Novel [2 + 2] photocycloaddition-induced rearrangement of bichromophoric naphthalene-tethered resorcinol ethers

Article abstract of DOI:10.1021/jo011143m

The first examples of sequential photocycloaddition-rearrangement reactions of naphthalenetethered resorcinol ethers are described. Bichromophoric aromatic compounds with naphthalene and resorcinol ether moieties were irradiated in the presence/absence of a small amount of acid to give the corresponding cycloaddition-rearrangement products. From the determination of quantum yields, steady-state fluorescence spectral studies, and fluorescence lifetime measurements, the mechanism of this novel photoinduced multistep reaction was elucidated to involve the initial intramolecular exciplex formation, followed by the intramolecular [2 + 2] photocycloaddition between the two aromatic rings and the subsequent acid-catalyzed skeletal rearrangement of the resulting cyclobutane derivative leading to the final products.

Full text of DOI:10.1021/jo011143m

J . Org. Chem. 2002, 67, 2315-2322
2315
Novel [2 + 2] P h otocycloa d d ition -In d u ced Rea r r a n gem en t of
Bich r om op h or ic Na p h th a len e-Teth er ed Resor cin ol Eth er s
Norbert Hoffmann* and J ean-Pierre Pete
Laboratoire des Re´actions Se´lectives et Applications,UMR CNRS et Universite´ de Reims
Champagne-Ardenne, UFR Sciences, B.P. 1039, F-51687 REIMS, Cedex 2, France
Yoshihisa Inoue* and Tadashi Mori*
Photochirogenesis Project, ERATO, J ST andDepartment of Molecular Chemistry, Osaka University,
2-1 Yamada-oka, Suita 565-0871, J apan
norbert.hoffmann@univ-reims.fr
Received December 13, 2001
The first examples of sequential photocycloaddition-rearrangement reactions of naphthalene-
tethered resorcinol ethers are described. Bichromophoric aromatic compounds with naphthalene
and resorcinol ether moieties were irradiated in the presence/absence of a small amount of acid to
give the corresponding cycloaddition-rearrangement products. From the determination of quantum
yields, steady-state fluorescence spectral studies, and fluorescence lifetime measurements, the
mechanism of this novel photoinduced multistep reaction was elucidated to involve the initial
intramolecular exciplex formation, followed by the intramolecular [2 + 2] photocycloaddition between
the two aromatic rings and the subsequent acid-catalyzed skeletal rearrangement of the resulting
cyclobutane derivative leading to the final products.
In tr od u ction
the [2 + 2] cycloaddition products were not always fully
characterized in earlier studies, simply because they were
obtained as a complex mixture. Hence, it is not unrea-
sonable that only recently people have recognized explic-
itly that the [2 + 2], as well as [3 + 2], cycloadditions
are much more abundantly occurring photoreactions
upon irradiation of arene with olefin.4
Earlier theoretical investigations predicted that polar
transition states of similar structures are involved in both
[2 + 2] and [3 + 2] photocycloadditions of alkenes to
electronically excited benzene derivatives.5 However, a
more recent theoretical study6 indicated the intervention
of nonpolar diradical intermediates rather than polar
Photocycloadditions of aromatic compounds to olefins
have been studied extensively, since these reactions
provide us with a convenient direct access to various
polyfunctionalized compounds in a single step.1 Among
them, the meta-arene photoaddition to olefin, giving rise
to [3 + 2] cycloadducts, is reported amply in the litera-
ture.2 It is also known that, depending on the substitution
pattern and/or redox potentials of relevant arene and
olefin, the major photochemical route can be switched to
[2 + 2] cycloaddition or less frequently to [4 + 2]
cycloaddition.3 However, especially in the absence of
electron-withdrawing substituents on the aromatic ring,
(3) (a) Bryce-Smith, D.; Gilbert, A.; Orger, B.; Tyrrell, H. J . Chem.
Soc., Chem. Commun. 1974, 334-336. (b) Leismann, H.; Mattay, J .;
Scharf, H. D. J . Am. Chem. Soc. 1984, 106, 3985-3991. (c) Mattay, J .;
Runsink, J .; Gersdorf, J .; Rumbach, T.; Ly, C. Helv. Chim. Acta 1986,
69, 442-455. (d) Mu¨ller, F.; Mattay, J . Chem. Rev. 1993, 93, 99-117.
(4) (a) V´ızva´rdi, K.; Toppet, S.; Hoonaert, G. J .; De Keukeleire, D.;
Bako´, P.; Van der Eycken, E. J . Photochem. Photobiol. A: Chem. 2000,
133, 135-146. (b) Van der Eycken, E.; De Keukeleire, D.; De Bruyn,
A. Tetrahedron Lett. 1995, 36, 3573-3576. (c) De Keukeleire, D.
Aldrichim. Acta 1994, 27, 59-69. (d) De Keukeleire, D.; He, S.-L.;
Blakemore, D.; Gilbert, A. J . Photochem. Photobiol. A.: Chem. 1994,
80, 233-240. (e) Gilbert, A.; Taylor, G. N.; bin Samsudin, M. W. J .
Chem. Soc., Perkin Trans. 1 1980, 869-876. (f) Mattay, J .; Leismann,
H.; Scharf, H. D. Chem. Ber. 1979, 112, 577-599. (g) Kishikawa, K.;
Akimoto, S.; Kohmoto, S.; Yamamoto, M.; Yamada, K. J . Chem. Soc.,
Perkin Trans. 1 1997, 77-84. (h) Mani, J .; Schu¨ttel, S.; Zhang, C.;
Bigler, P.; Mu¨ller, C.; Keese, R. Helv. Chim. Acta 1989, 72, 487-495.
(i) Cornelisse, J .; de Haan, R. In Molecular and Supramolecular
Photochemistry; Ramamurthy, V., Schanze, K. S., Eds.; Marcel Dek-
ker: New York, 2001, Vol. 8, pp 1-126. (j) Wagner, P. J . Acc. Chem.
Res. 2001, 34, 1-8. (k) De Keukeleire, D.; He, S.-L. Chem. Rev. 1993,
93, 359-380.
(5) (a) Bryce-Smith, D.; Gilbert, A. Tetrahedron 1976, 32, 1309-
1326. (b) Bryce-Smith, D.; Gilbert, A. Tetrahedron 1977, 33, 2459-
2490. (c) Houk, K. N. Pure Appl. Chem. 1982, 54, 1633-1650. (d) van
der Hart, J . A.; Mulder, J . J . C.; Cornelisse, J . THEOCHEM 1987,
151, 1-10. (e) van der Hart, J . A.; Mulder, J . J . C.; Cornelisse, J . J .
Photochem. Photobiol. A: Chem. 1991, 61, 3-13. (f) Stehouwer, A. M.;
van der Hart, J . A.; Mulder, J . J . C.; Cornelisse, J . THEOCHEM 1992,
92, 333-338. (g) van der Hart, J . A.; Mulder, J . J . C.; Cornelisse, J . J .
Photochem. Photobiol. A: Chem. 1995, 86, 141-148.
* To whom correspondence should be addressed. (N.H.) Fax: +33
(0)3 26 91 31 66. Y.I., T.M.) Fax: +81 (0)6 68 79 79 23. E-mail:
tmori@ap.chem.eng.osaka-u.ac.jp.
(1) (a) Barentsen, H. M.; Talman, E. G.; Piet, D. P.; Cornelisse, J .
Tetrahedron 1995, 51, 7469-7494. (b) Barentsen, H. M.; Sieval, A. B.;
Cornelisse, J . Tetrahedron 1995, 51, 7495-7520. (c) Van der Eycken,
E.; De Keukeleire, D.; De Bruyn, A.; Van der Eycken, J .; Gilbert, A.
Recl. Trav. Pays-Bas 1995, 114, 480-482. (d) Blakemore, D. C.; Gilbert,
A. Tetrahedron Lett. 1994, 35, 5267-5270. (e) Blakemore, D. C.;
Gilbert, A. Tetrahedron Lett. 1995, 36, 2307-2310. (f) Amey, D. M.;
Gilbert, A.; J ones, D. T. J . Chem. Soc., Perkin Trans. 2 1998, 213-218.
(g) Weber, G.; Runsink, J .; Mattay, J . J . Chem. Soc., Perkin Trans. 1
1987, 2333-2338. (h) Mattay, J .; Rumbach, T.; Runsink, J . J . Org.
Chem. 1990, 55, 5691-5696. (i) Wender, P. A.; Dore, T. M.; de Long,
M. A. Tetrahedron Lett. 1996, 37, 7687-7690. (j) Wender, P. A.; Dore,
T. M. Tetrahedron Lett. 1998, 39, 8589-8592. (k) Zhang, C.; Bourgin,
D. Keese, R. Tetrahedron 1991, 47, 3059-3074. (l) Baralotto, C.;
Chanon, M.; J ulliard, M. J . Org. Chem. 1996, 61, 3576-3577. (m)
Avent, A. G.; Bryne, P. W.; Penkett, C. S. Org. Lett. 1999, 1, 2073-
2075. (n) Wender, P. A.; Ternansky, R.; deLong, M.; Singh, S.; Olivero,
A.; Rice, K. Pure Appl. Chem. 1990, 62, 1597-1602. (o) Wender, P. A.,
Siggel, L.; Nuss, J . M. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Paquette, L. A., Eds.; Pergamon Press: Oxford, 1991;
Vol. 5, p 645-673. (p) Wender, P. A., Siggel, L.; Nuss, J . M. In Organic
Photochemistry; Padwa, A., Ed.; Marcel Dekker: New York, 1989; Vol.
10, pp 357-473. (q) Wender, P. A.; Dore, T. M. In CRC Handbook of
Photochemistry and Photobiology; Horspool, W. M., Song, P.-S., Eds.;
CRC Press: Boca Raton, 1995; pp 280-290.
(2) Cornelisse, J . Chem. Rev. 1993, 93, 615-669.
10.1021/jo011143m CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/13/2002

2316 J . Org. Chem., Vol. 67, No. 7, 2002
Hoffmann et al.
Sch em e 1. P h otoch em ica l Rea ction s of
transition states but, unfortunately, could not make a
plausible prediction about the competition between the
branching two [2 + 2] and [3 + 2] cycloaddition pathways.
Recently, we have demonstrated that the efficiency and
product yield of such photocycloaddition reactions of
various arenes can be enhanced dramatically by adding
a small amount of acid to the system.7 We have also
reported the intramolecular photocycloaddition reactions
of several bichromophoric aromatic compounds, all of
which possess an olefinic side chain tethered through an
ether linkage to salicylic ester,8 3,5-dihydroxybenzo-
nitrile,9 3,5-dihydroxybenzoic acid,9,10 and resorcinol and
1,2,4-trihydroxyphenol.11,12 It is noted that most of these
substrates do not show any appreciable photoreactivity
upon irradiation in neutral acetonitrile or methanol.
In sharp contrast, irradiation of resorcinol derivative
1 in acidic methanol afforded benzocyclobutenes 3a ,b and
rearrangement product 4 in good quantum and chemical
yields (Scheme 1).11 Upon irradiation of dimethyl ana-
logue 2 under identical conditions, only the rearrange-
ment products 5-7 were obtained. From the examina-
tions of the relevant electronic absorption and fluorescence
spectra in the presence/absence of acid, we proposed the
sequential photocycloaddition/acid-catalyzed rearrange-
ment mechanism illustrated in Scheme 1 for these
photoinduced reactions. In this mechanism, the initial
[2 + 2] cycloaddition process is believed to be photo-
reversible at the excitation wavelength employed (λ )
254 nm) and therefore be nonproductive in the neutral
media. However, in the acidic media, the photolabile
cycloadducts is readily protonated to give oxonium in-
termediates A and A′, which in turn suffer the ring-
opening of the tetrahydrofuran ring and/or the simulta-
neous alkyl shift to give 3a ,b and 4, the latter being
produced via the spiro cyclohexadienyl cation B. In the
case of 2, the acid-catalyzed ring opening of intermediates
A and A′ gives rise to stable tertiary carbenium ion C,
which is either trapped by the intramolecular hydroxyl
group or intermolecularly by solvent methanol or alter-
natively deprotonated to give products 5, 6, and 7,
respectively.
Resor cin ol Der iva tives P ossessin g a n Olefin ic Sid e
Ch a in in Meth a n ol a n d in th e P r esen ce of Acid 11
that the olefin moiety can be replaced by a naphthalene
chromophore. It is well documented that naphthalene
derivatives undergo [2 + 2] photocycloaddition with a
variety of olefins, but similar photoreactions between
naphthalene and benzene chromophores have never been
reported in the literature.13,14 In the present study, we
wish to elucidate the photochemical reactivity of resor-
cinol and 1,2,4-trihydroxybenzene derivatives carrying
a naphthyl substituent and the detailed reaction mech-
anisms in the presence/absence of acid.
Resu lts a n d Discu ssion
In our further attempts to expand the scope of this
useful intramolecular arenic photocycloaddition, we found
P h otor ea ction . When naphthalene-tethered resorci-
nol 8 (10 mM) was irradiated at λ ) 254 nm in neutral
acetonitrile, no appreciable decrease of the substrate was
detected upon gas chromatographic examination of the
irradiated solution. However, in the presence of sulfuric
acid (6 mM) added to the sample solution, the substrate
was smoothly consumed under the identical irradiation
conditions to give two photoproducts 10 and 11 in good
yields (Scheme 2), which were isolated from the solution
(6) Clifford, S.; Bearpark, M. J .; Bernardi, F.; Olivucci, M.; Robb,
M. A.; Smith, B. R. J . Am. Chem. Soc. 1996, 118, 7353-7360.
(7) Recently, such an important effect of acid on various photo-
reactions has been recognized. For other examples, see: (a) Kalena,
G. P.; Pradhan, P.; Banerji, A. Tetrahedron Lett. 1992, 55, 7775-7778.
(b) Kalena, G. P.; Pradhan, P.; Banerji, A. Tetrahedron 1999, 55, 3209-
3218. (c) Ohkura, K.; Kanazashi, N.; Seki, K. Chem. Pharm. Bull. 1993,
41, 239-243. (d) Ohkura, K.; Seki, K.; Hiramatsu, H.; Aoe; K.;
Terashima, M. Heterocycles 1997, 44, 467-478. (e) Ohkura, K.;
Noguchi, Y.; Seki, K. Heterocycles 1998, 47, 429-437. (f) Howell, N.;
Pincock, J . A.; Stefanova, R. J . Org. Chem. 2000, 65, 6173-6178. (g)
Matohara, K.; Lim, C.; Yasutake, M.; Nogita, R.; Koga, T.; Sakamoto,
Y.; Shinmyozu, T. Tetrahedron Lett. 2000, 41, 6803-6807. (h) Mallory,
F. B.; Mallory, C. W. Organic Reactions 1983, 30, p 1-456. (i) Ho, T.-
I.; Ho, J .-H.; Wu, J . Y. J . Am. Chem. Soc. 2000, 122, 8575-8576. (j)
Ho, J .-H.; Ho, T.-I.; Liu, R. S. H. Org. Lett. 2001, 3, 409-411. (k)
Schultz, A. G.; Antoulinakis J . Am. Chem. Soc. 1996, 61, 4555-4559.
(l) Chow, Y. L.; Liu, X. Can. J . Chem. 1991, 69, 1261-1272. (m) Mori,
T.; Wada, T.; Inoue, Y. Org. Lett. 2000, 2, 3401-3404. (n) Mori, T.;
Takamoto, M.; Tate, Y.; Shinkuma, J .; Wada, T.; Inoue, Y. Tetrahedron
Lett. 2001, 42, 2505-2508.
(13) (a) De Schryver, F. C.; Boens, N.; Put, J . In Advances in
Photochemistry; Pitts, J . N., J r., Hammond, G. S., Gollnick, K., Eds.;
J ohn Wiley: New York, 1977; Vol. 10, pp 359-463. (b) Davidson, R.
S. In Advances in Physical Organic Chemistry; Gold, V., Bethell, D.,
Eds.; Academic Press: London, 1983; Vol. 19, p 1-130.
(14) (a) McCullough, J . J . Chem. Rev. 1987, 87, 811-860. (b) Do¨pp,
D.; Memarian, H. R.; Kru¨ger, C.; Raabe, E. Chem. Ber. 1989, 122, 585-
588. (c) Do¨pp, D.; Memarian, H. R. Chem. Ber. 1990, 123, 315-319.
(d) Do¨pp, D.; Erian, A. W.; Henkel, G. Chem. Ber. 1993, 126, 239-
242. Lanfermann, H.; Do¨pp, D. J . Inform. Rec. Mat. 1994, 21, 545-
547. (e) Memarian, H. R.; Nasr-Esfahani, M.; Boese, R.; Do¨pp, D.
Liebigs Ann./ Receuil 1997, 1023-1027. (f) Memarian, H. R.; Nasr-
Esfahani, M.; Do¨pp, D. New J . Chem. 2001, 25, 476-478. (g) Al-J alal,
N. A. J . Chem. Res., Synop. 1995, 44. (h) Al-J alal, N. A.; Prichard, R.
G.; McAuliffe, C. A. J . Chem. Res., Synop. 1994, 452. (i) Mizuno, K.;
Konishi, S.; Yoshimi, Y.; Sugimoto, A. Chem. Commun. 1998, 1659-
1660. (j) Yokohama, A.; Mizuno, K. Org. Lett. 2000, 2, 3457-3459. (k)
Wagner, P. J ., Sakamoto, M. J . Am. Chem. Soc. 1989, 111, 9254-9256.
(l) Noh, T.; Kim, D.; Kim, Y.-J . J . Org. Chem. 1998, 63, 1212-1216.
(8) Hoffmann, N.; Pete, J . P. Tetrahedron Lett. 1995, 36, 2623-2326.
(9) Hoffmann, N.; Pete, J . P. Synthesis 2001, 1236.
(10) Hoffmann, N.; Pete, J . P. Tetrahedron Lett. 1998, 39, 5027-
5030.
(11) Hoffmann, N.; Pete, J . P. J . Org. Chem. 1997, 62, 6952-6960.
(12) (a) Hoffmann, N.; Pete, J . P. Tetrahedron Lett. 1996, 37, 2027-
2030. (b) Verrat, C.; Hoffmann, N.; Pete, J . P. Synlett 2000, 1166-
1168.

Bichromophoric Naphthalene-Tethered Resorcinol Ethers
J . Org. Chem., Vol. 67, No. 7, 2002 2317
Sch em e 2. P h otoch em ica l Rea ction s of Bich r om op h or ic Ar om a tic Com p ou n d s P ossessin g a Na p h th yl a n d
a Resor cin ol Moiety
Ta ble 1. Qu a n tu m Yield s (Φ) for th e F or m a tion of 3-7, 10, a n d 12 (See Sch em es 1 a n d 2)
Φ
substrate
solvent
[H2SO4], M
3
4
5
6
7
10
12
1
2
8
9
9
9
9
MeOH
MeOH
MeCN
MeCN
MeOH
MeCN
MeOH
6 × 10-3
6 × 10-3
6 × 10-3
0
0.1
0.03
0.075
0.065
0.07
0.20
0.004
0.02
0.14
0.13
0
6 × 10-3
6 × 10-3
Sch em e 3. P h otoch em ica l Rea ction of P r im a r y
P h otop r od u cts 10 a n d 11a
irradiated for 3 h. The quantum yield (Φ) of 10 (Φ of 10
and 11 are combined, since 11 is derived photochemically
from 10, as described below), determined by using a
conventional chemical actinometer, was fairly high (Φ
) 0.20).15 This value is comparable to those reported for
the photocycloaddition of 1 and 2 (Table 1). However, it
turned out that the irradiation in acetonitrile or in
methanol is difficult to perform at higher substrate
concentrations due to the low solubility of 8. Hence, we
have prepared the methoxyethyl ether 9 for the purpose
of more detailed study on photobehavior of bichro-
mophoric naphthalene-tethered resorcinol derivatives.
In the presence of acid, irradiation of 9 afforded three
products 12-14 in good combined yields (ca. 60%) in both
methanol and acetonitrile. The quantum yield of product
12 was almost the same (Φ ) 0.13-0.14) in the two
solvents (Table 1). In neutral media, only a slow, but
steady, consumption of 9 was observed with an ac-
companying formation of 12 in a low quantum yield
(Φ ) 0.004-0.02, depending on the solvent used).
a
Yields are given on the basis of transformed starting material.
To clarify whether all of the obtained products are
derived directly from 8 and 9 or in secondary photore-
action(s) of the primary product, the major products 10
and 12 were irradiated in neutral acetonitrile to give 11
and 13, respectively, in good (40-50%) yields (Scheme
3). However, the quantum yields of 11 and 13 were low
(Φ ) 0.01-0.02) and independent of the acidity of the
reaction media. The formation of 11 and 13 was rather
surprising, since it requires a loss of C2H4O fragment
from the tetrahydrofuran ring fused to dihydronaphtha-
lene. Apart from the cheletropic elimination of molecules
such as N2, CO, CO2, and SO2 and elimination of
anhydrides (in the case of ozonides), photochemical
extrusion reactions from five-membered ring compounds
are rare in the literature.16 The positive result of the
purpal test17 clearly indicates the formation of acetalde-
hyde upon irradiation of 10 and 12.
Upon heating in acidic acetonitrile in the dark (82 °C,
[H2SO4] ) 6 mM), 10 and 12 rearranged to 14 and 15,
respectively, in excellent yields (Scheme 4). These prod-
ucts were not found in appreciable amounts at least in
the early stages of the photolyses of 8 and 9 and also
(16) (a) Grivens, R. R. Organic Photochemistry; Padwa, A., Ed.;
Marcel Dekker: New York, 1981; Vol. 5, pp 227-346. (b) Criegee, R.
Chimia 1968, 22, 392-396.
(17) (a) Dickinson, R. G.; J acobsen, N. W. Chem. Commun. 1970,
1719-1720. (b) Hopps, H. B. Aldrichim. Acta 2000, 33, 28-30. Further
studies concerning this reaction will be carried out.
(15) Numao, N.; Hamada, T.; Yonemitsu, O. Tetrahedron Lett. 1977,
1661-1664.

2318 J . Org. Chem., Vol. 67, No. 7, 2002
Hoffmann et al.
Sch em e 4. Acid -Ca ta lyzed Th er m a l
Rea r r a n gem en ts of 10 a n d 11
study unambiguously demonstrates that the olefinic
moiety of 1 and 2 can be replaced by a naphthalene ring
without damaging the photoreactivity for [2 + 2] cyclo-
addition. Interestingly, even in the absence of acid, the
substrate 9 undergoes the photocycloaddition and sub-
sequent rearrangement in low quantum yield (Table 1),
which would be rationalized by the ligating stabilization
of the protonated intermediate E by the adjacent meth-
oxyethyl group.
In the case of olefin-tethered resorcinol substrates
reported earlier,11 an elongated tether or further alkoxy-
lation of the resorcinol moiety did not spoil the photo-
cycloaddition reaction. In the present study, we also
prepared the corresponding naphthyl derivatives 16 (with
an extra methylene in the tether) and 17 (with an
additional methoxy group) (Chart 1), which were irradi-
ated under the identical conditions to exhibit no ap-
preciable photoreactivity. Furthermore, the anisyl-
naphthoxy analogue 18, an isomer of 8, also failed to give
any photocycloadducts. These results clearly indicate that
the photocycloaddition of naphthalene-tethered resorcinol
is highly intolerable to the structural alterations at the
tether or aromatic rings, and is specific to such com-
pounds as 8 and 9.
F lu or escen ce a n d Mech a n istic Stu d ies. To eluci-
date the origin of such a very strict structural require-
ment for photocycloaddition, we comparatively investi-
gated the excited-state interactions of these reactive and
nonreactive bichromophoric systems through the mea-
surements of fluorescence spectra and lifetimes in various
solvents. The results are summarized in Table 2. As
already reported in the previous study,11 compounds 1
and 2 showed exactly the same tendency as the reference
compound m-dimethoxybenzene (20). Thus, slightly shorter
lifetimes were obtained in MeOH than in MeCN, and the
addition of sulfuric acid (0.1 M) shortened the lifetimes
by 0.1-0.2 ns. It is interesting to note that the lifetimes
of 1 in MeCN and MeOH (with and without acid) are the
same as the respective lifetimes of 20 within the experi-
mental error (ca. 0.1 ns), but the relevant values for 2
are appreciably shorter by 0.2-0.4 ns than those for 1
or 20. This clearly indicates that the olefinic moiety of 1
does not interact with the aromatic moiety, whereas there
must be some electronic interaction between the two
moieties of 2 in the excited state, although no emission
attributable to the intramolecular exciplex was observed
at longer wavelengths. The apparently trivial, but con-
sistent, decreases by 0.1-0.2 ns in the fluorescence
lifetime of 1, 2, and 20 in the presence of sulfuric acid
presumably support some interaction of acid with the
fluorophore. This is also consistent with the slight
upon photolyses of 10 and 12. The formation of 14 and
15 is reasonably accounted for in terms of the acid-
catalyzed thermal isomerization of 10 and 12, respec-
tively, through spirocyclohexadienyl intermediate D, a
homologue of intermediate B in Scheme 1.
Previously, we proposed the mechanism outlined in
Scheme 1 for the photochemical transformation of olefin-
tethered resorcinols 1 and 2.11 In analogy, the formation
of the primary photoproducts 10 and 12 are well inter-
preted by the mechanism depicted in Scheme 5. In this
mechanism, the initial [2 + 2] photocycloaddition be-
tween the naphthalene to benzene rings and the subse-
quent protonation to the cycloadduct produced affords
intermediate E, which in turn suffers successive ring
opening to intermediate F and intramolecular trapping
by the hydroxyl group, leading to the final product. From
the fluorescence spectral examinations described below,
it was revealed that an exciplex intervenes as a key
intermediate in this photocycloaddition reaction and both
exciplex and cycloadducts could be trapped by proton in
the presence of acid leading to the efficient formation of
intermediate E.
To the best of our knowledge, photochemical cycload-
dition between naphthalene and benzene rings has never
been reported in the literature. However, the present
Sch em e 5. P r op osed Mech a n ism for th e P h otoch em ica l Rea ction of 8 a n d 9

Bichromophoric Naphthalene-Tethered Resorcinol Ethers
Ch a r t 1
J . Org. Chem., Vol. 67, No. 7, 2002 2319
decrease (5-15%) in the (steady-state) fluorescence in-
tensity reported previously.11
In the case of 8 and 9, added acid enhances the
quenching of naphthalene fluorescence and the formation
of product. In this context, it is noted that photochemi-
cally unreactive 16 exhibits completely different fluores-
cence behavior. Possessing a resorcinol moiety connected
with a longer tether, 16 gives the fluorescence lifetimes
around 13 ns, which are comparable to those observed
for reference 22 (12-13 ns) and are totally insensitive
to the solvent or acidity change. These observations
immediately mean that no excited-state interaction exists
between the naphthalene and resorcinol moieties. Prob-
ably, the “rule of three” upon exciplex formation, which
is abundantly exemplified in the literature, is very
strictly applied in the present case and hinders the
desirable approach of the naphthalene and resorcinol
moieties in 16.13,19
Among the naphthalene derivatives employed in this
study (8, 9, 16-18), only 8 and 9 undergo efficient
photocycloaddition in the presence and even in the
absence (in the case of 9) of added acid, while the
analogues 16-18 are completely unreactive photochemi-
cally. It is therefore intriguing and crucial to compare
the fluorescence behavior of these compounds. Although
naphthalene derivatives are known in general to be
highly fluorescent and frequently form exciplexes,13,18 no
appreciable fluorescence from exciplex was detected with
most of the present substrates, except for 17, which gave
very strong exciplex fluorescence and much smaller (by
a factor of 20-50:1) monomer fluorescence. Fluorescence
lifetime of the reference compound 22, excited at 280 nm,
was not significantly affected by changing solvent or by
adding 0.1 M sulfuric acid. This seems reasonable since
the fluorescing naphthyl group is electronically isolated
from the ether oxygen that would be solvated in methanol
or protonated in highly acidic media. In contrast, com-
pound 8 gave fairly shorter lifetimes of 8.9 and 9.6 ns in
neutral acetonitrile and methanol than those obtained
for 22 (12.2 and 12.5 ns, respectively), which is reason-
ably attributed to the intramolecular quenching of the
excited naphthyl by the anisyloxy group probably through
the charge-transfer interactions. The yet shorter lifetime
(8.0 ns) of 8 in acidic methanol may be ascribed to the
equilibrium shift caused by protonation to the initial
photoadduct giving intermediate E. The excitation of 8
at 230 nm, which leads to an increased excitation of the
ansyloxy chromophore, provides us with further informa-
tion about the excited-state interaction of the two teth-
ered chromophores. Upon excitation at 230 nm, both
chromophores are competitively activated and the fluo-
rescence decay profile becomes double-exponential, giving
short and long lifetimes of varying contributions shown
in parentheses of Table 2.
However, no photoproduct is formed upon irradiation
of 18, although the “rule of three” does not formally
prohibit an association of the two chromophores in 18.
The fluorescence lifetimes of 18 (7-8 ns) in neutral media
are much shorter than those of reference 22 (12-13 ns)
and are sensitive to added acid to give a yet shorter
lifetime of 5 ns in acidic methanol. These results are not
unexpected, as the alkoxynaphthalene chromophore in
18 should be different in fluorescence properties from
that of the alkylnaphthalene chromophore in 8, 16, or
22, and the protonation to the ether oxygen can easily
alter the fluorescence behavior. Probably incidentally,
reference compound 23 gives exactly the same lifetime
(5 ns). We tentatively conclude that added acid quenches
the excited alkoxynaphthalene moiety of 18 to give the
shorter lifetimes around 5 ns, while the excited alkylani-
sole moiety is not quenched by acid but gives lifetimes
around 1-2 ns, which are shorter than that of reference
23, probably through interaction with the naphthyl
chromophore.
Introduction of an extra methoxy to 8 dramatically
alters the fluorescence behavior of 17, which is distinctly
different from that of 8, 9, 16, or 18. Thus, the naphtha-
lene fluorescence of 17 was very efficiently quenched
intramolecularly by the trialkoxybenzene moiety to leave
an extremely weak monomer fluorescence at 328 and 334
nm, which is ca. 1000 times smaller in intensity than
that of 16. Instead, much stronger (by a factor of 5-20,
compared to monomer fluorescence of 17) exciplex emis-
sion emerged at a longer wavelength, which varies from
All of the long lifetimes are consistent with those
obtained by the 280 nm excitation. The short lifetimes
of 8, measured in neutral and acidic acetonitrile and/or
methanol, also nicely coincide with those of reference 20
measured under the comparable conditions. The relative
contribution of naphthalene fluorescence (longer lifetime)
decreases from 70% in neutral acetonitrile to 61% in
neutral methanol and then to 56% in acidic methanol in
good agreement with the declining tendency of lifetime
(i.e., 9.7, 9.2, and 7.9 ns, respectively).
(19) For intramolecular exciplex formation and photocycloaddition
between polycyclic aromatic compounds, see: (a) Rettig, W.; Paeplow,
B.; Herbst, H.; Mu¨llen, K.; Desvergne, J .-P.; Bouas-Laurent, H. New
J . Chem. 1999, 23, 453-460. (b) J olibois, F.; Bearpark, M. J .; Klein,
S.; Olivucci, M.; Robb, M. A. J . Am. Chem. Soc. 2000, 122, 5801-5810.
(c) Bouas-Laurent, H.; Castellan, A.; Desvergne, J .-P., Lapoujade, R.
Chem. Soc. Rev. 2000, 29, 43-55.
(18) (a) Pac, C.; Yasuda, M.; Shima, K.; Sakurai, H. Bull. Chem.
Soc. J pn. 1982, 55, 1605-1616. (b) Mizuno, K.; Konishi, S.; Takata,
T.; Inoue, H. Tetrahedron Lett. 1996, 37, 7775-7778. (c) Yoshimi, Y.;
Sugimoto, H.; Mizuno, K. Tetrahedron Lett. 1998, 39, 4683-4686. (d)
Kawakami, J .; Sata, H.; Ebina, K.; Ito, S. Chem. Lett. 1998, 535-536.
(e) Chow, Y. L.; J ohansson, C. I. Can. J . Chem. 1994, 72, 2011-2020.

2320 J . Org. Chem., Vol. 67, No. 7, 2002
Hoffmann et al.
Ta ble 2. F lu or escen ce Sp ectr a a n d Lifetim es of Va r iou s
Bich r om op h or ic Ar en es
395 nm in pentane to 450 nm in methanol, indicating its
charge-transfer character.
compd solvent [H2SO4]/M
λ
em/nma
λ
ex/nmb
τ/nsc
Both of the time-resolved fluorescence profiles obtained
with 16 and 17 upon excitation at 230 nm can be fitted
to a double-exponential decay curve, giving two lifetimes.
However, the origins of the two lifetimes are completely
different. The long lifetime of 13 ns obtained for 16 upon
excitation at 230 and 280 nm is assigned to the singlet
naphthalene moiety, while the short lifetime of 1 ns is
attributed to the singlet m-anisyloxy moiety, since the
latter lifetime appears only upon excitation at 230 nm
which is absorbed by both m-anisyloxy and naphthalene
moieties (cf. the data for 20 and 22).
1
2
8
MeCN
MeOH
MeOH
MeCN
MeOH
MeOH
MeCN
0
0
0.1
0
0
300
270
270
270
270
270
270
280
230
2.1
1.9
1.8
1.8
1.6
1.5
9.8
300
0.1
0
320, 326,
335, 340
9.7 (70%),
2.1 (30%)
9.6
9.2 (61%),
1.7 (39%)
8.0
7.9 (56%),
1.7 (44%)
10.3
10.0 (59%),
1.9 (41%)
9.8
9.8 (55%),
1.9 (45%)
8.6
8.2 (49%),
1.4 (51%)
13.3
13.3 (37%),
1.0 (63%)
13.1
13.1 (36%),
1.2 (64%)
13.3
13.5 (31%),
1.0 (69%)
6.5 [6.4]
6.2 [6.6]
7.2 [7.1]
7.3 (53%),
1.3 (47%)
[7.1 (45%),
1.1 (55%)]
5.4 [5.4]
5.3 (55%),
1.0 (45%)
[5.2 (61%),
1.1 (39%)]
1.0 [1.0]
0.9 [0.9]
6.7
6.5 (74%),
1.4 (26%)
7.7
7.8 (75%),
2.0 (25%)
5.0
4.9 (77%),
2.1 (23%)
7.5d
MeOH
MeOH
MeCN
MeOH
MeOH
MeCN
MeOH
MeOH
0
280
230
Similarly, 17 gave two lifetimes of 5-7 ns and 1 ns
upon excitation at 230 nm, which might be assigned to
the fluorescence from the naphthalene and trialkoxyben-
zene moieties, as is the case with 16. However, it turned
out that this assignment is erroneous and two exciplexes
with different lifetimes exist in the system, since the use
of a short-cut filter Y-44 (50% transmission at 440 nm
and 0% at 410 nm) to completely eliminate the originally
weak monomer fluorescence of naphthalene and tri-
alkoxybenzene moieties did not alter the lifetimes or their
relative contribution. Probably, the reduced oxidation
potential of trialkoxybenzene moiety in 17 is responsible
for such an efficient fluorescence quenching and forma-
tion of exciplexes with different structures and lifetimes.20
Clearly, we do not have enough data for discussing in
detail the structural differences of the two exciplexes, but
it seems reasonable to conclude that the short-lived
species is produced more favorably by excitation at
shorter wavelength (230 nm), is more populated in polar
solvents than in pentane (probably more polarized and/
or solvated), and is not subjected to acid quenching
(probably as a result of the short lifetime and/or heavy
solvation). It is also mentioned that the two exciplex
species do not appear to have significant difference in
spectral profile (and therefore in conformation or degrees
of stacking and charge transfer), since the relative
contribution of the two species is practically independent
of the observation wavelength (with and without Y-44).
The intervention of stable exciplexes with strong charge-
transfer character may hinder the photocycloaddition of
17.
0.1
0
280
230
9
16
17
321, 328,
338, 340
280
230
0
280
230
0.1
0
280
230
327, 336
280
230
0
280
230
0.1
280
230
C5H12
MeCN
0
0
328; 395
280
230
280
230
328, 334;
444
MeOH
0
328, 339;
450
280
230
MeOH
MeCN
0.1
0
328, 339;
453
326, 339,
354
280
230
280
230
18
MeOH
MeOH
0
280
230
Con clu sion
The [2 + 2] photocycloaddition between naphthalene
and benzene rings was shown to occur for the first time
upon irradiation of naphthalene-tethered resorcinol ethers
8 and 9 in the presence of sulfuric acid. The added acid
traps the initially generated “labile” tetrahydrofuran
derivatives 10 and 12 and accelerates their thermal
rearrangement to the corresponding final products 11
and 13/14, respectively. However, this photocycloaddition
reaction is not very tolerant to the structural modifica-
tions in tether or chromophore, as the analogues 16-18
are totally inactive photochemically.
0.1
280
230
19
20
Pd
0
0
0
0.1
0
0
0.1
0
0
0.1
0
MeCN
MeOH
MeOH
MeCN
MeOH
MeOH
MeCN
MeOH
MeOH
MeCN
MeOH
MeOH
300
325
270
270
270
280
280
280
280
280
280
270
270
270
2.2
1.9
1.7
0.8
0.8
0.7
12.2
12.5
13.0
4.9
5.0
4.9
21
22
23
321, 326,
335, 340
The photophysical properties of naphthyl derivatives
8 and 9 were compared with those of olefinic analogues
1 and 2. Although the photochemical reactivity is es-
sentially the same for 1/2 and 8/9, the fluorescence
295
0
0.1
a
Fluorescence maxima; values in italic after a semicolon are
those for exciplex emissions. Excitation wavelength used. c Rela-
b
(20) (a) van Stokkum, I. H. M.; Scherer, T.; Brouwer, A. M.;
Verhoeven, J . W. J . Phys. Chem. 1994, 98, 852-866. (b) Lauteslager,
X. Y.; van Stokkum, I. H. M.; van Ramesdonk, H. J . Brouwer, A. M.;
Verhoeven, J . W. J . Phys. Chem. 1999, 103, 653-659.
tive amplitudes for double-exponential decay in the parentheses,
d
and values obtained with a Y-44 filter in brackets. In polar
solvent.23

Bichromophoric Naphthalene-Tethered Resorcinol Ethers
J . Org. Chem., Vol. 67, No. 7, 2002 2321
was subjected to flash chromatography (petroleum ether/ethyl
acetate 5:1). Yield: 4.15 g (30%). H NMR (250 MHz, CDCl3):
behavior, particularly in the presence of added acid, is
quite different in both cases, showing practically no effect
for 1/2 but significant quenching for 8/9. Similar fluo-
rescence quenching by acid was observed also for 17 and
18. Hence, the presence of acid not only accelerates the
transformation of the primary photocycloadduct to the
final products (as in photoreactions of 8 and 9) but also
quenches the exciplex fluorescence (of 17).
We have demonstrated in the present study that the
intramolecular [2 + 2] photocycloaddition of aromatic
substrates is not restricted to the conventional olefin-
benzene pair but can be extended to unprecedented
naphthalene-benzene pair. Fluorescence spectral and
lifetime measurements may provide us with some criteria
for judging the photoreactivity of a given bichromophoric
substrate. Thus, highly efficient intramolecular fluores-
cence quenching and subsequent formation of an emissive
exciplex seems unfavorable, while moderately quenched
fluorescence and shortened lifetime without accompany-
ing formation of emissive exciplex appears to be more
suitable for the product formation. In this connection, it
is important to examine the effect of added acid as a
trapping agent for “labile” photoproduct, even if the
bichromophoric system does not appear to give any
photoproduct in neutral media.
1
δ 8.12 (m, 1H), 7.90 (m, 1H), 7.80 (m, 1H), 7.43-7.58 (m, 4H),
7.19 (m, 1H), 7.52-6.60 (m, 3H), 4.32 (t, J ) 7.5 Hz, 2H), 4.10
(m, 2H), 3.74 (m, 2H), 360 (t, J ) 7.5 Hz, 2H), 3.47 (s, 3H). 13
C
NMR (62 MHz, CDCl3): δ 160.0 (2×), 134.0, 133.8, 132.0,
129.8, 128.8, 127.3, 127.0, 126.2, 125.5 (2×), 123.5, 107.1,
107.0, 101.6, 70.9, 67.9, 67.1, 59.1, 32.7. IR (film): ν 3046, 2926,
2878, 1593, 1493, 1127, 777. MS m/z (relative intensity): 322
(M+, 32), 155 (100), 154 (58), 141 (21), 115 (16). UV (3.88 ×
10-5 M, MeCN): λ(ꢀ) 282 (9200), 224 (69 000), 202 (52 000).
HRMS: calcd for C21H22O3 322.1569, found 322.1581.
Syn th esis of Com p ou n d 16. Compound 16 was synthe-
sized from 3-methoxyphenol (2.2 g, 17.7 mmol) and 3-(1-
naphthyl)propan-1-yl tosylate (6 g, 17.6 mmol) in the same
1
way as compound 9. Yield: 2.04 g (40%). H NMR (250 MHz,
CDCl3): δ 8.13 (m, 1H), 7.90 (m, 1H), 7.78 (m, 1H), 7.38-7.60
(m, 4H), 7.25 (m, 1H), 6.54-6.63 (m, 3H), 4.06 (t, J ) 7.5 Hz,
2H), 3.83 (s, 3H), 3.33 (t, J ) 7.5 Hz, 2H), 2.30 (pen, J ) 7.5
Hz, 2H). 13C NMR (62 MHz, CDCl3): δ 160.8, 160.3, 137.5,
133.9, 131.8, 129.8, 128.7, 126.7, 126.2, 125.8, 125.5, 125.4,
123.7, 106.7, 106.2, 101.0, 67.0, 55.2, 30.1, 29.2. IR (film): ν
3044, 2940, 2874, 2836, 1597, 1493, 1154, 779. MS m/z (relative
intensity): 292 (M+, 23), 168 (100), 152 (85), 141 (70), 115 (32).
UV (2.64 × 10-5 M, MeCN): λ (ꢀ) 282 (7700), 224 (70 000).
Anal. Calcd for C20H20O2: C, 82.19; H, 6.85. Found: C, 82.28;
H, 6.54.
Syn th esis of Com p ou n d 17. Compound 17 was synthe-
sized from 3,4-dimethoxyphenol and 2-(1-naphthyl)ethyl to-
sylate in the same way as compound 9. Yield: 2.65 g (56%).
1
Exp er im en ta l Section
Mp: 66 °C. H NMR (250 MHz, CDCl3): δ 8.13 (m, 1H), 7.90
(m, 1H), 7.80 (m, 1H), 7.44-7.60 (m, 4H), 6.77 (d, J ) 8.5 Hz,
1H), 6.55 (d, J ) 3.0 Hz, 1H), 6.42 (d/d, J ) 3.0/8.5 Hz, 1H),
4.29 (t, J ) 7.5 Hz, 2H), 3.85 (s, 6H), 3.60 (t, J ) 7.5 Hz, 2H).
13C NMR (62 MHz, CDCl3): δ 153.3, 149.8, 143.4, 134.0, 133.8,
132.0, 128.7, 127.2, 127.0, 126.0, 125.5, 125.4, 123.5, 111.8,
103.9, 100.7, 68.4, 56.3, 55.7, 32.8. IR (KBr): ν 3043, 3005,
2914, 2839, 1596, 1516, 1231, 1200, 1139, 1036, 795. MS m/z
(relative intensity): 308 (M+, 12), 155 (100), 153 (26), 127 (8),
115 (10). UV (2.42 × 10-5 M, MeCN): λ (ꢀ) 283 (11 000), 224
(82 000). Anal. Calcd for C20H20O3: C, 77.92; H, 6.49. Found:
C, 77.64; H, 6.55.
Gen er a l Meth od s. Irradiations of the solution were carried
out in quartz tubes (i.d. 1 cm), with a Rayonet apparatus
(model RPR-100) from the Southern New England Ultraviolet
Co. RPR-2537 A lamps were used. Solutions were degassed
with argon before irradiation.
Syn th esis of Com p ou n d 8. A suspension of 3-methoxy-
phenol (3 g, 16.1 mmol), 2-(1-naphthyl)-ethyl tosylate (5 g, 15.3
mmol) and K2CO3 (5 g, 36.2 mmol) in DMF (20 mL) was heated
at 80 °C for 4 h. After evaporation of the solvent, the residue
was treated with water and CH2Cl2. The aqueous phase was
extracted twice with CH2Cl2. The organic phase was then
washed subsequently with 10% NaOH and with water. After
drying with MgSO4 and evaporation of the solvent, the residue
was subjected to flash chromatography (petroleum ether/ethyl
acetate 5:1). Yield: 2.4 g (56%). Mp: 108 °C. 1H NMR (250
MHz, CDCl3): δ 8.13 (m, 1H), 7.90 (m, 1H), 7.81 (m, 1H), 7.45-
7.62 (m, 4H), 7.22 (d/d, J ) 7/14 Hz, 1H), 6.50-6.59 (m, 3H),
4.32 (t, J ) 7.5 Hz, 2H), 3.81 (s, 3H), 4.33 (t, J ) 7.5 Hz, 2H).
13C NMR (62 MHz, CDCl3): δ 160.8, 160.0, 134.0, 133.8, 132.0,
129.9, 128.8, 127.3, 127.0, 126.1, 125.6, 125.5, 123.5, 106.6,
106.4, 100.9, 68.0, 55.2, 32.8. IR (KBr): ν 3040, 3005, 2934,
2841, 1510, 1169, 1036, 837, 792, 768. MS m/z (relative
intensity): 278 (M+, 51), 155 (100), 154 (62), 141 (31), 128 (13),
115 (21). UV (2.52 × 10-5 M, MeCN): λ (ꢀ) 282 (9200), 224
(81 000). Anal. Calcd for C19H18O2: C, 82.01; H, 6.47. Found:
C, 82.02; H, 6.62.
Syn th esis of Com p ou n d 9. A suspension of resorcinol
monoacetate (technical grade, 7.3 g, 48.0 mmol), 2-methoxy-
ethyl tosylate (10 g, 43 mmol), and K2CO3 (14.5 g, 105 mmol)
in 60 mL of DMF was heated at 80 °C for 4 h. After evaporation
of the solvent, the residue was treated with 20% NaOH (120
mL). After careful acidification with hydrochloric acid, the
resulting mixture was extracted with CH2Cl2. The organic
phase was dried with MgSO4. The solvent was evaporated, and
the crude material was used for further conversion.
Syn th esis of Com p ou n d 18. Compound 18 was synthe-
sized from R-naphthol (2.35 g, 16.3 mmol) and 2-(3-methoxy-
phenyl)ethyl tosylate (5 g, 16.3 mmol) in the same way as
1
compound 9. Yield: 2.8 g (62%). H NMR (250 MHz, CDCl3):
δ 8.26 (m, 1H), 7.77 (m, 1H), 7.20-7.50 (m, 5H), 6.90-6.97
(m, 2H), 6.75-6.81 (m, 2H), 4.33 (t, J ) 7.0 Hz, 2H), 3.78 (s,
3H), 3.20 (t, J ) 7.0 Hz, 2H). 13C NMR (62 MHz, CDCl3): δ
159.7, 154.5, 140.1, 134.5, 129.5, 127.4, 126.3, 125.8, 125.1,
122.1, 121.4, 120.2, 114.8, 111.9, 104.6, 68.8, 55.1, 35.9. IR
(film): ν 3052, 2953, 2873, 2834, 1595, 1460, 1268, 1100, 772.
MS m/z (relative intensity): 278 (M+, 90), 194 (30), 170 (35),
144 (44), 135 (86), 126 (36), 121 (100), 115 (44), 105 (97). UV
(2.36 × 10-5 M, MeCN): λ (ꢀ) 294 (6300), 281 (6700), 229
(3200), 211 (49 000). Anal. Calcd for C19H18O2: C, 82.01; H,
6.47. Found: C, 82.06; H, 6.22.
Com p ou n d s 22 a n d 23. These compounds were synthe-
sized according to ref 21.
P h otoch em ical Tr an sfor m ation s on P r epar ative Scale.
A solution of 8 (1.2 × 10-2 M) or 9 (1 × 10-2 M) and H2SO4 (6
× 10-3 M) in acetonitrile (120 mL) was distributed into eight
quartz tubes. After percolation with argon for 0.5 h, the
solutions were irradiated for 3 h. The solvent was evaporated
in the presence of NaHCO3. The residue was subjected to flash
chromatography (petroleum ether/ethyl acetate: first 5:1, then
1:1, and finally pure ethyl acetate).
1
A suspension of 3-(2-methoxyethoxy)phenol (9 g, ∼ 60
mmol), 2-(1-naphthyl)ethyl tosylate (14 g, 42.9 mmol), and
K2CO3 (16 g, 116 mmol) in 60 mL of DMF was heated at 80
°C for 4 h. After evaporation of the solvent, the residue was
treated with water and CH2Cl2. The aqueous phase was
extracted twice with CH2Cl2. The organic phase was then
washed subsequently with 10% NaOH and with water. After
drying with MgSO4 and evaporation of the solvent, the residue
Com p ou n d 10. Yield: 190 mg (48%). H NMR (500 MHz,
CD3COCD3): δ 7.01-7.22 (m, 5H), 6.85 (d/m, J ) 8.0 Hz, 1H),
6.80 (t, J ) 2.5 Hz, 1H), 6.75 (d/d, J ) 2.5/8.0 Hz, 1H), 6.68 (d,
J ) 10.0 Hz, 1H), 6.08 (d/d, J ) 4.5/10.0 Hz, 1H), 4.56 (d, J )
(21) (a) Xu, J .; Vasella, A. Helv. Chim. Acta 1999, 82, 1728-1752.
See also: (b) Carrea, G.; Danieli, B.; Palmisano, G.; Riva, S.; Stana-
gostino, M. Tetrahedron: Asymmetry 1992, 3, 775-784.

2322 J . Org. Chem., Vol. 67, No. 7, 2002
Hoffmann et al.
4.5 Hz, 1H), 3.93 (d/t, J ) 6.5/7.5 Hz, 1H), 3.71 (s, 3H), 3.66
(d/t, J ) 6.5/7.5 Hz, 1H), 2.95 (d/d/d, J ) 6.5/7.5/13.0 Hz, 1H),
2.69 (d/d/d, J ) 6.5/7.5/13.0 Hz, 1H). 13C NMR (126 MHz, CD3-
COCD3): δ 160.5, 149.2, 141.7, 132.2, 130.3, 130.1, 129.2,
129.0, 128.2, 127.5, 126.7, 119.8, 114.1, 111.8, 82.6, 66.5, 55.3,
53.8, 41.3. IR (film): ν 3025, 2938, 2872, 2834, 1582, 1485,
1256, 1159, 1051, 750. MS m/z (relative intensity): 278 (M+,
100), 249 (31), 247 (31), 202 (24), 189 (29), 178 (24), 171 (51),
170 (55), 141 (25), 135 (49), 115 (36). UV (2.09 × 10-5 M,
MeCN): λ (ꢀ) 266 (11 000), 218 (38 000). Anal. Calcd for
A solution of 10 (160 mg, 0.58 mmol) and H2SO4 (6 × 10-3
M) in acetonitrile (53 mL) was distributed into three quartz
tubes and irradiated for 4.5 h. The solvent was evaporated in
the presence of NaHCO3, and the residue was subjected to
flash chromatography (petroleum ether/ethyl acetate 5:1): 10,
27 mg (conversion 83%); 11, 42 mg (yield 38%).
Acid -Ca ta lyzed Rea r r a n gem en t of 10 a n d 12. Solutions
of 10 (100 mg, 0.43 mmol) or 12 (100 mg, 0.31 mmol) and H2-
SO4 (6 × 10-3 M) in 16 mL of acetonitrile were heated under
reflux for 5 to 6 h. The solvent was evaporated in the presence
of NaHCO3, and the residue was subjected to flash chroma-
tography (petroleum ether/ethyl acetate 2:1): 15, 88 mg (yield
88%); 12, 7 mg (conversion 93%); 14, 78 mg (83%).
Com p ou n d 15. 1H NMR (500 MHz, CD3COCD3): δ 8.24
(d, J ) 8.5 Hz, 1H), 7.94 (d, J ) 8.0 Hz, 1H), 7.80 (d, J ) 8.5
Hz, 1H), 7.60 (d/d/d, J ) 1.0, 7.0, 8.0 Hz, 1H), 7.53 (d/d/d, J )
1.0, 7.0, 8.0 Hz, 1H), 7.38 (m, 1H), 7.33 (d, J ) 8.5 Hz, 1H),
6.94-7.00 (m, 3H), 3.85 (s, 3H), 3.74-3.80 (m, 2H), 3.30 (t, J
) 7.5 Hz, 2H). 13C NMR (126 MHz, CD3COCD3): δ 160.4,
144.9, 140.9, 134.2, 133.3, 132.5, 130.0, 129.4, 129.0, 127.2,
127.1, 126.3, 125.4, 122.4, 115.7, 113.4, 63.1, 55.5, 33.9. IR
(KBr): ν 3231, 3058, 3007, 2963, 2934, 2830, 1590, 1460, 1217,
1020, 833, 793, 754, 704. MS m/z (relative intensity): 278 (M+,
42), 247 (100), 232 (21), 216 (26), 215 (52), 203 (33), 202 (32),
189 (10). Anal. Calcd for C19H18O2: C, 82.01; H, 6.47. Found:
C, 81.70; H, 6.28.
C
19H18O2: C, 82.01; H, 6.47. Found: C, 82.14; H, 6.20.
1
Com p ou n d 11.22 Yield: 60 mg (18%). H NMR (500 MHz,
CD3COCD3): δ 7.97 (d, J ) 8.0 Hz, 1H), 7.91 (t, J ) 9.0 Hz,
2H), 7.40-7.50 (m, 5H), 7.00-7.10 (m, 3H), 3.85 (s, 3H). 13C
NMR (126 MHz, CD3COCD3): δ 160.6, 142.8, 140.9, 1.34,8,
132.2, 130.2, 129.2, 128.5, 127.5, 126.9, 126.7, 126.5, 126.3,
123.0, 116.3, 113.7, 55.5.
1
Com p ou n d 12. Yield: 102 mg (26%). H NMR (250 MHz,
CD3COCD3): δ 7.13-7.21 (m, 5H), 6.74-6.90 (m, 3H), 6.68
(d, J ) 10.0 Hz, 1H), 6.09 (d/d, J ) 4.5/10.0 Hz, 1H), 4.56 (d,
J ) 4.5 Hz, 1H), 4.00-4.10 (m, 2H), 3.93 (d/t, J ) 6.5/7.5 Hz,
1H), 3.60-3.72 (m, 3H), 3.32 (s, 3H), 2.95 (d/d/d, J ) 6.5/7.0/
13.0 Hz, 1H), 2.70 (d/d/d, J ) 6.5/7.0/13.0 Hz, 1H). 13C NMR
(63 MHz, CD3COCD3): δ 159.7, 148.2, 141.6, 132.2, 130.3,
130.1, 129.2, 129.0, 128.2, 127.4, 126.7, 119.9, 114.7, 112.3,
82.6, 71.6, 67.8, 66.5, 58.8, 53.7, 41.3. IR (film): ν 3032, 2927,
2874, 1580, 1451, 1256, 1127, 1053, 752. MS m/z (relative
intensity): 322 (M+, 100), 294 (15), 263 (18), 247 (16), 202 (17),
171 (27), 170 (36), 141 (57), 115 (30). UV (2.92 × 10-5 M,
MeCN): λ (ꢀ) 265 (8500), 219 (33 000). Anal. Calcd for
Det er m in a t ion of t h e Qu a n t u m Yield s. Solutions
(Schemes 1-3, Table 1) possessing an optical density of 3.5
(λ ) 254 nm, optical path ) 0.5 cm) were irradiated until the
conversion reached between 10 and 20%. N,N-Dimethyluracil
(formation of the monohydrate) was used as actinometer.15
C
21H22O3: C, 78.26; H, 6.83. Found: C, 78.13; H, 6.98.
Com p ou n d 13. Yield: 52 mg (15%). 1H NMR (250 MHz,
F lu or escen ce Lifet im e Mea su r em en t s of Bich r om o-
p h or ic Ar om a tic Com p ou n d s a n d Rela ted Com p ou n d s.
Absorption spectra were recorded on a J ASCO V-550 spec-
trometer fitted with an ETC-505T temperature controller, and
fluorescence spectra on J ASCO FP-777. Fluorescence lifetime
measurements were performed for an argon-saturated solution
of sensitizers (ca. 0.1 mM) on a Horiba NAES-550 fitted with
SCN-121A (optical chamber), NFL-111A (pulsed H2 light
source), SGM-121A (monochromator), SSU-111A (photo-
multiplier), LPS-111 (lamp power supply), and Advantec LCH-
111 Labo Thermo-Cool temperature controller. The radiation
from the lamp was made monochromatic by 10 nm monochro-
mator (centered at 230 or 270/280 nm) and the emission from
the sample solution was detected through a Toshiba UV31 or
UV33 filter, unless otherwise stated. There must be some
ambiguity in smaller components of fluorescence lifetimes,
especially for the shorter lifetimes obtained, since our instru-
ment does not measure the lifetime in a range of <1 ns much
correctly, which will be studied with ps fluorescence spectrom-
eter in due course.
CD3COCD3): δ 7.88-8.00 (m, 3H), 7.39-7.60 (m, 5H), 7.00-
7.09 (m, 3H), 4.20 (m, 2H), 3.74 (m, 2H), 3.35 (s, 3H). 13C NMR
(63 MHz, CD3COCD3): δ 159.9, 142.9, 140.9, 134.8, 132.3,
130.2, 129.2, 128.5, 127.6, 127.0, 126.7, 126.5, 126.3, 123.1,
116.8, 114.4, 71.7, 68.2, 58.9. IR (film): ν 3059, 2926, 2878,
1577, 1485, 1224, 1129, 781. MS m/z (relative intensity): 278
(M+, 100), 220 (50), 203 (53), 202 (50), 189 (35), 165 (15). Anal.
Calcd for C19H18O2: C, 82.01; H, 6.47. Found: C, 81.74; H,
6.73.
Com p ou n d 14. Yield: 66 mg (17%). 1H NMR (250 MHz,
CD3COCD3): δ 8.23 (d, J ) 8.5 Hz, 1H), 7.92 (d/d, J ) 1.5, 8.0
Hz, 1H), 7.80 (d, J ) 8.5 Hz, 1H), 7.48-7.63 (m, 2H), 7.30-
7.41 (m, 2H), 6.91-7.01 (m, 3H), 4.15-4.20 (m, 2H), 3.70-
3.90 (m, 4H), 3.36 (s, 3H), 3.26-3.36 (m, 2H). 13C NMR (63
MHz, CD3COCD3): δ 159.7, 144.9, 140.8, 134.2, 133.6, 132.5,
130.0, 129.4, 129.0, 127.2, 127.1, 126.3, 125.4, 122.5, 116.2,
114.0, 71.7, 68.1, 63.1, 58.9, 33.9. IR (film): ν 3404, 3052, 2927,
2880, 1594, 1466, 1293, 1095, 1038, 823, 706. MS m/z (relative
intensity): 322 (M+, 60), 292 (43), 259 (37), 245 (36), 233 (46),
215 (100), 203 (40), 202 (54), 189 (22). Anal. Calcd for
C
21H22O3: C, 78.26; H, 6.83. Found: C, 78.06; H, 7.38.
Ir r a d ia tion of 10 a n d 12. Solutions of 10 (160 mg, 0.58
Ack n ow led gm en t. Financial support (to T.M.) of
this work by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Culture, Sports, Science, and
Technology of J apan (No. 12740346) and by a grant from
the Shorai Foundation for Science and Technology are
gratefully acknowledged.
mmol) or 12 (160 mg, 0.50 mmol) in acetonirile (50 mL) were
distributed into three quartz tubes and irradiated for 4.5 h.
The solvent was evaporated and the residue was subjected to
flash chromatography (petroleum ether/ethyl acetate 5:1): 10,
34 mg (conversion 79%); 11, 51 mg (yield 48%); 12, 24 mg
(conversion 85%); 13, 60 mg (yield 51%).
Su p p or tin g In for m a tion Ava ila ble: UV and fluorescence
spectra of compounds 8, 9, and 17. This material is available
free of charge via the Internet at http://pubs.acs.org.
(22) (a) Leznoff, C. C.; Hayward, R. J . Can. J . Chem. 1970, 48, 1843-
1849. (b) Nasipuri, D.; Choudhury, S. R. R.; Bhattacharya, A. J . Chem.
Soc., Perkin Trans. 1 1973, 1451-1456.
(23) Murov, S. L.; Carmichael, I.; Hug, G. L. In Handbook of
Photochemistry, 2nd ed.; Marcel Dekker: New York, 1993.
J O011143M