3286 J. Am. Chem. Soc., Vol. 119, No. 14, 1997
Adam et al.
and 400 mg (1.45 mmol) of 9,10-bis(chloromethyl)anthracene (6b) in
40 mL of dry acetone was allowed to reflux for 20 h. The solvent
was removed under reduced pressure (ca. 20 °C, 18 Torr) and 10 mL
of distilled water was added. The aqueous solution was extracted with
methylene chloride (3 × 10 mL), the combined organic phases were
washed with saturated, aqueous Na2CO3 solution (2 × 10 mL) and
with saturated aqueous NaCl solution (2 × 10 mL) and dried over
MgSO4, and the solvent was removed under reduced pressure (ca. 20
°C, 18 Torr). After recrystallization from ethanol, 410 mg (72%) of
bisether 1b was obtained as pale yellow needles, mp 242-244 °C dec.
IR (KBr) 3040, 2890, 1570, 1460, 1200, 1010, 835 cm-1; UV (CH3-
CH2Cl2 by the electronically excited radical intermediate, a
mechanistic speculation that requires at least three additional
photons in analogy to the formation of 6a from 1a (Scheme 3).
In methanol as solvent, the dimerization of 9,10-anthraquin-
odimethane to the paracyclophane 3b is the exclusive pathway
(Table 3, entry 3). The bisether 7b expected to be formed by
sequential double photoionization of the diradical 2b and
methanol trapping is observed only in traces. While this route
is effective in the laser-jet photolysis of monoether 1a to afford
7a (Scheme 3), for the formation of 7b from bisether 1b the
photon densities are just about at the limits of the possible for
the laser-jet technique in observing such a demanding multiple-
photon process.
1
CN) λ (log ꢀ) 259 (4.13), 356 (2.82), 373 (3.06), 394 nm (3.06); H
NMR (CDCl3, 200 MHz) δ 5.99 (s, 4 H), 7.07 (m, 2 H), 7.18 (m, 4
H), 7.41 (m, 4 H), 7.56 (m, 4 H), 8.36 (m, 4 H); 13C NMR (CDCl3,
50.3 MHz) δ 62.6 (t), 114.8 (d), 121.2 (d), 124.7 (d), 124.9 (d), 126.2
(d), 129.6 (s), 130.8 (s), 159.1 (s). Anal. Calcd for C28H22O2 (390.5):
C, 86.13; H, 5.68. Found: C, 86.16; H, 5.69.
Photodimer of 9-(Phenoxymethyl)anthracene (8a). A solution of
284 mg (1.00 mmol) of monoether 1a in 10 mL of benzene was
degassed as described above and irradiated for 15 h under an argon
gas atmosphere in a Rayonet Photochemical Reactor [RPR (800 W,
110 V)], which was equipped with 350-nm lamps. During the
photolysis a solid precipitated, which was collected by filtration, and
after recrystallization from benzene, 120 mg (42%) of dimer 8a was
obtained as colorless needles, mp 275-276 °C; IR (KBr) 3000, 2880,
2820, 1560, 1450, 1270, 1200, 1040, 840 cm-1; 1H NMR (d6-DMSO,
200 MHz, 100 °C) δ 4.32 (s, 2 H), 5.15 (s, 4 H), 6.8-7.3 (m, 26 H).
Anal. Calcd for C42H32O2 (568.7): C, 88.70; H, 5.67. Found: C,
88.91; H, 5.48.
Laser-Jet Irradiations. The previously described experimental
setup21ab was employed. The beam of the argon-ion laser (3.3-3.9 W
over the 333-, 351-, and 364-nm UV lines) was focused by means of
a quartz lens (f ) 80 mm) onto a free-falling liquid jet of the photolysis
solution. The free-falling liquid jet was generated by passing the
substrate solution to be irradiated through a 50-µm capillary and
maintained by means of a Bischoff 2200 HPLC pump. The irradiation
chamber was kept under a positive argon gas pressure and the substrate
solution was passed once through the focal region of the laser beam
for the irradiation.
Control Experiments. (a) Normal Laser Irradiations. These
were carried out in a Schlenk tube by irradiation at the 333-, 351-, and
363-nm lines of the Coherent INNOVA 100 argon-ion laser (3.0 W
over all UV lines), supplied with quartz optics. The beam was widened
with a quartz lens (f ) 50 mm) to the size of ca. 1 cm in diameter and
the 10-mL sample was irradiated for 5 min (benzene, n-hexane,
methylene chloride) or 10 min (methanol) under an argon gas
atmosphere.
(b) Photolysis of Dimer 3a. A solution of 5.00 mg (13.1 µmol) of
3a in 0.7 mL of CDCl3 was irradiated for 5 min at the 333-, 351-, and
363-nm lines of the Coherent INNOVA 100 argon-ion laser (3.0 W
over all UV lines) under an argon gas atmosphere. NMR analysis
showed complete conversion and the dimer 5a was obtained (>99%).
(c) Competition Experiments. A solution of monoether 1a (3.50
× 10-3 M) in 4:1 MeOH/CH2Cl2 was irradiated in the LJ apparatus at
different light intensities, the solvent was removed under reduced
pressure (ca. 20 °C, 18 Torr), and the residue was analyzed by 1H NMR
spectroscopy. The results are summarized in Table 2.
(d) Photolysis of Dimer 3b. A solution of 5.00 mg (12.2 µmol) of
3b in 0.7 mL of CDCl3 was irradiated for 2 min at the 333-, 351-, and
363-nm lines of the Coherent INNOVA 100 argon-ion laser (2.0 W
over all UV lines) under an argon gas atmosphere. NMR analysis
showed complete conversion and the dimer 5b was obtained (>99%).
Both examples, the photolyses of monoether 1a (Table 1)
and bisether 1b (Table 3) show similar multiple-photon chem-
istry in terms of C-O bond homolysis and ionization of the
resulting arylmethyl radical intermediates under the high-
intensity conditions of the laser-jet, with a pronounced solvent
dependence. Thus, in benzene the C-O bond cleavage engages
at least two photons to afford the dimers 3a and 4a from 1a
and 3b from 1b. While the [4 + 4] photocycloaddition of 3a
leads efficiently to 5a, such that only traces of dimer 3a remain,
the dimer 3b persists and no corresponding [4 + 4] photoadduct
5b was detectable. Since the double C-O bond photolysis
requires already several photons to generate the dimer 3b from
the bisether 1b, the photon density is not high enough during
the total residence time (ca. 50 µs) in the laser focus to effect
the further [4 + 4] cycloaddition of dimer 3b to 5b. In contrast,
in methylene chloride the chloride 6a results efficiently from
the monoether 1a and the chlorides 6b and 9b from the bisether
1b at the expense of the respective photodimers 3a (5a) and 3b
in benzene. For both chlorinated photoproducts 6a and 6b (9b),
their photolytically generated precursor arylmethyl radicals
require subsequent excitation for the electron transfer with
methylene chloride. Finally, for methanol, in which the
corresponding ether products 7a and 7b are formed through
ionization of the intermediary arylmethyl radicals, for the latter
bisether the laser-jet technique is at its limits of the possible as
concerns the photon density essential for such a multiple-photon
process. Thus, while the monoether 1a leads to the ether
product 7a highly efficiently, for the bisether 1b only traces of
7b are produced because the latter multiple-photon process
requires probably as many as four or more photons. Neverthe-
less, the anthracene substrates 1a and 1b have been very
valuable to demonstrate the efficacy of the laser-jet mode to
explore high-intensity photochemistry through product studies,
which nicely complements the time-resolved laser-flash studies
for the mechanistic elucidation of multiphoton processes.
Experimental Section
Materials and General Aspects. The solvents benzene, n-hexane,
methanol, acetonitrile, and methylene chloride were distilled and the
latter was passed immediately before photolysis through an alumina
column to remove traces of acid. 2-Propanol (reagent grade) was used
as purchased. All solutions were degassed by purging with a slow
stream of dry argon gas for 45 min before irradiation. NMR spectra
were recorded on a Bruker AC 200 or a Bruker AC 250 spectrometer.
Quantitative product studies were determined by 1H NMR analysis
(CDCl3) of the identified products directly on the photolysates after
removal of the solvent under reduced pressure (ca. 20 °C, 18 Torr).
The IR spectra were recorded on a Perkin-Elmer 1420 infrared
spectrophotometer. The known ethers 1a,20a 7a,20f and 7b,20g dimers
3a,20b 3b,20c and 4a,11 and chlorides 6a20d and 6b20c were prepared
according to reported procedures. Chloride 9b was identified by
(20) (a) Kornblum, N.; Lurie, A. P. J. Am. Chem. Soc. 1959, 81, 2705-
2715. (b) Schreiber, K. C.; Emerson, W. J. Org. Chem. 1966, 31, 95-99.
(c) Golden, J. H. J. Chem. Soc. 1961, 3741-3748. (d) Rohrbach, W. D.;
Gerson, F.; Mo¨ckel, R.; Boekelheide, V. J. Org. Chem. 1984, 49, 4128-
4132. (e) Fieser, L. F.; Novello, F. C. J. Am. Chem. Soc. 1940, 62, 1855-
1859. (f) Mancilla, J. M.; Nonhebel, D. C.; Russell, J. A. Tetrahedron 1975,
31, 3097-3101. (g) Kruyt, W.; Veldstra, H. Landbouwk. Tijdschr. 1951,
63, 398-403.
(21) (a) Wilson, R. M.; Schnapp, K. A.; Hannemann, K.; Ho, D. M.;
Memarian, H. R.; Azadnia, A.; Pinhas, A. R.; Figley, T. M. Spectrochim.
Acta, Part A 1990, 46A, 551-558. (b) Wilson, R. M.; Adam, W.; Schulte
Oestrich, R. Spectrum 1991, 4, 8-17.
1
comparison of H NMR data.
9,10-Bis(phenoxymethyl)anthracene (1b). A solution of 942 mg
(10.0 mmol) of phenol, 1.32 g (9.57 mmol) of potassium carbonate,