Design and synthesis of a photoaromatization-based two-stage photobase generator for pitch division lithography

Article abstract of DOI:10.1021/jo3021488

The synthesis of a two-stage photobase generator (PBG) based on photoinduced aromatization is described. This material was designed for use in resolution-enhanced photolithography. Computer modeling predicts that a delay in the onset of base generation ca

Full text of DOI:10.1021/jo3021488

Article
pubs.acs.org/joc
Design and Synthesis of a Photoaromatization-Based Two-Stage
Photobase Generator for Pitch Division Lithography
Yuji Hagiwara,†,⊥ Ryan A. Mesch,† Takanori Kawakami,‡,∥ Masahiro Okazaki,‡ Steffen Jockusch,§
Yongjun Li,§ Nicholas J. Turro,§ and C. Grant Willson*,†,‡
‡
†Department of Chemistry and Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712,
United States
§Department of Chemistry, Columbia University, New York, New York 10027, United States
S
* Supporting Information
ABSTRACT: The synthesis of a two-stage photobase
generator (PBG) based on photoinduced aromatization is
described. This material was designed for use in resolution-
enhanced photolithography. Computer modeling predicts that
a delay in the onset of base generation can lead to improved
image quality. This delay can be realized by a PBG that must
undergo two sequential photoreactions for each molecule of base generated. Toward that end, latent PBGs were designed that
are oxime esters of aliphatic acids, which undergo Norrish type II reactions to yield oxime esters of aromatic acids that are
efficient PBGs.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
The microelectronics manufacturing industry is taking extreme
measures to extend the resolution limit of current 193 nm tools
beyond their physical limits in order to keep pace with Moore’s
Law.1 These extreme measures come at the cost of several
added processing steps, which lead to increased production
costs.2 We have previously demonstrated a “trick” that exploits
chemistry to double the resolution of 193 nm lithography and
does not require any extra processing steps. The trick only
requires adding a photobase generator (PBG) to the
formulation of a typical 193 nm resist.3 If the stoichiometry
and the kinetics are right, the image recorded in such a resist
has twice the pitch of the projected mask image. Unfortunately,
when sub-100 nm features are printed, they suffer from line
edge roughness (LER). This LER is undoubtedly caused by the
convolution of several issues, but we believe that the major
contributor is the fact that the slope of the acid concentration
gradient at the line edge is not as steep as it is in normal
imaging.
Modeling suggests that a delay in onset of base generation as
a function of dose would increase the fidelity of the printed
image.4 Therefore a “two-stage” PBG was designed, one that
requires a sequence of two photolysis reactions to generate a
molecule of base. If a latent PBG reacts with a photon to
produce an active PBG that can in turn react with a second
photon to produce base, and the relative rates of the reactions
are closely matched, a significant delay in base generation can
be realized, which results in steepening the gradient of the net
acid generation curve. This paper describes the design and
synthesis of a two-stage PBG based on photoinduced
aromatization.
Oxime esters of aromatic acids are a well-studied class of
PBGs.5 Oxime esters of aliphatic acids do not produce base at a
significant rate upon exposure at 193 nm, but aromatic
analogues are efficient PBGs. Therefore, an oxime ester of an
aliphatic acid that undergoes photoaromatization reaction to
create an active, aromatic PBG can serve as the latent PBG, as
depicted in Scheme 1.
First Approach. Several examples of photoaromatization
reactions are known, but most are based on 1,4-dihydropyr-
idines6 or more complicated systems that are not suited for our
purpose.7,8 A basic design for a photoaromatization type two-
stage PBG is illustrated in Scheme 1, based on a photo-
aromatization mechanism achieved by the Norrish type II
photoelimination.9 A major obstacle in this design is the fact
that dienes are efficient triplet quenchers. Luckily, they are not
efficient singlet quenchers. Wagner teaches that the strength of
the γ-CH bond of the ketone dictates whether the type II
reaction proceeds via the singlet or triplet state.10 Clearly, we
needed a singlet pathway. According to Wagner’s studies,
ketones with stronger γ-CH bonds, such as those in 2-
pentanone (98 kcal/mol), proceed via a triplet state, whereas
those with weaker γ-CH bonds, such as 5-methyl-2-hexanone
(91 kcal/mol), proceed mostly via the singlet.9 As shown in
Scheme 2, compound 5a is an oxime ester of cyclo-
hexyldienylcarboxylic acid with an allylic and tertiary γ-
hydrogen. On the basis of Wagner’s studies, we hoped that
Special Issue: Howard Zimmerman Memorial Issue
Received: September 30, 2012
Published: October 31, 2012
© 2012 American Chemical Society
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Scheme 1. First Design Approach of a Two-Step PBG
Scheme 2. Synthesis of 5a,b
Scheme 3. Second Design Approach of a Two-Step PBG
Scheme 4. Synthesis of 13
this compound would undergo a fast type II cleavage and
aromatization via the singlet manifold.
desired ketone. The first attempts at the D−A reaction were
not successful, presumably because the dioxide is too strongly
electron-withdrawing, but luckily, the reaction proceeded
smoothly with thiophene oxide. Attempts were made to oxidize
the secondary alcohol and the sulfoxide simultaneously to
facilitate SO2 loss, but these reactions gave mixtures, so a
stepwise approach was taken that ultimately provided the
desired bicyclic sulfone (4).
The expulsion of SO2 from the sulfone was more facile than
expected and proceeded cleanly during silica column
chromatography to yield a mixture of cyclohexadiene isomers
(5a,b). Sadly, exposure of compounds 5a,b to UV radiation
showed no significant photoreactivity under our photolysis
conditions. These substances are essentially inert at 248 and
193 nm. Upon prolonged exposure, a complex mixture of
products was produced. This disappointing observation could
be the result of the fact that the aliphatic ketones in compounds
5a,b are inefficient light absorbers, whereas the diene
chromophore absorbs UV light much more efficiently.
Additionally, the intersystem crossing of the singlet to the
We envisioned making the cyclohexadiene platform via a
Diels−Alder (D−A) reaction (Scheme 2). The dienophile is
well-suited for installation of the oxime ester due to its electron-
withdrawing properties and offers a means to incorporate
various photolabile moieties as substituents on the alkene. We
predicted that the D−A adduct of thiophene dioxide and our
tailored dienophile could lead to the cyclohexadiene through
loss of SO2. Unfortunately, thiophene dioxide dimerizes at a
lower temperature than that required to activate the addition of
the desired dienophile (Supporting Information Figure S4).
Only traces of the cross-products could be detected. Previous
work by Nakayama11 demonstrated that sufficiently bulky
substituents, such as t-butyl in the 3,4 position of the
thiophene, block the dimerization and allow for cross D−A
reactions. The use of parasorbic acid as the dienophile was
appealing since it set the position of the ester alpha to the
cyclohexyl backbone and could be hydrolyzed to give a methyl
ester and a secondary alcohol which can be oxidized to the
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3,4-Di-tert-butylthiophene-1-oxide was synthesized according to the
work of Nakayama, and the spectroscopic properties matched those
reported in literature.11,12
4-Hydroxy-6-methyltetrahydro-2H-pyran-2-one was synthesized ac-
cording to the procedure of Dumesic and Chia13 on a 119 mmol scale
to provide 15.2 g (117 mmol, 98%) of product.
6-Methyl-5,6-dihydro-2H-pyran-2-one (2) was synthesized according
to the procedure of Sato and co-workers14 on a 117 mmol scale to
provide 4.57 g (40.8 mmol, 35%) of product with spectroscopic
properties that match those reported in literature.15
triplet could be faster than abstraction of the γ-hydrogen, in
which case energy transfer to the diene would quench the
triplet very quickly. Since no photoaromatization was observed
for 5a,b, a new strategy outlined in Scheme 3 was pursued.
Second Approach. The goal of the second design was to
avoid a diene in favor of an enone in the first step and to
achieve aromatization after elimination via a favorable
tautomerization (Scheme 3). Our hope was that while it is
well-known that enones also quench triplet states, this
structural variation would change the rates in our favor. An
additional goal of the second design was to increase the UV
absorption efficiency of the chromophore in the first reaction
step. Whereas the first design approach depends on absorbance
by a weak acetone chromophore, the second design
incorporates an acetophenone chromophore, which has 3
orders of magnitude higher molar absorptivity than acetone.
The design outlined in Scheme 3 was validated by preliminary
exposure studies that showed that the oxime esters of
hydroxybenzoic acid perform just as efficiently as their benzoyl
oxime counterparts in pitch division formulations.
The synthesis of this new target (13) was achieved via a
Birch reduction of methyl 3-methoxybenzoate (a) followed by
installation of the photolabile groups via enolate chemistry (b)
(Scheme 4). Reduction and installation of acetophenone
proceeded in acceptable yields, but attempts to cleave the
methyl ether and hydrolyze the ester simultaneously were
unsuccessful, so these deprotection steps were carried out in
sequence (c−d) followed by installation of the oxime via
carbodiimide-mediated esterification (e). Even in the absence
of extensive reaction optimization, this pathway gave a > 15%
yield over six steps and is sufficiently flexible to allow
installation of acetophenone derivatives. The two-stage PBG
13 functions effectively in pitch division formulations
(Supporting Information Figure S3), but the control PBG 15
does not. On the basis of these functional tests, the details of
the photochemistry of these compounds were studied. The
results of that work are described in the accompanying paper.20
7-Thiabicyclo[2.2.1]hept-5-ene-2-carboxylic Acid, 3-(Prop-
an-2-ol)-oxide (3). A solution of 3,4-di-tert-butylthiophene-1-oxide
(0.177 g, 0.832 mmol, 1 equiv) and parasorbic acid (2) (0.121 g, 1.00
mmol, 1.2 equiv) in 1-butyl-3-methylimidazolium tetrafluoroborate
([BMIm]BF4, 1.0 g) was heated to 120 °C and stirred for 16 h. The
reaction was partitioned between Et2O and H2O, and the organic layer
was dried (MgSO4) and then concentrated in vacuo. The crude
colorless oil (0.270 g) was dissolved in MeOH and chilled to 0 °C
before treating with NaOH (2 M in H2O) then warmed to rt while
stirring for 16 h. The reaction was quenched with HCl (1 N in H2O)
until the reaction solution was at pH 1 and then extracted with EtOAc
(150 mL). The organic layer was washed with H2O (2 × 50 mL) and
brine (1 × 50 mL), dried (MgSO4), filtered, and concentrated in
vacuo. The colorless oil was then purified by trituration in acetone and
hexane at 0 °C to yield 0.260 g (0.760 mmol, 91%) of a white powder,
1
mp 151−154 °C. H NMR (300 MHz, DMSO-d6): δ 4.61−4.53 (m,
1H), 4.27−4.16 (m, 1H), 3.99−3.87 (m, 1H), 3.50−3.47 (m, 1H),
3.19−3.08 (m, 2H), 2.09 (s, 3H), 1.22−1.15 (m, 18H). 13C NMR (75
MHz, DMSO-d6): δ 171.9, 143.7, 141.5, 74.5, 69.5, 67.3, 34.6, 33.5,
31.9, 31.8, 30.6, 29.4, 20.0. IR (neat): 3216, 2965, 1712, 1204, 1000.
HRMS: exact mass calcd for C18H30O4S [M + Na]+ 365.1762, found
365.1757.
7-Thiabicyclo[2.2.1]hept-5-ene-2-carboxylic Acid, 3-(Prop-
an-2-one)-oxide (4). To a chilled (0 °C) solution of pyridinium
dichromate (0.384 g, 1.02 mmol, 3.5 equiv) in DMF (3 mL) was
added a solution of compound 3 (0.100 g, 0.292 mmol, 1 equiv) in
DMF (3 mL) and warmed to rt while stirring for 16 h. The reaction
was partitioned with EtOAc (75 mL) and H2O (100 mL), and the
organic layer was washed with H2O (50 mL) and brine (50 mL), dried
(MgSO4), filtered, and concentrated in vacuo. The reaction yielded 65
mg (0.191 mmol, 65%) of colorless oil. 1H NMR (300 MHz, CDCl3):
δ4.18 (s, 1H), 3.95 (s, 1H), 3.42−3.39 (m, 1H), 3.19−2.98 (m, 2H),
2.71−2.61 (m, 1H), 2.05 (s, 3H), 1.16−1.15 (m, 18H). 13C NMR (75
MHz, CDCl3): δ 208.1, 176.8, 142.4, 69.8, 68.9, 43.5, 41.5, 34.7, 34.4,
33.5, 32.9, 32.5, 32.5, 32.4, 30.1. IR (neat): 2961, 1718. HRMS: exact
mass calcd for C18H28O4S [M + H]+ 340.1708, found 341.1788.
Compounds 5a and 5b. A solution of compound 4 (0.055 g,
0.161 mmol, 1 equiv) and m-CPBA (0.033 g, 0.193, 1.2 equiv) in
DCM (5 mL) and THF (5 mL) was stirred overnight at rt. The
reaction was partitioned between EtOAc (40 mL) and H2O (50 mL),
and the organic layer was washed with H2O (50 mL) and brine (50
mL), dried (MgSO4), filtered, and concentrated in vacuo. The crude
yellow oil was purified by flash chromatography (silica gel 2:1 = Hex/
EtOAc) to yield a mixture of isomers of compound 5 as a colorless oil
CONCLUSION
■
We have reported a new approach to photoaromatization and a
two-stage photoreaction that leads to basic photoproducts. The
synthesis of PBG 13 is flexible and allows for modification of
the acetophenone moiety.
EXPERIMENTAL SECTION
■
1
General Information. H NMR spectra were recorded on 300 or
400 MHz spectrometers at ambient temperature unless otherwise
noted and are reported in parts per million using solvent as the
internal standard (CDCl3 at 7.26 ppm or CD3OD at 3.31 ppm). Data
are reported as multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, m = multiplet), integration and coupling constant(s) in hertz.
13C NMR spectra were recorded on a 75 or 100 MHz spectrometer.
Chemical shifts are reported in parts per million from tetramethylsi-
lane, with the residual solvent resonance employed as the internal
standard (CDCl3 at 77.0 ppm). High-resolution mass spectra (HRMS)
by ESI-QTOF are reported as m/z (relative intensity). UV light
exposures were performed at 248 nm using a KrF excimer laser, and
the 193 nm exposures were carried out with a ArF excimer laser. Films
were spin-coated on a Brewer CEE 100CB spin coater. Film
thicknesses were determined with an ellipsometer using wavelengths
from 382 to 984 nm with a 65° angle of incidence. A hot plate open to
air was used to bake the photoresists.
1
(0.030 g, 0.102 mmol, 64% yield). H NMR (300 MHz, CDCl3): δ
6.51 (d, J = 7.2 Hz, 1H), 5.95 (s, 1H), 4.89 (s, 1H), 3.89 (s, 1H), 3.25
(m, 2H), 3.0 (m, 1H), 2.78−2.45 (m, 6H), 2.19−2.16 (m, 6H), 1.78−
1.64 (m, 1H), 1.55−1.51 (m, 4H), 1.29−1.66 (m, 34H). 13C NMR
(75 MHz, CDCl3): δ 209.3, 206.2, 174.2, 172.9, 153.6, 150.2, 131.7,
127.9, 96.4, 92.8, 76.2, 71.6, 47.6, 45.6, 44.1, 43.1, 37.7, 37.5, 37.32,
36.33, 32.9, 30.7, 30.0, 29.0. IR (neat): 1749, 1721. HRMS: exact mass
calcd for C18H28O3 [M + Na]+ 315.1936, found 315.1931.
Cyclohexanone O-(3-Hydroxybenzoyl)oxime (7). To a chilled
solution (0 °C) of 3-hydroxybenzoic acid (3.0 g, 21.7 mmol, 1 equiv),
cyclohexanone oxime (2.5 g, 21.7 mmol, 1 equiv), and N,N-dimethyl-
4-aminopyridine (0.27 g, 2.2 mmol, 0.1 equiv) in dichloromethane
(150 mL) was added 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (4.16 g, 21.7 mmol, 1 equiv) and stirred for 1 h at 0 °C.
Upon warming to rt and stirring for an additional 4 h, the reaction
mixture was quenched with saturated NaHCO3 (2 × 100 mL), water
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(1 × 100 mL), and brine (1 × 100 mL). The organic layer was
subsequently dried (MgSO4), filtered, and concentrated in vacuo. The
resulting crude pale yellow solid was purified by flash chromatography
(silica gel 4:1 = Hex/EtOAc) to yield cyclohexanone O-(3-hydroxy-
benzoyl)oxime as a white solid (1.5 g, 6.4 mmol, 30% yield), mp 134
129.5, 128.8, 128.1, 52.7, 46.0, 45.5, 45.0, 33.7. IR (neat): 1726, 1673.
HRMS: exact mass calcd for C16H16O4 [M + H]+ 273.1127, found
273.1126.
5-Oxo-1-(2-oxo-2-phenylethyl)cyclohex-3-ene carboxylic
acid (12). To a chilled solution (0 °C) solution of methyl 5-oxo-1-
(2-oxo-2-phenylethyl)cyclohex-3-enecarboxylate (1.20 g, 4.41 mmol, 1
equiv) in THF (60 mL) was added a solution of lithium hydroxide
(116 mg, 4.85 mmol, 1.1 equiv) in H2O (60 mL), and the resulting
solution was stirred for 1 h, warmed to rt, and stirred for an additional
2 h then quenched with 1 N HCl (10 mL) and partitioned between
EtOAc (100 mL) and H2O (50 mL). The organic layer was washed
with brine (1 × 50 mL), dried (MgSO4), filtered, and concentrated in
vacuo. The resulting yellow solid was purified by flash chromatography
(silica gel 2:1 = Hex/EtOAc) to yield 5-oxo-1-(2-oxo-2-phenylethyl)-
cyclohex-3-enecarboxylic acid as a pale yellow solid (1.0 g, 3.9 mmol,
1
°C. H NMR (300 MHz, CDCl3): δ 7.63−7.53 (m, 2H), 7.27 (t, J =
8.1 Hz, 1H), 7.17−7.12 (m, 1H), 2.60 (t, J = 6.0 Hz, 2H), 2.35 (t, J =
6.0 Hz, 2H), 1.74−1.52 (m, 6H). 13C NMR (75 MHz, CDCl3): δ
170.3, 165.1, 156.7, 130.1, 129.7, 121.3, 121.1, 116.6, 23.0, 27.2, 26.8,
25.9, 25.4. IR (neat): 1720, 2930, 2861, 3356. HRMS: exact mass calcd
for C13H15NO3 [M + Na]+ 256.0950, found 256.0946.
Methyl 3-Methoxycyclohexa-2,5-dienecarboxylate (9). The
following procedure was adapted from the method of Rabideau.16−18
A solution of methyl 3-methoxybenzoate (5.00 g, 30.1 mmol, 1 equiv)
in THF (50 mL) was cooled to −78 °C, and then H2O (0.81 g, 45.1
mmol, 1.5 equiv), NH3 (100 mL), and sodium (1.0 g, 45.1 mmol, 1.5
equiv) were added, and the resulting mixture was stirred for 30 min at
−78 °C. The mixture was quenched with a concentrated NH4Cl
solution and then stirred for 30 min at rt, extracted with ethyl acetate
(3 × 100 mL), and the combined organic layers were washed with
water (2 × 150 mL) and brine (1 × 100 mL), dried (MgSO4), filtered,
and concentrated in vacuo. The resulting oil was purified by flash
chromatography (silica gel 20:1 = Hex/EtOAc) to yield 3-methoxy-
cyclohexa-2,5-dienecarboxylate as a colorless oil (2.80 g, 16.6 mmol,
55%). 1H NMR (300 MHz, CDCl3): δ 5.80−5.68 (m, 2H), 4.72−4.62
(m, 1H), 3.87−3.74 (m, 1H), 3.61 (s, 3H), 3.51 (s, 3H), 2.69−2.60
(m, 2H). 13C NMR (75 MHz, CDCl3): δ 173.5, 154.4, 125.1, 122.2,
89.5, 53.8, 51.9, 42.9, 28.3. IR (neat): 1724, 1194, 1166. HRMS: exact
mass calcd for C9H12O3 [M + H]+ 169.0865, found 169.0859.
Methyl 3-Methoxy-1-(2-oxo-2-phenylethyl)cyclohexa-2,5-
dienecarboxylate (10). To a chilled (−10 °C) solution of
diisopropylamine (1.80 g, 18.8 mmol, 1.2 equiv) in THF (30 mL)
was added 2.5 M solution of n-BuLi in hexanes (7.50 mL, 18.8 mmol,
1.2 equiv) and stirred for 30 min. The reaction mixture was cooled to
−78 °C, and methyl 3-methoxycyclohexa-2,5-dienecarboxylate (2.60 g,
15.5 mmol 1 equiv) was added dropwise. After stirring for 15 min, 2-
bromoacetophenone (6.20 g, 31.0 mmol, 2 equiv) in hexamethyl-
phosphoric triamide (15 mL) was added, and the reaction mixture was
stirred for 30 min at −78 °C. Upon warming to rt and stirring for an
additional 2 h, the reaction mixture was partitioned with H2O and
EtOAc. The organic layer was washed with H2O (2 × 150 mL) and
brine (1 × 100 mL), dried (MgSO4), filtered, and concentrated in
vacuo. The resulting crude oil was purified by flash chromatography
(silica gel 10:1 = Hex/EtOAc) to yield methyl 3-methoxy-1-(2-oxo-2-
phenylethyl)cyclohexa-2,5-dienecarboxylate as a pale yellow oil (4.1 g,
1
90% yield), mp 149−151 °C. H NMR (300 MHz, CDCl3): δ 8.06−
7.85 (m, 2H), 7.72−7.58 (m, 1H), 7.58−7.42 (m, 2H), 7.00−6.82 (m,
1H), 6.05−5.93 (m, 1H), 3.56 (d, J = 18.3 Hz, 1H), 3.45 (d, J = 18.3
Hz, 1H), 2.90 (d, J = 16.5 Hz, 1H), 2.90−2.76 (m, 1H), 2.72−2.58
(m, 1H), 2.45 (d, J = 16.5 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
197.5, 197.4, 176.5, 147.5, 137.6, 134.4, 129.8, 129.7, 128.9, 46.8, 46.3,
45.6, 35.0. IR (neat): 2909, 1697, 1678. HRMS: exact mass calcd for
C15H14O4 [M + H]+ 259.0965, found 259.0962.
5-(((Cyclohexylideneamino)oxy)carbonyl)-5-(2-oxo-2-
phenylethyl)cyclohex-2-enone (6). To a chilled solution (0 °C) of
5-oxo-1-(2-oxo-2-phenylethyl)cyclohex-3-enecarboxylic acid (0.18 g,
0.70 mmol, 1 equiv), cyclohexanone oxime (0.11 g, 0.98 mmol, 1.4
equiv), and N,N-dimethyl-4-aminopyridine (8.6 mg, 0.07 mmol, 0.1
equiv) in DCM (10 mL) was added 1-(3-dimethylaminopropyl)-3-
ethylcarbodiimide hydrochloride (0.155 g, 0.81 mmol, 1.2 equiv) and
stirred for 1 h. Upon warming to rt and stirring for an additional 2 h,
the reaction mixture was quenched with saturated NaHCO3 (2 × 50
mL), water (1 × 50 mL), and brine (1 × 50 mL). The organic layer
was subsequently dried (MgSO4), filtered, and concentrated in vacuo.
The resulting crude yellow oil was purified by flash chromatography
(silica gel 4:1 = Hex/EtOAc) to yield 5-(((cyclohexylideneamino)-
oxy)carbonyl)-5-(2-oxo-2-phenylethyl)cyclohex-2-enone as a pale
1
yellow oil (0.16 g, 0.45 mmol, 65%). H NMR (300 MHz, CDCl3):
δ 7.90−7.80 (m, 2H), 7.54−7.46 (m, 1H), 7.38 (t, J = 7.8 Hz, 2H),
6.84 (dt, J = 9.9 and 4.2 Hz, 1H), 6.04 (dt, J = 9.9 and 1.8 Hz, 1H),
3.55 (d, J = 18.0 Hz, 1H), 3.40 (d, J = 18.0 Hz, 1H), 3.09 (d, J = 16.5
Hz, 1H), 3.02−2.90 (m, 1H), 2.73−2.61 (m, 1H), 2.56 (d, J = 16.5
Hz, 1H), 2.34 (t, J = 6.3 Hz, 1H), 2.29 (t, J = 6.3 Hz, 1H), 1.71−1.42
(m, 6H). 13C NMR (75 MHz, CDCl3): δ 196.3, 172.2, 170.2, 146.8,
136.2, 133.5, 129.5, 128.6, 127.9, 46.0, 45.6, 44.8, 34.2, 31.9, 27.1, 26.6,
25.6, 25.2. IR (neat): 2938, 2861, 1747, 1677. HRMS: exact mass calcd
for C21H23NO4 [M + Na]+ 376.1525, found 376.1523.
1
14.2 mmol, 92% yield). H NMR (300 MHz, CDCl3): δ 7.93−7.83
(m, 2H), 7.55−7.46 (m, 1H), 7.45−7.35 (m, 2H), 5.92−5.83 (m, 1H),
5.79 (dt, J = 9.9 and 3.3 Hz, 1H), 4.83−4.78 (m, 1H), 3.68 (s, 3H),
3.51 (s, 3H), 3.44 (s, 2H), 2.80−2.59 (m, 2H). 13C NMR (75 MHz,
CDCl3): δ 197.2, 175.2, 154.6, 136.6, 133.2, 128.5, 128.0, 127.1, 124.6,
95.0, 54.0, 52.4, 50.1, 47.4, 28.6. IR (neat): 1723, 1683. HRMS: exact
mass calcd for C17H18O4 [M + H]+ 287.1283, found 287.1273.
Methyl 5-Oxo-1-(2-oxo-2-phenylethyl)cyclohex-3-enecar-
boxylate (11). To a solution of methyl 3-methoxy-1-(2-oxo-2-
phenylethyl)cyclohexa-2,5-dienecarboxylate (2.0 g, 7.0 mmol, 1 equiv)
in 1,4-dioxane (50 mL) and H2O (10 mL) was added p-
toluenesulfonic acid monohydrate (1.3 g, 7.0 mmol, 1 equiv), and
the mixture was then heated to 100 °C and stirred for 1.5 h and cooled
to rt. The reaction mixture was then extracted with EtOAc (200 mL),
and the organic layer was washed with saturated NaHCO3 (1 × 100
mL), H2O (1 × 100 mL), and brine (1 × 100 mL), dried (MgSO4),
filtered, and concentrated in vacuo. The crude oil was then purified by
flash chromatography (silica gel 4:1 = Hex/EtOAc) to yield methyl 5-
oxo-1-(2-oxo-2-phenylethyl)cyclohex-3-enecarboxylate as a white solid
1-Methyl-5-oxocyclohex-3-enecarboxylic Acid (13). The
following procedure was adapted from Smith and Richmond.19 To a
chilled solution (−78 °C) of 3-methoxybenzoic acid (1.5 g, 9.9 mmol,
1 equiv) in THF (10 mL) were added ammonia (50 mL) and lithium
metal (0.274 g, 39.4 mmol, 4 equiv). The resulting solution was stirred
for 1 h at −78 °C, after which a solution of methyl iodide (2.8 g, 19.7
mmol) in THF (2 mL) was then added, and the resulting mixture was
stirred for 1 h at −78 °C, quenched with solid ammonium chloride,
and the ammonia was then evaporated under a stream of nitrogen. The
resulting crude solid was dissolved in HCl (2 N H2O) and refluxed for
30 min. After cooling, the solution was extracted with EtOAc (600
mL), and the organic fraction was washed with H2O (2 × 100 mL)
and brine (1 × 50 mL), dried (MgSO4), filtered, and concentrated in
vacuo. The resulting pale yellow solid was purified by flash
chromatography (silica gel 2:1 = Hex/EtOAc) to yield 1-methyl-5-
oxocyclohex-3-ene carboxylic acid as a pale yellow solid (0.670 g, 16.6
1
1
mmol, 44%), mp 78−80 °C. H NMR (300 MHz, CDCl3): δ 10.94
(0.98 g, 3.6 mmol, 52%), mp 112−114 °C. H NMR (300 MHz,
(br s, 1H), 6.93−6.82 (m, 1H), 6.03−5.97 (m, 1H), 2.90−2.75 (m,
2H), 2.32 (d, J = 16.5, 2H), 1.32 (s, 3H). 13C NMR (75 MHz,
CDCl3): δ 198.0, 181.4, 148.0, 129.6, 46.9, 44.7, 35.3, 24.8. IR (neat):
2974, 1770. HRMS: exact mass calcd for C8H10O3 [M + H]+
155.0708, found 155.0702.
CDCl3): δ 7.92−7.85 (m, 2H), 7.62−7.55 (m, 1H), 7.45 (t, J = 7.8 Hz,
2H), 6.87 (dt, J = 9.9 and 4.2 Hz, 1H), 6.08 (dt, J = 9.9 and 1.8 Hz,
1H), 3.67 (s, 3H), 3.52−3.36 (m, 2H), 3.06−2.97 (m, 1H), 2.98 (d, J
= 16.2 Hz, 1H), 2.68−2.59 (m, 1H), 2.56 (d, J = 16.2 Hz, 1H). 13C
NMR (75 MHz, CDCl3): δ 196.7, 196.5, 175.1, 146.8, 136.5, 133.7,
1733
dx.doi.org/10.1021/jo3021488 | J. Org. Chem. 2013, 78, 1730−1734

The Journal of Organic Chemistry
Article
5-(((Cyclohexylideneamino)oxy)carbonyl)-5-methyl-
cyclohex-2-enone (14). To a chilled solution (0 °C) of 1-methyl-5-
oxocyclohex-3-enecarboxylic acid (0.30 g, 2.0 mmol, 1 equiv),
cyclohexanone oxime (0.31 g, 2.7 mmol, 1.4 equiv), and N,N-
dimethyl-4-aminopyridine (24 mg, 0.20 mmol 0.1 equiv) in DCM (30
mL) was added 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (0.42 g, 2.7 mmol, 1.4 equiv), and the reaction mixture
was stirred for 1 h at 0 °C. After warming to rt and stirring for 2 h, the
reaction mixture was washed with saturated NaHCO3 (2 × 30 mL),
H2O (1 × 30 mL), and brine (1 × 30 mL). The organic layer was
dried (MgSO4), filtered, and concentrated in vacuo to leave a crude
yellow oil that was purified by flash chromatography (silica gel 4:1 =
Hex/EtOAc) to yield 5-(((cyclohexylideneamino)oxy)carbonyl)-5-
methylcyclohex-2-enone as a white solid (0.36 g, 1.4 mmol, 74%
yield), mp 47−49 °C. 1H NMR (300 MHz, CDCl3): δ 6.92−6.84 (m,
1H), 6.01 (dt, J = 9.9 and 2.1 Hz, 1H), 3.00−2.83 (m, 2H), 2.48−2.27
(m, 6H), 1.75−1.52 (m, 6H), 1.38 (s, 3H). 13C NMR (75 MHz,
CDCl3): δ 197.0, 172.9, 170.1, 147.5, 129.6, 46.9, 44.9, 35.9, 32.1, 27.1,
26.7, 25.8, 25.4, 25.0. IR (neat): 2933, 2859, 1743. HRMS: exact mass
calcd for C14H19NO3 [M + H]+ 250.1438, found 250.1436.
(12) Nakayama, J.; Yu, T.; Sugihara, Y.; Ishii, A. Chem. Lett. 1997,
499−500.
(13) Dumesic, J. A.; Chia, M. Production of 2,4-Hexanoic Acid and
1,3-Pentadiene from 6-Methyl-5,6-dihydro-2-pyrone. U.S. Patent
2012116119, 2010.
(14) Sato, M.; Sakaki, J.-I.; Sugita, Y.; Nakano, T.; Kaneko, C.
Tetrahedron Lett. 1990, 31, 7463−7466.
(15) Frimer, A. A.; Bartlett, P. D.; Boschung, A. F.; Jewett, J. G. J. Am.
Chem. Soc. 1977, 99, 7977−7986.
(16) Kraus, G. A.; Cui, W. Synlett 2003, 14, 95−96.
(17) Rabideau, P. W.; Wetzel, D. M.; Young, D. M. J. Org. Chem.
1984, 49, 1544−1549.
(18) Rabideau, P. W.; Marcinow, Z. Org. React. 2004, 42, 1.
(19) Smith, A. B., III; Richmond, R. E. J. Am. Chem. Soc. 1983, 105,
575−585.
(20) Turro, N. J.; Li, Y.; Jockusch, S.; Hagiwara, Y.; Okazaki, M.;
Mesch, R. A.; Schuster, D. I.; Willson, C. G. J. Org. Chem. 2012,
DOI: 10.1021/jo302149u.
ASSOCIATED CONTENT
■
S
* Supporting Information
Film UV exposure studies and NMR spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Tel: (+1) 512-471-3975. E-mail: willson@che.utexas.edu.
Present Addresses
⊥Central Glass Co, Kawagoe-Shi, Saitama 350-1151, Japan.
∥JSR Corporation, Yokkaichi-city, Mie 510-8552, Japan.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors at The University of Texas thank Intel for the
generous funding of this project and additionally thank JSR
Corporation and Central Glass Co., Ltd. for their support. The
authors at Columbia thank the National Science Foundation for
financial support through Grant NSF-CHE-11-11398.
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