Regioselective formation of 3-selanyl-3-siloxyoxetanes in the Paternò - Büchi reaction of silyl O,Se-ketene acetals (O,Se-SKA)

Article abstract of DOI:10.1055/s-2001-15052

The photochemical [2+2] cycloaddition (Paternò - Büchi reaction) of silyl O,Se-ketene acetal (SKA) 2 with aromatic aldehyde 3 affords regioselectively 3-selanyl-3-siloxyoxetane 4 (trans:cis ? 65:35-85:15) in good to high yields under the aldehyde excitation conditions (hv > 320 nm). A 70:30 mixture of the regioisomers 4aa (trans:cis = 50:50) and 5aa (= 6a), however, is produced in the 9,10-diphenylanthracene (DPA)-sensitized photoreaction (hv >400 nm) of 2a and 3a. A 1,4-diradical 1,4-DR is proposed for the n-π* excited aldehyde reaction, which regioselectively produces the 3-selanyloxetane 4. The regio-random formation of the oxetanes 4 and 5 (= 6) under the DPA-sensitized conditions is reasonably rationalized by the intervention of radical ion intermediate RI.

Full text of DOI:10.1055/s-2001-15052

PAPER
1243
Regioselective Formation of 3-Selanyl-3-siloxyoxetanes in the Paternò–Büchi
Reaction of Silyl O,Se-Ketene Acetals (O,Se-SKA)
R
egioselective Format
a
n
anyl-3-siloxy
a
oxetanes bu Abe,* Kei Tachibana, Kiyotada Fujimoto, Masatomo Nojima
Department of Materials Chemistry, Graduate School of Engineering, Osaka University, Suita 565–0871, Osaka, Japan
Fax +81(6)68797930; E-mail: abe@ap.chem.eng.osaka-u.ac.jp
Received 10 January 2001
the 3-siloxyoxetanes (3-siloxy-:2-siloxyoxetane 80:20)
Abstract: The photochemical [2+2] cycloaddition (Paternò–Büchi
reaction) of silyl O,Se-ketene acetal (SKA) 2 with aromatic alde-
with trans configuration (trans:cis 80:20) was observed
for the sulfur derivative O,S-SKA (Epox = 1.22 V versus
SCE).6 The 1,4-diradical intermediate 1,4-DR has been
hyde
3 affords regioselectively 3-selanyl-3-siloxyoxetane 4
(trans:cis 65:35–85:15) in good to high yields under the aldehyde
excitation conditions (hv >320 nm). A 70:30 mixture of the regioi- proposed for the photoreaction. The contrastive mecha-
somers 4aa (trans:cis = 50:50) and 5aa (= 6a), however, is produced
nism can be best rationalized by the electron donating
ability of O,X-SKA, i.e., O,O-SKA (Epox = 0.90 V) > O,S-
in the 9,10-diphenylanthracene (DPA)-sensitized photoreaction (hv
>400 nm) of 2a and 3a. A 1,4-diradical 1,4-DR is proposed for the
SKA (Epox = 1.22 V).
n- * excited aldehyde reaction, which regioselectively produces the
3-selanyloxetane 4. The regio-random formation of the oxetanes 4
and 5 (= 6) under the DPA-sensitized conditions is reasonably ratio-
nalized by the intervention of radical ion intermediate RI.
OTBDMS
Ar
XR
Me
O
O
Key words: Paternò Büchi reaction, photochemical [2+2] cy-
cloaddition, oxetane, regioselectivity
Ar
H
Me
Me
Ar
Me
Me
OTBDMS
OR
Me
XR
O
Synthetic demand of oxetanes goes on increasing because
of their biological activity1 as well as their synthetic utili-
ty.2 The [2+2] photocycloaddition of excited carbonyl
compounds with alkenes, so-called Paternò–Büchi reac-
tion,3 is probably the most direct and flexible method for
constructing the oxetane ring. The regio- and stereoselec-
tive preparation of oxetanes continues to represent a sub-
ject of interest, although the highly selective formation of
oxetanes has been uncovered in many cases.4 We have re-
cently found that the unique chalcogen atom effects on the
regio- and stereoselective formation of oxetanes in Pater-
nò–Büchi reaction of silyl O,X (= O, S)-ketene acetals
(SKA) with aromatic aldehydes, as shown in Scheme 1.5,6
OTBDMS
1,4-DRs
RI
Figure 1
While the chalcogen atom effects on the regio- and stere-
oselectivity are quite interesting from the mechanistic
point, the synthetic application of the oxetanes, e.g., their
chemical transformation or functionalization, seems to be
difficult. Since the chemistry of selenium compounds is
rich,8–10 selenium-substituted oxetanes would be good
candidates as synthetic intermediates for preparing a vari-
ety of functionalized oxetanes. In this regard, we have de-
cided to examine the Paternò–Büchi reaction of silyl
O,Se-ketene acetals (O,Se-SKA) 2,11 which can be easily
prepared from the corresponding selenoesters 1a,b
(Scheme 2).
OTBDMS
XR
Me
Ar
Ar
O
Me
XR
O
Me
O
Ar
H
hv
Me
OTBDMS
2-siloxyoxetane
Me
Me
OTBDMS
XR
3-siloxyoxetane
Me
(1) LDA, –78 °C
Me
Me
OTBDMS
SeR
X = O
X = S
< 5 : > 95
80 : 20
SeR
(2) TBDMSCl
Me
O,X-SKA
O
1a (R = Ph)
b (R = Me)
2a (R = Ph)
b (R = Me)
Scheme 1
In the photoreaction of O,O-SKA (Epox = 0.90 V versus
SCE),5 the regioselective formation was found to give the
2-siloxyoxetane via radical ion pair intermediates RI
(Figure 1).7 Alternatively, the preferential formation of
Scheme 2
First of all, in order to reveal the regio- and stereoselectiv-
ity, the photoreactions of O,Se-SKA 2a,b with aromatic
aldehydes 3a–c were performed with a high-pressure Hg
lamp (500 W) through an uranium filter (>320 nm)
(Scheme 3 and Table).
Synthesis 2001, No. 8, 18 06 2001. Article Identifier:
1437-210X,E;2001,0,08,1243,1247,ftx,en;C00301SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

1244
M. Abe et al.
PAPER
Table Photocyclization of Silyl O,Se-Ketene Acetals 2 with Aromatic Aldehydes 3a
Entry
2
3
Solvent
CH3CN
benzene
CH2Cl2
CH3CN
CH3CN
CH3CN
4 (%)b
trans/ cisc
68/32
Convn (%)d
1
2
3
4
5
6e
2a
2a
2a
2a
2b
2a
3a
3a
3a
3b
3a
3c
94
61
45
80
35
78
85
62/38
81
62/38
84
68/32
70
86/14
no reaction
a The photoreaction was performed with a high pressure Hg lamp (500 W) through a uranium filter (>320 nm).
b Isolated yields after column chromatography on silica gel.
c The ratios (trans-4:cis-4) were determined by 1H NMR (270 MHz) analysis of the photolysate; error 3%.
d The conversions (%) were after 5 h irradiation.
e The starting materials 2a and 3c (>90%) were recovered.
NOE
O
OTBDMS
Me
Ar
Ar
2a,b (0.1 M)
hv (> 320 nm)
SeR
Me
Ar OTBDMS
SeR
Ha OTBDMS
SeR
Ar
H
O
Me
Me
O
SeR
CH3CN
(0.05 M)
H
Ar
OTBDMS
3a (Ar = p-CNC6H4)
b (Ar = Ph)
O
Me
O
Me
4
5
Me
trans-4
Me
c (Ar = 2-Naph)
cis-4
Scheme 3
Figure 2
Interestingly, in the photoreaction of 3a,b, the perfect re-
gioselectivity was found to give the 3-selanyl-3-siloxyox-
etanes 4 (4:5 > 95:5) in good to high yields at approx.
50~80% conversions of the aldehyde (entries 1–5, Ta-
ble).12 The 2-selanyloxetane 5 or its derivative 6 could not
be detected in all of the cases. The observed regioselectiv-
ity was not dependent upon the solvent (entries 1–3), the
substituent on the phenyl ring, nor the SeR group (entries
1, 4, 5). The negligible solvent and substituent effects on
the product distribution are quite similar to the results of
the photoreaction with O,S-SKA,6 in which the 1,4-dirad-
ical 1,4-DR have been proposed as a key intermediate. In
the photoreaction of 2-naphthaldehyde 3c (entry 6), in
which the lowest excited state possesses the - * charac-
ter, the starting compounds 2a and 3c were recovered (>
90%) without the formation of the oxetane 4ac. The re-
sults clearly suggest that the n- * excited state of carbon-
yls is indispensable for the oxetane production.
In order to determine the mechanistic information on the
regioselective formation of the oxetane 4 in the direct
photoreaction of aromatic aldehydes (electron transfer
versus 1,4-diradical), the quantum chemical calculations,
(UB3LYP/3–21G*//UHF/3–21G*),13 were performed to
estimate the positions of the spin densities ( ) of the mod-
el radical cations RC-X (X = O, S, Se). As expected, the
spin densities for RC-O and RC-S were calculated to be
mainly localized at C2 position, i.e., for RC-O; C1 = 0.17
and C2 = 0.54, for RC-S; C1 = 0.18, C2 = 0.53 (Figure 3).
The calculated results are quite consistent with the exclu-
sive formation of 2-siloxyoxetanes under the DPA-sensi-
tized (electron transfer) conditions, as reported by us.5,6 In
the case of RC-Se, however, the delocalization of the spin
was found to be at C1 ( C1 = 0.18), C2 ( C2 = 0.40) and Se-
atom ( Se = 0.30). The spin density on the Se-atom sug-
gests the stabilization of the alkyl radical by selenium at-
om, as evidenced by ESR measurements of -selenoalkyl
With respect to the stereoselectivity, the diastereomer radicals reported by Scaiano and Ingold14 (Figure 4).15
with trans configuration between the seleno group and the Thus, the regio-random formation of oxetanes is predicted
aromatic moiety was preferentially formed in all of the from the O,Se-KSA radical cation intermediates.
cases (entries 1–5, trans-4:cis-4 65:35–85:15). The ob-
served stereoselectivity was again quite comparable to the
spin density (ρ)
X
C1
0.17 0.54
0.18 0.53 0.09
C2
X
results of photoreaction with O,S-SKA (trans:cis = 75:25–
85:15).6 The stereochemical determination of the 3-sela-
nyloxetane 4 was performed on the basis of the 1H NMR
NOE measurements (Figure 2). The clear NOE enhance-
ments (3~5%) were observed between the Ha proton and
the silyl group in cis-4, thus, the stereochemical determi-
nation was feasible.
OSiH3
Me
Me
O
S
2
1
XMe
RC-X
Se 0.18 0.40 0.30
Figure 3
Synthesis 2001, No. 8, 1243–1247 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Regioselective Formation of 3-Selanyl-3-siloxyoxetanes
1245
OTBDMS
Ar
SeR
SeR
hv (> 320 nm)
SeR
4
O
Me
Figure 4
Me
1,4-DR
In order to confirm the theoretical prediction, the photore-
action (> 400 nm) of O,Se-SKA 2a and p-cyanobenzalde-
hyde 3a (Ered = –1.38 V versus SCE) was performed in the
presence of 9,10-diphenylanthracene (DPA, ES = 3.15 eV,
Eox = 1.22 V, Ered = –1.94 V versus SCE)16 as a sensitizer
(Scheme 4), in which the electron transfer reaction would
be the most promising process as judged by their redox
potentials, to generate the cation radical of 2a and anion
radical of 3a (Scheme 5).17 After irradiation for 40 hours
(conversion of 3a, 25%), the aldol-type adduct 6a (7%)
derived from the 2-selanyloxetane 5aa was obtained to-
gether with the 3-selanyloxetane 4aa (16%,
trans:cis = 50:50) and pinacol 7a (30%). The prolonged
irradiation, up to 40% conversion of 3a, did not change
the product distributions. The product ratios, i.e.,
4aa:6a = 70:30 and trans-4:cis-4 were quite different
from the results observed in the direct irradiation condi-
tions (entry 1). The notable chalcogen atom effect on the
regioselectivity in the DPA-sensitized reactions can be
best rationalized by the intervention of the cation radical
intermediates.
2 + 3
Me
Ar
Me
5
O
SeR
hv (> 320 nm)
OTBDMS
1,4-DR'
Scheme 6
tion. The findings in this study would expand the synthetic
utility of the oxetane ring. The chemical transformation of
the selanyloxetane 4 is now under investigation and will
be published.
All of reagents and solvents were purchased from Wako Pure
Chemical Industries. THF and benzene were dried and distilled
from Na benzophenone ketyl prior to use. CH2Cl2 and diisopropy-
lamine were dried over CaH2 and distilled before use. Selenoesters
1a,b were prepared by the reported methods.18 Chromatographic
purification of products was carried out using flash chromatography
on silica gel (Wako C-300) as a normal phase. TLC was performed
on Merck 0.25 mm silica gel 60F plates (230–400 mesh) as a normal
phase. Visualization of the developed chromatogram was per-
formed by UV (254 nm) irradiation. 1H and 13C NMR spectra were
recorded on JEOL JNM-EX-270 spectrometer at 270 MHz and 68
OH
O
H3O+
DPA, hv (> 400 nm)
Ar
SePh
4aa
5aa
2a + 3a
1
MHz, respectively. H NMR chemical shifts are reported in ppm
CH3CN
(
H) using residual CHCl3 ( = 7.26 ppm) in the perdeuterated sol-
6a (Ar = p-CNC6H4)
vent as the internal standard. Mutiplicities are reported with s (sin-
glet), d (doublet), and m (multiplet). 13C NMR (DEPT) chemical
shifts are reported in ppm ( C) relative to the internal standard
CDCl3 ( = 77.00 ppm). IR spectra were measured on a Horiba FT-
720 spectrophotometer with samples prepared as either KBr pellets
or thin films on NaCl salts plates and are reported in terms of fre-
quency of absorption (cm–1). Mass spectrometric data were ob-
tained on a JEOL JNS-BX 303-HF mass spectrometer. Elemental
analyses were carried out at the Analytical Division of the Faculty
of Engineering, Osaka University. Photolyses (> 320 nm) were con-
ducted with an Eikohsha 500 W high-pressure mercury lamp though
a uranium filter.
Scheme 4
3a
DPA*
(Ar = p-CNC6H4)
hv
OH
O
Ar
7a
2
Ar
H
DPA
DPA
4aa + 5aa
Me
Me
OTBDMS
SeR
2a
1-(tert-Butyldimethylsiloxy)-1-phenylselanyl-2-methyl-1-prop-
ene (2a); Typical Procedure
Scheme 5
To a solution of diisopropylamine (1.7 g, 17 mmol) in anhyd THF
(100 mL) was added slowly a solution of n-BuLi (10.9 mL, 17
mmol) in n-hexane (1.6 M) at –78°C. After stirring for 30 min, a so-
lution of selenoester 1a (3.4 g, 15 mmol) in anhyd THF (10 mL) was
added dropwise under an Ar atm. A solution of HMPA (3.1 mL, 17
mmol) and TBDMSCl (2.6 g, 17 mmol) in anhyd THF (10 mL) was
added slowly. After stirring for 18 h, the mixture was warmed up to
r.t. and quenched with H2O. The organic layer was extracted by n-
hexane (2 50 mL), and washed with sat. NaCl (50 mL). Removal
of the solvent by rotary evaporation provided the crude product.
Purification by column chromatography on silica gel (n-hexanes)
afforded 1-(tert-butyldimethylsiloxy)-1-phenylselanyl-2-methyl-1-
propene (2a) (2.7 g, 7.8 mmol, 52%) as pale yellow oil. TLC (hex-
anes): Rf = 0.85.
The experimental and theoretical results suggest that the
possibility of the intervention of radical ion intermediates
seems to be low under the direct irradiation conditions.
Thus, the 1,4-diradical, which can be formed by the nu-
cleophilic attack of the n- * carbonyl to SKA, would be
the most reasonable intermediate for the regioselective
formation of 3-selanyloxetanes 4 (Scheme 6). The Se-
atom stabilization of -alkyl radicals would also play an
important role for the selective generation for the 1,4-
diradical 1,4-DR over the regioisomeric diradical 1,4-
DR .
IR (thin film): = 2860 3070, 1633, 1579, 1168 cm–1.
1H NMR (CDCl3, 270 MHz): = 0.09 (s, 6H), 086 (s, 9H), 1.83 (s,
Thus, we have developed the regioselective synthesis of
selanyloxetanes by using the simple photochemical reac-
3H), 1.90 (s, 3H), 7.11–7.36 (m, 5H).
Synthesis 2001, No. 8, 1243–1247 ISSN 0039-7881 © Thieme Stuttgart · New York

1246
M. Abe et al.
PAPER
13C NMR (CDCl3, 68 MHz): = –4.1 (2 q), 18.1 (s), 18.4 (q), 22.9
(q), 25.8 (3 q), 123.5 (s), 125.6 (d), 128.9 (2 d), 129.7 (2 d),
132.1 (s), 133.6 (s).
2,2-Dimethyl-3-(tert-butyldimethylsiloxy)-4-(4-cyanophenyl)-3-
methyllselanyloxetane (trans-4ba)
White powder; mp 97–98°C; TLC (hexanes–EtOAc, 90:10):
Anal. Calcd for C16H26OSeSi: C, 56.29; H, 7.68. Found: C, 56.36;
H, 7.84.
Rf = 0.30.
IR (KBr): = 3000–2860, 2230, 1610, 1500–1370, 1250, 1160,
1140 cm–1.
1-(tert-Butyldimethylsiloxy)-1-methylselanyl-2-methyl-1-prop-
ene (2b)
Prepared using selenoester 1b. Purification by distillation (60°C/0.6
mmHg) afforded 1-(tert-butyldimethylsiloxy)-1-methylselanyl-2-
methyl-1-propene (2b) (66%) as a colorless oil.
1H NMR (CDCl3, 270 MHz): = 0.10 (s, 3H), 0.14 (s, 3H), 0.55 (s,
9H), 1.40 (s, 3H), 1.67 (s, 3H), 2.19 (s, 3H), 5.81 (s, 1H), 7.42–7.45
(m, 2H), 7.63–7.66 (m, 2H).
13C NMR (CDCl3, 68 MHz): = –3.0 (q), –2.8 (q), 3.7 (q), 18.2 (s),
25.8 (3 q), 26.0 (q), 27.8 (q), 85.5 (s), 91.1 (d), 94.5 (s), 110.7 (s),
119.0 (s), 126.9 (2 d), 131.6 (2 d), 144.2 (s).
IR (thin film): = 2960–2860, 1640, 1470–1360, 1250, 1160, 1050
cm–1.
1H NMR (CDCl3, 270 MHz): = 0.21 (s, 6H), 0.97 (s, 9H), 1.71 (s,
3H), 1.82 (s, 3H), 2.08 (s, 3H).
Anal. Calcd for C19H29NO2SeSi (as a mixture of trans- and cis-iso-
mer): C, 55.59; H, 7.12; N, 3.41. Found: C, 55.45; H, 7.04; N, 3.41.
13C NMR (CDCl3, 68 MHz): = –4.4 (2 q), 5.7 (q), 18.2 (s), 18.3
(q), 22.4 (q), 25.9 (3 q), 119.2 (s), 133.91 (s).
cis-4ba
White powder; mp 94–95°C; TLC (hexanes–EtOAc, 90:10):
Anal. Calcd for C11H24OSeSi: C, 47.30; H, 8.66. Found: C, 47.35;
H, 8.78.
Rf = 0.40.
IR (KBr): = 2960–2860, 2230, 1610, 1500–1360, 1250, 1210,
1150 cm–1.
Photochemical Reactions of O,Se-SKA 2 with Aromatic
Aldehyde 3; General Procedure
1H NMR (CDCl3, 270 MHz): = 0.23 (s, 3H), 0.32 (s, 3H), 0.98 (s,
9H), 1.60 (s, 3H), 1.63 (s, 3H), 1.65 (s, 3H), 5.61 (s, 1H), 7.58–7.66
(m, 4H).
13C NMR (CDCl3, 68 MHz): = –3.3 (q), –2.3 (q), 2.81 (q), 18.5 (s),
24.9 (q), 25.8 (3 q), 27.7 (q), 89.4 (d), 89.4 (s), 93.5 (s), 112.0 (s),
118.7 (s), 127.7 (2 d), 131.5 (2 d), 143.0 (s).
A solution of O,Se-SKA 2 (1.5 mmol) and aromatic aldehyde 3
(0.75 mmol) in anhyd solvent (15 mL) was degassed by Ar bubbling
(15 min). The test-tube shaped reaction apparatus was equipped
parallel to the high-pressure Hg lamp (500 W). After irradiation for
5 h at ca. 10°C, the solvent was removed using a rotary evaporator
to give the products. The photolysate was analyzed by 1H NMR in
order to determine the product ratios (Table). Purification of the
products using flash column chromatography afforded the starting
materials 2, 3 and the 3-selanyl-3-siloxyoxeane 4. The yields (%)
and conversions (%) are given in the Table.
2,2-Dimethyl-3-(tert-butyldimethylsiloxy)-4-phenyl-3-phenylse-
lanyloxetane (trans-4ab)
Viscous oil; TLC (hexanes–EtOAc, 95:5): Rf = 0.31.
IR (KBr): = 3050–2857, 1579, 1463, 1256, 1139 cm–1.
2,2-Dimethyl-3-(tert-butyldimethylsiloxy)-4-(4-cyanophenyl)-3-
phenylselanyloxetane (trans-4aa)
1H NMR (CDCl3, 270 MHz): = –0.03 (s, 3H), 0.11 (s, 3H), 0.68 (s,
9H), 1.54 (s, 3H), 1.75 (s, 3H), 5.66 (s, 1H), 7.16–7.69 (m, 10H).
Viscous oil. TLC (hexanes–EtOAc, 70:30): Rf = 0.74.
13C NMR (CDCl3, 68 MHz): = –2.4 (q), –2.0 (q), 18.6 (s), 25.7 (q),
26.0 (3 q), 29.1 (q), 89.3 (d), 90.5 (s), 94.5 (s), 127.8 (d), 128.3
(d), 128.4 (2 d), 128.6 (2 d), 128.8 (2 d), 135.2 (2 d), 137.7
(s), 137.9 (s).
IR (thin film): = 3070–3060, 2960–2860, 2230, 1720, 1610, 1580,
1250, 1170, 1140 cm–1.
1H NMR (CDCl3, 270 MHz): = 0.15 (s, 3H), 0.16 (s, 3H), 0.64 (s,
Anal. Calcd for C23H32O2SeSi (as a mixture of trans- and cis-iso-
9H), 1.48 (s, 3H), 1.77 (s, 3H), 5.61 (s, 1H), 7.14–7.73 (m, 9H).
mer): C, 61.72; H, 7.21. Found: C, 61.45; H, 7.26.
13C NMR (CDCl3, 68 MHz): = –2.11 (q), –1.9 (q), 18.5 (s), 25.8
(q), 25.9 (3 q), 29.2 (q), 88.2 (d), 89.9 (s), 95.2 (s), 110.9 (s), 119.0
(s), 127.6 (2 d), 128.5 (s), 128.8 (d), 129.4 (2 d), 131.4 (2 d),
136.0 (2 d), 143.7 (s).
CIMS (CH4): m/z (%) = 474 (M+1+, 5), 342 (51), 316 (100), 185
(82).
cis-4ab
Viscous oil; TLC (hexanes–EtOAc, 95:5): Rf = 0.33.
IR (KBr): = 3063–2857, 1704, 1472, 1251 cm–1.
1H NMR (CDCl3, 270 MHz): = –0.03 (s, 3H), 0.39 (s, 3H), 0.94 (s,
9H), 1.65 (s, 3H), 1.75 (s, 3H), 5.71 (s, 1H), 7.10–7.60 (m, 10H).
13C NMR (CDCl3, 68 MHz): = –3.6 (q), –1.9 (q), 18.5 (s), 25.5 (q),
25.8 (3 q), 28.9 (q), 90.8 (d), 92.8 (s), 93.7 (s), 125.6 (d), 127.3 (2
d), 128.0 (2 d), 128.6 (2 d), 128.8 (d), 130.3 (2 d), 132.2 (s),
137.3 (s).
HRMS (CI): Anal. Calcd for C24H32NO2SeSi (M+1)+: 474.1367.
Found: 474.1379.
Anal. Calcd. for C24H31NO2SeSi (as a mixture of trans- and cis-iso-
mer): C, 61.00; H, 6.61; N, 2.96. Found: C, 60.90; H, 6.73; N, 2.90.
cis-4aa
9,10-Diphenylanthracene (DPA) Sensitized Photoreaction of
O,Se-SKA 2a with p-Cyanobenzaldehyde (3a)
Viscous oil. TLC (hexanes–EtOAc, 70:30): Rf = 0.78.
1H NMR (CDCl3, 270 MHz): = 0.00 (s, 3H), 0.37 (s, 3H), 0.95 (s,
9H), 1.61 (s, 3H), 1.63 (s, 3H), 5.72 (s, 1H), 7.14–7.73 (m, 9H).
13C NMR (CDCl3, 68 MHz): = –3.5 (q), –2.2 (q), 18.7 (s), 25.4 (q),
26.9 (3 q), 28.8 (q), 90.1 (d), 91.9 (s), 94.6 (s), 112.3 (s), 118.7 (s),
126.0 (d), 127.8 (2 d), 128.3 (2 d), 130.3 (2 d), 131.7 (2 d),
132.8 (s), 142.6 (s).
A solution of 2a (916 L, 3.0 mmol), 3a (200 mg, 1.5 mmol), and
DPA (10 mg) in CH3CN (20 mL) was degassed by Ar bubbling (15
min). The test-tube shaped reaction flask was placed parallel to the
high pressure Hg lamp (500 W). The mixture was irradiated (> 400
nm) through a CuSO4 solution in aq NH3. After irradiation for 40 h,
the solvent was removed using a rotary evaporator. Purification by
silica gel chromatography afforded 3-selanyloxetane 4aa (28 mg,
16%, trans / cis = 51 / 49), selenoester 6a (10 mg, 7%), pinacol 7a19
(13 mg, 30%), and p-cyanobenzaldehyde 3a (150 mg, 75%).
Synthesis 2001, No. 8, 1243–1247 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Regioselective Formation of 3-Selanyl-3-siloxyoxetanes
1247
Se-Phenyl 2,2-dimethyl-3-(4-cyanophenyl)-3-hydroxy-
propanoate (6a)
White powder; mp 105–107°C; TLC (hexanes–EtOAc, 70:30):
Rf = 0.51.
Kather, K.; Fröhlich, R. J. Am. Chem. Soc. 1997, 119, 2437.
(e) Bach, T.; Bergmann, H.; Harms, K. J. Am. Chem. Soc.
1999, 121, 10650. (f) Bach, T. Tetrahedron Lett. 1999, 40,
9003. (g) Fleming, S. A.; Gao, J. J. Tetrahedron Lett. 1997,
38, 5407. (h) Shima, K.; Sakurai, H. Bull. Chem. Soc. Jpn.
1966, 39, 1806. (i) Schreiber, S. L.; Satake, K. J. Am. Chem.
Soc. 1983, 105, 6723. (j) Carless, H. A. J.; Halfhide, A. F. E.
J. Chem. Soc., Perkin Trans. 1 1992, 1081. (k) Adam, W.;
Peters, K.; Peters, E. V.; Stegmann, V. R. J. Am. Chem. Soc.
2000, 122, 2958. (l) Abe, M.; Torii, E.; Nojima, M. J. Org.
Chem. 2000, 65, 3426.
IR (KBr): = 3600–3300, 2974, 2230, 1670, 1364, 1055 cm–1.
1H NMR (CDCl3, 270 MHz): = 1.19 (s, 3H), 1.29 (s, 3H), 2.09 (d,
J = 4.0 Hz, 1H, -OH), 5.04 (d, J = 4.0 Hz, 1H), 7.32–7.49 (m, 7H),
7.63–7.66 (m, 2H).
13C NMR (CDCl3, 68 MHz): = 19.1 (q), 22.9 (q), 57.6 (s), 77.1 (d),
111.8 (s), 118.7 (s), 125.5 (s), 128.5 (2 d), 129.2 (d), 129.4 (2 d),
131.6 (2 d), 136.2 (2 d), 144.9 (s), 209.8 (s).
CIMS (CH4): m/z (%) = 360 (M+1+, 100), 314 (84), 229 (41), 202
(40), 158 (36).
HRMS (CI): Calcd for C18H18NO2Se (M+1)+: 360.0497. Found:
360.0509.
(5) (a) Abe, M.; Ikeda, M.; Shirodai, Y.; Nojima, M.
Tetrahedron Lett. 1996, 37, 5901. (b) Abe, M.; Shirodai, Y.;
Nojima, M. J. Chem. Soc., Perkin Trans. 1 1998, 3253.
(c) Abe, M.; Ikeda, M.; Nojima, M. J. Chem. Soc., Perkin
Trans. 1 1998, 3261.
(6) Abe, M.; Fujimoto, K.; Nojima, M. J. Am. Chem. Soc. 2000,
122, 4005.
(7) The formation of oxetanes via contact ion pair has been
reported, see; Cruciani, G.; Rathjen, H.-J.; Margaretha, P.
Helv. Chim. Acta 1990, 73, 856.
Anal. Calcd for C18H17NO2Se: C, 60.34; H, 4.78; N, 3.91. Found: C,
60.37; H, 4.97; N, 3.80.
(8) (a) Noltes, J. G.; Van derKerk, G. J. M. Chem. Ind. 1959,
294. (b) Kuivila, H.-G. Synthesis 1970, 499.
Acknowledgement
This work was supported in part by the grant-in-aid for Scientific
Research on Priority Areas “Molecular Physical Chemistry” and
grant No. 10750610 from the Ministry of Education, Science,
Sports, and Culture of Japan. We thank the Analytical Division of
Faculty of Engineering, Osaka University, for measuring elemental
analyses and mass spectra.
(c) Motherwell, W. B.; Crich, D. In Free Radical Chain
Reactions in Organic Synthesis; Academic Press: London,
1992.
(9) Clive, D. L. J.; Chittatu, G. J.; Farina, V.; Kiel, W. A.;
Menchen, S. M.; Russell, C. G.; Singh, A.; Wong, C. K.;
Curtis, N. J. J. Am. Chem. Soc. 1980, 102, 4438.
(10) Keck, G. E.; Enholm, E. J.; Yates, J. B.; Wiley, M. R.
Tetrahedron 1985, 41, 4079.
(11) Although the irreversible oxidation peaks of 2a,b (2a:
Epox = 1.33 V versus SCE; 2b: Epox = 1.29 V versus SCE in
CH3CN, tetraethylammonium perchlorate as a supporting
electrolyte) were observed, the signals were broad; thus, the
values are not accurate for determining the oxidation
potentials.
References and Notes
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(12) The prolonged irradiation led to some decomposition of
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anobenzaldehyde 2a (kq = 1.90 1010 s–1M–1), whose rate
constant was determined by Stern–Volmer plot.
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Synthesis 2001, No. 8, 1243–1247 ISSN 0039-7881 © Thieme Stuttgart · New York