M. Kaftory, V. Shteiman, T. Lavy, John R. Scheffer, J. Yang, V. Enkelmann
FULL PAPER
1-Methyl-5,6-diphenylpyrazine-2-one (1): Dimethyl sulfate (0.252 g,
2 mmol) was added dropwise at room temperature to a stirred solu-
tion of 2-hydroxy-5,6-diphenylpyrazine (0.5 g, 2 mmol) and sodium
methoxide [formed from 64 mg (2 mmol) of sodium and 40 mL of
methanol] and the reaction mixture was refluxed for 1 h. The solu-
tion was then concentrated under reduced pressure, poured into
10% HCl solution, and extracted with dichloromethane. The ex-
tract was washed in turn with 10% NaHCO3 solution and water
and dried with anhydrous magnesium sulfate. After removal of the
of the solvent, the residue was chromatographed with diethyl ether
(BA). The geometry of these hydrogen bonds is as follows:
O1b···H7a
=
2.487(3) Å, O1b···C7a
=
3.364(3) Å,
O1b···H7a–C7a = 157.3(3)°, and O1a···H11b = 2.560(3) Å,
O1a···C11b = 3.447(3) Å, O1a···H11b–C11b = 155.0(3)°;
the closest intermolecular O···H distances in (BA) are
O1a···H7b and O1b···H11a [3.708(3) and 3.527(3) Å,
respectively]. The hydrogen bonds hold the two molecules
together, thus facilitating the photochemical reaction (see
Figure 7).
The position of the hydrogen atoms of the dimer could and petroleum ether (50:50, v/v) to give 1 (0.4 g; yield: 76%), which
was recrystallized from ethanol to afford yellow prisms. M.p. 165–
not be located; however, the distances between the oxygen
atoms and carbon atoms involved in the hydrogen bonding
do not vary significantly: O1b···.C7a = 3.487 Å, and
O1a···C11b = 3.515 Å. These results imply that hydrogen
bonding is essential for the discrimination during the pho-
todimerization.
167 °C. IR (KBr): ν
= 3027, 1646 (C=O), 1578, 1556, 1483,
˜
max
1442, 1414, 1319, 1241, 1185, 1155 cm–1. MS: m/z (%) = 262 (74)
[M+], 233 (100), 218 (11), 165 (66), 118 (32), 89 (42), 77 (45). H
1
NMR (CDCl3, 200 MHz): δ = 8.30 (s, 1 H, 3-H), 7.42–7.12 (m, 10
H), 3.32 (s, 3 H, CH3) ppm. 13C NMR (CDCl3, 200 MHz): δ =
156.09 (C=O), 146.54 (3-C), 138.59, 137.40, 133.85, 132.11, 129.90,
129.67, 129.17, 129.12, 127.81, 127.12, 33.80 (CH3) ppm.
(1α,2α,5α,6α)-3,7-Dimethyl-2,6,10,12-tetraphenyl-3,7,9,11-tetraaza-
Conclusions
tricyclo[4.2.2.22,5]dodeca-9,11-diene-4,8-dione (2): Photodimer
2
was isolated after the solid-state photolysis of pyrazinone 1. A typi-
cal photolysis is given below: a single crystal of 1 (23 mg,
0.09 mmol) was photolyzed for 20 h with a medium-pressure mer-
cury lamp equipped with a Pyrex filter. The resulting solid was
dissolved in a small amount of ethyl acetate, and the photodimer
2 was isolated by column chromatography with 20% diethyl ether
in petroleum ether (v/v). Recrystallization from ethyl acetate gave
colorless needles (17 mg; yield: 74%). M.p. 148–150 °C. IR (KBr):
We have carried out the single-crystal irradiation and
crystal-structure determination of three different crystals
and found that in these cases a photodimer is formed be-
tween the two molecules that are held together by hydrogen
bonds. It should be noted, however, that the experiments
were performed on a single crystal. One cannot rule out the
possibility that crystals of the monomer having the opposite
chirality will photodimerize to the dimer of the opposite
handedness. Therefore the main conclusion of this work is
ν
max = 3058, 2967, 1657 (C=O), 1494, 1446, 1423, 1387, 1266, 1098,
˜
1039, 1001 cm–1. MS: m/z (%) = 262 (100), 233 (82), 165 (83), 118
1
that intermolecular interactions can be dominant in the de- (90), 89 (79), 77 (90). H NMR (CDCl3, 200 MHz): δ = 7.35–6.85
(m, 20 H), 6.30 (s, 2 H), 2.52 (s, 6 H, CH3) ppm.
termination of photoproduct.
Determination of Enantiomeric Excess: The enantiomeric excess of
the solid-state photoproduct 2 was determined by chiral HPLC
Chiral Column: Chiralcel OD, Chiral Technologies Inc. Detector:
UV detector at λ = 261 nm. Solvents: 2-propanol 1%, hexane 90%.
Flow Rate: 1 mL min–1.
Experimental Section
Preparation of the Materials: Commercially available reagents were
purchased from Aldrich and used without further purification.
Thin-layer chromatography (TLC) was carried out using alumin-
ium sheets precoated with silica gel 60F (Merck 5554). The plates
were inspected under UV light. Column chromatography was car-
ried out using silica gel 60F (Merck 9385, 0.040–0.063 mm). Infra-
red spectra were recorded with a Nicolet Impact 400 Fourier trans-
form spectrometer using KBr pellets. 1H and 13C NMR spectra
were recorded (at room temperature) with a Bruker Avance 200
spectrometer (200 MHz), using residual solvent as the internal
standard. All chemical shifts are quoted on a δ scale, and all coup-
ling constants (J) are expressed in Hertz (Hz). Samples were pre-
pared using CDCl3 or [D6]DMSO purchased from Aldrich.
Irradiation: The irradiation system consisted of an Osram Xe short-
arc lamp (150 W) using a commercial glass filter that blocks light
of wavelengths lower than 450 nm. A single crystal of pyrazinone
1 was attached with grease to a thin piece of glass connected to a
solid piece of metal, and mounted on a device that revolved at
1 rpm. The crystal was irradiated for 6 h. Similar results were ob-
tained with a laser at 488 nm. A single crystal was cooled during
the irradiation for 3 h.
Crystal-Structure Determination and Refinement: Details of crystal-
lographic data collection and crystal structure determination are
given in Table 2. The refinement procedure of the irradiated crystal
needs some comments. After locating the atomic positions of the
dimer, the refinement proceeded as follows: the site occupancy of
the atoms belonging to the monomer was refined as a free variable,
which, after refinement, converged at 0.81 for the monomer (0.19
for the dimer). All the atoms of the dimer were refined isotropically,
and the phenyl rings were refined as rigid groups. The absolute
structure of the crystal of the monomer and of the dimer could not
be assigned. The diffractometer intensities were collected with a
Nonius KappaCCD diffractometer. The software programs used
for data collection and reduction were KappaCCD[15] and DENZO
SMN;[16] for structure solution and refinement SHELXS-97
and SHELXL-97;[17] and for graphic presentations ORTEP-3 for
Windows.[18] CCDC-216315 (for the monomer) and CCDC-216316
2-Hydroxy-5,6-diphenylpyrazine: Sodium hydroxide (12.5 m, 3.2 mL
40 mmol) was added over 30 minto a refluxing mixture of glycine
amide hydrochloride (2.2 g, 20 mmol), benzil (4.2 g, 20 mmol), and
50 mL of methanol. After refluxing for another 30 min, the mixture
was treated with 2.5 mL of 12 m hydrochloric acid, followed by 2 g
of solid potassium hydrogen carbonate. The yellow solid formed
was filtered off, washed well with water, and recrystallized from
tert-butyl alcohol. Yellow needles of 2-hydroxy-5,6-diphenylpyr-
azine were obtained after filtration (3.0 g; yield: 60%). M.p. 240–
250 °C. IR (KBr): ν
= 3050–2500 (broad), 1657, 1588, 1562,
˜
max
1496, 1438, 1376, 1228, 1163, 1026 cm–1. MS: m/z (%) = 248 (100)
[M+], 229 (5), 219 (62), 165 (28). 1H NMR ([D6]DMSO, 200 MHz):
δ = 12.25 (br. s, 1 H, OH), 8.18 (s, 1 H, 3-H), 7.30 (m, 5 H) ppm.
852
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2005, 847–853