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1
for 48 h followed by aqueous work-up in 86% yield. H
NMR (CDCl3, TMS): d 6.55 (m, 1H), 6.46 (m, 2H),
6.37 (t, J¼8.0 Hz, 1H), 6.12 (dt, 1H), 4.95 (m, 1H),
2.55 (m, 2H), 2.02 (s, 3H), 1.8 (m, 2H), 1.55 (m, 2H),
1.33 (m, 2H), 0.9 (t, J¼7.2 Hz, 3H); 13C NMR (CDCl3,
TMS): d 170.8, 146.2, 141.5, 133.4, 131.1, 125.6,
118.9, 73.5, 36.3, 33.9, 27.1, 21.2, 18.7, 14.0 ppm. Anal.
Calcd for C14H20O2: C, 76.33; H, 9.15. Found: C, 76.28;
H, 9.13.
4.3. Typical procedure for the DBU-catalyzed
isomerizations
Three drops of DBU were added to a solution of endoper-
oxide 57, obtained as described above, in 250 mL CH2Cl2
at 0 ꢀC, and the solution was stirred at room temperature
for 12–15 h. Then the mixture was concentrated at reduced
pressure, and the residue chromatographed on SiO2, eluting
with hexane/ether (3:1).
1
4.1.2. Fulvene 28. Yield 78%. H NMR (CDCl3, TMS):
4.3.1. 2-Isopropenyl-2-cyclopentenone (21). 1H NMR
(CDCl3, TMS): d 7.5 (t, J¼3.0 Hz, 1H), 6.07 (s, 1H), 5.16
(s, 1H), 2.60 (m, 2H), 2.47 (m, 2H), 1.94 (s, 3H); 13C
NMR (CDCl3, TMS): d 208.5, 158.5, 143.7, 135.1, 117.3,
36.7, 26.3, 22.0 ppm. FTIR (film): 2973, 2927, 2855,
1710, 1453, 1387, 1262, 1177, 1038, 913, 802 cmꢁ1. Anal.
Calcd for C8H10O: C, 78.65; H, 8.25. Found: C, 78.61; H,
8.24.
d 6.6–6.4 (m, 4H), 6.2 (m, 1H), 4.1 (q, J¼7.5 Hz, 2H),
2.54 (q, J¼7.5 Hz, 2H), 2.30 (t, J¼7.2 Hz, 2H), 1.65 (m,
2H), 1.50 (m, 2H), 1.4 (m, 2H), 1.25 (t, J¼7.5 Hz, 3H);
13C NMR (CDCl3, TMS): d 173.7, 146.1, 142.8, 133.1,
130.8, 125.6, 119.1, 60.2, 34.2, 30.9, 29.1, 28.8, 24.8,
14.3 ppm. Anal. Calcd for C14H20O2: C, 76.33; H, 9.15.
Found: C, 76.31; H, 9.15.
1
4.1.3. Fulvene 38. Yield 49%. H NMR (CDCl3, TMS):
4.3.2. (E)-(2)-Pent-1-enyl-2-cyclopentenone (24). 1H
NMR (CDCl3, TMS): d 7.4 (t, J¼3.0 Hz, 1H), 6.6 (dt,
J¼16.0, 7.0 Hz, 1H), 6.1 (d, J¼16.0 Hz, 1H), 2.6 (m, 2H),
2.45 (m, 2H), 2.1 (q, J¼7.0 Hz, 2H), 1.50 (sext, J¼7.0 Hz,
2H), 0.94 (t, J¼7.0 Hz, 3H); 13C NMR (CDCl3, TMS):
d 208.3, 156.5, 141.2, 135.7, 119.8, 35.57, 35.52, 26.2,
22.2, 13.7 ppm. Anal. Calcd for C10H14O: C, 79.96; H,
9.39. Found: C, 79.95; H, 9.38.
d 6.53 (m, 2H), 6.45 (m, 1H), 6.40 (t, J¼7.5 Hz, 1H), 6.2
(m, 1H), 3.63 (m, 1H), 2.65 (q, J¼7.5 Hz, 2H), 1.67 (m,
2H), 1.44 (m, 2H), 1.30 (m, 4H), 0.9 (t, J¼7.5 Hz, 3H);
13C NMR (CDCl3, TMS): d 146.2, 142.6, 133.2, 130.8,
125.6, 119.1, 71.3, 37.6, 36.9, 31.9, 27.5, 25.3, 22.7,
14.1 ppm. Anal. Calcd for C12H18O: C, 80.85; H, 10.18.
Found: C, 80.82; H, 10.23.
1
4.1.4. Fulvene 50. Yield 39%. H NMR (CDCl3, TMS):
4.3.3. (E)-1-(5-Oxocylopent-1-enyl)hept-1-en-4-yl ace-
tate (27). H NMR (CDCl3, TMS): d 7.3 (br s, 1H), 6.45
1
d 6.75 (m, 2H), 6.5–6.2 (m, 5H), 5.4 (m, 2H), 2.3 (m, 2H),
2.2 (m, 2H), 2.05 (m, 2H), 1.0 (t, J¼7.5 Hz, 3H) ppm.
Anal. Calcd for C14H18: C, 90.26; H, 9.74. Found: C,
90.25; H, 9.73.
(dt, J¼15.6, 7.2 Hz, 1H), 6.0 (d, J¼15.6 Hz, 1H), 4.85
(quin, J¼6.0 Hz, 1H), 2.5 (m, 2H), 2.35 (m, 2H), 2.26 (m,
2H), 1.94 (s, 3H), 1.45 (m, 2H), 1.24 (m, 2H), 0.82 (t,
J¼7.2 Hz, 3H); 13C NMR (CDCl3, TMS): d 207.8, 170.4,
157.4, 157.2, 140.6, 129.9, 122.3, 72.9, 38.0, 35.3, 26.0,
20.1, 18.3, 13.7, 13.5 ppm. Anal. Calcd for C14H23O3: C,
70.20; H, 9.69. Found: C, 70.17; H, 9.66.
4.2. Typical procedure for the preparation of the
saturated endoperoxides
A solution of 6,6-dimethylfulvene (1.06 g, 10 mmol) and
5 mg of TPP (meso-tetraphenylporphyrin) in 200 mL
CH2Cl2 was cooled to ꢁ78 ꢀC in a flat Dewar containing
dry ice–acteone. The mixture was stirred while being irradi-
ated with a 250 W high-pressure sodium lamp for 3 h under
an oxygen atmosphere (a ballon filled with oxygen served
this purpose). Then the lamp was turned off, 8.7 g
(45 mmol) of potassium azodicarboxylate was added to the
mixture in small portions, a pressure-equalizing dropping
funnel fitted with a drying tube containing Drierite was at-
tached to the flask. A solution of 5.1 g (85 mmol) of acetic
acid in 20 mL CH2Cl2 was added dropwise to the stirred
slurry at ꢁ78 ꢀC, and the mixture was slowly warmed up
to ꢁ35 ꢀC and stirred at this temperature for 1 h. The mix-
ture was then slowly warmed up to 0 ꢀC for an additional
30 min. Then the salt was filtered by suction, the filtercake
washed with cold CH2Cl2, while keeping the filter flask in
an ice bath. The filtrate was washed with saturated aqueous
NaHCO3, dried over MgSO4, filtered into a 250 mL round-
bottomed flask. An aliquot was concentrated at reduced
pressure (caution: saturated fulvene endoperoxides—
when neat—are potentially explosive!), and dissolved in
CDCl3 for NMR spectroscopy. The product was practically
4.3.4. (E)-Ethyl 7-(5-oxocyclopent-1-enyl)hept-6-enoate
1
(30). H NMR (CDCl3, TMS): d 7.3 (t, J¼3 Hz, 1H), 6.5
(dt, J¼16.0, 7.2 Hz, 1H), 4.0 (q, J¼7.2 Hz, 2H), 2.5 (m,
2H), 2.35 (m, 2H), 2.2 (m, 2H), 2.05 (m, 2H), 1.60 (m,
2H), 1.35 (m, 2H), 1.7 (t, J¼7.2 Hz, 3H); 13C NMR
(CDCl3, TMS): d 208.4, 173.6, 157.0, 141.0, 135.1, 120.1,
60.2, 35.6, 34.1, 33.1, 28.4, 26.3, 24.5, 14.2 ppm. Anal.
Calcd for C14H20O3: C, 70.20; H, 9.69. Found: C, 70.19;
H, 9.66.
1
4.3.5. 2-Cycloheptenylcyclopent-2-enone (33). H NMR
(CDCl3, TMS): d 7.4 (t, J¼3.0 Hz, 1H), 6.7 (t, J¼6.6 Hz,
1H), 2.56 (m, 2H), 2.45 (m, 2H), 2.37 (m, 2H), 2.25 (m,
2H), 1.8 (m, 2H), 1.55 (m, 4H); 13C NMR (CDCl3, TMS):
d 208.2, 155.5, 145.0, 135.8, 133.0, 36.0, 32.2, 31.1, 28.4,
26.4, 26.3, 25.3 ppm. Anal. Calcd for C12H16O: C, 81.77;
H, 9.15. Found: C, 81.77; H, 9.14.
4.3.6. (E)-5-(3-Hydroxybutan-2-ylidene)cyclopent-2-
enone (36). H NMR (CDCl3, TMS): d 7.54 (m, 1H), 6.30
1
(m, 1H), 5.2 (br s, 1H, OH), 5.05 (q, J¼7.0 Hz, 1H), 3.2
(s, 2H), 1.32 (d, J¼7.0 Hz, 3H) ppm.
1
pure according to its H NMR spectrum.5 For the DBU-
catalyzed isomerizations, the endoperoxides need not be
isolated.
4.3.7. 2-(3-Hydroxybut-1-en-2-yl)cyclopent-2-enone (37).
1H NMR (CDCl3, TMS): d 7.7 (t, J¼3.0 Hz, 1H), 5.65 (s,