), 1.72 (3H, d, J = 6.2 Hz), 5.11 (1H, q, J =
6.2 Hz), 5.57 (1H, q, J = 6.2 Hz), 7.23–7.38 (3H, m), 7.72–7.74
(2H, m); 13C NMR (CDCl3) δ 22.9 (q), 23.7 (q), 73.1 (d), 89.3 (s),
126.2 (d), 128.2 (d), 130.6 (d), 140.0 (s), 157.5 (s). Found: C,
51.45; H, 5.01; N, 5.40%. Calcd for C11H13NOSe: C, 51.98; H,
5.15; N, 5.51%.
2a (R1 = C6H5): Yellow needles, mp 124.0–124.5 °C (Ref. 51,
126.0–126.5 °C ).
2c (R1 = p-ClC6H4): Yellow needles, mp 126.0–128.0 °C
(Ref. 51, 127.5–128.5 °C ).
6b (R1 = C6H5, R2 = t-C4H9):44
Pale yellow needles, mp
94.0–95.0 °C (Ref. 44, 98.0–98.5 °C); MS m/z (%) 252 (M+ – t-
BuCHO – 1; 14, 80Se), 42 (bp); IR (neat) 2953, 1622, 1479, 1392,
General Procedure for the Preparation of 2,6-Dialkyl-4-
aryl-6H-1,3,5-oxathiazines (5) and 6H-1,3,5-Oxaselenazines
(6). A 20 ml dichloromethane solution of arenecarbothioamide 1
(10.0 mmol) or arenecarboselenoamide 2 (10.0 mmol) was treated
with 2,4,6-trimethyl-1,3,5-trioxane (paraldehyde, 3, 1.04 g, 8.00
1165, 1073, 1058, 999, 764, 694 cm–1; H NMR (CDCl3) δ 1.06
1
(9H, s), 1.08 (9H, s), 4.61 (1H, s), 5.41 (1H, s), 7.35–7.41 (3H, m),
7.79–7.82 (2H, m); 13C NMR (CDCl3) δ 25.3 (q), 25.5 (q), 36.4 (s),
36.9 (s), 89.0 (s), 99.0 (br. s), 126.6 (d), 128.3 (d), 130.6 (d), 140.7

520 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
51.15; H, 4.29; N, 3.98%.
(s), 157.9 (s). Found: C, 59.84; H, 7.27; N, 4.02%. Calcd for
C17H25NOSe: C, 60.35; H, 7.45; N, 4.14%.
11b (R1 = C6H5, R2 = t-C4H9, R3 = R4 = CO2CH3):
Yellow
6c (R1 = p-ClC6H4, R2 = CH3): Pale yellow needles, mp
88.7–89.1 °C; MS m/z (%) 245 (M+ – MeCHO; 79, 80Se), 108 (bp);
IR (KBr) 2976, 2921, 1607, 1487, 1397, 1225, 1163, 1089, 1058,
955, 828, 582 cm–1; 1H NMR (CDCl3) δ 1.64 (3H, d, J = 6.2 Hz),
1.78 (3H, d, J = 6.0 Hz), 5.15 (1H, q, J = 6.2 Hz), 5.65 (1H, q, J =
6.0 Hz), 7.34–7.37 (2H, m), 7.66–7.69 (2H, m); 13C NMR (CDCl3)
δ 22.9 (q), 23.8 (q), 73.5 (d), 89.5 (s), 127.7 (d), 128.6 (d), 136.8
(s), 138.5 (s), 156.5 (s). Found: C, 45.78; H, 4.18; N, 4.87%. Calcd
for C11H12ClNOSe: C, 45.77; H, 4.19; N, 4.85%.
oil; MS m/z (%) 316 (M+ – Se + 1; bp); IR (neat) 3324, 2953, 1716,
1
1488, 1440, 1237, 1208, 1133, 1072, 763, 698 cm–1; H NMR
(CDCl3) δ 1.39 (9H, s), 3.67 (3H, s), 3.83 (3H, s), 7.34–7.37 (3H,
m), 7.47–7.49 (2H, m), 8.54 (1H, s); 13C NMR (CDCl3) δ 29.5 (q),
32.5 (s), 51.3 (q), 51.9 (q), 112.3 (s), 113.3 (s), 128.16 (d), 128.22
(d), 128.5 (d), 131.2 (s), 133.0 (s), 140.8 (s), 165.1 (s), 167.6 (s).
The signal, revealed at δ 8.54, disappeared upon a similar 1H NMR
measurement of 11b using CDCl3 and a small amount of CD3OD.
All of the spectral data strongly suggested a highly conjugated
enolic structure for 11b. Found: C 54.39; H, 5.13; N, 3.40%. Calcd
for C18H21NO4Se: C, 54.83; H, 5.37; N, 3.55%.
Thermal Reaction of 6H-1,3,5-Oxathiazines (5) or 6H-1,3,5-
Oxaselenazines (6) in the Presence of anAcetylenic Dienophile,
p-Benzoquinone, or Diethyl Azodicarboxylate (DEAD).
Af-
11c (R1 = p-ClC6H4, R2 = CH3, R3 = R4 = CO2CH3):
Or-
ter a 50 ml benzene solution of 6H-1,3,5-oxathiazine (5, 2.00
mmol) or 6H-1,3,5-oxaselenazine (6, 2.00 mmol) was treated with
a trappimg agent (10.0 mmol), such as dimethyl acetylenedicar-
boxylate (DMAD), methyl propiolate, p-benzoquinone, or diethyl
azodicarboxylate (DEAD), the reaction mixture was heated at re-
fluxing temperature for several hours. The reaction mixture was
then cooled to room temperature, quenched with an aqueous NaOH
solution, and extracted with benzene. The organic layer was
washed with water, and then dried over anhydrous Na2SO4 powder.
After removing the solvent in vacuo, the crude product was purified
by using column chromatography on silica gel to afford the cy-
cloadducts in high-to-moderate yields.
ange oil; MS m/z (%) 387 (M+; 5, 80Se), 328 (11), 250 (84), 218
(bp); IR (neat) 2951, 1716, 1591, 1251, 834, 582 cm–1; H NMR
1
(CDCl3) δ 1.59 (3H, d, J = 7.0 Hz), 3.84 (3H, s), 3.86 (3H, s), 4.47
(1H, q, J = 7.0 Hz), 7.37–7.40 (2H, m), 7.77–7.79 (2H, m);
13C NMR (CDCl3) δ 15.8 (q), 52.7 (q), 53.0 (q), 62.5 (d), 127.9 (s),
128.8 (d), 129.1 (d), 135.7 (s), 136.9 (s), 137.6 (s), 157.5 (s), 163.7
(s), 166.1 (s). Found: C, 46.90; H, 3.60; N, 3.75%. Calcd for
C15H14ClNO4Se: C, 46.59; H, 3.65; N, 3.62%.
12a (R1 = C6H5, R2 = CH3, R3 = CO2CH3, R4 = H):
Yellow
oil; MS m/z (%) 296 (M+ + 1; 10, 80Se), 192 (bp), 160 (32), 131 (37);
IR (KBr) 2950, 1713, 1435, 1280, 1050, 910, 745, 651, 621 cm–1;
1H NMR (CDCl3) δ 1.30 (3H, d, J = 7.0 Hz), 3.80 (3H, s), 5.65 (1H,
q, J = 7.0 Hz), 7.39–7.48 (3H, m), 7.77–7.79 (2H, m), 8.24 (1H, s);
13C NMR (CDCl3) δ 15.3 (q), 52.1 (q), 56.0 (d), 125.8 (s), 127.4
(d), 128.6 (d), 131.0 (d), 131.4 (d), 138.3 (s), 152.8 (s), 163.4 (s).
Found: C, 53.31; H, 4.48; N, 4.68%. Calcd for C13H13NO2Se: C,
53.07; H, 4.45; N, 4.76%.
9a (R1 = C6H5, R2 = CH3, R3 = R4 = CO2CH3): Pale yellow
oil; MS m/z (%) 305 (M+; 3), 202 (bp); IR (neat) 2953, 1732, 1635,
1435, 1267, 940, 767, 692 cm–1; 1H NMR (CDCl3) δ 1.48 (3H, d, J
= 6.9 Hz), 3.84 (3H, s), 3.85 (3H, s), 4.92 (1H, q, J = 6.9 Hz),
7.28–7.49 (3H, m), 7.88–7.91 (2H, m); 13C NMR (CDCl3) δ 16.0
(q), 52.6 (q), 53.1 (q), 57.3 (s), 127.4 (d), 128.5 (d), 129.0 (s), 131.4
(d), 135.9 (s), 156.1 (s), 163.2 (s), 165.7 (s). Found: C, 58.94; H,
4.86; N, 4.70%. Calcd for C15H15NO4S: C, 59.00; H, 4.95; N,
4.59%.
12c (R1 = p-ClC6H4, R2 = CH3, R3 = CO2CH3, R4 = H): Or-
ange oil; MS m/z (%) 329 (M+; 8, 80Se), 248 (5), 192 (bp), 160 (45),
132 (51); IR (neat) 2950, 1713, 1435, 1280, 1051, 917, 832, 746,
711, 591, 555 cm–1; 1H NMR (CDCl3) δ 1.28 (3H, d, J = 6.9 Hz),
3.80 (3H, s), 5.64 (1H, q, J = 6.9 Hz), 7.36–7.38 (2H, m), 7.71–7.73
(2H, m), 8.21 (1H, s); 13C NMR (CDCl3) δ 15.2 (q), 52.1 (q), 56.1
(d), 125.8 (s), 128.6 (d), 128.7 (d), 130.9 (d), 136.6 (s), 137.1 (s),
151.6 (s), 163.2 (s). Found: C, 47.58; H, 3.63; N, 4.35%. Calcd for
C13H12ClNO2Se: C, 47.51; H, 3.68; N, 4.26%.
9b (R1 = C6H5, R2 = t-C4H9, R3 = R4 = CO2CH3): Colorless
needles, mp 86.2–86.3 °C (dec.); MS m/z (%) 348 (M+ + 1; 2), 292
(M+ + 1 – C4H8; 55), 75 (bp); IR (neat) 3089, 2976, 1724, 1643,
1
1435, 1264, 1046, 992, 936, 767 cm–1; H NMR (CDCl3) δ 1.05
(9H, s), 3.80 (3H, s), 3.86 (3H, s), 5.27 (1H, s), 7.35–7.55 (3H, m),
7.85–7.90 (2H, m); 13C NMR (CDCl3) δ 26.5 (q), 42.3 (s), 52.6 (q),
53.1 (q), 70.8 (d), 126.2 (s), 127.3 (d), 128.6 (d), 131.4 (d), 131.9
(s), 136.4 (s), 153.1 (s), 164.3 (s), 167.4 (s). Found: C, 62.28; H,
6.11; N, 3.98%. Calcd for C18H21NO4S: C, 62.23; H, 6.09; N,
4.03%.
13a (R1 = C6H5, R2 = CH3): Red needles, mp 126.0–127.0
°C; MS m/z (%) 317 (M+; 53, 80Se), 212 (bp); IR (KBr) 3056, 1650,
1587, 1292, 889, 841, 770, 693 cm–1; 1H NMR (CDCl3) δ 1.30 (3H,
d, J = 7.0 Hz), 5.87 (1H, q, J = 7.0 Hz), 6.80 (1H, d, J = 10.0 Hz),
6.89 (1H, d, J = 10.0 Hz), 7.40–7.50 (3H, m), 7.80–7.83 (2H, m);
13C NMR (CDCl3) δ 15.3 (q), 55.7 (d), 127.4 (d), 128.7 (d), 131.4
(d), 135.9 (dd), 136.7 (s), 137.0 (dd), 138.0 (s), 141.7 (s), 154.6 (s),
181.0 (s), 182.7 (s). Found: C, 57.03; H, 3.50; N, 4.27%. Calcd for
C15H11NO2Se: C, 56.97; H, 3.51; N, 4.43%.
10a (R1 = C6H5, R2 = CH3, R3 = CO2CH3, R4 = H):
Pale
yellow plates, mp 68.0–69.0 °C; MS m/z (%) 247 (M+; 8), 144 (bp);
IR (KBr) 2980, 1698, 1439, 1289, 1236, 1219, 1059, 936, 769, 752,
691 cm–1; 1H NMR (CDCl3) δ 1.31 (3H, d, J = 6.9 Hz), 3.80 (3H, s),
5.44 (qd, J = 6.9, 1.4 Hz), 7.39–7.48 (3H, m), 7.69 (1H, d, J = 1.4
Hz), 7.83–7.86 (2H, m); 13C NMR (CDCl3) δ 16.9 (q), 52.0 (q),
52.9 (s), 123.9 (s), 127.1 (d), 128.5 (d), 131.0 (d), 131.1 (d), 136.8
(s), 153.0 (s), 163.9 (s). Found: C, 63.07; H, 5.21; N, 5.67%. Calcd
for C13H13NO2S: C, 63.13; H, 5.21; N, 5.62%.
14a (R1 = C6H5, R2 = CH3): Pale yellow oil; MS m/z (%) 385
(M+; 0.4, 80Se), 43 (bp); IR (neat) 2984, 2936, 1733, 1713, 1627,
1447, 1374, 1283, 1091, 1039, 908, 764, 692, 592 cm–1; 1H NMR
(CDCl3) δ 1.27–1.34 (6H, m), 1.56 (3H, d, J = 6.3 Hz), 4.23–4.31
(4H, m), 6.40 (1H, q, J = 6.3 Hz), 7.39–7.49 (3H, m), 7.57–7.59
(2H, m); 13C NMR (CDCl3) δ 14.3 (q), 14.5 (q), 18.6 (q), 41.5 (d),
63.3 (t), 63.8 (t), 125.6 (d), 129.0 (d), 131.6 (d), 137.5 (s), 150.5 (s),
154.8 (s), 155.3 (s). Found: C, 47.03; H, 5.02; N, 10.50%. Calcd for
C15H19N3O4Se: C, 46.88; H, 4.98; N, 10.93%.
11a (R1 = C6H5, R2 = CH3, R3 = R4 = CO2CH3): Yellow oil;
MS m/z (%) 354 (M+ + 1; 13, 80Se), 250 (bp), 218 (97); IR (neat)
2952, 1729, 1617, 1434, 1255, 765, 692 cm–1; 1H NMR (CDCl3) δ
1.59 (3H, d, J = 7.0 Hz), 3.84 (3H, s), 3.86 (3H, s), 4.52 (1H, q, J =
7.0 Hz), 7.38–7.49 (3H, m), 7.82–7.85 (2H, m); 13C NMR (CDCl3)
δ 15.8 (q), 52.6 (q), 53.1 (q), 62.3 (d), 127.9 (d), 128.3 (s), 128.7
(d), 131.4 (d), 136.4 (s), 137.3 (s), 158.5 (s), 164.0 (s), 166.2 (s).
Found: C, 51.42; H, 4.31; N, 4.28%. Calcd for C15H15NO4Se: C,
Heating of 6H-1,3,5-Oxathiazine (5) or 6H-1,3,5-Ozaselena-
zines (6) in an Alcoholic Media. An alcoholic solution (20 ml)
of 6H-1,3,5-oxathiazine (5, 2.00 mmol) or 6H-1,3,5-oxaselenazine
(6, 2.00 mmol) was heated at refluxing temperature for a several

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 521
hours. After cooling to room temperature and quenching with wa-
ter, the reaction mixture was subjected to the usual workup. The
crude product was purified using column chromatography on silica
gel to afford N-(1-alkoxyethyl)arenecarbothioamide (15, 16) or N-
(1-alkoxyalkyl)arenecarboselenoamides (17, 18) as major prod-
ucts.
4.49; N, 4.93%. Calcd for C10H12ClNOSe: C, 43.42; H, 4.37; N,
5.06%.
18c (R1 = p-ClC6H4, R2 = CH3, Nu = OC2H5): Yellow nee-
dles, mp 85.0–86.0 °C; MS m/z (%) 289 (M+; 4, 80Se), 246 (8), 44
(bp); IR (KBr) 3222, 2977, 1589, 1515, 1481, 1404, 1374, 1231,
1110, 1093, 1052, 932, 725 cm–1; 1H NMR (CDCl3) δ 1.24 (3H, t, J
= 7.0 Hz), 1.53 (3H, d, J = 5.8 Hz), 3.65–3.81 (2H, m), 6.08 (1H,
dq, J = 7.9, 5.8 Hz), 7.29–7.31 (2H, m), 7.65–7.67 (2H, m), 8.27
(1H, br. s); 13C NMR (CDCl3) δ 15.1 (q), 20.3 (q), 64.9 (t), 86.4 (d),
127.6 (d), 128.5 (d), 137.3 (s), 142.7 (s), 202.1 (s). Found: C,
45.43; H, 4.88; N, 4.78%. Calcd for C11H14ClNOSe: C, 45.46; H,
4.85; N, 4.82%.
15b (R1 = C6H5, R2 = t-C4H9, Nu = OC2H5): Yellow oil; MS
m/z (%) 251 (M+; 50), 222 (M+ – C2H5; 84), 207 (M+ – OC2H5; 91),
87 (bp); IR (neat) 3397, 3290, 2963, 2904, 1501, 1481, 1449, 1370,
1
1362, 1116, 1069, 961, 736, 693 cm–1; H NMR (CDCl3) δ 1.04
(9H, s), 1.21 (3H, br. t, J = 6.9 Hz), 3.64 (1H, dq, J = 9.9, 7.0 Hz),
3.73 (1H, dq, J = 9.9, 6.9 Hz), 5.81 (1H, d, J = 8.0 Hz), 7.30–7.50
(3H, m), 7.55–7.70 (1H, m), 7.72–7.75 (2H, m); 13C NMR (CDCl3)
δ 15.0 (q), 24.9 (q), 36.5 (s), 64.7 (t), 90.4 (d), 126.4 (d), 128.5 (d),
131.1 (d), 142.3 (s), 200.9 (s). Found: C, 66.85; H, 8.76; N, 5.40%.
Calcd for C14H21NOS: C, 66.89; H, 8.42; N, 5.57%.
Heating of 6H-1,3,5-Oxaselenazines (6) in the Presence of a
Thiol. After a benzene solution (20 ml) of 6H-1,3,5-oxaselena-
zine (6, 2.00 mmol) was treated with an excess amount of ben-
zenethiol or phenylmethanethiol (20 mmol), the reaction mixture
was heated at refluxing temperature for 4 h. Then, after cooling to
room temperature and quenching with an aqueous NaOH solution,
the reaction mixture was subjected to the usual workup. The crude
product was purified using column chromatography on silica gel to
afford N-(1-arylthioethyl)selenobenzamide (19a) or N-(1-alkylth-
ioethyl)selenobenzamide (20a), respectively, in good yields.
19a (R1 = C6H5, R2 = CH3, Nu = SC6H5): Orange oil; MS
m/z (%) 321 (M+; 2, 80Se), 211 (M+ – C6H5SH; 38, 80Se), 66 (bp); IR
(neat) 3210, 2979, 1583, 1483, 1447, 1361, 1246, 1124, 1025, 878,
765, 691, 570 cm–1; 1H NMR (CDCl3) δ 1.74 (3H, d, J = 6.7 Hz),
6.37 (1H, dq, J = 8.5, 6.7 Hz), 7.25–7.33 (5H, m), 7.42–7.46 (3H,
m), 7.49–7.51 (2H, m), 8.12 (1H, br. s); 13C NMR (CDCl3) δ 19.9
(q), 60.8 (d), 126.3 (d), 127.8 (d), 128.5 (d), 129.3 (d), 131.2 (d),
131.5 (d), 132.0 (s), 144.7 (s), 203.5 (s). Found: C, 56.69; H, 4.74;
N, 4.18%. Calcd for C15H15NSSe: C, 56.25; H, 4.72; N, 4.37%.
20a (R1 = C6H5, R2 = CH3, Nu = SCH2C6H5): Red oil; MS
m/z (%) 342 (M+; 37, 80Se), 211 (M+ – C6H5CH2SH; 38, 80Se), 66
(bp); IR (neat) 3333, 3210, 3059, 3027, 2980, 2923, 1507, 1483,
1448, 1362, 1237, 1120, 1034, 877, 767, 694, 661, 570 cm–1;
1H NMR (CDCl3) δ 1.61 (3H, d, J = 6.8 Hz), 3.86 (1H, d, J = 14.0
Hz), 3.97 (1H, d, J = 14.0 Hz), 6.08 (1H, dq, J = 8.5, 6.8 Hz),
7.19–7.34 (7H, m), 7.44–7.49 (3H, m), 7.99 (1H, br. s); 13C NMR
(CDCl3) δ 20.2 (q), 36.2 (t), 60.4 (d), 126.5 (d), 127.2 (d), 128.4
(d), 128.7 (d), 128.8 (d), 131.2 (d), 138.2 (s), 144.2 (s), 202.6 (s).
Found: C, 57.09; H, 5.16; N, 4.10%. Calcd for C16H17NSSe: C,
57.48; H, 5.12; N, 4.19%.
16a (R1 = C6H5, R2 = CH3, Nu = Oi-C3H7): Yellow powder,
mp 66.2–66.3 °C; MS m/z (%) 223 (M+; 5), 121 (bp); IR (KBr)
3253, 2976, 1710, 1519, 1447, 1379, 1245, 1109, 1086, 999, 965,
725, 697 cm–1; 1H NMR (CDCl3) δ 1.21 (3H, d, J = 6.2 Hz), 1.25
(3H, d, J = 6.2 Hz), 1.50 (3H, d, J = 5.8 Hz), 3.96 (1H, septet, J =
6.2 Hz), 6.13 (dq, J = 8.2, 5.8 Hz), 7.38–7.49 (3H, m), 7.64 (1H, br.
s), 7.73–7.75 (2H, m); 13C NMR (CDCl3) δ 21.3 (q), 21.9 (q), 23.3
(q), 70.4 (d), 81.1 (d), 126.5 (d), 128.5 (d), 131.3 (d), 141.5 (s),
198.5 (s). Found: C, 64.49; H, 7.93; N, 6.22%. Calcd for
C12H17NOS: C, 64.53; H, 7.67; N, 6.27%.
17a (R1 = C6H5, R2 = CH3, Nu = OCH3): Yellow oil; MS m/z
(%) 243 (M+; bp, 80Se), 211 (M+ – CH3OH; 64, 80Se), 185 (83), 104
(95); IR (neat) 3211, 2989, 1510, 1449, 1378, 1131, 1093, 693
1
cm–1; H NMR (CDCl3) δ 1.55 (3H, d, J = 5.8 Hz), 3.53 (3H, s),
6.06 (1H, dq, J = 8.4, 5.8 Hz), 7.36–7.53 (3H, m), 7.75–7.77 (2H,
m), 8.05 (1H, br.s); 13C NMR (CDCl3) δ 20.3 (q), 57.1 (q), 87.9 (d),
126.4 (d), 128.6 (d), 131.4 (d), 144.8 (s), 204.7 (s). Found: C,
49.16; H, 5.29; N, 5.66%. Calcd for C10H13NOSe: C, 49.60; H,
5.41; N, 5.78%.
18a (R1 = C6H5, R2 = CH3, Nu = OC2H5): Yellow needles,
mp 94.0–95.0 °C; MS m/z (%) 257 (M+; 11, 80Se), 211 (M+ –
C2H5OH; 15, 80Se), 44 (bp); IR (KBr) 3241, 2980, 1510, 1483,
1448, 1231, 1113, 1087, 1054, 693, 675 cm–1; 1H NMR (CDCl3) δ
1.25 (3H, d, J = 7.0 Hz), 1.55 (3H, d, J = 5.8 Hz), 3.68–3.84 (2H,
m), 6.13 (1H, dq, J = 8.1, 5.8 Hz), 7.35–7.51 (3H, m), 7.73–7.75
(2H, m), 8.14 (1H, br. s); 13C NMR (CDCl3) δ 15.2 (q), 20.5 (q),
65.0 (t), 86.3 (d), 126.4 (d), 128.5 (d), 131.3 (d), 144.7 (s), 203.9
(s). Found: C, 51.48; H, 6.04; N, 5.44%. Calcd for C11H15NOSe: C,
51.57; H, 5.90; N, 5.47%.
Heating of 6H-1,3,5-Oxaselenazines (6a) in the Presence of
Propylamine. After a benzene solution (30 ml) of 6H-1,3,5-oxa-
selenazine 6a (508 mg, 2.00 mmol) was treated with an excess
amount of propylamine (1.30 g, 22.0 mmol), the reaction mixture
was heated at refluxing temperature for 4 h or was kept standing at
room temperature with stirring for 4 h. Then, after cooling to room
temperature and quenching with water, the reaction mixture was
subjected to the usual workup. The crude product was purified by
using column chromatography on silica gel to afford N-propylsele-
nobenzamide (253 mg, 56%) as a major product.
18b (R1 = C6H5, R2 = t-C4H9, Nu = OC2H5): Orange oil; MS
m/z (%) 297 (M+; 12, 80Se), 115 (bp); IR (neat) 3376, 3250, 2963,
1503, 1481, 1447, 1372, 1112, 1063, 695 cm–1; 1H NMR (CDCl3) δ
1.07 (9H, s), 1.23 (3H, t, J = 7.0 Hz), 3.70 (1H, dq, J = 10.0, 7.0
Hz), 3.77 (1H, dq, J = 10.0, 7.0 Hz), 5.95 (1H, d, J = 9.4 Hz),
7.36–7.52 (3H, m), 7.73–7.75 (2H, m), 8.05 (1H, br. s); 13C NMR
(CDCl3) δ 15.1 (q), 25.0 (q), 36.6 (s), 65.1 (t), 93.5 (d), 126.3 (d),
128.7 (d), 131.2 (d), 145.7 (s), 206.5 (s). Found: C, 56.14; H, 7.30;
N, 4.41%. Calcd for C14H21NOSe: C, 56.37; H, 7.10; N, 4.70%.
17c (R1 = p-ClC6H4, R2 = CH3, Nu = OCH3): Yellow nee-
dles, mp 101.0–102.0 °C; MS m/z (%) 277 (M+; 15, 80Se), 246 (M+
– OCH3; 10, 80Se), 59 (bp); IR (KBr) 3254, 2988, 2930, 1588, 1510,
1481, 1399, 1372, 1238, 1132, 1086, 1039, 883, 822, 719 cm–1;
1H NMR (CDCl3) δ 1.53 (3H, d, J = 5.8 Hz), 3.50 (3H, s), 5.59 (1H,
dq, J = 8.1, 5.8 Hz), 7.30–7.33 (2H, m), 7.66–7.69 (2H, m), 8.22
(1H, br. s); 13C NMR (CDCl3) δ 20.1 (q), 57.0 (q), 87.9 (d), 127.7
(d), 128.5 (d), 137.4 (s), 142.8 (s), 202.8 (s). Found: C, 43.48; H,
Thermal Reaction of 6H-1,3,5-Oxathiazines (5a).
A
tolu-
ene solution (20 ml) of 6H-1,3,5-oxathiazine (5a or 5c, 2.00 mmol)
was heated at refluxing temperature for 3 h. After cooling to room
temperature, the solvent was removed in vacuo. The crude product
was then purified by using column chromatography on silica gel to
afford 5,6-dihydro-4H-1,3,5-thiadiazines 21, 5,6-dihydro-4H-1,3-
thiazines 22, 3H-1,2,4-dithiazoles 23, and 6H-1,3,5-thiadiazines
24 besides several unidentified products.
21a (R1 = C6H5, R2 = CH3): Yellow oil; MS m/z (%) 265 (M+
– C2H6S; 3,), 205 (M+ – C7H5S; 0.8), 163 (M+/2; bp), 131 (M+/2 – S;

522 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
5); IR (neat) 2984, 1620, 1444, 1402, 1271, 952, 759, 693 cm–1;
1H NMR (CDCl3, –30 °C) major-21a:minor-21a = 4:1, major iso-
mer δ 1.71 (3H, d, J = 6.9 Hz), 1.77 (3H, d, J = 6.9 Hz), 1.90 (3H,
d, J = 6.9 Hz), 1.98 (3H, d, J = 6.9 Hz), 5.60 (1H, q, J = 6.9 Hz),
5.88 (1H, q, J = 6.9 Hz), 7.08 (1H, q, J = 6.9 Hz), 7.26–7.30 (2H,
m), 7.44–7.58 (4H, m), 7.83–7.85 (2H, m); 13C NMR (CDCl3, –30
°C) δ 21.2 (q), 22.9 (q), 23.2 (q), 23.7 (q), 52.9 (d), 70.0 (d), 71.1
(d), 124.2 (d), 125.0 (d), 127.0 (d), 128.6 (d), 129.0 (d), 131.4 (d),
137.8 (s), 153.5 (d), 198.2 (s), 201.3 (s). Found: C, 66.22; H, 5.50;
N, 8.31%. Calcd for C18H18N2S2: C, 66.22; H, 5.56; N, 8.58%.
4.41; N, 6.98%. Calcd for C9H9NS2: C, 55.35; H, 4.64; N, 7.17%.
23b (R1 = C6H5, R2 = t-C4H9): Yellow oil; MS m/z (%) 237
(M+; 2), 205 (M+ – S, 5), 121 (bp); IR (neat) 2955, 1633, 1448,
1210, 1056, 1000, 766, 606 cm–1; 1H NMR (CDCl3) δ 1.14 (9H, s),
6.32 (1H, s), 7.40–7.51 (3H, m), 7.83–7.85 (2H, m); 13C NMR
(CDCl3) δ 26.7 (q), 38.9 (s), 104.1 (d), 128.7 (d), 129.0 (d), 131.7
(d), 132.1 (s), 165.1 (s). Found: C, 60.91; H, 6.56; N, 5.89%. Calcd
for C12H15NS2: C, 60.71; H, 6.37; N, 5.90%.
Thermal Reaction of 6H-1,3,5-Oxathiazines (5b).
A
tolu-
ene solution (20 ml) of 6H-1,3,5-oxathiazine (5b, 2.00 mmol) was
heated at refluxing temperature for 3 h. After cooling to room tem-
perature, the solvent was removed in vacuo. The crude product was
then purified by using column chromatography on silica gel to af-
ford a complex mixture including a small amount of a pair of dias-
tereomers of 26b and a trace amount of 23b besides several uniden-
tified products.
21c (R1 = p-ClC6H4, R2 = CH3):
Yellow needles, mp
63.8–64.4 °C (dec.); MS m/z (%) 396 (M+; 1), 229 (M+ – C9H5ClS;
10) 196 (M+/2; bp); IR (KBr) 2985, 1714, 1621, 1592, 1488, 1399,
1091, 834 cm–1; 1H NMR (CDCl3, –30 °C) major-21c:minor-21c =
2:1, major isomer δ 1.71 (3H, d, J = 6.9 Hz), 1.77 (3H, d, J = 6.8
Hz), 1.88 (3H, d, J = 7.0 Hz), 1.95 (3H, d, J = 6.9 Hz), 5.57 (1H, q,
J = 10.1 Hz), 5.82 (1H, q, J = 10.4 Hz), 7.03 (1H, q, J = 10.2 Hz),
7.21–7.29 (1H, m), 7.36–7.47 (5H, m), 7.79 (2H, d, J = 8.5 Hz);
13C NMR (CDCl3, –30 °C) δ 21.1 (q), 22.8 (q), 23.1 (q), 23.7 (q),
53.0 (d), 55.8 (d), 70.2 (d), 71.1 (d), 125.7 (d), 126.7 (d), 128.7 (d),
128.9 (d), 129.1 (d), 129.3 (d), 134.9 (s), 136.0 (s), 137.4 (s), 140.9
(s), 152.2 (s), 155.2 (s), 196.8 (s), 200.0 (s). Found: C, 55.06; H,
4.09; N, 7.04%. Calcd for C18H16Cl2N2S2: C, 54.68; H, 4.08; N,
7.09%.
Major-26b (R1 = C6H5, R2 = t-C4H9): Yellow solid, mp
100.4–101.5 °C; MS m/z (%) 239 (M+ – C12H16NS; 8), 205 (M+ –
C12H16NS2; 98), 121 (bp); IR (neat) 3280, 2964, 1708, 1484, 1356,
1229, 770, 639 cm–1; 1H NMR (CDCl3) δ 1.19 (18H, s), 5.86 (2H,
d, J = 9.6 Hz), 7.36–7.48 (6H, m), 7.71–7.73 (4H, m), 8.09 (2H, d,
J = 9.6 Hz); 13C NMR (CDCl3) δ 26.7 (q), 38.4 (s), 68.4 (d), 126.8
(d), 128.5 (d), 131.2 (d), 142.0 (s), 198.9 (s). Found: C, 64.22; H,
7.27; N, 6.26%. Calcd for C24H32N2S3: C, 64.82; H, 7.25; N, 6.30%.
Minor-26b (R1 = C6H5, R2 = t-C4H9): Yellow needles, mp
189.5–190.2 °C; MS m/z (%) 238 (M+ – C12H15NS; 4), 205 (M+ –
C12H17NS2; 98), 77 (bp); IR (neat) 3354, 2963, 1502, 1448, 1356,
1229, 776, 695 cm–1; 1H NMR (CDCl3) δ 1.20 (18H, s), 6.20 (2H,
d, J = 10.3 Hz), 7.22–7.27 (4H, m), 7.39–7.43 (6H, m), 8.14 (2H,
br. d, J = 10.3 Hz); 13C NMR (CDCl3) δ 27.0 (q), 39.0 (s), 67.9 (d),
127.2 (d), 128.2 (d), 131.2 (d), 140.9 (s), 197.6 (s). Found: C,
64.30; H, 7.32; N, 6.56%. Calcd for C24H32N2S3: C, 64.82; H, 7.25;
N, 6.30%.
Thermal Reaction of 6H-1,3,5-Oxathiazines (5a) in the Pres-
ence of Thiobenzamide. After a toluene solution (20 ml) of 6H-
1,3,5-oxathiazine (5a, 420 mg, 2.00 mmol) was treated with
thiobenzamide (1a, 274 mg, 2.00 mmol) in the presence or absence
of Et2O•BF3 (284 mg, 2.00 mmol), the reaction mixture was heated
at refluxing temperature for 5 h. Then, after cooling the reaction
mixture to room temperature, the reaction mixture was filtered to
remove the unreacted thiobenzamide, and the solvent was removed
in vacuo from the filtrate. The crude product was then purified by
using column chromatography on silica gel to afford an epimeric
mixture of 22a, 23a, and 24a.
22a (R1 = C6H5, R2 = CH3): Yellow crystals, mp 178.1–179.5
°C (dec.); MS m/z (%) 326 (M+; 2), 294 (M+ – S; 1), 189 (M+ –
C6H5CSN; bp); IR (KBr) 3265, 2968, 1705, 1606, 1448, 1362,
1229, 942, 768, 694 cm–1; 1H NMR (CDCl3) major-22a:minor-22a
= 4:3, major isomer δ 1.54 (3H, d, J = 6.9 Hz), 1.79 (1H, ddd, J =
14.4, 10.8, 4.0 Hz), 2.35 (1H, ddd, J = 14.2, 4.2, 3.2 Hz), 3.74 (1H,
qdd, J = 6.8, 4.0, 3.2 Hz), 6.31 (1H, ddd, J = 8.2, 4.2, 4.0 Hz),
7.38–7.44 (6H, m), 7.48–7.51 (1H, m), 7.74–7.89 (3H, m), 7.90
(1H, d, J = 8.4 Hz), minor isomer δ 1.41 (1H, ddd, J = 12.5, 5.4, 3.5
Hz), 1.56 (3H, d, J = 6.9 Hz), 2.52 (1H, ddd, J = 12.9, 5.8, 2.3 Hz),
3.74 (1H, qdd, J = 6.8, 4.0, 3.2 Hz), 6.55 (1H, ddd, J = 11.6, 8.7, 5.7
Hz), 7.38–7.44 (6H, m), 7.48–7.51 (1H, m), 7.70 (1H, d, J = 8.4
Hz), 7.74–7.83 (3H, m); 13C NMR (CDCl3) δ 22.9 (q), 23.5 (q),
31.0 (q), 33.7 (q), 49.1 (d), 54.1 (d), 54.3 (d), 56.7 (d), 126.5 (d),
128.3 (d), 130.7 (d), 131.6 (d), 138.6 (s), 141.0 (s), 156.4 (s), 198.5
(s), 203.0 (s). Found: C, 65.97; H, 5.57; N, 8.56%. Calcd for
C18H18N2S2: C, 66.22; H, 5.56; N, 8.58%.
22c (R1 = p-ClC6H4H4, R2 = CH3):
Yellow crystals, mp
98.2–99.6 °C (dec.); MS m/z (%) 394 (M+; 2), 223 (M+ –
C7H6ClNS; bp); IR (KBr) 3208, 2927, 1591, 1485, 1403, 1228,
1092, 1012, 940, 832, 753 cm–1; 1H NMR (CDCl3) major-
22c:minor-22c = 2:1, major isomer δ 1.53 (3H, d, J = 6.9 Hz),
1.76 (1H, ddd, J = 14.4, 10.6, 3.9 Hz), 2.31 (1H, ddd, J = 14.2, 3.9,
3.5 Hz), 3.71 (1H, qdd, J = 13.8, 10.3, 3.3 Hz), 6.26 (1H, ddd, J =
8.0, 4.1, 4.0 Hz), 7.26–7.37 (2H, m), 7.60–7.70 (2H, m), 7.73–7.77
(4H, m), minor isomer δ 1.44 (1H, ddd, J = 12.4, 12.4, 12.4 Hz),
1.56 (3H, d, J = 6.9 Hz), 2.49 (1H, ddd, J = 5.7, 2.9, 2.2 Hz), 3.63
(1H, qdd, J = 12.4, 12.4, 2.3 Hz), 6.50 (1H, ddd, J = 11.6, 8.7, 5.7
Hz), 7.26–7.37 (2H, m), 7.60–7.70 (2H, m), 7.73–7.77 (4H, m);
13C NMR (CDCl3) δ 22.9 (q), 23.5 (q), 30.9 (d), 31.5 (d), 33.6 (d),
49.3 (t), 54.2 (d), 54.5 (d), 57.0 (d), 90.1 (d), 128.0 (d), 128.2 (d),
128.6 (d), 128.8 (d), 136.6 (s), 136.9 (s), 139.0 (s), 139.1 (s), 155.4
(s), 157.4 (s), 197.1 (s), 197.9 (s). Found: C, 55.11; H, 4.08; N,
7.05%. Calcd for C18H16Cl2N2S2: C, 54.68; H, 4.08; N, 7.09%.
23a (R1 = C6H5, R2 = CH3): Red oil; MS m/z (%) 195 (M+;
48), 64 (bp); IR (neat) 2925, 1624, 1476, 1443, 1368, 1256, 1089,
920, 765, 689 cm–1; 1H NMR (CDCl3) δ 1.74 (3H, d, J = 6.4 Hz),
6.34 (1H, q, J = 9.6 Hz), 7.41–7.50 (5H, m). Found: C, 54.82; H,
24a (R1 = C6H5, R2 = CH3): Yellow oil; MS m/z (%) 266 (M+;
93), 251 (M+ – CH3; 93), 225 (bp); IR (neat) 2975, 1601, 1571,
1524, 1489, 1447, 1316, 768, 690 cm–1; 1H NMR (CDCl3) δ 1.74
(3H, d, J = 6.7 Hz), 5.01 (1H, q, J = 6.7 Hz), 7.43–7.54 (5H, m),
7.52–7.62 (1H, m), 8.21–8.23 (2H, m), 8.30–8.32 (2H, m);
13C NMR (CDCl3) δ 22.0 (q), 57.2 (s), 128.0 (d), 128.2 (d), 128.7
(d), 128.8 (d), 130.8 (d), 133.2 (d), 136.7 (s), 137.4 (s), 161.6 (s),
172.5 (s). Found: C, 71.99; H, 5.21; N, 10.07%. Calcd for
C16H14N2S: C, 72.15; H, 5.30; N, 10.25%.
Thermal Reaction of 6H-1,3,5-Oxathiazines (5b) in the Pres-
ence of Thioacetamide or Thiobenzamide (1a). After a toluene
solution (30 ml) of 6H-1,3,5-oxathiazine (5b, 298 mg, 1.00 mmol)
was treated with thioacetamide or thiobenzamide (1a, 1.00 mmol),
the reaction mixture was heated at refluxing temperature for 5 h.
Then, after cooling the reaction mixture to room temperature, the
reaction mixture was filtered to remove the unreacted thioaceta-
mide, and the solvent was removed in vacuo from the filtrate. The
crude product was then purified by using column chromatography

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 523
on silica gel to afford an epimeric mixture of 26b (major-
26b:minor-26b = 5:3–5:4) and 23b along with several unidenti-
fied products.
(14), 204 (39), 138 (52), 108 (bp); IR (neat) 3449, 1889, 1595,
1535, 1486, 833 cm–1; 1H NMR (CDCl3) δ 1.86 (3H, d, J = 6.7 Hz),
5.11 (1H, q, J = 6.7 Hz), 7.38–7.41 (2H, m), 7.45–7.49 (2H, m),
8.06–8.09 (2H, m), 8.17–8.20 (2H, m); 13C NMR (CDCl3) δ 23.0
(q), 56.6 (s), 128.4 (d), 129.0 (d), 129.4 (d), 130.4 (d), 135.2 (s),
137.0 (s), 137.4 (s), 139.4 (s), 162.4 (s), 173.2 (s). Found: C, 50.19;
H, 3.12; N, 6.96%. Calcd for C16H12Cl2N2Se: C, 50.29; H, 3.16; N,
7.33%.
Thermal Reaction of 5,6-dihydro-4H-1,3,5-thiadiazine
(21a). A toluene solution (30 ml) of 5,6-dihydro-4H-1,3-thiazine
21a (195 mg, 0.60 mmol) was heated at refluxing temperature for
12 h. After cooling to room temperature, the solvent was removed
in vacuo. The crude product was then purified by using column
chromatography on silica gel to afford an epimeric mixture of 22a
(31 mg, 16%) besides the recovery of 21a (131 mg, 73%).
Heating of 5,6-dihydro-4H-1,3,5-thiadiazine (21a) in the
28a (R1 = C6H5, R2 = CH3): Red oil; MS m/z (%) 291 (M+;
bp, 80Se), 188 (27), 160 (46), 132 (63), 108 (69); IR (neat) 3059,
2965, 2917, 1637, 1446, 1235, 1087, 891, 761, 688, 663, 586 cm–1;
1H NMR (CDCl3) δ 1.90 (3H, d, J = 6.4 Hz), 6.64 (1H, q, J = 6.4
Hz), 7.19–7.55 (3H, m), 7.65–8.00 (2H, m); 13C NMR (CDCl3) δ
24.4 (q), 80.3 (d), 128.8 (d), 129.5 (d), 131.6 (d), 133.9 (s), 160.4
(s); 77Se NMR (CDCl3) δ 480.0 (d, JSe–Se = 190 Hz), 568.0 (d, JSe–Se
= 190 Hz). Found: C, 37.58; H, 3.20; N, 4.69%. Calcd for
C9H9NSe2: C, 37.39; H, 3.14; N, 4.84%.
Presence of Dimethyl Acetylenedicarboxylate (DMAD).
Af-
ter a toluene solution (30 ml) of 5,6-dihydro-4H-1,3,5-thiadiazines
21a (175 mg, 0.55 mmol) was treated with dimethyl acetylenedi-
carboxylate (DMAD, 1.549 g, 22 mmol), the reaction mixture was
heated at refluxing temperature for 12 h. The reaction mixture was
then cooled to room temperature, quenched with an aqueous NaOH
solution, and extracted with dichloromethane. The organic layer
was washed with water, and then dried over anhydrous Na2SO4
powder.After removing the solvent in vacuo, the crude product was
purified by using column chromatography on silica gel to afford the
cycloadduct 9a (66 mg, 20%) besides the recovery of 21a (137 mg,
78%).
Heating of 5,6-dihydro-4H-1,3,5-thiadiazine (21a) in the
Presence of 2-Propanol. After a toluene solution (30 ml) of 5,6-
dihydro-4H-1,3,5-thiadiazine (21a, 195 mg, 0.55 mmol) was treat-
ed with 2-propanol (10 ml, excess), the reaction mixture was heat-
ed at refluxing temperature for 8 h. Then, after cooling to room
temperature and quenching with water, the reaction mixture was
subjected to the usual workup. The crude product was purified by
using column chromatography on silica gel to afford N-(1-isopro-
poxyethyl)thiobenzamide (16a, 83 mg, 34%) besides the recovery
of 21a (113 mg, 58%).
28b (R1 = C6H5, R2 = t-C4H9): Red oil; MS m/z (%) 333 (M+;
99, 80Se), 158 (bp); IR (neat) 2960, 1649, 1447, 1362, 1243, 1046,
1
894, 762, 688, 587 cm–1; H NMR (CDCl3) δ 1.35 (9H, s), 6.66
(1H, s), 7.36–7.45 (3H, m), 7.78–7.80 (2H, m); 13C NMR (CDCl3)
δ 27.3 (q), 38.7 (s), 101.1 (d), 128.6 (d), 129.3 (d), 131.4 (d), 134.1
(s), 159.2 (s). Found: C, 43.76; H, 4.59; N, 4.17%. Calcd for
C12H15NSe2: C, 43.52; H, 4.57; N, 4.23%.
28c (R1 = p-ClC6H4, R2 = CH3): Red oil; MS m/z (%) 291
(M+; bp, 80Se); IR (neat) 3059, 2965, 2917, 1637, 1446, 1235, 1087,
891, 761, 688, 663, 586 cm–1; 1H NMR (CDCl3) δ 1.89 (3H, d, J =
6.5 Hz), 6.62 (1H, q, J = 6.5 Hz), 7.37–7.41 (2H, m), 7.72–7.75
(2H, m); 13C NMR (CDCl3) δ 24.3 (q), 80.2 (d), 123.0 (d), 130.7
(d), 132.4 (s), 137.7 (s), 159.1 (s). Found: C, 33.36; H, 2.51; N,
4.21%. Calcd for C9H8ClNSe2: C, 33.41; H, 2.49; N, 4.33%.
29a (R1 = C6H5, R2 = CH3): Yellow crystals; MS m/z (%) 342
(M+; 60, 80Se), 300 (M+ – CH3CH=N; 19, 80Se), 261 (M+ – SeH; bp),
172 (M+ – PhCHSe; 80), 169 (PhC=Se; 10, 80Se), 117 (49); IR
(neat) 3056, 2980, 2931, 1625, 1437, 1264, 1004, 739, 694 cm–1;
1H NMR (CDCl3) major isomer δ 1.29 (3H, d, J = 6.4 Hz), 1.83
(3H, d, J = 6.4 Hz), 5.78 (1H, q, J = 6.4 Hz), 5.97 (1H, q, J = 6.4
Hz), 7.26–7.94 (10H, m), minor isomer δ 1.29 (3H, d, J = 6.4 Hz),
1.91 (3H, d, J = 6.4 Hz), 5.02 (1H, q, J = 6.4 Hz), 6.57 (1H, q, J =
6.4 Hz), 7.26–7.94 (10H, m); 13C NMR (CDCl3) δ 18.8 (q), 20.5
(q), 20.6 (q), 22.0 (q), 64.3 (d), 67.7 (d), 86.7 (d), 89.9 (d), 123.9
(d), 124.1 (d), 127.8 (d), 127.9 (d), 128.0 (d), 128.3 (d), 128.4 (d),
128.5 (d), 128.8 (d), 128.9 (d), 130.5 (s), 130.6 (s), 131.6 (d), 131.8
(d), 145.5 (s), 146.2 (s), 168.6 (s), 170.9 (s), 200.9 (s), 201.1 (s).
Found: C, 63.44; H, 5.51; N, 7.80%. Calcd for C18H18N2Se: C,
63.34; H, 5.32; N, 8.21%.
Thermal Reaction of 6H-1,3,5-Oxaselenazines (6). A ben-
zene solution (20 ml) of 6H-1,3,5-oxaselenazine (6, 2.00 mmol)
was heated at refluxing temperature for a several hours. After cool-
ing to room temperature, the solvent was removed in vacuo. The
crude product was then purified by using column chromatography
on silica gel to afford 6H-1,3,5-selenadiazines 27, 3H-1,2,4-disel-
enazoles 28, epimeric mixtures of 2H-1,3-imidazolines, 29, and se-
lenoamides 30.
27a (R1 = C6H5, R2 = CH3): Yellow needles, mp 63.8–64.0
°C; MS m/z (%) 314 (M+; 31, 80Se), 273 (4), 211 (17), 169 (27), 104
(bp); IR (KBr) 3060, 2961, 2926, 2870, 1727, 1599, 1570, 1533,
1447, 1316, 1288, 1223, 1120, 924, 765, 706, 691, 673 cm–1;
1H NMR (CDCl3) δ 1.89 (3H, d, J = 6.7 Hz), 5.13 (1H, q, J = 6.7
Hz), 7.44–7.61 (6H, m), 8.18–8.21 (2H, m), 8.28–8.31 (2H, m);
13C NMR (CDCl3) δ 23.0 (q), 56.5 (d), 128.0 (d), 128.2 (d), 128.7
(d), 129.5 (d), 130.8 (d), 133.1 (d), 136.9 (s), 139.2 (s), 163.5 (s),
174.0 (s); 77Se NMR (CDCl3) δ 235.0. Found: C, 61.47; H, 4.50; N,
8.91%. Calcd for C16H14N2Se: C, 61.35; H, 4.50; N, 8.94%.
27b (R1 = C6H5, R2 = t-C4H9): Yellow oil; MS m/z (%) 356
(M+; 34, 80Se), 168 (bp); IR (neat) 2955, 1605, 1573, 1533, 1487,
1448, 1365, 1312, 1289, 1224, 1096, 943, 903, 762, 715, 689, 669,
657 cm–1; 1H NMR (CDCl3) δ 1.22 (9H, s), 4.75 (1H, s), 7.43–7.57
(6H, m), 8.19–8.21 (2H, m), 8.32–8.35 (2H, m); 13C NMR (CDCl3)
δ 27.6 (q), 36.4 (s), 74.1 (br. s), 128.06 (d), 128.12 (d), 128.7 (d),
129.5 (d), 130.6 (d), 132.9 (d), 137.1 (s), 139.4 (s), 163.3 (s), 174.7
(s). Found: C, 64.73; H, 5.80; N, 7.70%. Calcd for C19H20N2Se: C,
64.22; H, 5.67; N, 7.88%.
29c (R1 = p-ClC6H4, R2 = CH3): Yellow oil; MS m/z (%) 410
(M+; 27, 80Se), 365 (8), 329 (19), 294 (14), 245 (bp), 206 (43), 165
(60), 137 (89), 108 (99), 73 (61); IR (neat) 2979, 2228, 1627, 1591,
1439, 1091, 833 cm–1; 1H NMR (CDCl3) major isomer δ 1.30 (3H,
d, J = 6.4 Hz), 1.80 (3H, d, J = 6.4 Hz), 5.74 (1H, q, J = 6.4 Hz),
5.89 (1H, q, J = 6.4 Hz), 7.21–7.83 (8H, m), minor isomer δ 1.30
(3H, d, J = 6.4 Hz), 1.88 (3H, d, J = 6.4 Hz), 4.93 (1H, q, J = 6.4
Hz), 6.53 (1H, q, J = 6.4 Hz), 7.23–7.67 (8H, m); 13C NMR
(CDCl3) major isomer δ 18.7 (q), 22.1 (q), 67.7 (d), 86.8 (d), 125.6
(d), 128.6 (d), 129.0 (d), 129.2 (d), 129.3 (d), 135.4 (s), 135.4 (s),
138.9 (s), 144.7 (s), 169.9 (s), 170.9 (s), 199.6 (s), minor isomer δ
20.4 (q), 20.7 (q), 64.2 (s), 90.1 (d), 125.4 (d), 128.7 (d), 128.8 (d),
129.2 (d), 129.2 (d), 135.2 (s), 135.2 (s), 138.8 (s), 145.4 (s), 167.4
(s), 168.4 (s), 198.8 (s). Found: C, 52.90; H, 4.08; N, 6.48%. Calcd
for C18H16Cl2N2Se: C, 52.71; H, 3.93; N, 6.83%.
27c (R1 = p-ClC6H4, R2 = CH3):
135.0–135.5 °C; MS m/z (%) 382 (M+; 41, 80Se, 35Cl), 339 (6), 245
Yellow needles, mp
30a (R1 = C6H5, R2 = CH3): Yellow plates, mp 129.0–130.0

524 Bull. Chem. Soc. Jpn., 74, No. 3 (2001)
Generation of 1,3-Chalcogenaza-1,3-butadienes
°C; MS m/z (%) 317 (M+; 32, 80Se), 236 (M+ – Se; bp), 169 (43),
105 (24); IR (KBr) 3316, 1690, 1674, 1523, 1446, 1387, 971, 769,
699 cm–1; 1H NMR (CDCl3) δ 1.71 (3H, d, J = 7.0 Hz), 6.29 (1H,
quintet, J = 7.0 Hz), 7.38–7.69 (6H, m), 7.84–7.86 (2H, m),
8.07–8.09 (2H, m), 9.25 (1H, br. s); 13C NMR (CDCl3) δ 18.3 (q),
59.5 (d), 126.7 (d), 128.5 (d), 128.9 (d), 129.0 (d), 131.3 (d), 133.2
(s), 133.4 (d), 144.4 (s), 198.3 (s), 203.1 (s). Found: C, 60.48; H,
4.79; N, 4.41%. Calcd for C16H15NOSe: C, 60.76; H, 4.78; N,
4.43%.
mixed two isomers with two positions (equatorial and axial) in the
methyl group of C(4). The occupancy ratio was about 65%:35%
for two isomers with equatorial:axial positions. The final cycle of
refinement was carried out using 1720 observed reflections within
Io > 2.0σ(Io) converged to the final R = ||Fo| – |Fc||/ |Fo| value of
0.059 and Rw = [ w (|Fo| – |Fc|)2/ wFo2)]1/2 of 0.055. The maxi-
mum and minimum peaks on the final difference Fourier map cor-
respond to 0.38 and –0.34 eÅ–3, respectively.
Crystallographic data have been deposited at the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK, and the copies can be ob-
tained on request, free of charge, by quoting the publication cita-
tion and the deposition number CCDC 154951. The data are also
deposited as Document No. 74020 at the Office of the Editor of
Bull. Chem. Soc. Jpn.
30b (R1 = C6H5, R2 = t-C4H9): Yellow oil; MS m/z (%) 359
(M+; 13, 80Se), 104 (bp); IR (KBr) 3285, 2957, 1667, 1522, 1447,
1375, 1221, 736, 693, 684 cm–1; 1H NMR (CDCl3) δ 1.08 (9H, s),
6.74 (1H, d, J = 9.6 Hz), 7.38–7.65 (6H, m), 7.76–7.81 (2H, m),
8.13–8.15 (2H, m), 8.75–8.77 (1H, m); 13C NMR (CDCl3) δ 27.4
(q), 37.0 (s), 68.9 (d), 126.7 (d), 128.6 (d), 128.9 (d), 129.0 (d),
131.2 (d), 133.9 (d), 137.6 (s), 145.2 (s), 201.1 (s), 205.7 (s).
Found: C, 63.36; H, 5.93; N, 3.70%. Calcd for C19H21NOSe: C,
63.68; H, 5.91; N, 3.91%.
This work was partially supported by a Grant-in-Aid for Sci-
entific Research (No. 07651044) from the Ministry of Educa-
tion, Science, Sports, and Culture and also by a Nagase Science
and Technology Foundation.
30c (R1 = p-ClC6H4, R2 = CH3): Yellow plates, mp 157.0
–158.0 °C; MS m/z (%) 385 (M+; 24, 80Se, 35Cl), 303 (M+ – Se; bp),
203 (38), 139 (48%); IR (neat) 3265, 3029, 1671, 1590, 1529,
1485, 1404, 1229, 970, 737 cm–1; 1H NMR (CDCl3) δ 1.69 (3H, d,
J = 7.0 Hz), 6.21 (1H, dq, J = 8.0, 7.0 Hz), 7.36–7.38 (2H, m),
7.52–7.54 (2H, m), 7.77–7.79 (2H, m), 8.00–8.02 (2H, m), 9.14
(1H, br. s); 13C NMR (CDCl3) δ 18.3 (q), 59.6 (d), 128.0 (d), 128.8
(d), 129.0 (d), 129.5 (d), 130.3 (d), 131.5 (s), 137.7 (s), 141.2 (s),
142.6 (s), 197.1 (s), 201.7 (s). Found: C, 49.89; H, 3.40; N, 3.60%.
Calcd for C16H13Cl2NOSe: C, 49.90; H, 3.40; N, 3.64%.
References
1
2
C. Giordano, Synthesis, 1972, 34.
D. S. L. Blackwell, P. de Mayo, and R. Suau, Tetrahedron
Lett., 1974, 91.
3
4
A. Schultze and J. Goerdeler, Tetrahedron Lett., 1974, 221.
K. Burger, J. Albanbauer, and M. Eggersdorfer, Angew.
Chem., 87, 816 (1975).
Conversion of Selenoamide 30a into the Corresponding
Amide 31a by Treating with mCPBA. To a dichloromethane
solution (20 ml) of selenoamide 30a (31 mg, 1.00 mmol) was add-
ed a dichloromethane solution of mCPBA (259 mg(80%), 1.20
mmol); the reaction mixture was stirred at –78 °C for 3 h. The reac-
tion mixture was then quenched with an aqueous Na2SO3 solution,
and extracted with dichloromethane. The organic layer was washed
with an aqueous NaHCO3 solution and with water, and then dried
over anhydrous Na2SO4 powder. After removing the solvent in vac-
uo, the crude product was purified by using column chromatogra-
phy on silica gel using chloroform as an eluent to give 2-amino-N-
benzoylpropiophenone (31a, 16 mg, 63%).
5
K. Burger, J. Albanbauer, and W. Foag, Angew. Chem., 87,
816 (1975).
6
K. Burger, J. Albanbauer, and W. Strych, Synthesis, 1975,
57.
7
8
9
C. Giordano and A. Belli, Synthesis, 1975, 789.
C. Giordano and A. Belli, Synthesis, 1977, 193.
K. Burger, R. Ottlinger, and J.Albanbauer, Chem. Ber., 110,
2114 (1977).
10 K. Burger and R. Ottlinger, Tetrahedron Lett., 11, 973
(1978).
11 K. Burger and R. Ottlinger, Synthesis, 1978, 44.
12 C. Giordano, A. Belli, and L. Abis, Tetrahedron Lett., 17,
1537 (1979).
13 K. Burger and H. Goth, Angew. Chem., 92, 836 (1980).
14 K. Burger, R. Ottlinger, H. Goth, and J. Firl, Chem. Ber.,
113, 2699 (1980).
15 J. Goerdeler and K. Nandi, Chem. Ber., 114, 549 (1981).
16 K. Burger, R. Ottlinger, H. Goth, and J. Firl, Chem. Ber.,
115, 2494 (1982).
31a (R1 = C6H5, R2 = CH3): Colorless solid, mp 100.5–101.5
°C (Ref. 46–48, 104.0–105.0 °C); 1H NMR (CDCl3) δ 1.55 (3H, d,
J = 7.0 Hz), 5.77 (1H, quintet, J = 7.0 Hz), 7.37–7.38 (1H, m),
7.44–8.06 (10H, m); 13C NMR (CDCl3) δ 19.9 (q), 50.5 (d), 127.0
(d), 128.5 (d), 128.7 (d), 128.9 (d), 131.6 (d), 133.7 (s), 134.0 (d),
134.1 (s), 166.5 (s), 199.1 (s). Found: C, 75.48; H, 5.79; N, 5.52%.
Calcd for C16H15NO2: C, 75.87; H, 5.97; N, 5.53%.
X-Ray Crystallographic Analysis of 27a.
with sizes of 0.25 × 0.20 × 0.4 mm were used for data collection on
Rigaku automated four-cycle diffractiometer (AFC5PR),
Single crystals
17 J. Barluenga, M. Tomás, A. Ballesteros, and L. A. Lopèz,
Tetrahedron Lett., 30, 6923 (1989).
18 J. Barluenga, M. Tomás, A. Ballesteros, and L. A. Lopèz,
Synthesis, 1995, 985.
19 A. S. Bell, C. W. G. Fishwick, and J. E. Reed, Tetrahedron
Lett., 37, 123 (1995).
20 J. C. Meslin and H. Quiniou, Bull. Soc. Chim. Fr., 1979, II-
347.
21 J. P. Pradère, J. C. Roze, G. Duguay, A. Guevel, C. T.
Gokou, and H. Quiniou, Sulfur Lett., 1, 115 (1983).
22 C. T. Gokou, J. P. Pradère, and H. Quiniou, J. Org. Chem.,
50, 1545 (1985).
23 C. T. Gokou, M. Chehna, J. P. Pradère, G. Duguay, and L.
Toupet, Phosphorus and Sulfur, 27, 327 (1986).
24 J. P. Pradère, J. C. Roze, H. Quiniou, R. Danion-Bougot, D.
a
equipped with a rotating anode (45 kV, 200 mA), using graphite-
monochromated Mo Κα radiation (λ = 0.71069 Å). The crystal
data are as follows: a = 30.816(4), b = 10.524(2), c = 8.684(2) Å, β
= 93.97(2)°, V = 2809.3(9) Å3, the space group = C2/c, Z = 8, Dcalcd
= 1.48 g cm3, µ(MoKα) = 26.31 cm–1. The 2θ-ω scan mode with a
scan rate of 8° min–1 (ω) was employed with a scan range of (1.20
+ 0.30tan θ). A total of 4305 reflections within 2θ = 60° were col-
lected.
The structure was solved by a direct method and refined by a
full-matrix least-squares method.All non-hydrogen atoms were re-
fined anisotropically and hydrogen atoms found in the successive
D-Fourier map were refined isotropically. In the crystal, there were

K. Shimada et al.
Bull. Chem. Soc. Jpn., 74, No. 3 (2001) 525
Shimada, Tetrahedron Lett., 30, 6047 (1989).
38 Y. Takikawa, Y. Koyama, T. Yoshida, K. Shimada, and C.
Kabuto, Chem. Lett., 1995, 277.
Danion, and L. Toupet, Can. J. Chem., 64, 597 (1986).
25 J. Liebscher, M. Pätzel, and U. Bechstein, Z. Chem., 1986,
289.
26 C. Cellerin, C. T. Gokou, J. P. Pradère, A. Guingant, and P.
Guenot, Sulfur Lett., 8, 205 (1988).
27 J. Liebscher, Synthesis, 1988, 655, and the references cited
therein.
39 Y. Takikawa, T. Yoshida, Y. Koyama, K. Sato, Y. Shibata,
and S. Aoyagi, K. Shimada, C. Kabuto, Chem. Lett., 2000, 870.
40 K. Shimada, K. Aikawa, T. Fujita, S. Aoyagi, Y. Takikawa,
and C. Kabuto, Chem. Lett., 1997, 701.
28 J. Liebscher, M. Pätzel, and U. Bechstein, Synthesis, 1989,
968.
41 Y. Takikawa and S. Takizawa, Nippon Kagaku Kaishi, 1972,
766.
29 J. P. Pradère, F. Tonnard, A. Abouelfida, C. Cellerin, M.
Andriamanamihaja, B. Jousseaume, L. Toupet, and P. Guenot,
Bull. Soc. Chim. Fr., 130, 610 (1993).
30 D. Dubreuil, J. P. Pradère, N. Giraudeau, M. Goli, and F.
Tonnard, Tetrahedron Lett., 36, 237 (1995).
31 A. Marchand, D. Mauger, A. Guingant, and J. P. Pradère,
Tetrahedron: Asymmetry, 6, 853 (1995).
32 A. Beckmann, R. Fröhlich, and E.-U. Würthwein, Tetrahe-
dron Lett., 38, 5481 (1997).
33 F. Purseigle, D. Dubreuil, A. Marchand, J. P. Pradère, N.
Giraudeau, M. Goli, and L. Toupet, Tetrahedron, 54, 2545 (1998).
34 G. T. Manh, F. Purseigle, D. Dubreuil, J. P. Pradère, A.
Guingant, R. Danion-Bougot, D. Danion, and L. Toupet, J. Chem.
Soc., Perkin Trans. 1, 1999, 2821.
35 Y. Takikawa, K. Shimada, T. Makabe, and S. Takizawa,
Chem. Lett., 1983, 1503.
36 Y. Takikawa, T. Makabe, N. Hirose, T. Hiratsuka, R. Takoh,
and K. Shimada, Chem. Lett., 1988, 1517.
42 J. R. Cashman and R. P. Hazlik, J. Org. Chem., 47, 4645
(1982).
43 K. Shimada, S. Hikage, Y. Takeishi, and Y. Takikawa,
Chem. Lett., 1990, 1403.
44 M. Sekiguchi, A. Ogawa, S. Fujiwara, I. Ryu, N. Kambe,
and N. Sonoda, Chem. Lett., 1990, 913.
45 E. C. Taylor and J. A. Zoltewicz, J. Am. Chem. Soc., 82,
2656 (1960).
46 G. H. Cleland and C. Niemann, J. Am. Chem. Soc., 71, 841
(1949).
47 W. Siedel and H. Nahm, Chem. Ber., 88, 900 (1955).
48 F. W. Fowler and A. Hassner, J. Am. Chem. Soc., 90, 2875
(1968).
49 K. S. Kochhar, D. A. Cottrell, and H. W. Pinnick, Tetrahe-
dron Lett., 24, 1323 (1983).
50 K. Shimada, S. Akimoto, H. Itoh, H. Nakamura, and Y.
Takikawa, Chem. Lett., 1994, 1743.
51 A. Ogawa, J. Miyake, Y. Karakasa, S. Murai, and N.
Sonoda, J. Org. Chem., 50, 384 (1989).
37 Y. Takikawa, A. Uwano, H. Watanabe, M. Asanuma, and K.