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The yield calculated based on the weight of the isolated which was used as an internal standard. Sulfolane was selected
anhydride (3) after washing with diethyl ether (cooled to as internal standard because of its high stability against strong
253 K), filtering and drying was consistent with results found acids as well as thermal stability.39 (For reactions performed
1
by qNMR. The product was analyzed by H NMR and found to using binary mixtures, the second chemical was added to this
be exo-4,10-dioxa-tricyclo[5.2.1.0]dec-8-ene-3,5-dione. For reac- mixture at this point.) The mixture was then stirred for
tions run “on-water”, excess water was first filtered off and the 5 minutes at room temperature. In the case of acetic anhy-
reported yield was evaluated by the weight of the isolated oxa- dride, MSA and acetic anhydride reacted to form acetyl
norbornene after washing with diethyl ether (cooled to 253 K) methanesulfonate [1H NMR (400 MHz, CDCl3) δ 2.28 (3H, s,
rather than by qNMR.
COCH3), 3.33 (3H, s, SO2CH3)]36 which was accompanied by an
1H NMR (400 MHz, DMSO) δ 6.58 (2H, s, –CHv), 5.35 (2H, exotherm. The reaction was then heated to the desired temp-
s, –CH–O–), 3.33 (2H, s, –CH–) ppm; IR (neat) ν 575, 634, 675, erature and 6.02 mmoles of oxanorbornene were slowly added
690, 733, 849, 877, 883, 920, 922, 1020, 1080, 1150, 1210, 1220, while monitoring the temperature. The rate of addition was
1280, 1310, 1780 cm−1
.
maintained such that the reaction temperature did not exceed
Equilibrium experiments were conducted in a 600 mL Parr the desired temperature. The vial was then flushed with nitro-
reactor (Parr Instrument Company – model 452HC3) equipped gen. Conversion and selectivity were calculated using the
with a pressure and temperature sensor. 0.10 moles of oxanor- internal standard by qNMR. All the reactions were conducted
bornene dicarboxylic anhydride (3) were loaded under a nitro- such that the total solution volume was 5 mL to avoid the con-
gen atmosphere (10 psig of N2). The temperature of the reactor founding effects associated with the side-reactions.
was increased stepwise as the pressure was monitored. For
Following reaction, the reaction product was cooled to
equilibrium experiments conducted “on-water”, 3.09 mL of room temperature and extracted with anhydrous toluene
water were first loaded into the reactor before the addition of 3. (99.8%, Sigma Aldrich) (10 mL, 3 times). The toluene fractions
exo-cis-1-Methyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic were combined and the solvent was removed in a rotary evap-
anhydride, the adduct of 2-methylfuran and maleic anhydride, orator. The isolated solid was then recrystallized from acetic
was prepared by reacting 0.0666 moles (6.53 g) of maleic anhy- anhydride and washed with cold hexane to give phthalic anhy-
dride and 0.0666 moles (5.47 g) of 2-methylfuran in a 45 mL dride (white crystal). Yields calculated based on the weight of
closed Parr reactor (series 4703–4714, General Purpose phthalic anhydride were consistent with those determined by
Pressure Vessels) for 24 h at room temperature under a nitro- qNMR.
gen atmosphere. Following the reaction, the solid was washed
with diethyl ether (253 K) to give 10.068 g of a white product (2H, dd, –CHv); IR (neat) ν 534, 642, 677, 710, 798, 839, 903,
1H NMR (400 MHz, DMSO) δ 8.09 (2H, dd, –CHv), 8.01
(84% yield).
1000, 1110, 1160, 1260, 1360, 1470, 1600, 1760, 1790,
1H NMR (400 MHz, DMSO-d6) δ 6.58 (dd, J = 5.5, 1.8 Hz, 1840 cm−1; m/z 148.
7H), 6.41 (d, J = 5.6 Hz, 7H), 5.22 (d, J = 1.9 Hz, 7H), 3.44 (d, J =
(rac) (3aS,4S,5S,7aS)-1,3-Dioxo-1,3,3a,4,5,7a-hexahydroiso-
6.6 Hz, 8H), 3.20 (d, J = 6.6 Hz, 7H), 1.62 (s, 22H); IR (neat) benzofuran-4,5-diyl diacetate was isolated by running the reac-
ν 579, 615, 661, 673, 735, 845, 876, 895, 922, 955, 982, 1070, tion at conditions such that only this reaction intermediate
1090, 1140, 1230, 1320, 1390, 1770, 1840 cm−1
.
formed (0.039 moles of MSA and 0.0264 moles of acetic anhy-
The adduct of 2,5-dimethylfuran and maleic anhydride, 1,7- dride, 24 h, 298 K). The intermediate was separated using a
dimethyl-4,10-dioxa-tricyclo[5.2.1.02,6]dec-8-ene-3,5-dione, was 2 : 1 mixture of hexanes (99.9%, Fisher Scientific) and ethyl
similarly prepared by reacting 0.0618 moles (6.06 g) of maleic acetate (99.9%, Fisher Scientific) by flash chromatography
anhydride and 0.0618 moles (5.94 g) of 2,5-dimethylfuran in a using Supelco® spherical flash silica (45–75 μm). The inter-
45 mL closed Parr reactor for 24 h. The solid was washed with mediate was analyzed by 2D NMR correlation spectroscopy
diethyl ether (cooled to 253 K) to give 8.981 g of a white solid (COSY), heteronuclear multiple bond correlation (HMBC), and
(75% yield).
heteronuclear multiple quantum coherence (HMQC)40 (see
1H NMR (400 MHz, DMSO-d6) δ 6.41 (s, 5H), 3.32 (s, 6H), Fig. S1 in the ESI† section).
1.58 (s, 16H); IR (neat) ν 579, 625, 669, 744, 831, 862, 918, 976,
1H NMR (400 MHz, Chloroform-d) δ 6.30 (dd, J = 10.0,
1040, 1080, 1210, 1240, 1320, 1390, 1440, 1760, 1850, 3.8 Hz, 1H), 6.22–6.12 (m, 1H), 5.47–5.40 (m, 1H), 5.23 (dd, J =
2990 cm−1
.
5.4, 3.8 Hz, 1H), 3.82 (ddd, J = 9.3, 3.8, 2.6 Hz, 1H), 3.73 (dd,
J = 9.3, 4.2 Hz, 1H), 2.10 (s, 3H), 2.05 (s, 3H). HRMS (EI) m/z,
calcd for [C12H12O7]: 269.0661; found: 269.0661.
Dehydration reaction
Methanesulfonic acid (99.5%+, Sigma Aldrich), acetic anhy-
The yields of 3,6-dimethyl phthalic anhydride and 3-methyl
dride (99.4%, Fisher Scientific), glacial acetic acid (99.9%, phthalic anhydride were calculated by qNMR. For the dehy-
Fisher Scientific), methanesulfonic anhydride (97%, Sigma dration of the cycloadduct 2,5-dimethylfuran and maleic anhy-
Aldrich) maleic anhydride (99.0+%, Sigma-Aldrich) and sulfo- dride the peaks at 7.68 (2H, s, –CHv) and 7.62 (2H, s, –CHv)
lane (99%+, Sigma Aldrich) were used as received and stored corresponding to 3,6-dimethyl phthalic anhydride and 3,6
under a dry inert atmosphere. In a 20 mL disposable scintil- dimethyl phthalic acid were integrated. For the dehydration of
lation vial the desired amount of MSA was loaded in addition the cycloadduct of 2-methylfuran and maleic anhydride the
to 3.01 mmol (0.362 grams) of sulfolane (99%+, Sigma Aldrich) yield was calculated by integrating the peaks found between
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Green Chem.