Venneri and Warkentin
1201
3
(s, 6H), 2.91 (s, 6H). 13C NMR (50 MHz, C6D6) δ: 18.8,
22.8, 48.6, 50.3, 54.4, 103.9, 208.3 (C=O), 215.5 (C=O).
NMR (500 MHz, C6D6) δ: 1.75 (t, J = 7.0 Hz, 2H), 3.25 (s,
6H), 3.50 (t, J = 7.0 Hz, 2H). 13C NMR (125 MHz, C6D6)
3
δ: 33.5, 50.2, 60.4, 110.0, 202.8 (C=O).
Thermolysis of 1 in the presence of 1,2-
diphenylcyclopropenone (23)
Synthesis of 1,1-diethoxyethene
A solution of 1 (0.200 g, 1.25 mmol) and 1,2-
diphenylcyclopropenone (23) (Aldrich, 0.450 g, 2.20 mmol)
in benzene (5.0 g), in a 25 mL thermolysis tube, was treated
as described above. Flash column chromatography (silica
gel, 5% ethyl acetate in hexanes, Rf = 0.23) of the residue
left after pumping off the volatile components, afforded 4, 4-
dimethoxy-2, 3-diphenyl-2-cyclobuten-1-one (26) in 60%
yield. IR (CCl4) (cm–1): 1758. MS (EI) m/z (rel. intensity):
280 (M+., 16), 265 (M+. –15, 6), 249 (M+. –31, 18), 220 (38),
205 (16), 192 (55), 178 (100), 152 (29), 121 (38), 115 (77),
91 (38). MS (HR) m/z: calcd. for C18H16O3: 280.1090;
found: 280.1099. 1H NMR (200 MHz, C6D6) δ: 3.47 (s, 6H),
6.98–7.03 (m, 6H), 7.76–7.81 (m, 2H), 7.87–7.92 (m, 2H).
13C NMR (50 MHz, C6D6) δ: 53.6, 118.1, 128.3, 128.7,
128.9, 129.0, 129.2, 130.0, 130.9, 131.6, 149.0, 170.7,
193.2.
1,1-Diethoxyethene was prepared according to the proce-
dure by Thweatt and co-workers (39). A fractional distilla-
tion apparatus consisting of a two-necked, round-bottomed
flask (50 mL), magnetic stirring bar, addition funnel
(20 mL), fractionating column (20 cm), three-way Claisen
head with thermometer, condenser (20 cm), and a receiving
flask (50 mL) with a vacuum attachment was flame-dried
under vacuum. The addition funnel was removed and solid
potassium tert-butoxide (11.4 g, 102 mmol) was added to
the flask. The addition funnel was reattached and 2-bromo-
1,1-diethoxyethane (15.3 mL, 20.0 g, 101.5 mmol) was
added with a glass syringe to the addition funnel through a
rubber septum. The reaction flask was cooled with an ice
water mixture (5 min) and 2-bromo-1,1-diethoxyethane was
dispensed into the round bottom flask (1 min). A white
dense smoke formed immediately. After the reaction ap-
peared to be complete (5 min), the mixture was heated with
an oil bath (120–130°C), and tert-butyl alcohol (82–
83°C/760 mmHg) generated from the reaction was removed
by distillation. The system was then attached to a water aspi-
rator and 1,1-diethoxyethene was distilled from the crude re-
Thermolysis of 1 in the presence of 3,4-dimethoxy-3-
cyclobutene-1,2-dione (24)
A solution of 1 (0.200 g, 1.25 mmol) and 3,4-dimethoxy-
3-cyclobutene-1,2-dione (24) (Aldrich, 0.170 g, 1.20 mmol)
in benzene (5.0 g) was heated as described above. Flash col-
umn chromatography of the residue left after removal of the
volatiles (10–30% ethyl acetate in hexanes) gave, from the
first yellow band, 2,2,4,5-tetramethoxy-4-cyclopentene-1,3-
dione (27) in 54% yield as a yellow solid, mp 37.0–38.0°C.
IR (CCl4) (cm–1): 1702. MS (EI) m/z (rel. intensity): 216
(M+., 100), 185 (M+. –31, 57), 173 (85), 157 (28), 129 (29),
86 (14), 75 (51), 59 (81). MS (CI–NH3) m/z : 234(M+. +18).
MS (HR) m/z: calcd. for C9H12O6: 216.0641; found:
1
action mixture (46°C/28 mmHg) (6.70 g, 57%). H NMR
3
(200 MHz, C6D6) δ: 1.02 (t, J = 7.0 Hz, 6H), 3.17 (s, 2H),
3
3.55 (q, J = 7.0 Hz, 4H). 13C NMR (25 MHz, C6D6) δ:
14.5, 56.6, 63.4, 165.7. The product was used on the same
day in the next step.
Synthesis of methyl (2,2-diethoxycyclobutane)carboxylate
A solution of 1,1-diethoxyethene (6.70 g, 58.0 mmol) and
methyl acrylate (4.97 g, 58 mmol) was refluxed in dry
acetonitrile (40 mL) for eight days. Acetonitrile was distilled
out through a Vigreux column, followed by methyl (2,2-
diethoxycyclobutane)carboxylate (48°C/0.8 mmHg) (2.0 g,
1
216.0634. H NMR (200 MHz, C6D6) δ: 3.47 (s, 6H), 3.60
(s, 6H). 13C NMR (50 MHz, C6D6) δ: 51.8, 59.2, 91.0,
150.8, 188.6 (C=O).
1
17%), (lit. (38, 40) 60–63%). H NMR (200 MHz, C6D6) δ:
Thermolysis of 1 in the presence of 2-azetidinone (30)
The procedure described above gave, from 1 (0.200 g,
1.25 mmol) and 2-azetidinone (30) (Aldrich, 0.178 g,
2.5 mmol) in benzene (5.0 g), a residue that was worked up
by semipreparative gas chromatography. 1-(Dimethoxymethyl)-
2-azetidinone (31) (76% by GC) was isolated as an oil. IR
(CCl4) (cm–1): 1770. MS (EI) m/z (rel. intensity): 145 (M+.,
1), 130 (M+. –15, 1), 114 (18), 87 (33), 75 ((MeO)2CH,
0.97–1.24 (m, 1H), 1.01 (t, 3H, 7.0 Hz), 1.11 (t, 3H, 7.0 Hz),
1.58–2.37 (m, 4H), 3.17–3.65 (m, 4H), 3.42 (s, 3H). 13C
NMR (125 MHz, C6D6) δ: 14.8, 15.3, 15.4, 31.0, 49.6, 51.1,
56.6, 57.1, 102.6, 170.8.
Synthesis of (2,2-diethoxycyclobutyl)methanol (47)
To a suspension of LiAlH4 (0.25 g, 6.70 mmol) in ether
(15 mL) was added, dropwise with stirring, methyl (2,2-
diethoxycyclobutane)carboxylate (1.35 g, 6.70 mmol). After
the addition the mixture was heated to boiling for 1.5 h be-
fore it was cooled with an ice water bath and the excess
LiAlH4 was quenched with ethyl acetate (15 mL), followed
by water (15 mL, slow addition). The heterogeneous solu-
tion left after the fine-grained Al(OH)3 was filtered off with
a sintered glass funnel was extracted with diethyl ether (3 ×
25 mL) and the combined organic fractions were dried with
magnesium sulphate. Filtration through a sintered glass fun-
nel and removal of the volatiles afforded (2,2-diethoxycyclo-
butyl)methanol in 95% yield. The crude product was used
without purification. Purification by distillation (61°C/0.8 mmHg)
1
(100), 72 (30), 42 (35). H NMR (200 MHz, C6D6) δ: 2.24
3
3
(t, J = 4.5 Hz, 2H), 2.79 (t, J = 4.5 Hz, 2H), 2.99 (s, 6H),
5.38 (s, 1H). 13C NMR (50 MHz, C6D6) δ: 35.5, 36.1, 53.2,
99.5, 166.5.
Thermolysis of 1 in the presence of β-propiolactone (34)
Heating of a solution of 1 (0.200 g, 1.25 mmol) and β-
propiolactone (34) (Aldrich, 0.090 g, 1.20 mmol) in benzene
(5.0 g), and workup as described above, left a yellow oil.
Flash column chromatography (silica gel – 30% ethyl ace-
tate in hexanes, Rf = 0.50) afforded 2,2-dimethoxy-3-
oxacyclopentanone (36) as an oil in 65% yield. IR (CCl4)
(cm–1): 1741. MS (EI–GC–MS) m/z (rel. intensity): 118
1
has been reported (47). H NMR (200 MHz, C6D6) δ: 0.92
1
3
3
(M+.–28, loss of CO, 29), 115 (40), 91 (90), 59 (100). H
(t, J = 7.1 Hz, 3H), 1.08 (t, J = 7.1 Hz, 3H), 1.35–2.60 (m,
© 2000 NRC Canada