Notable temperature effect on the stereoselectivity in the photochemical [2+2] cycloaddition reaction (Paternò-Büchi reaction) of 2,3-dihydrofuran-3-ol derivatives with benzophenone

Article abstract of DOI:10.1016/j.tetlet.2006.02.046

A notable temperature effect (nonlinear Eyring plot) on stereoselectivity, trans-configured oxetane 2 versus cis-configured oxetane 2, is reported in the photochemical [2+2] cycloaddition reaction (Paternò-Büchi reaction) of 2,3-dihydrofuran-3-ol derivatives 1 with benzophenone.

Full text of DOI:10.1016/j.tetlet.2006.02.046

Tetrahedron Letters 47 (2006) 2527–2530
Notable temperature effect on the stereoselectivity
in the photochemical [2+2] cycloaddition reaction
(
Patern o` –B u¨ chi reaction) of 2,3-dihydrofuran-3-ol
derivatives with benzophenone
a,
a
b
*
Manabu Abe, Midori Terazawa, Koichi Nozaki,
a
a
Araki Masuyama and Takashi Hayashi
a
Department of Applied Chemistry, Graduate School of Engineering, Osaka University (HANDAI), Suita 565-0871, Japan
b
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka 560-0043, Osaka, Japan
Received 12 January 2006; revised 6 February 2006; accepted 9 February 2006
Available online 28 February 2006
Abstract—A notable temperature effect (nonlinear Eyring plot) on stereoselectivity, trans-configured oxetane 2 versus cis-configured
oxetane 2, is reported in the photochemical [2+2] cycloaddition reaction (Patern o` –B u¨ chi reaction) of 2,3-dihydrofuran-3-ol deriv-
atives 1 with benzophenone.
ꢀ
2006 Elsevier Ltd. All rights reserved.
1
Like epoxides, oxetane derivatives are synthetically and
ling the stereoselectivity. They also found that the threo
2
biologically important because they possess a high
strain-energy of 26 kcal/mol. The photochemical
selectivity increases with increasing steric bulk of the
3
0 0
substituent R ; threo/erythro = 90/10 (R = Me), 93/7
t
0
0
[
2+2] cycloaddition reaction of alkenes with carbonyl
(R = Et), >95/5 (R = Bu). The substituent effect
4
0
compounds, the so-called Patern o` –B u¨ chi reaction, is a
useful method for constructing the strained structures.
However, the elucidation of the factors that control
the regio- and stereoselectivity in oxetane formation
clearly indicates that the steric bulk of the R substituent
also plays an important role in controlling the diastereo-
selectivity of the reaction. In the present study, we
selected cyclic allylic-alcohol derivatives (2,3-dihydro-
furan-3-ols) 1 for the cycloaddition reaction and exam-
ined the effect of temperature on the stereoselectivity
in the Patern o` –B u¨ chi reaction with benzophenone
(Table 1 and Fig. 1). If hydroxy-directed diastereoselec-
tivity applies to the cyclic system, the cis-selective forma-
tion of oxetanes 2 would be expected.
5
remains a challenging subject. Adam and co-workers
recently reported on the hydroxy-directed diastereo-
selective formation of threo-oxetanes in the Patern o` –B u¨ chi
reaction of acyclic allylic alcohols with benzophenone
Scheme 1). They proposed that a hydrogen-bonded
interaction in exciplex is an important factor in control-
6
,7
(
8
Ph
Ph
OH
Me
Me
Me
Ph C=O*
Me
O
OH
2
OH
+
R'
Me
Me
O H
Ph
Ph
H
R'
H
R'
threo
major)
erythro
(minor)
(
Scheme 1. The Patern o` –B u¨ chi reaction of acyclic allylic alcohols with benzophenone.
Keywords: The Patern o` –B u¨ chi reaction; Photochemical [2+2] cycloaddition; Stereoselectivity; Oxetane; Triplet diradical.
*
Corresponding author. Tel./fax: +81 6 6879 7930; e-mail: abe@chem.eng.osaka-u.ac.jp
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.02.046

2528
M. Abe et al. / Tetrahedron Letters 47 (2006) 2527–2530
a
Table 1. The Patern o` –B u¨ chi reaction of allylic-alcohol derivatives 1a–c with benzophenone
XO
R
R
O
1
a-c
XO
XO
H
H
H
H
OH
O
Ph
Ph
Ph
Ph
hν (>290 nm)
R
R
O
O
Ph
Ph
Ph
+
+
+
o
Ph
Ph
21 C
R
R
OH
O
Ph
Ph
O
Ph
Ph
OH
3
4
trans-2a-c
cis-2a-c
b
c
b
b
Entry
Substrate
X
R
Solvent
Yield of 2 (%)
trans-2/cis-2
Yield of 3 (%)
Yield of 4 (%)
1
2
3
4
5
6
1a
1a
1b
1b
1b
1c
H
H
H
H
H
H
H
Me
Me
Me
Me
Toluene
Methanol
Benzene
Toluene
Methanol
Toluene
78
40
70
57
55
45
53/47
96/4
24/76
24/76
87/13
>97/3
12
30
18
28
25
36
6
—
—
14
—
Trace
d
TBDMS
a
The photoreaction was conducted as follows: a degassed solution of 1 (0.11 M) and benzophenone (0.075 M) was irradiated for 3–4 h with a high-
pressure Hg lamp (300 W) through a Pyrex filter. After removing the solvent, the product ratio, trans-2/cis-2, was directly determined by H NMR
1
(
400 MHz) spectroscopic analysis.
b
c
Isolated yield after column chromatography on silica gel.
Determined by H NMR (400 MHz) spectroscopic analysis, error ± 3%.
TBDMS = tert-butyldimethylsilyl group.
1
d
NOE1'
HO
R
R
NOE1
H
H
H
O
H
H
NOE
H
Me
HO
NOE
H
Me
O
O
NOE1 4% 4%
R
NOE1' 3% 3%
NOE2' 1% 2%
R
R
Ph
Ph
R
O
Ph
Ph
NOE2 3% 1% NOE2
NOE3 1% 1%
H
NOE3' 3% 1% NOE2'
NOE3'
NOE3
trans-2
cis-2
ation for 3–4 h at 21 ꢁC, the stereoselectivity of the oxe-
1
1
tanes 2a, trans-2a/cis-2a, was directly determined by
1
H NMR (400 MHz) spectroscopic analyses, error ±
3
%. The configuration of the oxetanes 2 formed in the
1
reaction was unequivocally determined by H NMR
600 MHz) NOE measurements. The photoreaction in
(
toluene gave approximately 1:1 mixture of the bicyclic
oxetanes trans-2a and cis-2a together with ca. a 20%
yield of side reaction products 3 and 4 (entry 1). In
methanol, the trans-configured oxetane 2a was selec-
tively produced (entry 2). The photoreaction of 1b with
benzophenone was next performed under conditions
similar to those described for the reaction of 1a (entries
1
2
3
–5). In aprotic solvents, the cis-configured oxetane 2b
was obtained as the major product, trans-2b/
cis-2b = 24/76 (entries 3–4). In contrast, the trans-iso-
mer 2b was selectively produced when the reaction was
conducted in methanol (entry 5). When the silyl ether
Figure 1. Eyring plots of the diastereoselectivity in the Patern o` –B u¨ chi
reaction of benzophenone with (a) 1a and (b) 1b in toluene.
1
c (TBDMS = tert-butyldimethylsilyl) was used in the
photochemical reaction, the highly stereoselective
1
3
formation of the trans-configured oxetane 2c was
observed together with the formation of products 3
and 4 (entry 6). All the product ratios did not change
after prolonged irradiation.
The allylic-alcohol derivatives 1a, 1b, and 1c10 were
prepared according to reported methods. The Patern o` –
B u¨ chi reaction of 1a (0.11 M) with benzophenone
9
10
(
0.075 M) was first carried out using a high-pressure
mercury lamp (300 W) through a Pyrex filter in degassed
toluene or methanol at 21 ꢁC (entries 1–2). After irradi-
To obtain information concerning the mechanism for
the stereoselectivity observed in oxetane formation, the

M. Abe et al. / Tetrahedron Letters 47 (2006) 2527–2530
2529
effect of temperature on the stereoselectivity was exam-
ined. As shown in Figure 1, the Eyring plots, ln(trans-
intermediates in the photochemical reactions, transient
absorption spectra were obtained for the reaction with
1a on a picosecond time scale (kexc = 355 nm, 20 ps
pulse width, Fig. 2). In the absence of 1a, the triplet state
2
/cis-2) against 1/T, were not linear for the formation
of both 2a and 2b, in which the trans-selectivity, trans-
/cis-2, increased nonlinearly with decreasing reaction
1
5
16
2
of benzophenone (s > 1 ls,
kmax = 523 nm ) was
temperature. Thus, the trans-configured oxetanes 2a
and 2b were the major isomers at low temperatures,
for example, trans-2a/cis-2a = 86/14 at ꢀ80 ꢁC and
trans-2b/cis-2b = 58/42 at ꢀ56 ꢁC were produced. The
trans-selectivity observed in the formation of oxetanes
observed within 20 ps after laser excitation in degassed
acetonitrile. Upon the addition of a 4.4 M acetonitrile
solution of 1a, the triplet state of benzophenone
(Fig. 2a) was quenched within 1 ns, generating a new
species (Fig. 2b) with an absorption maximum at
535 nm. The transient species decayed with almost
first-order kinetics (s = ca. 1.8 ns, kd = ca. 5.6 ·
2
a and 2b cannot be explained based on hydrogen-
6
bonded interaction. As judged by the high trans-selec-
tivity found for the reaction in methanol and of silyl
ether 1c (entries 2 and 6), steric factors appear to play
an important role in controlling the faceselectivity, at
least at low temperatures. Thus, the hydroxyl group is
sterically more bulky in protic solvents than that in
aprotic solvents. The silyloxyl group is sterically more
hindered than the hydroxyl group.
8
ꢀ1
10 s ) at 25 ꢁC. The absorption spectrum of the new
species is similar to that of the triplet diradical (k
=
max
1
7
535 nm, s = 1.5 ns in acetonitrile) reported for the
photoreaction of 1,4-dioxene with benzophenone. Thus,
it is reasonable to conclude that the new species are the
3
triplet diradicals trans- and cis- DR as shown in Scheme
2.
The nonlinear Eyring plots clearly suggest that oxetanes
A plausible mechanism for the photochemical reaction
is shown in Scheme 2. There are two steps that deter-
mine the stereoselectivity of the reaction: (1) the initial
faceselectivity by triplet benzophenone, that is,
2
a and 2b are formed in a reaction that involves two or
1
4
more steps. To obtain information on the nature of the
3
3
[
trans- DR] versus [cis- DR], and (2) the ratio of the rel-
ative rate constant of the bond-forming and bond-
1
breaking step from the singlet 1,4-diradicals trans- DR
1
0
/k versus k /k . Although
cis
5b
and cis- DR, that is, k
trans
the conclusive elucidation of the nonlinearity of the Eyr-
ing plots is currently under investigation, hydrogen-
bonded interactions between the allylic alcohol and the
triplet-excited carbonyl compound seems to be not
the major factor in controlling the stereoselectivity in
the formation of the oxetanes 2a,b. Thus, the ‘hydroxy-
6
directed diastereoselectivity’ cannot simply apply to
the case of the Patern o` –B u¨ chi reaction of cyclic allylic
alcohols.
In summary, a notable temperature effect on the stereo-
selectivity in the Patern o` –B u¨ chi reaction of 2,3-
dihydrofuran-3-ol derivatives 1 with benzophenone is
found in this study. The remarkable finding should stim-
ulate future studies on the mechanistically and synthe-
tically fascinating stereoselectivity in Patern o` –B u¨ chi
reactions of allylic alcohols.
Figure 2. Transient absorption spectra of (a) triplet benzophenone and
(
b) triplet 1,4-diradicals formed during the irradiation of 4.4 M 2,3-
dihydrofuran-3-ol (1a) with 0.02 M benzophenone in acetonitrile at
ns.
1
HO
O
Ph
R
R
ktrans
ISC
trans-1DR
trans-2
Ph
trans-3DR
O
Ph C=O*
2
HO
k
R
R
1
+ Ph C=O
2
O
k'
HO
1
O
Ph
ISC
Ph C=O*
R
cis-1DR
2
cis-2
kcis
Ph
R
O
cis-3DR
Scheme 2. A plausible mechanism for the formation of oxetane 2 in the Patern o` –B u¨ chi reaction of 1 with benzophenone.

2530
M. Abe et al. / Tetrahedron Letters 47 (2006) 2527–2530
(d), 126.9 (d), 127.3 (d), 127.9 (d), 128.4 (d), 141.0 (s),
Acknowledgements
1
1
2
44.2 (s); IR (neat): m = 3420, 3058, 2949, 1494, 1447,
ꢀ
1 +
096 cm
; HRMS (M ) m/z calcd for C H O :
17 16 3
This work was partially supported by the Ministry
of Education, Science, Sports, and Culture, Japan,
Grant-in-Aid for Scientific Research (B), No.
68.1099. Found: 268.1095.
cis-4-Hydroxy-7,7-diphenyl-2,6-oxabicyclo[3.2.0]heptane
(
1
3
cis-2a): H NMR (600 MHz, CDCl ): d 2.24 (d,
1
7350019, and Mitsubishi Chemical Corporation Fund.
J = 10.8 Hz, OH), 3.02 (t, J = 9.0 Hz, 1H), 3.94 (dd,
J = 9.0, 7.2 Hz, 1H), 4.24 (m, 1H), 4.99 (d, J = 4.2 Hz,
1
H), 5.10 (t, J = 4.2 Hz, 1H), 7.18 (m, 3H), 7.28 (t,
13
References and notes
J = 7.2 Hz, 3H), 7.38 (m, 2H), 7.45 (m, 2H); C NMR
(
67.8 MHz, CDCl ): d 71.1 (d), 71.8 (t), 80.5 (d), 84.1 (d),
3
1
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Griesbeck, A. G. In Organic Photochemistry and Photo-
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92.4 (s), 124.6 (d · 2), 127.1 (d), 127.4 (d), 128.2 (d),
128.6 (d), 140.4 (s), 144.2 (s); IR (KBr): m = 3518, 2984,
ꢀ
1
+
2952, 1103, 1082 cm ; HRMS (M ) m/z calcd for
: 268.1099. Found: 268.1101.
17 16 3
C H O
12. Spectroscopic data for new compound 2b.
trans-4-Hydroxy-3,3-dimethyl-7,7-diphenyl-2,6-dioxabicyclo-
1
[3.2.0]heptane (trans-2b): H NMR (270 MHz, C
D
6
): d
6
0.89 (br s, 1H), 1.01 (s, 3H), 1.08 (s, 3H), 3.84 (br s, 1H),
4.82 (dd, J = 4.3, 1.4 Hz, 1H), 4.96 (d, J = 4.3 Hz, 1H),
6.97–7.02 (m, 2H), 7.09–7.15 (m, 4H), 7.53–7.56 (m, 4H);
1
3
2
C NMR (67.8 MHz, C D ): d 23.3 (q), 27.0 (q), 82.0 (d),
6 6
1
988, 110, 7217; (b) Huang, J.-M.; Yokokawa, R.; Yang,
84.1 (d), 88.2 (s), 88.9 (d), 91.3 (s), 125.4 (d), 126.5 (d),
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1
3
4
IR (KBr): m = 3424, 2984, 2939, 1451, 1114 cm ; HRMS
+
3
11.
. (a) Patern o´ , E.; Chieffi, G. Gazz. Chim. Ital. 1909, 39, 341;
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(M ) m/z calcd for C19
H
20
O
3
: 296.1412. Found: 296.1417.
Anal. Calcd for C19
76.75; H, 6.77.
cis-4-Hydroxy-3,3-dimethyl-7,7-diphenyl-2,6-dioxabicyclo-
H O : C, 77.00; H, 6.80. Found: C,
20 3
(
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Ohata, S.; Nozaki, K.; Nojima, M. J. Am. Chem. Soc.
1
6 6
[3.2.0]heptane (cis-2b): H NMR (270 MHz, C D ): d 0.82
(s, 3H), 1.09 (s, 3H), 3.06 (d, J = 9.2 Hz, 1H), 3.53 (dd,
J = 9.2, 5.9 Hz, 1H), 4.64 (d, J = 4.3 Hz, 1H), 4.81 (dd,
J = 5.9, 4.3 Hz, 1H), 6.94–7.02 (m, 2H), 7.08–7.13 (m,
5
1
3
6 6
4H), 7.39–7.51 (m, 4H); C NMR (67.8 MHz, C D ): d
22.2 (q), 26.9 (q), 76.9 (d), 82.1 (d), 82.6 (d), 88.2 (s), 91.7
(s), 125.2 (d), 125.9 (d), 127.2 (d), 127.4 (d), 128.1 (d),
128.7 (d), 142.0 (s), 145.0 (s); IR (KBr): m = 3487, 3061,
2004, 126, 2838; (c) Griesbeck, A. G.; Abe, M.; Bondock,
S. Acc. Chem. Res. 2004, 37, 919; (d) Hei, X. M.; Song, Q.
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Stegmann, V. R. Synthesis 2001, 1203.
ꢀ1
+
2966, 1451, 1397, 1106, 1065 cm ; HRMS (M ) m/z calcd
for C19 : 296.1412. Found: 296.1419. Anal. Calcd for
: C, 77.00; H, 6.80. Found: C, 76.95; H, 6.73.
6
20 3
H O
C H O
19 20 3
13. Spectroscopic data for new compound 2c.
trans-4-(tert-Butyl)dimethysiloxy-3,3-dimethyl-7,7-diphen-
7
8
. Griesbeck, A. G.; Bondock, S. J. Am. Chem. Soc. 2001,
1
123, 6191.
yl-2,6-dioxabicyclo[3.2.0]heptane (trans-2c):
(600 MHz, C
H NMR
. For the concept of hydrogen-bonding as a tool for
directing photochemical reactions, see: (a) Yokoyama,
A.; Mizuno, K. Org. Lett. 2000, 2, 3457; (b) Bach, T.;
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6
D
6
): d 0.01 (s, 3H), 0.09 (s, 3H), 0.90 (s,
9H), 1.09 (s, 3H), 1.13 (s, 3H), 4.22 (d, J = 1.8 Hz, 1H),
4.94 (dd, J = 4.8, 1.8 Hz, 1H), 5.04 (d, J = 4.8 Hz, 1H),
6.98–7.02 (m, 2H), 7.08–7.18 (m, 4H), 7.54–7.60 (m, 4H);
1
3
10650; (c) Sieburth, S. McN; McGee, K. F., Jr. Org. Lett.
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6
D
6
): d ꢀ5.2 (q), ꢀ4.7 (q), 18.1 (s),
1999, 1, 1775; (d) Sydnes, L. K.; Hansen, K. I.; Oldroyd,
23.3 (q), 25.9 (q · 3), 26.7 (q), 83.3 (d), 84.2 (d), 87.8 (d),
88.9 (s), 91.0 (s), 125.5 (d), 126.6 (d), 126.9 (d), 127.2 (d),
127.8 (d), 128.6 (d), 142.6 (s), 145.5 (s); IR (KBr):
m = 3430, 2952, 2861, 1470, 1254, 1106 cm ; HRMS
25 34 3
(M ) m/z calcd for C H O Si: 410.2277. Found:
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1
1
4
1. Spectroscopic data for new compound 2a.
trans-4-Hydroxy-7,7-diphenyl-2,6-oxabicyclo[3.2.0]heptane
15. Poter, G.; Wilkinson, F. Trans. Faraday Soc. 1962, 58,
1686.
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103, 6255; (b) Freilich, S. C.; Peters, K. S. J. Am. Chem.
Soc. 1985, 107, 3819.
1
(trans-2a): H NMR (270 MHz, CDCl
3
): d 1.61 (br s, OH),
3
4
1
7
.71 (dd, J = 10.5, 3.2 Hz, 1H), 3.88 (d, J = 10.5 Hz, 1H),
.39 (m, 1H), 5.17 (d, J = 3.5 Hz, 1H), 5.22 (d, J = 3.5 Hz,
1
3
H), 7.22–7.53 (m, 10H); C NMR (67.8 MHz, CDCl
3
): d
3.8 (d), 75.4 (t), 84.4 (d), 86.0 (d), 92.4 (s), 124.7 (d), 124.8