Photoaddition Reactions of Benzoxazole-2(3H)-thiones to Cycloalkenes and Heteroaromatics

Article abstract of DOI:10.1002/hlca.200390266

Photoaddition reactions of benzoxazole-2-thiones 1 with cycloalkenes 2 and heteroaromatics 3 were examined. Irradiation of N-acylbenzoxazole-2-thiones 1a and 1b, and 3-(methoxycarbonyl)- and 3-(phenoxycarbonyl)benzoxazole-2(3H)-thiones (1f and 1h, resp.)

Full text of DOI:10.1002/hlca.200390266

Helvetica Chimica Acta Vol. 86 (2003)
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Photoaddition Reactions of Benzoxazole-2(3H)-thiones to Cycloalkenes
and Heteroaromatics
by Takehiko Nishio*a), Kiyoko Shiwaa), and Masami Sakamotob)
a) Department of Chemistry, University of Tsukuba, Tsukuba-shi, Ibaraki, 305-8571Japan
b) Department of Materials Technology, Faculty of Engineering, Chiba University, Yayoi-cho, Inage-ku, Chiba,
263-8522 Japan
Photoaddition reactions of benzoxazole-2-thiones 1 with cycloalkenes 2 and heteroaromatics 3 were
examined. Irradiation of N-acylbenzoxazole-2-thiones 1a and 1b, and 3-(methoxycarbonyl)- and 3-(phenox-
ycarbonyl)benzoxazole-2(3H)-thiones (1f and 1h, resp.) in the presence of cycloalkenes 2a 2c, cyclohexa-1,4-
diene (2d), and indene (2e) yielded 2-substituted benzoxazoles 4 13, 18 and 19, and iminothietanes 14 17, by
intramolecular trapping of the acyl or MeOCO and PhOCO groups by thiolate anion of the zwitterionic
intermediate I and by the phenolate anion of the zwitterionic intermediate II, respectively, derived from the
spirocyclic amino-thietanes AT formed by [2 ‡ 2] cycloaddition of the CˆS bond of 1 and CˆC bond of 2.
Irradiation of 1 in the presence of heteroaromatics 3 gave the 2-substituted benzoxazoles 20 33 exclusively.
1. Introduction.
The photochemistry of thiocarbonyl compounds such as
thioketones [1a c][1e,f], thioimides, and thioamides [1d][1g m] has been of
considerable synthetic and mechanistic interest. These compounds behave like
carbonyl compounds in many respects. In the course of our studies on the photo-
chemistry of cyclic conjugated nitrogen-thiocarbonyl systems [1j m][2][3], we have
reported the photoaddition reactions of the benzoxazole-2-thiones [2] and benzothia-
zole-2-thiones [3] with alkenes. For example, irradiation of N-acylbenzoxazole-2-
thiones, in the presence of alkenes gave 2-alkylated benzoxazoles and/or iminothie-
tanes, via the [2 ‡ 2] cycloaddition intermediates, spirocyclic amino-thietanes [2b],
depending on the nature of substituents present in the alkenes, while that of N-
(alkoxycarbonyl)- and N-(aryloxycarbonyl)-benzoxazole-2-thiones, in the presence of
alkenes, gave [2 ‡ 2] cycloadducts, spirocyclic amino-thietanes [2c]. To investigate the
scope and limitation of the photocycloaddition of benzoxazole-2(3H)-thiones 1 and
alkenes, we examined the photoreactions of 1 and cycloalkenes 2a 2c, cyclohexa-1,4-
diene (2d) and indene (2e), and heteroaromatics 3, and our results are described in this
paper (Schemes 1 and 2).
2. Results and Discussion. When a solution of 3-acetylbenzoxazole-2(3H)-thione
(1a) in MeOH was irradiated in the presence of cyclopentene (2a) with a high-pressure
Hg lamp through a Pyrex filter under Ar at room temperature, 2-substituted
benzoxazole, S-[2-(benzoxazol-2-yl)cyclopentyl] thioacetate (4), and iminothietane,
2-[(6-thiabicyclo[3.2.0]heptan-7-ylidene)amino]phenyl acetate (14), were obtained,
which were 1:1 adducts of 1a and 2a, in 34 and 25% isolated yields, respectively. A
similar result was obtained when benzene was used as solvent. The structures of
photoproducts 4 and 14 were elucidated on the basis of spectral data and elemental

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Helvetica Chimica Acta Vol. 86 (2003)
Scheme 1. Photoaddition of Benzoxazole-2(3H)-thiones 1a, 1b, 1f, and 1h, and Cyclic Alkenes 2
Scheme 2. Photoaddition of Benzoxazole-2(3H)-thiones 1a 1h and Heteroaromatics 3
analyses. The cis relationship between the two substituents, benzoxazolyl and thioacetyl
groups at C(2) and C(1), repectively, of the cyclopentane ring in 4 was established by an
X-ray structure determination (Fig.). The configuration of the cyclopentane ring in 4 is
predictable on the basis of mechanistic considerations, where are initially formed

Helvetica Chimica Acta Vol. 86 (2003)
3257
Figure. ORTEP View of S-[2-(benzoxazol-2-yl)cyclopentyl] thioacetate (4) with crystallographic numbering
scheme
amino-thietane AT by [2 ‡ 2] cycloaddition of the CˆS bond of 1a and CˆC bond of
2a (cf. Scheme 4). Irradiation of 1b and 1f in the presence of cyclopentene (2a), and 1f
in the presence of indene (2e) gave 2-substituted benzoxazoles 8 and 9, 13, respectively,
and iminothietanes 15 17. Irradiation of 1a, 1f, and 1h in the presence of cyclic alkenes
2b and 2c, cyclohexa-1,4-diene (2d), and indene (2e) afforded 2-substituted benzox-
azoles 5 7, 10 12, and 18 and 19, respectively, as the sole products (Table 1). For the
Table 1. Yields of the Photoproducts 4 19
R
Cycloalkene
Solvent
Product (Yield [%]a))
1a
1a
1a
1a
1a
1a
1b
1f
1f
1f
1f
1f
1h
1h
Me
Me
Me
Me
Me
Me
Me2CH
MeO
MeO
MeO
MeO
MeO
PhO
PhO
2a
2b
2d
2e
2e
2e
2a
2a
2b
2c
2d
2e
2a
2b
MeOH
MeOH
MeOH
Benzene
Benzeneb)
MeOH
MeOH
Benzene
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
4 (34), 14 (25)
5 (84)
6 (37)
7 (63)
7 (trace)
7 (91)
8 (32), 15 (46), 1i (20)
9 (61), 16 (trace)
10 (78)
11 (52)
12 (43)
13 (43), 17 (21)
18 (69)
19 (67)
a) Isolated yield. b) Under an O2 atmosphere

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1:1 adducts, 2-substituted benzoxazoles derived from 1a and 1f and indene 2e, and
imino-thietane derived from 1f and 2e, the formation of two regioisomers (i.e., 7 and 7',
13 and 13', and 17 and 17') is to be expected, in principle. The regioisomers of these
photoproducts could not be determined from their spectral data. However, the
structures of these compounds were tentatively assigned as 7, 13, and 17 from the
following evidence. 2-Substituted benzoxazole 7 was converted gradually at room
temperature or easily on distillation to 2-(1H-inden-3-yl)benzoxazole (34) by the
elimination of MeCOSH (Scheme 3). 2-Substituted benzoxazole 13 was also heated to
reflux in toluene for 10 h to yield 34 in 50% yield. In the 1H-NMR spectrum of 34, the
signal of the CH2 H-atoms appeared as doublet with a coupling constant of 2.3 Hz [4],
indicating that the compound 34 is to be 3-substituted 1H-indene. The regiochemistry
of 7, 13, and 17 is reasonably explained by a mechanism in that the photoexcited
thioamide 1 initially attacks the C(2)-atom of indene (2e) to give the stabilized
intermediate biradical BR (cf. Scheme 4). The two modes of cleavage in this reaction
intermediate AT might be explained in terms of the stability of zwitterions I and II
affected by a ring-size effect [2b]. In the photoreaction of 3-isobutyrylbenzoxazole-
2(3H)-thione 1b and 2a, the deacylation product, benzoxazole-2(3H)-thione 1i, was
Scheme 3

Helvetica Chimica Acta Vol. 86 (2003)
3259
Scheme 4
obtained in 20% yield, accompanied by 2-substituted benzoxazole 8 (32%) and
iminothietane 15 (46%). Probably, compound 1i arises from the g-H abstraction by the
excited thioamide S-atom, followed by elimination of ketene. Analogous g-H
abstractions were observed in the photolysis of N-acylthiazolidine-2-thiones [5] and
N-acylindoline-2-thiones [6]. The 1:1 adduct 7 was not formed when a benzene
solution of 1a and indene 2e was irradiated under an O2 atmosphere.
Irradiation of N-acylbenzoxazole-2-thiones 1a 1e in the presence of heteroar-
omatics such as furan derivatives 3a 3e and thiophene (3f) in MeOH (or benzene)
under the same conditions as described above gave 1:1 adducts of 1 and 3, 2-
substituted benzoxazoles 20 29, along with a deacylation product, benzoxazole-
2(3H)-thione (1i; Scheme 2 and Table 2).
Table 2. Yields of the Products 20 33
R
Heteroaromatic
Solvent
Product (Yield [%]a))
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
1d
1e
1f
1f
1g
1h
Me
Me
Me
Me
Me
Me
Me
Me
Me2CH
Me2CHCH2
PhCH2
PhCH2CH2
MeO
3a
3a
3b
3c
3d
3e
3f
3g
3a
3a
3a
3a
3a
3b
3a
3a
MeOH
20 (75)
20 (6)
21 (20) 1i (27)
22 (47)
23 (30)
MeOHb)
MeOH
Benzene
MeOH
Benzene
MeOH
Benzene
MeOH
Benzene
Benzene
Benzene
MeOH
24 (35)
25 (20)
c
)
26 (55) 1i (40)
27 (67) 1i (30)
28 (13) 1i (50)
29 (65) 1i (25)
30 (69)
31 (39)
32 (53)
33 (59)
MeO
MeOH
Benzene
MeOH
CH2ˆCHCH2O
PhO
a) Isolated yield. b) Under an O2 atmosphere. c) No reaction.

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The formation of 1i can be explained in terms of the pathway involving g-H
abstraction by the excited thioamide S-atom as already described above. In contrast,
when a benzene solution of 1a and an excess of 1-methyl-1H-pyrrole (3g) was
irradiated, no photoproducts were obtained, and unchanged starting material 1a was
recovered quantitatively. Irradiation of 3-(alkoxycarbonyl)- and 3-(aryloxycarbonyl)-
benzoxazole-2(3H)-thiones (1f 1h) gave in the presence of furans 3a and 3b 1:1
adducts of 1 and 3, 2-substituted benzoxazoles 30 33. Irradiation of 1a and furan 3a in
MeOH under an O2 atmosphere gave the 1:1 adduct 20 (6%), but in low yield. The
structures of photoproducts 20 33 were elucidated on the basis of their spectral
properties and chemical evidence (see Exper. Part). The 1:1adducts 20 and 21, 24 30,
and 32 are not stable and converted gradually at room temperature and easily on
distillation into 2-(furan-3-yl)benzoxazole derivatives 35 37, and 2-(thiophen-3-
yl)benzoxazole 38 by elimination of the corresponding alkanethioic S-acid or O-alkyl
hydrogen thiocarbonate (Scheme 3). Irradiation of the parent benzoxazole-2(3H)-
thione (1i) and 3-methylbenzoxazole-2(3H)-thione (1j) in benzene in the presence of
furan (3a) resulted in recovery of unchanged starting materials 1i and 1j.
The mechanism for the formation of 2-substituted benzoxazoles 4 13, 18 33, and
iminothietane derivatives 14 17 in the photoaddition reaction of 3-acylbenzoxazole-
2(3H)-thiones (1a 1e), and 3-(alkoxycarbonyl)- and 3-(aryloxycarbonyl)benzoxa-
zole-2(3H)-thiones (1f 1h, resp.) with cycloalkenes 2a 2c, cyclohexa-1,4-diene (2d),
and indene (2e), and heteroaromatics 3 could be understood in terms of the pathways
shown in Scheme 4, which we had proposed for the photoreactions of thioamides and
alkenes [2][3][5]. The spirocyclic amino-thietanes AT were formed initially through
the regioselective [2 ‡ 2] photocycloaddition of the CˆS bond of 1 and CˆC bond of 2
or 3. The regiochemistry of the addition of 1 to heteroaromatics 3 could be explained by
the thietane formation in the first step, where the photo-excited 1 initially attacks C(2)
of the heteroaromatics 3. This addition mechanism is similar to that proposed by Oda
and Machida for the photoaddition reaction of arenecarbothioamides and furans [7].
The chemoselectivity in the addition of 1 to 3 seems to reflect the steric effect of an a-
substituent on an unsymmetrically substituted furan 3b [7]. Amino-thietane AT then
underwent CÀS bond cleavage of the thietane ring or CÀO bond cleavage of oxazole
ring assisted by the lone-pair electrons on the N-atom to yield the zwitterions I or II.
Intramolecular trapping of acyl group by the thiolate (path a) or phenolate moiety
(path b) of the zwitterions gave the 2-substituted benzoxazoles 3 13, 18 33, and
iminothietanes 14 17 [2c].
Experimental Part
General. M.p. and b.p.: Yanako micro melting-point apparatus (MP-3J) and a Shibata glass-tube oven-
distillation apparatus (GTO-350RD), resp.; uncorrected. Flash chromatography (FC): silica gel Wakogel C-300
1
and Merck 60. IR Spectra: JASCO FT/IR-300 spectrophotometer, in cmÀ1. H- and 13C-NMR spectra: JEOL-
JNM-EX270 (270 MHz) spectrometer; in CDCl3, with Me4Si as internal standard; d in ppm, J in Hz. Irradiation:
Eikosha HALos (500 W) high-pressure Hg lamp.
General Procedure for the Photochemical Reactions of the Benzoxazole-2(3H)-thiones 1 and Cycloalkenes 2
or Heteroaromatics 3. A soln. of 1 (1mmol) and 2 (or 3) (ca. 0.5 ml) in MeOH (or benzene) (70 ml) was
irradiated in a Pyrex vessel with the high-pressure Hg lamp under Ar for 5 15 h at r. t. After removal of the
solvent, the residual oil was chromatographed on a silica-gel column with toluene/AcOEt 50 :1 9 :1to yield the
2-substituted benzoxazoles 4 13, 18 33, and iminothietanes 14 17. For yields, cf. Tables 1 and 2.

Helvetica Chimica Acta Vol. 86 (2003)
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S-[2-(Benzoxazol-2-yl)cyclopentyl] Thioacetate (4). M.p. 55 568. IR (CHCl3): 1685, 1610. 1H-NMR: 1.76
2.34 (m, 6 H); 2.17 (s, 3 H); 3.87 (dd, J ˆ 7.6, 14.9, 1 H); 4.23 (dd, J ˆ 7.6, 14.9, 1 H); 7.27 7.34 (m, 2 H); 7.45
7.52 (m, 1H); 7.66 7.73 ( m, 1 H). 13C-NMR: 23.3; 29.4; 30.5; 32.4; 42.8; 46.6; 110.4; 119.8; 124.1; 124.6; 141.0;
150.6; 167.3; 195.2. Anal. calc. for C14H15NO2S (261.27): C 64.36, H 5.79, N 5.36; found: C 64.49, H 5.82, N 5.33.
2-[(6-Thiabicyclo[3.2.0]heptan-7-ylidene)amino]phenyl Acetate (14). B.p. 2008/3 Torr. IR (CHCl3): 1760,
1
1670. H-NMR: 1.58 2.38 (m, 6 H); 2.29 (s, 3 H); 4.00 (t, J ˆ 5.9, 1H); 4.39 ( dd, J ˆ 5.9, 8.6, 1H); 6.98 7.26
(m, 4 H). 13C-NMR: 20.7; 23.0; 31.4; 32.8; 41.3; 63.6; 120.4; 122.8; 125.6; 126.5; 140.3; 142.8; 168.4; 168.9. Anal.
calc. for C14H15NO2S (261.27): C 64.36, H 5.79, N 5.36; found C 64.25, H 5.85, N 5.63.
S-[2-(Benzoxazol-2yl)cyclohexyl] Thioacetate (5). M.p. 62 638. IR (CHCl3): 1690, 1610. 1H-NMR: 1.43
1.54 (m, 1H); 1.63 2.18 ( m, 7 H); 2.17 (s, 3 H); 3.42 3.49 (m, 1H); 4.21 4.38 ( m, 1H); 7.26 7.33 ( m, 2 H);
7.46 7.51( m, 1H); 7.56 7.73 ( m, 1 H). 13C-NMR: 23.2; 23.7; 30.7; 31.2; 40.9; 44.2; 110.4; 119.9; 124.0; 124.7;
141.0; 150.5; 167.0; 194.5. Anal. calc. for C15H17NO2S (275.29): C 65.44, H 6.22, N 5.09; found C 65.29, H 6.27 N
4.97.
S-[6-(Benzoxazol-2yl)cyclohex-3-enyl] Thioacetate (6). M.p. 107 1088. IR (KBr): 1685. 1H-NMR: 2.21
(s, 3 H); 2.41 2.85 ( m, 4 H); 3.58 3.65 (m, 1H); 4.45 4.55 ( m, 1H); 5.70 5.85 ( m, 2 H); 7.26 7.34 (m, 2 H);
7.48 7.53 (m, 1H); 7.68 7.73 ( m, 1 H). 13C-NMR: 26.5; 30.7; 31.7; 37.4; 41.0; 110.4; 119.9; 124.1; 124.7; 125.1;
141.0; 150.8; 166.5; 194.9.
S-[1-(Benzoxazol-2-yl)-2,3-dihydro-1H-inden-3-yl] Thioacetate (7). B.p. > 2508/2 Torr (dec.). IR (CHCl3):
1
1690. H-NMR: 2.22 (s, 3 H); 3.37 3.45 (m, 2 H); 4.73 (dd, J ˆ 8.3, 17.5, 1 H); 5.06 (d, J ˆ 8.3, 1H); 7.17 7.34
(m, 6 H); 7.40 7.46 (m, 1H); 7.67 7.72 ( m, 1 H). 13C-NMR: 30.4; 38.1; 45.7; 48.8; 110.5; 120.0; 124.2; 124.8;
125.1; 127.2; 128.3; 140.1; 140.9; 141.8; 150.7; 165.4; 195.1. The photoproduct 7 was gradually converted to 34
at r.t.
2-(1H-Inden-3-yl)benzoxazole (34). M.p. 93 948. IR: 1630, 1515, 1450, 1380, 1240, 1145, 985, 955, 745.
1H-NMR: 3.63 (d, J ˆ 2.3, 2 H); 7.28 7.59 (m, 7 H); 7.78 7.84 (m, 1H); 8.47 ( d, J ˆ 7.6, 1H). 13C-NMR: 38.9;
110.3; 120.3; 122.6; 123.8; 124.4; 125.3; 125.8; 126.7; 132.1; 139.3; 140.5; 141.9; 143.5; 150.0; 159.6. Anal. calc. for
C16H11NO (233.26): C 82.38, H 4.75, N 6.01; found C 82.44, H 4.84, N 5.73.
S-[2-(Benzoxazol-2-yl)cyclopentyl] 2-Methylpropanethioate (8). B.p. 2058/2 Torr. IR (CHCl3): 1680, 1615.
1H-NMR: 0.96 (d, J ˆ 6.9, 3 H); 1.04 (d, J ˆ 6.9, 3 H); 1.70 2.42 (m, 6 H); 2.53 (sept., J ˆ 6.9, 1H); 3.86 ( dd, J ˆ
7.6, 14.8, 1 H); 4.22 (dd, J ˆ 7.6, 14.8, 1 H); 7.25 7.35 (m, 2 H); 7.43 7.53 (m, 1H); 7.65 7.74 ( m, 1 H).
13C-NMR: 19.1; 19.2; 22.8; 29.3; 32.3; 42.9; 46.0; 110.3; 119.7; 124.0; 141.0; 150.6; 167.4; 203.4. Anal. calc. for
C16H19NO2S (289.32): C 66.41, H 6.62, N 4.84; found C 66.02, H 6.29, N 4.62.
2-[(6-Thiabicyclo[3.2.0]heptan-7-ylidene)amino]phenyl 2-Methylpropanoate (15). B.p. 2008/3 Torr. IR
(film): 1755, 1670. 1H-NMR: 1.32 (d, J ˆ 6.9, 6 H); 1.54 2.37 (m, 6 H); 2.84 (sept., J ˆ 6.9, 1H); 3.97 ( t, J ˆ 5.9,
1H); 4.32 4.39 ( m, 1H); 6.99 7.20 ( m, 4 H). 13C-NMR: 19.0; 19.1; 22.9; 31.3; 32.8; 33.9; 41.1; 63.6; 120.3;
122.8; 125.6; 126.3; 140.3; 142.9; 168.0; 174.8. Anal. calc. for C16H19NO2S (289.32): C 66.41, H 6.62, N 4.84; found
C 66.26, H 6.73, N 4.84.
S-[2-(Benzoxazol-2-yl)cyclopentyl] O-Methyl Thiocarbonate (9) and Methyl 2-[(6-Thiabicyclo[3.2.0]hep-
tan-7-ylidene)amino]phenyl Carbonate (16). Compounds 9 and 16 could not be separated completely. B.p. (a
mixture of 9 and 16) 2008/3 Torr. IR (film; a mixture of 9 and 16): 1750, 1705, 1605. 1H-NMR of 9: 1.76 1.88
(m, 1H); 2.01 2.38 ( m, 5 H); 3.70 (s, 3 H); 3.85 (dd, J ˆ 7.3, 14.2, 1 H); 4.12 (dd, J ˆ 7.3, 14.2, 1 H); 7.26 7.32
(m, 2 H); 7.45 7.51( m, 1H); 7.66 7.72 ( m, 1 H). 13C-NMR of 9: 23.1; 29.3; 32.4; 43.1; 48.6; 54.0; 110.4; 119.8;
124.1; 124.6; 141.0; 150.7; 167.0; 170.8. 1H-NMR of 16: 1.68 2.35 (m, 6 H); 3.31 3.40 ( m, 1H); 3.68 3.77
(m, 1H); 3.75 ( s, 3 H); 7.04 7.09 (m, 1H); 7.23 7.36 ( m, 2 H); 8.12 8.16 (m, 1 H). 13C-NMR of 16: 22.8; 26.5;
36.6; 41.3; 51.3; 52.4; 154.0; 171.2 in addition to the signals of aromatic C-atoms. Anal. calc. for C H15NO3S
14
(277.27; a mixture of 9 and 16): C 60.63, H 5.45, N 5.05; found C 60.29, H 5.45, N 5.10.
S-[2-(Benzoxazol-2-yl)cyclohexyl] O-Methyl Carbonate (10). M.p. 74 758. IR (CHCl3): 1710. 1H-NMR:
1.41 1.59 (m, 1H); 1.61 1.85 ( m, 3 H); 1.93 2.27 (m, 4 H); 3.47 3.55 (m, 1H); 3.65 ( s, 3 H); 4.19 4.25
(m, 1H); 7.26 7.36 ( m, 2 H); 7.45 7.53 (m, 1H); 7.63 7.73 ( m, 1 H). 13C NMR: 23.0; 23.7; 27.1; 31.3; 41.1; 46.7;
54.0; 110.4; 119.9; 124.1; 124.7; 141.1; 150.6; 166.8; 170.7. Anal. calc. for C15H17NO3S (291.29): C 61.85, H 5.88, N
4.81; found C 61.45, H 5.90, N 4.75.
S-[2-(Benzoxazol-2-yl)cyclooctyl] O-Methyl Carbonate (11). B.p. 2108/3 Torr. IR (film): 1730, 1610.
1H-NMR: 1.55 2.25 (m, 12 H); 3.26 3.33 (m, 1H); 3.67 3.74 ( m, 1H); 3.75 ( s, 3 H); 7.05 (d, J ˆ 4.3, 1H);
7.13 7.27 (m, 1H); 7.42 (br. s, 1H); 8.12 (br. d, J ˆ 8.3, 1H). 13C-NMR: 24.1; 25.9; 26.4; 27.6; 35.8; 40.8; 47.9;
52.4; 120.5; 122.2; 123.3; 126.7; 130.6; 139.9; 154.0; 172.4. Anal. calc. for C17H21NO3S (319.35): C 63.93, H 6.63, N
4.39; found C 64.16, H 6.76, N, 4.12.

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S-[6-(Benzoxazol-2-yl)cyclohex-3-enyl] O-Methyl Carbonate (12). B.p. 2208/3 Torr. IR (film): 1710, 1615.
1H-NMR: 2.52 2.81( m, 3 H); 3.65 (s, 3 H); 4.30 4.36 (m, 1H); 5.71 5.90 ( m, 2 H); 7.26 7.33 (m, 2 H); 7.46
7.51( m, 1H); 7.68 7.72 ( m, 1 H). 13C-NMR: 23.6; 31.8; 37.7; 43.3; 54.0; 110.4; 119.9; 124.1; 124.7; 124.8; 125.0;
141.1; 150.7; 166.7; 170.8. Anal. calc. for C15H15NO3S (289.28): C 62.28, H 5.23, H 4.84; found C 62.22, H 5.28, N
4.82.
S-[2-(Benzoxazol-2-yl)-2,3-dihydro-1H-inden-1-yl] O-Methyl Thiocarbonate (13). Oil. IR (CHCl3): 1710.
1H-NMR: 3.39 3.51( m, 2 H); 3.76 (s, 3 H); 4.63 (dd, J ˆ 8.3, 17.8, 1 H); 5.11 (d, J ˆ 7.9, 1H); 7.20 7.47
(m, 7 H); 7.66 7.71( m, 1 H). 13C-NMR: 30.3; 47.5; 49.1; 57.4; 110.4; 122.0; 124.2; 124.8; 125.1; 127.3; 128.4;
140.1; 141.6; 150.8; 165.2; 170.5. Anal. calc. for C18H15NO3S (325.31): C 66.45, H 4.65, N 4.32; found C 66.75, H
4.81, N 4.03.
Methyl 2-[(1,2a,3,7b-Tetrahydroindeno[2,1-b]thiet-1-yl)amino]phenyl Carbonate (17). M.p. 129 1308. IR
(CHCl3): 1735, 1615. 1H-NMR: 2.18 (d, J ˆ 9.2, 1H); 3.26 ( dd, J ˆ 7.6, 15.8, 1 H); 3.75 (s, 3 H); 4.06 (dd, J ˆ 7.6,
18.9, 1 H); 4.51 (d, J ˆ 7.6, 1H); 7.02 7.08 ( m, 2 H); 7.18 7.30 (m, 5 H); 7.70 (br. d, J ˆ 3.3, 1H). 13C-NMR:
40.8; 42.6; 52.1; 57.4; 122.1; 123.1; 124.8; 125.3; 126.8; 127.4; 128.5; 130.5; 138.3; 142.2; 153.8; 169.1. Anal. calc.
for C18H15NO3S (325.31): C 66.45, H 4.65, N 4.32; found C 66.24, H 4.61, N 4.08.
S-[2-(Benzoxazol-2-yl)cyclopentyl] O-Phenyl Thiocarbonate (18). B.p. 2208/3 Torr. IR (film): 1725.
1H-NMR: 1.80 2.47 (m, 6 H); 3.92 (dd, J ˆ 7.3, 14.2, 1 H); 4.18 (dd, J ˆ 7.3, 14.2, 1 H); 6.95 7.00 (m, 2 H);
7.21 7.36 ( m, 5 H); 7.47 7.54 (m, 1H); 7.72 7.77 ( m, 1 H). 13C-NMR: 23.3; 29.2; 32.2; 43.1; 48.9; 110.5; 119.9;
121.2; 124.2; 124.7; 128.3; 129.4; 141.1; 151.1; 167.0. Anal. calc. for C19H17NO3S (339.33): C 67.25, H 5.05, N 4.13;
found C 67.08, H 5.34, N 4.41.
S-[2-(Benzoxazol-2-yl)cyclohexyl] O-Phenyl Thiocarbonate (19). M.p. 97 988. IR (KBr): 1720, 1615.
1H-NMR: 1.39 1.59 (m, 1H); 1.62 1.85 ( m, 3 H); 1.93 2.15 (m, 3 H); 2.23 2.35 (m, 1H); 3.50 3.57
(m, 1H); 4.24 4.30 ( m, 1H); 6.88 6.95 ( m, 2 H); 7.11 7.34 (m, 5 H); 7.45 7.52 (m, 1H); 7.70 7.77 ( m, 1 H).
13C-NMR: 23.2; 23.6; 27.1; 31.1; 41.0; 47.1; 110.5; 119.9; 121.1; 124.1; 124.7; 125.9; 128.3; 129.3; 141.1; 151.1; 166.7.
Anal. calc. for C20H19NO3S (353.36): C 67.98, H 5.42, N 3.96; found C 67.67, H 5.49, N 3.85.
2-[2-(Acetylsulfanyl)-2,3-dihydrofuran-3-yl]benzoxazole (20). B.p. 175 1808/3 Torr (dec.). IR (film): 1695,
1
1605. H-NMR: 2.24 (s, 3 H); 4.95 (dt, J ˆ 2.3, 9.9, 1H); 5.40 ( dd, J ˆ 2.3, 2.6, 1H); 6.63 ( t, J ˆ 2.6, 1H); 6.73
(d, J ˆ 9.9, 1H); 7.32 7.40 ( m, 2 H); 7.51 7.56 ( m, 1H); 7.73 7.77 ( m, 1 H). 13C-NMR: 31.0; 46.4, 86.0; 101.0;
110.8; 120.3; 124.6; 125.4; 140.9; 147.8; 150.8; 163.5; 192.9. Anal. calc. for C13H11NO3S (261.23): C 59.77, H 4.24,
N 5.36; found C 60.08, H 4.04, N 5.44. The photoadduct 20 was unstable at r.t. and converted gradually or easily
on distillation (175 1808/3 Torr) to 35.
2-(Furan-3-yl)benzoxazole (35). M.p. 88 898. IR (CHCl3): 1645. 1H-NMR: 7.03 (dd, J ˆ 1.0, 2.0, 1 H);
7.26 7.36 (m, 2 H); 7.40 7.56 (m, 2 H); 8.22 (dd, J ˆ 1.0, 1.7, 1 H). 13C-NMR: 108.8; 110.2; 115.2; 119.5; 124.3;
124.7; 141.6; 144.1; 150.0; 158.1. Anal. calc. for C11H7NO2 (185.17): C 71.35, H 3.81, N 7.56; found C 71.36, H 3.71,
N 7.52.
2-[2-(Acetylsulfanyl)-2,3-dihydro-5-methylfuran-3-yl]benzoxazole (21). B.p. 1858/3 Torr (dec.). IR
(CHCl3): 1715. 1H-NMR: 1.95 (s, 3 H); 2.23 (s, 3 H); 4.96 (dt, J ˆ 2.0, 9.9, 1H); 5.02 ( dd, J ˆ 1.3, 2.0, 1 H);
6.27 (d, J ˆ 9.9, 1H); 7.31 7.39 ( m, 2 H); 7.49 7.55 (m, 1H); 7.73 7.77 ( m, 1 H). 13C-NMR: 13.7; 30.9; 47.4;
85.9; 95.7; 110.7; 120.2; 124.5; 125.2; 140.8; 150.8; 157.6; 164.2; 193.1. The photoadduct 21 was unstable at r.t. and
converted gradually or easily on distillation (185 1908/3 Torr) to 36.
2-(5-Methylfuran-3-yl)benzoxazole (36). M.p. 75 768. IR (CHCl3): 1645. 1H-NMR: 2.34 (d, J ˆ 1.0, 3 H);
6.59 (t, J ˆ 1.0, 1 H); 7.25 7.32 (m, 2 H); 7.44 7.52 (m, 1H); 7.65 7.77 ( m, 1H); 8.05 ( d, J ˆ 0.7, 1H).
13C-NMR: 13.3; 104.6; 110.2; 115.8; 119.4; 124.3; 124.6; 141.7; 142.7; 150.0; 154.1; 158.5. Anal. calc. for
C12H9NO2 (199.20): C 72.35, H 4.55, N 7.03; found C 72.39, H 4.51, N 6.93.
2-[2-(Acetylsulfanyl)-2,3-dihydro-2,5-dimethylfuran-3-yl]benzoxazole (22). M.p. 72 738. IR (film): 1695,
1610. 1H-NMR: 1.94 (d, J ˆ 2.0, 3 H); 2.07 (s, 3 H); 2.32 (s, 3 H); 4.60 (q, J ˆ 2.0, 1H); 5.06 ( s, 1H); 7.28 7.38
(m, 2 H); 7.52 7.56 (m, 1H); 7.73 7.78 ( m, 1 H). 13C-NMR: 14.0; 27.6; 31.3; 56.1; 96.1; 99.0; 110.7; 120.2; 124.5;
125.0; 141.0; 150.8; 156.6; 163.5; 193.5. Anal. calc. for C15H15NO3S (289.28): C 62.28, H 5.23, N 4.84; found C
62.14, H 5.21, N 4.75.
2-[2-(Acetylsulfanyl)-2,3,4,5-tetrahydrofuran-3-yl]benzoxazole (23). B.p. 198/3 Torr. IR (CHCl3): 1695,
1615. 1H-NMR: 2.21( s, 3 H); 2.33 2.56 (m, 2 H); 4.08 (dd, J ˆ 8.2, 15.2, 1 H); 4.35 4.44 (m, 2 H); 5.52 (d, J ˆ
7.3, 1H); 7.29 7.36 ( m, 2 H); 7.50 7.55 (m, 1H); 7.71 7.76 ( m, 1 H). 13C-NMR: 30.2; 31.2; 44.0; 68.1; 76.0;
110.7; 120.3; 124.3; 125.2; 140.5; 150.3; 163.7; 194.2. Anal. calc. for C13H13NO3S (263.24): C 59.31, H 4.98, N 5.32;
found C 59.08, H 4.99, N 5.36.
2-[2-(Acetylsulfanyl)-2,3-dihydrobenzofuran-3-yl]benzoxazole (24). Oil. IR (CHCl3): 1705. 1H-NMR: 2.25
(s, 3 H); 5.45 (d, J ˆ 9.2, 1H); 6.94 7.05 ( m, 3 H); 7.24 7.40 (m, 4 H); 7.50 7.54 (m, 1H); 7.74 7.99 ( m, 1 H).

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13C-NMR: 30.3; 46.2; 87.4; 110.9; 120.4; 122.3; 124.1; 124.6; 125.5; 125.6; 130.0; 140.8; 150.9; 158.4; 162.5; 192.8.
The photoadduct 24 was unstable at r.t. and gradually converted to 37.
2-(Benzofuran-3-yl)benzoxazole (37). M.p. 128 1308. IR (CHCl3): 1645. 1H-NMR: 7.26 7.47 (m, 4 H);
7.53 7.59 (m, 2 H); 7.75 7.83 (m, 1H); 8.35 8.43 ( m, 2 H). 13C-NMR: 110.3; 111.1; 111.7; 119.8; 122.2; 124.1;
124.5 125.0; 125.6; 141.9; 147.0; 150.0; 155.6; 158.0. Anal. calc. for C15H9NO2 (235.23): C 75.58, H 3.86, N 5.95;
found C, 75.89, H 3.78, N 5.88.
2-[2-(Acetylsulfanyl)-2,3-dihydrothiophen-3-yl]benzoxazole (25). Oil. 1H-NMR: 2.15 (s, 3 H); 4.95 (td, J ˆ
2.3, 7.9, 1H); 5.81( d, J ˆ 7.9, 1H); 6.03 ( dd, J ˆ 2.3, 6.3, 1H); 6.58 ( dd, J ˆ 3.0, 6.3, 1H); 7.31 7.39 ( m, 3 H);
7.51 7.56 ( m, 1H); 7.73 7.81 ( m, 2 H). 13C-NMR: 30.5; 51.8; 55.3; 110.7; 120.2; 120.4; 124.6; 125.4; 129.0;
140.8; 150.8; 163.0; 193.9. The photoadduct 25 was unstable at r.t. and converted to 38.
2-(Thiophen-3-yl)benzoxazole (38). M.p. 139 1408. IR (KBr): 1620. 1H-NMR: 7.29 7.37 (m, 2 H); 7.41
7.45 (m, 1H); 7.50 7.56 ( m, 1H); 7.72 7.80 ( m, 2 H); 8.17 8.20 (m, 1 H). 13C-NMR: 110.4; 119.9; 124.5;
125.0; 126.6; 127.0; 128.0; 129.2; 141.9; 150.3; 159.7. Anal. calc. for C11H7NOS (201.17): C 65.67, H 3.51, N 6.96;
found C 65.67, H 3.46, N 6.87.
2-{2,3-Dihydro-2-[(2-methylpropanoyl)sulfanyl]furan-3-yl}benzoxazole (26). B.p. 1758/3 Torr (dec.). IR
(CHCl3): 1695, 1620. 1H-NMR: 1.02 (d, J ˆ 6.9, 3 H); 1.09 (d, J ˆ 6.9, 3 H); 2.56 (sept., J ˆ 6.9, 1H); 4.97 ( td, J ˆ
2.3, 9.9, 1H); 5.40 ( t, J ˆ 2.3, 1H); 6.64 ( t, J ˆ 2.6, 1H); 6.71( d, J ˆ 9.9, 1H); 7.31 7.39 ( m, 2 H); 7.49 7.55
(m, 1H); 7.72 7.77 ( m, 1 H). 13C-NMR: 18.9; 19.0; 43.5; 46.6; 85.7; 100.9; 110.7; 120.2; 124.5; 125.2; 140.8;
147.8; 150.8; 163.6; 201.1. Anal. calc. for C15H15NO3S (289.28): C 62.28, H 5.23, N 4.84; found 62.49, H 4.94, N
4.66. The photoadduct 26 was unstable at r.t. and converted to 35.
2-{2,3-Dihydro-2-[(3-methylbutanoyl)sulfanyl]furan-3-yl}benzoxazole (27). B.p. 1808/3 Torr (dec.). IR
(CHCl3): 1700, 1620, 1610. 1H-NMR: 0.82 (d, J ˆ 6.6, 3 H); 0.86 (d, J ˆ 6.6, 3 H); 1.95 2.09 (m, 1H); 2.23 2.39
(m, 2 H); 4.96 (td, J ˆ 2.3, 9.9, 1H); 5.36 5.41( m, 1H); 6.63 ( t, J ˆ 2.3, 1H); 6.74 ( d, J ˆ 9.9, 1H); 7.31 7.39
(m, 2 H); 7.48 7.56 (m, 1H); 7.70 7.76 ( m, 1 H). 13C-NMR: 22.0, 22.1; 26.1; 46.6; 53.1; 85.8; 100.9; 110.7; 120.3;
124.5; 125.2; 140.9; 147.8; 150.8; 163.6; 195.9. The photoadduct 27 was unstable at r.t. and converted gradually or
easily on distillation (175 1808/3 Torr) to 35.
2-{2,3-Dihydro-2-[(2-phenylethanoyl)sulfanyl]furan-3-yl}benzoxazole (28). Oil. IR (CHCl3): 1700, 1645,
1610. 1H-NMR: 3.67 (s, 2 H); 4.97 (td, J ˆ 2.3, 9.9, 1H); 5.37 ( t, J ˆ 2.3, 1H); 6.59 ( t, J ˆ 2.6, 1H); 6.70 ( d, J ˆ
9.9, 1H); 7.01 9.07 ( m, 2 H); 7.12 7.19 (m, 2 H); 7.26 7.41( m, 3 H); 7.44 7.52 (m, 1H); 7.69 7.78 ( m, 1 H).
13C-NMR: 46.6; 50.5; 86.0; 100.9; 110.7; 120.2; 124.5; 152.2; 127.4; 128.5; 129.4; 132.3; 140.7; 147.7; 150.7; 163.4;
194.5. The photoadduct 28 was unstable at r.t. and converted gradually or easily on distillation (175 1808/
3 Torr) to 35.
2-{2,3-Dihydro-2-[(3-phenylpropanoyl)sulfanyl]furan-3-yl}benzoxazole (29). Oil. IR (CHCl3): 1700, 1645.
1H-NMR: 2.63 3.05 (m, 4 H); 4.95 (td, J ˆ 2.3, 9.9, 1H); 5.39 ( t, J ˆ 2.3, 1H); 6.62 ( t, J ˆ 2.5, 1H); 6.76 ( d, J ˆ
9.9, 1H); 7.02 7.40 ( m, 4 H); 7.48 7.55 (m, 1H); 7.69 7.78 ( m, 1 H). 13C-NMR: 30.8, 45.8; 46.5; 85.8; 101.0;
110.7; 120.3; 124.5; 125.3; 126.3; 128.1; 128.4; 139.5; 140.8; 147.7; 150.8; 163.5; 195.6. The photoadduct 29 was
unstable at r.t. and converted gradually or easily on distillation (175 1808/3 Torr) to 35.
S-[3-(Benzoxazol-2-yl)-2,3-dihydrofuran-2-yl] O-Methyl Thiocarbonate (30). Oil. IR (CHCl3): 1720, 1610.
1H-NMR: 3.78 (s, 3 H); 4.98 (dt, J ˆ 2.3, 9.6, 1H); 5.41( t, J ˆ 2.3, 1H); 6.63 ( t, J ˆ 2.3, 1H); 6.70 ( d, J ˆ 9.6,
1H); 7.27 7.39 ( m, 2 H); 7.51 7.55 ( m, 1H); 7.70 7.76 ( m, 1 H). 13C-NMR: 46.4; 54.6; 88.3; 101.1; 110.7;
120.2; 124.5; 125.3; 140.7; 147.5; 150.7; 163.0; 168.8. The photoadduct 30 was unstable at r.t. and converted
gradually or easily on distillation (175 1008/3 Torr) to 35.
S-[3-(Benzoxazol-2-yl)-2,3-dihydro-5-methylfuran-2-yl] O-Methyl Thiocarbonate (31). B.p. 1908/3 Torr
(dec.). IR (CHCl3): 1720, 1610. 1H-NMR: 1.95 (dd, J ˆ 1.3, 2.3, 3 H); 2.35 (s, 3 H); 3.62 (s, 3 H); 4.63 (t, J ˆ 2.3,
1H); 5.09 (br. s, 1H); 7.28 7.37 ( m, 2 H); 7.49 7.55 (m, 1H); 7.72 7.76 ( m, 1 H). 13C-NMR: 13.9; 27.9; 53.5;
55.9; 96.2; 98.7; 110.6; 120.1; 124.4; 125.2; 140.8; 150.7; 156.5; 163.0; 167.9. The result of the elemental analysis of
31 was not in agreement with the calculated values, since 31 decomposed on distillation.
S-[3-(Benzoxazol-2-yl)-2,3-dihydrofuran-2-yl] O-(Prop-2-enyl)Thiocarbonate (32). Oil. IR (CHCl3):
1720, 1610. 1H-NMR: 4.66 (m, 2 H); 4.98 (td, J ˆ 2.3, 9.9, 1H); 5.20 5.31( m, 2 H); 5.41( t, J ˆ 2.3, 1H); 5.76
5.91( m, 1H); 6.63 ( t, J ˆ 2.6, 1H); 6.69 ( d, J ˆ 9.9, 1H); 7.30 7.40 ( m, 2 H); 7.48 7.55 (m, 1H); 7.72 7.77
(m, 1 H). 13C NMR: 46.5; 68.4; 88.3; 101.2; 110.7; 119.5; 120.3; 124.6; 125.4; 130.9; 140.8; 147.5; 150.8; 163.1;
168.1. The photoadduct 32 was unstable at r.t. and converted gradually or easily on distillation (175 1808/
3 Torr) to 35.
S-[3-(Benzoxazol-2-yl)-2,3-dihydrofuran-2-yl] O-Phenyl Thiocarbonate (33). M.p. 112 1138. IR (KBr):
1725, 1625, 1610. 1H-NMR: 5.03 (dt, J ˆ 2.3, 9.9, 1H); 5.44 ( t, J ˆ 3.0, 1H); 6.65 ( t, J ˆ 3.0, 1H); 6.74 ( d, J ˆ 9.9,
1H); 7.02 7.08 ( m, 2 H); 7.17 7.41 (m, 5 H); 7.53 7.58 (m, 1H); 7.73 7.80 ( m, 1 H). 13C-NMR: 46.7; 88.5;

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101.3; 110.8; 120.4; 121.0; 124.7; 125.6; 126.4; 128.3; 129.5; 140.8; 147.6; 150.9; 163.0; 167.5. Anal. calc. for
C18H13NO4S (339.29): C 63.72, H 3.86, N 4.13; found C 63.95, H 3.71, N 4.10.
X-Ray Crystal-Structure Determination of 4. The crystal of 4 from CHCl3/hexane (approximate dimensions
of 0.30 Â 0.35 Â 0.20 mm) was mounted on a glass fiber and used for the X-ray study.
Crystal Data. C14H15NO2S, Mr 261.343, monoclinic, space group P21/c, a ˆ 12.054(3), b ˆ 5.564(2), c ˆ
20.413(5) ä, a ˆ 90.008, b ˆ 104.36(2)8, g ˆ 90.008, Vˆ 1326.2(7) ä3, Z ˆ 4, Dx ˆ 1.309 g cmÀ3, colorless rod,
F(000) ˆ 552, m(CuKa) ˆ 2.12 mmÀ1
.
Data Collection, Structure Solution, and Refinement. The intensity data were collected in a Mac Science
MXC 18 diffractometer with graphite-monochromated CuKa radiation (l 1.54 ä) by means of w-2q scan
technique in the range 2q < 70.008. Out of 2892 total reflections, 2274 reflections with intensities greater than 3.0
s(I) were used, but no absorption correction was made. The structure was solved by direct methods with maXus.
Least-squares refinement including anisotropic thermal parameters for non-H-atoms and isotropic refinement
of H-atoms located in difference Fourier synthesis terminated at R 0.055 and RW 0.265 (F2).
Tables of crystal data are available as supplementary data. Atomic coordinates, bond lengths and angles,
and thermal parameters of X-ray crystal structure of 4 (CCDC-208836) have been deposited with Cambridge
Crystallographic Data Centre. Copies of the data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: ‡44-1223/336-033; e-mail: deposit@ccdc.scan.ac.uk).
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Received May 13, 2003