Tetraphenylporphine-sensitized photooxygenation of (E,E)- and (E,Z)-1- aryl-1,3-pentadienes generating cis-endoperoxides

Article abstract of DOI:10.1021/jo981506r

Photooxygenation of either (E,E)- or (E,Z)-1-aryl-1,3-pentadienes (1a- c) sensitized with tetraphenylporphine (TPP) in benzene gave almost all cis- endoperoxides (2a-c) (cis-3-aryl-6-methyl-1,2-dioxacyclohex-4-enes) in good yields. A time course study of photooxygenation of (E,Z)-rich dienes measured by ¹H NMR showed that singlet oxygen added exclusively to (E,E)-dienes converted from (E,Z)-dienes by photoinduced isomerization, and both rates increased when electron-donating groups were attached to the aryl group. A concerted [4 + 2] cycloaddition mechanism is suggested by the exclusive formation of cis-endoperoxides from (E,E)-dienes, despite the small energy difference between cis- and trans-endoperoxides calculated by ab initio methods. Some experiments were made to explore the observed isomerization.

Full text of DOI:10.1021/jo981506r

J . Org. Chem. 1999, 64, 493-497
493
Tetr a p h en ylp or p h in e-Sen sitized P h otooxygen a tion of (E,E)- a n d
(E,Z)-1-Ar yl-1,3-p en ta d ien es Gen er a tin g cis-En d op er oxid es
J iro Motoyoshiya,* Yasuyuki Okuda, Ichiro Matsuoka, Sadao Hayashi,
Yutaka Takaguchi, and Hiromu Aoyama
Department of Chemistry, Faculty of Textile Science & Technology, Shinshu University,
Ueda, 386-8567, J apan
Received J uly 29, 1998
Photooxygenation of either (E,E)- or (E,Z)-1-aryl-1,3-pentadienes (1a -c) sensitized with tetraphe-
nylporphine (TPP) in benzene gave almost all cis-endoperoxides (2a -c) (cis-3-aryl-6-methyl-1,2-
dioxacyclohex-4-enes) in good yields. A time course study of photooxygenation of (E,Z)-rich dienes
measured by 1H NMR showed that singlet oxygen added exclusively to (E,E)-dienes converted from
(E,Z)-dienes by photoinduced isomerization, and both rates increased when electron-donating groups
were attached to the aryl group. A concerted [4 + 2] cycloaddition mechanism is suggested by the
exclusive formation of cis-endoperoxides from (E,E)-dienes, despite the small energy difference
between cis- and trans-endoperoxides calculated by ab initio methods. Some experiments were made
to explore the observed isomerization.
In tr od u ction
be stereospecific. Thus, cis- or trans-endoperoxide should
be generated from (E,E)-dienes or (E,Z)-dienes, respec-
tively. However, others report more complex stereochem-
istry. Gollnick et al.8 showed that while (E,E)-2,6-
hexadiene gave only cis-endoperoxide (cis-3,6-dimethy-
1,2-dioxacyclohex-4-ene) from reaction with singlet oxygen,
the (E,Z)-isomer also gave the cis-isomer predominantly.
Additionally, Foote et al.9 reported that a similar reaction
of (E,Z)-2,6-hexadienes was accompanied by isomeriza-
tion to form cis-endoperoxides via intermediate zwitte-
rions that could be trapped as methanol adducts. In
contrast, the photooxygenation behavior of dienes with
aromatic substituents is not well-documented, although
their endoperoxides have sometimes appeared in the
literature.10 Herein, we report that photooxygenation of
either (E,E)- or (E,Z)-4-aryl-1,3-pentadienes sensitized
with tetraphenylporphine (TPP) in benzene gave mainly
cis-endoperoxides (cis-3-aryl-6-methyl-1,2-dioxacyclohex-
4-enes). Also, photoisomerization of these aromatic dienes
occurred more readily than that of their aliphatic ana-
logues.
Photooxygenation of conjugated dienes generating en-
doperoxides (1,2-dioxacyclohex-4-enes) is an important
part of singlet oxygen chemistry,1 and its value is
increasing in organic synthesis2 because there are several
naturally occurring endoperoxides3 with biological activi-
ties, and endoperoxides can be used as the synthetic
intermediates for introduction of oxygen functionalities
to conjugated dienes.2 Despite many investigations into
the photooxygenation of aromatic systems or cyclic
dienes,1,4 relatively little attention has been paid to
acyclic conjugated dienes.5 Some examples of endoper-
oxide formation from acyclic dienes were documented by
Matsumoto et al.,6 in which a concerted Diels-Alder type
mechanism7 was suggested. If the addition proceeds via
a simple concerted mechanism, the cycloaddition should
(1) (a) Kearns, D. R. Chem. Rev. 1971, 71, 395. (b) Turro, N. J .
Modern Molecular Photochemistry; The Benjamin/Cummings Publish-
ing Co., Inc.: Reading, MA, 1978. Chapter 14. (c) Saito, I.; Matsuura,
T. Singlet Oxygen; Wassermann, H. H., Murray, R. W., Eds.; Academic
Press: New York, 1979; Chapter 10. (d) Frimer, A. A. Chem. Rev. 1979,
79, 359. (e) Saito, I.; Nittala, S. S. The chemistry of peroxides; Patai,
S., Ed.; J ohn Wiley & Sons: New York, 1983; Chapter 11.
(2) (a) Wassermann, H. H.; Ives, J . L. Tetrahedron 1981, 37, 1825.
(b) Suzuki, M.; Noyori, R. Tetrahedron Lett. 1981, 44, 4413. (c) Koo, S.
S.; Lerpiniere, J .; Linney, I. D.; Wrigglesworth, R. J . Chem. Soc., Chem.
Comunn. 1994, 1775 and ref 1.
(3) Repesentative naturally occurring endoperoxides: (i) Ascari-
dole: (a) Schenk. G. O.; Kinkel, K. G.; Mertens, H.-J . Liebigs Ann.
Chem. 1953, 584, 125. (ii) Prostagrandinendoperoxides, (b) Nicolaou,
K. C.; Gacic, G. P.; Barnette, W. E. Angew. Chem., Int. Ed. Engl. 1978,
17, 293. (iii) Qinghaosu: (c) Schmid, G.; Hofheinz, W. J . Am. Chem.
Soc. 1983, 105, 624. (d) Xu, X.; Zhu, J .; Huang, D.-Z.; Zhou, W.-S.
Tetrahedron 1986, 42, 819. (iv) Yingzhaosu C: (e) Zhang, L.; Zhau,
W.-S.; Xu, X.-X. J . Chem. Soc., Chem. Commun. 1988, 523. (f) Xu, X.-
X.; Dong, H.-Q. J . Org. Chem. 1995, 60, 3039.
Resu lts a n d Discu ssion
P h otooxygen a tion of Dien es a n d Str u ctu r a l As-
sign m en t of En d op er oxid es. The dienes 1a -c em-
ployed in this study were prepared from (E)-cinnamal-
dehydes by the Grignard reaction of methylmagnesium
iodide followed by acid-catalyzed dehydration or by the
salt free Wittig reaction.11 While the former preparation
gave (E,E)-rich 4-aryl-1,3-pentadienes, the latter led to
(E,Z)-rich dienes. The isomer ratios, E,Z/ E,Z ) 83/17 for
(E,E)-rich 1a and 16/84 for (E,Z)-rich 1a were determined
(4) (a) Denny, R. W.; Nickon, A. Org. React. 1973, 20, Chapter 2.
(b) Clennan, E. L.; Nagraba, K. J . Org. Chem. 1987, 52, 294 and ref 1.
(5) (a) Rio, G.; Berthelot, J . Bull. Soc. Chim. Fr. 1969, 1664. (b)
Kondo, K.; Matsumoto, M. J . Chem. Soc., Chem. Commun. 1972, 1332.
(c) Demole, E.; Demole, C.; Berthet, D. Helv. Chim. Acta. 1973, 56,
265. (d) Matsumoto, M.; Kondo, K. J . Org. Chem. 1975, 40, 2259. (e)
Matsumoto, M.; Kuroda, K. Tetrafedron Lett. 1982. 23, 1285. (f)
Clennan, E, L.; L′Esperace, R. P. J . Am. Chem. Soc. 1985, 107, 5178.
(6) Matsumoto, M.; Dobashi, S.; Kuroda, K.; Kondo, K. Tetrahedron
1985, 41, 2147.
(8) Gollnick, K.; Griesbeck, A. Tetrahedron Lett. 1983, 24, 3303.
(9) O’Shea, K. E.; Foote, C. S. J . Am. Chem. Soc. 1988, 110, 7167.
(10) (a) Takahashi, Y.; Wakamatsu, K.; Morishima, S.-I.; Miyashi,
T. J . Chem. Soc., Perkin Trans. 2 1993, 243. (b) Takahashi, Y.;
Morishima, S.; Wakamatsu, K.; Suzuki, T.; Miyashi, T. Chem. Com-
mun. 1994, 13.
(11) (a) Sholosser, M.; Christmann, K. F. Angew. Chem., Int. Ed.
Engl. 1965, 4, 689. (b) Shlosser, M.; Muller, G.; Christmann, K. F. 1966,
5, 667.
(7) Kearns, D. R. J . Am. Chem. Soc. 1969, 91, 6554.
10.1021/jo981506r CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/29/1998

494 J . Org. Chem., Vol. 64, No. 2, 1999
Motoyoshiya et al.
F igu r e 1. NOESY spectrum of 2a (400 MHz in CDCl3).
Sch em e 1
by comparing integration of the decoupled two-proton
signals in 1H NMR. Photooxygenation of the (E,E)- or
(E,Z)-rich 1a was performed in benzene in the presence
of TPP as a sensitizer at ambient temperature by
irradiation with a 100 W tungsten lamp. The reaction of
either (E,E)-rich or (E,Z)-rich 1a gave almost all cis-
endoperoxide (cis-3-methyl-6-phenyl-1,2-dioxacyclohex-
4-ene, 2a ) in good yield (74% from (E,E)-rich 1a and 84%
from (E,Z)-rich 1a ) (Scheme 1). A trace amount of trans-
isomer (cis/trans ) up to 3/25) was found in the photo-
lyzate of (E,E)-rich 1a . A simple [4 + 2] concerted
mechanism does not explain the exclusive formation of
cis-endoperoxide from (E,Z)-rich diene in a yield exceed-
ing the initial molar amount of the (E,E)-diene.
F igu r e 2. Structures of cis- and trans-endoperoxides opti-
mized by ab initio (6-31G*).
Ta ble 1. P h otooxygen a tion of Dien es 1a -ca
The structural assignment of the generated endoper-
oxide was based on the proton NMR spectrum. A NOE
experiment showing interaction between the methyl and
aromatic protons confirmed the stereochemistry of en-
doperoxide 2a (Figure 1). The cis-structure suggested by
the observed NOE was consistent with the structure
predicted by an ab initio SCF method (6-31G*), in which
the benzene ring was perpendicular to the 1,2-dioxacy-
clohexene ring and the distance between methyl and one
of the ortho-protons was estimated to be ca. 2.68 Å. In
trans-2a this distance is 5.75 Å (Figure 2). Only a slight
energy difference between both isomers was found in this
calculation (vide infra). In the isomeric mixture of 2a ,
the methyl signal of the cis-isomer was observed as a
doublet (δ 1.34) while that of the trans-isomer was seen
at δ 1.26. The allylic and benzylic protons of the cis-
isomer appeared as a quartet and singlet (δ 4.75 and
5.46), respectively, and that of the trans-isomer appeared
at δ 4.90 and 5.62, respectively. These NMR data agrees
dienes
R
E,E/E,Zb
endoperoxide
yield (%)c
1a
H
83/17
16/84
82/18
16/84
81/19
8/92
2a
73d
84
72
81
72
83
1b
1c
Me
2b
2c
OMe
a
TPP (tetraphenylporphorine) was used as a sensitizer in
benzene. Determined by 1H NMR (see text). c Yields after puri-
b
d
fication by column chromatography. Small amount of trans-
isomer was included.
with that reported for the photooxygenation products of
2,4-hexadienes.9
Dienes 1b and 1c having p-methyl or p-methoxy
substituents afforded only cis-endoperoxides 2b and 2c,
respectively when the solutions were irradiated under
the same conditions. The NOE’s between the methyl and
ortho-aromatic protons in the endoperoxides in 2b and

Tetraphenylporphine-Sensitized Photooxygenation
J . Org. Chem., Vol. 64, No. 2, 1999 495
Sch em e 2
2c afforded additional evidence for the cis-structure.
Table 1 summarizes the isomer ratios obtained in these
photooxygenation studies.
The exclusive formation of the cis-endoperoxides from
these aromatic dienes was unexpected based on previous
studies with aliphatic dienes.8,9 The energy difference
between cis- and trans-endoperoxides (2a ) was estimated
to be 0.01 kcal/mol by 3-21G* and 0.83 kcal/mol by
6-31G* by ab initio methods. These data suggest that
preferential formation of cis-endoperoxides is driven by
the photoisomerization of the (E,Z)-dienes to (E,E)-dienes
rather than the thermal stability of the product endop-
eroxides.
The cis-endoperoxide formation from dienes with ter-
minal aromatic substituents is potentially applicable to
the synthesis of a sesquiterpene peroxide, yingzhoasu
C,3e,f a component isolated from the root of yingzhao
Artabotrys unciatus (L.) Meer. Unfortunately, photooxy-
genation of (3E, 5E)-2-methyl-3-(4-methylphenyl)-3,5-
heptadien-4-ol (3) gave only the ene-product 4 in 45%
yield rather than the desired endoperoxide 5 (Scheme 2).
Tim e Cou r se Stu d y a n d Kin etics. Interconversion
of (E,Z)-rich dienes 1a -c to (E,E)-dienes and subsequent
formation to endoperoxides was monitored by proton
NMR (Figure 3). Initially, the concentration of the (E,Z)-
dienes decreased as the concentration of the (E,E)-dienes
increased. The (E,E)-dienes began to decrease as the
endoperoxides increased throughout the course of the
reaction. Thus, photooxygenation was accompanied by
photoisomerization of (E,Z)-dienes to (E,E)-dienes and
singlet oxygen added exclusively to the (E,E)-dienes to
give cis-endoperoxides.
F igu r e 3. Time course of photooxygenation of E,Z-rich diens
1a -c (measured by NMR). (b) (E,Z)-Diene; (9) (E,E)-diene;
(2) endoperoxide.
Sch em e 3
To estimate the relative rates of isomerization and
photocycloaddition, a qualitative kinetic study was car-
ried out. Assuming isomerization to be a preequilibrium
state prior to singlet oxygen addition, the formation of
endoperoxide can be generally described by Scheme 3 and
specified in eqs 1 and 2, where [1O2] represents singlet
oxygen.
Steady-state techniques suggest that singlet oxygen
generation is constant because d[1O2]/dt ) 0. Thus, eq 2
can be simplified to eq 3, where k2[1O2] ) k3.
d[E,E]
d[E,Z]
-
) -k1[E,Z] + k-1[E,E] + k3[E,E] (3)
dt
-
) k1[E,Z] - k-1[E,E]
(1)
dt
) -k1[E,Z] + k-1[E,E] + k2[E,E][1O2] (2)
d[E,E]
dt
As endoperoxide concentration [PO] increases, the
diene concentration decreases (eq 4).
-

496 J . Org. Chem., Vol. 64, No. 2, 1999
[PO] ) [E,Z]0 + [E,E]0 - [E,Z] - [E,E]
Motoyoshiya et al.
Ta ble 2. Rela tive Ra tios of Com p u ta tion a lly Estim a ted
Kin etic Con sta n ts in P h otooxygen a tion
(4)
diene
R
k1
k-1
k3
The relative ratios of k1, k-1, and k3 can be estimated
from the concentration values measured by 1H NMR
(Figure 3) and are listed in Table 2. The data showed
that k1 and k3 for 1b were slightly greater than k1 and
k3 for 1a . However, for 1c, these values were increased
by a factor of 2.5 compared to 1a . These relative rate
constants are comparable to those observed for the
fluorescence quenching of 9,10-dicyanoanthracene (DCA)
by 1,1-bis(4-methylphenyl)ethylene, 1,1-bis(4-methox-
yphenyl)ethene, and 1,1-diphenylethylene12 if this isomer-
ization involves an electron or charge transfer.13 These
observations are inconsistent with the substituent effect
on cis-trans isomerization of stilbene derivatives.14 The
electrophilic nature of singlet oxygen corroborates the
higher reactivity of 1b and 1c compared to 1a . The
exclusive formation of cis-endoperoxides from the (E,E)-
dienes produced by photoisomerization of the (E,Z)-dienes
suggests that the addition of singlet oxygen is a concerted
[4 + 2] cycloaddition process.6,15
Some experiments were made to explore how (E,Z)-
dienes were getting isomerized during the present pho-
tooxygenation.16 In the presence of singlet oxygen quench-
ers such as â-carotene and DABCO (1,4-diazabicyclo-
[2.2.2]octane), 1a underwent neither photoisomerization
nor photooxygenation. Detection of methanol adducts9,17
expected from zwitterionic intermediates is unsuccessful
at present. Chemically generated singlet oxygen from
(PhO)3P-O3 complex18 or hypochlorite-hydrogen perox-
ide19 partially led to isomerization of 1a , decreasing the
(E,Z)/(E,E) ratio of 86/14 to 60/40 and 62/38, respectively,
with loss of a certain amount of the diene. On the other
hand, quinonoid sensitizers such as rose bengal20 and a
heterocoerdianthrone21 having lower oxidation potentials
rapidly decreased the ratio to 20/80 and 22/78, respec-
tively, under a nitrogen atmosphere (for 1 h), but TPP
did not change the ratio for itself.22 No mechanistic
conclusion can be drawn from these experiments at
present but some comments can be given that rapid
photoinduced isomerization is induced in the presence
of both TPP and singlet oxygen or sensitizers with low
oxidation potentials. In addition to the previously docu-
mented mechanisms through zwitterionic intermedi-
ates9,17 or exciplex8 of singlet oxygen and diene, partici-
pation of a recently reported complex between singlet
oxygen and ground state TPP may be considered, which
is relatively long-lived and retains singlet oxygen and
1a
1b
1c
H
0.15
0.16
0.35
0.01
0.01
0.02
0.18
0.22
0.47
Me
OMe
charge-transfer character in benzene.23,24 This problem
is to be elucidated by further investigation.
Exp er im en ta l Section
1H NMR (90, 400, and 500 MHz) and 13C NMR (67.5 MHz)
spectra were recorded in CDCl3 as solvent and tetramethyl-
silane (TMS) as internal standard. Mass spectra were deter-
mined at an ionizing voltage of 70 eV. Column chromatography
was performed on silica gel (Wacogel C-200). The dienes 1a -c
were prepared according to the established methods. Thus,
(E,E)-rich dienes were obtained by acid-catalyzed dehydration
of 1-aryl-1-penten-3-ol, prepared from the Grignard reaction
of (E)-cinnamaldehydes and methylmagnesium iodide. On the
other hand, (E,Z)-rich dienes were prepared by the salt free
Wittig reaction
triphenylphosphorane. All dienes were purified by column
chromatography, and the ratios of E,Z/E,E were determined
by 1H NMR (90 MHz), comparing the integration of the
decoupled olefinic protons at C-4.
TP P -Sen sitized P h otooxygen a tion of Dien es. Photo-
oxygenation was done with a 100 W tungsten lamp under
bubbling oxygen for 15 h otherwise noted, and the reacting
solutions were kept at up to 30 °C cooling with a fan. After
irradiation of the solutions of the dienes (1a -c) (1.89-4.85
mmol) and TPP (1/20 mol toward the dienes) in 60-100 mL
of benzene, the solvent was removed by an evaporator, and
the residue was chromatographed using benzene, hexane/ethyl
acetate (5-2/1), and hexane/methanol/ether (10/1/0.1) as elu-
ants to give the endoperoxides 2a -c. The spectral data were
as follows;
11
of (E)-cinnamaldehydes with ethylidene-
cis-3-Meth yl-6-p h en yl-1,2-d ioxa cycloh ex-4-en e (2a ). 1H
NMR (500 MHz) δ 1.35 (d, 3H, CH3CH, J ) 6.7 Hz), 4.71-
4.75 (m, 1H, CH3CH), 5.46 (s, 1H, PhCH), 5.99-6.08 (m, 2H,
CH)CH), 7.32-7.39 (m, 5H, ArH). 13C NMR (125 Hz) δ 18.39
(CH3), 74.44 (C-3), 80.00 (C-6), 126.01 (C-4), 129.77 (C-5),
137.86 (arom C-1′). MS (m/z) 174[M+ - 2], 158(22), 144(36),
129(44), 115(13), 105(82), 77(87), 51(71), 43(100). These data
are somewhat different from those previously reported, which
may be due to a different solvent in 1H NMR or a different
ionizing voltage in mass spectrum.
cis-3-Meth yl-6-(4-m eth ylp h en yl)-1,2-d ioxa cycloh ex-4-
en e (2b). H NMR (400 MHz) δ 1.34 (d, 3H, CH3CH, J ) 6.7
1
Hz), 2.32 (s, 3H, ArCH3), 4.68-4.74 (m, 1H, CH3CH), 5.43 (s,
1H, aryl-CH), 5.99-6.06 (m, 2H, CHdCH), 7.15 and 7.26 (d,
4H, arom H, J ) 8.00 Hz). 13C NMR (125 Hz) δ 18.56 (CH3),
21.30 (CH3Ph), 74.51 (C-3), 79.93 (C-6), 126.28 (C-4), 129.78
(C-5), 134.93 (arom C-1′), 138.60 (arom C-4′). MS (m/z) 190-
[M+](1.5), 173(18), 158(32.2), 143(43), 119(100), 91(60), 65(34),
43(38).
(12) Gollnick, K.; Schnatterer, A.; Utschick, G. J . Org. Chem. 1993,
58, 6049.
(13) Wakamatsu, K.; Takahashi, K.; Kikuchi, K.; Miyashi, T. J .
Chem. Soc., Perkin Trans. 2 1996, 2105. Takahashi, Y.; Wakamatsu,
K.; Kikuchi, K.; Miyashi, T. J . Phys. Org. Chem. 1990, 3, 509.
(14) Gegiou, D.; Muszkat, K. A.; Fischer, E. J . Am. Chem. Soc. 1968,
90, 3907.
(15) Gollnick, K.; Griesbeck, A. Tetrahedron 1984, 40, 3235.
(16) Clennan, E. L.; Mehrsheikh-Mohammadi, M. E. J . Am. Chem.
Soc. 1984, 106, 7112.
(17) Manring, L. E.; Kanner, R. C.; Foote, C. S. J . Am. Chem. Soc.
1983, 105, 4707, 4710.
(18) Murray, R. W.; Kaplan, M. L. J . Am. Chem. Soc. 1969, 91. 5358.
(19) Foote, C. S.; Wexler, S.; Ando, W.; Higgins, R. J . Am. Chem.
Soc. 1968, 90, 975.
(20) (a) Hatsui, T.; Takeshita, H. J . Photochem. Photobiol. A: Chem.
1991, 57, 257. (b) Chem. Lett. 1993, 123.
cis-3-Meth yl-6-(4-m eth oxyp h en yl)-1,2-d ioxa cycloh ex-
4-en e (2c). 1H NMR (400 MHz) δ 1.36 (d, 3H, CH3CH, J )
6.7 Hz), 3.79 (s, 3H, CH3O), 4.70-4.75 (m, 1H, CH3CH), 5.44
(s, 1H, aryl-CH), 6.00-6.10 (m, 2H, CHdCH), 6.88 and 7.31
(d, 4H, ArH, J ) 8.7 Hz). 13C NMR (125 Hz) δ 18.49 (CH3),
55.20 (CH3O), 74.39 (C-3), 79.58 (C-6), 113.81 (arom C-2′),
126.19 (C-4), 129.72 (C-5), 129.78 (arom C-1′), 130.06 (arom
C-3′), 159.96 (arom C-4′). MS (m/z) 206[M+](5), 174(100), 159-
(49), 135(41), 77(31), 43(29).
2-Hydr oxy-2-m eth yl-5-h ydr oper oxy-6-(4-m eth ylph en yl)-
h ep ta -3,7-d ien e (4). 2-Methyl-3-(4-methylphenyl)-3,5-hepta-
dien-4-ol (3) was prepared in five steps. The Horner-
(21) Motoyoshiya, J .; Masunaga, T.; Harumoto, D.; Ishiguro, S.;
Narita, S.; Hayashi, S. Bull. Chem. Soc. J pn. 1993, 66, 1166.
(22) (a) Akasaka, T.; Ando, W. J . Am. Chem. Soc. 1987, 109, 1260.
(b) Mizuno, K.; Tamai, T.; Hashida, I.; Otsuji, Y.; Kuriyama, Y.;
Tokumaru, K. J . Org. Chem. 1994, 59, 7329.
(23) Tanielian, C.; Wolff, C. J . Phys. Chem. 1995, 99, 9825.
(24) Our attempts to obtain evidence of the electron transfer for TPP-
1O2 in benzene using 1,1-dianisylethylene as
a
probe have been
unsuccessful. Mattes, S.; Farid, S. J . Am. Chem. Soc. 1986, 108, 7356.

Tetraphenylporphine-Sensitized Photooxygenation
J . Org. Chem., Vol. 64, No. 2, 1999 497
Wadsworth-Emmons (HWE) reaction of p-tolualdehyde and
triethyl phosphonoacetate in the presence of sodium hydride
in THF gave ethyl 3-(4-methylphenyl)crotonate in 86% yield
as a geometrical mixture (E/Z ) 5/1). Reduction of this ester
with LiAlH4 in THF followed by oxidation with manganese
oxide in petroleum ether afforded 3-(4-methylphenyl)-2-butenal
in 51% yield. The HWE reaction of this aldehyde with triethyl
phosphonoacetate in the similar manner described above gave
1-carbethoxy-4-methyl-4-(4-methylphenyl)-1,3-butadiene in 93%
yield, whose reaction with 2 equiv of methyllithium in ether
furnished 3 in 95% yield. 3: 1H NMR (500 MHz) δ 1.37 (s,
6H, C(CH3)2OH), 1.85 (brs, 1H, C(CH3)2OH), 2.15 (s, 3H,
ArCH3), 2.32 (s, 3H, 5.91 (d, 1H, CdCHC(CH3)2OH, J ) 15.2
Hz), 6.40 (d, 1H, (CH3)CdCHCH, J ) 10.9 Hz), 6.63 (dd, 1H,
(CH3)CdCHCH)CH, J ) 15.2, 10.9 Hz), 7.10-7.33 (m, 4H,
ArH).
Photooxygenation of this diene (0.6 g, 12.5 mmol) was done
in a similar manner described above using 1/20 equiv of TPP
toward 3. After 13 h irradiation, solvent was removed under
reduced pressure, and the residue was chromatographed using
benzene, n-hexane/ethyl acetate (4/1), ethyl acetate as eluants.
The ene product 4 was obtained as a colorless liquid (0.29 g,
45%). 4: 1H NMR (500 MHz) δ 1.27 (two s, 6H, C(CH3)2OH),
1.39 (s, 1H, C(CH3)2OH), 2.33 (s, 3H, ArCH3), 5.26 (d, 1H, d
CHCH(OOH)C(Ar)d, J ) 7.1 Hz), 5.35 and 5.50 (s, 1H, CH2d
C(Ar)), 5.74 (dd, 1H, CH)CHC(CH3)2OH, J ) 7.1, 15.7 Hz),
6.29 (d, 1H, CHdCHC(CH3)2OH, J ) 15.7 Hz), 7.12, 7.31 (d,
4H, ArH, J ) 8.0 Hz). 13C NMR (125 Hz) δ 21.10 (ArCH3),
29.32, 29.53 (CH3-1,2), 70.83 (C-2), 87.38 (C-5), 115.49 (C-7),
123.62 (C-4), 126.67, 128.34, 129.03, 136.30, 137.61, 143.52,
145.90 (aromatic C and C-6).
Qu a lita tive Kin etic Stu d y. A mixture of 1a (0.75 g, 5.2
mmol) and TPP (0.16 g, 0.26 mmol) in benzene (100 mL) was
irradiated by 100 W tungsten lamp as described above. After
every stated time, 10 mL of the solution was removed and
concentrated. The ratios of (E,Z)/(E,E) were determined by 90
MHz 1H NMR in CDCl3 and plotted as shown in Figure 3. The
simultaneous eqs 1, 3, and 4 were computationally solved using
Mathematica (2.0.3) program (Wolfram Research), and the
relative concentration values obtained as above were adapted
to estimate the relative ratios of k1, k-1, and k3.
Ack n ow led gm en t. The authors thank Professor
Ryozo Irie (Faculty of Agriculture, Shinshu University)
for the measurements of 1H (400 and 500 MHz) and 13C
NMR spectrum and Associate Professor Tomoshige
Kobayashi (Faculty of Science, Shinshu University) for
the measurement of mass spectra. This work was
partially supported by Grant-in-Aid for COE Research
(10CE2003) by the Ministry of Education, Science,
Sports and Culture of J apan.
Su p p or tin g In for m a tion Ava ila ble: Copies of the 1H and
13C NMR spectra of compounds 2a -c, 3, and 4 (12 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O981506R