Casey and Strotman
(silica gel, 20:1 pentane:ether) to afford cis-1 (25 mg, 14%) as
a yellow solid, though there was extensive dimerization and
material loss on the column. In most cases the crude brown
oil was used for reactions. 1H NMR (300 MHz, CDCl3)9a δ 7.97
(d, J ) 8.0 Hz, 2H), 7.59 (tt, J ) 7.3, 1.2 Hz, 1H), 7.48
(t, J ) 7.7 Hz, 2H), 7.20 (dd, J ) 11.7, 0.9 Hz, 1H), 6.21 (dd,
J ) 11.6, 2.6 Hz, 1H), 3.51 (dd, J ) 2.7, 1.2 Hz, 1H). 13C {1H}
NMR (75 MHz, CDCl3) δ 189.4, 137.4, 135.5, 133.5, 128.9
(2 C), 128.8 (2 C), 120.3, 88.3, 80.8.
trans-1,2-Di(2-(5-phenylfuryl))ethene (trans-2), cis-1,2-
Di(2-(5-phenylfuryl))ethene (cis-2), and trans,trans-1,2,3-
Tri(2-(5-phenylfuryl))cyclopropane (4). A solution of cis-3
(250 mg,1.09 mmol) and anhydrous KF (0.43 g, 7.3 mmol) in
MeOH (10 mL) was stirred at room temperature for 2 h,
poured into NH4Cl(aq) (20 mL), and extracted with EtOAc
(3 × 15 mL). The organic layer was washed with water
(3 × 10 mL), dried (MgSO4), and concentrated by rotary
evaporation. This crude product was dissolved in CDCl3 and
the percent yields of trans-2 and cis-2 were determined to be
53% and 10%, respectively, by 1H NMR spectroscopy relative
to an added internal standard.
SCHEME 16
mal extrusion of N2 from 1-diazo-1-(2-furyl)alkanes,
designed to generate the corresponding 1-(2-furyl)-1-
alkylcarbenes, gave rearranged 2-alken-4-yn-1-ones
(Scheme 16).10 This reaction represents the microscopic
reverse of cyclization of a cis-2-alken-4-yn-1-one to give
a 2-furylcarbene. While our furan-forming reactions do
not proceed through free high energy 2-furylcarbene
intermediates, the products are those expected from such
a carbenoid.
Experimental Section
1-Phenyl-5-trimethylsilyl-cis-2-penten-4-yn-1-one (cis-
3) and 1-Phenyl-5-trimethylsilyl-trans-2-penten-4-yn-1-
one (trans-3). Toluene (32 mL), Et3N (1.60 mL, 11.5 mmol),
and cis-3-chloro-1-phenyl-2-propen-1-one5 (1.00 g, 6.00 mmol)
and then (trimethylsilyl)acetylene (1.06 mL, 7.50 mmol) were
added by syringe to a flask containing CuI (57 mg, 0.30 mmol)
and Pd(PPh3)4 (139 mg, 0.120 mmol). The mixture was stirred
at room temperature under N2 for 7 h, quenched with
saturated aqueous ammonium chloride (27 mL), and extracted
with EtOAc (3 × 15 mL). The extract was dried (MgSO4) and
concentrated on a rotary evaporator, and chromatographed
(silica gel, 100:4 pentane:ether) to give cis-3 (0.79 g, 57% yield)
as a brown oil and trans-3 (0.16 g, 12%) as a tan solid. For
cis-3: 1H NMR (300 MHz, CDCl3) δ 7.94 (dd, J ) 8.5, 1.7 Hz,
2H), 7.57 (tt, J ) 7.4, 1.4 Hz, 1H), 7.46 (t, J ) 7.5 Hz, 2H),
6.97 (d, J ) 12.0 Hz, 1H), 6.22 (d, J ) 11.7 Hz, 1H), 0.13 (s,
9H). 13C {1H} NMR (75 MHz, CDCl3) δ 190.8, 137.8, 135.0,
133.2, 129.0 (2C), 128.8 (2C), 120.9, 107.8, 101.8, -0.3 (3C).
HRMS (ESI) calcd for C14H16OSiNa (M + Na+) 251.0868, found
251.0866. For trans-3: 1H NMR (300 MHz, CDCl3) δ 7.96
(dd, J ) 8.4, 1.5 Hz, 2H), 7.59 (tt, J ) 7.4, 1.4 Hz, 1H), 7.48
(t, J ) 7.7 Hz, 2H), 7.38 (d, J ) 15.6 Hz, 1H), 6.88 (d, J ) 15.6
Hz, 1H), 0.25(s, 9H). 13C {1H} NMR (75 MHz, CDCl3) δ 189.0,
137.3, 134.4, 133.4, 128.9 (2C), 128.8 (2C), 106.1, 102.8, -0.2
(3C). HRMS (ESI) calcd for C14H16OSiH (M + H+) 229.1049,
found 229.1047.
1-Phenyl-trans-2-penten-4-yn-1-one (trans-1). A solu-
tion of trans-3 (250 mg,1.09 mmol) and anhydrous KF (0.43 g,
7.3 mmol) in MeOH (10 mL) was stirred at room temperature
for 2 h, poured into NH4Cl(aq) (20 mL), and extracted with
EtOAc (3 × 15 mL). The organic layer was washed with water
(3 × 10 mL), dried (MgSO4), and concentrated by rotary
evaporation. Flash column chromatography (silica gel, 20:1
pentane:ether) gave trans-1 (103 mg, 60%) as a pale yellow
powder. 1H NMR (300 MHz, CDCl3) δ 7.96 (d, J ) 6.9 Hz, 2H),
7.60 (tt, J ) 7.4, 1.4 Hz, 1H), 7.49 (t, J ) 7.5 Hz, 2H), 7.44
(dd, J ) 15.9, 0.6 Hz, 1H), 6.85 (dd, J ) 15.6, 2.7 Hz, 1H),
3.45 (dd, J ) 2.7, 0.7 Hz, 1H). 13C {1H} NMR (75 MHz, CDCl3)
δ 188.8, 137.1, 135.5, 133.6, 129.0 (2 C), 128.8 (2 C), 124.0,
86.7, 81.6; HRMS (ESI) calcd for C11H8ONa (M + Na+)
179.0473, found 179.0478.
The yield of 2 was increased by use of an acid catalyst. A
solution of cis-1, obtained from deprotection of cis-3 (50 mg,
0.219 mmol) as described above, and HOAc (19 µL, 0.33 mmol)
in CDCl3 (∼0.75 mL) was monitored by 1H NMR spectroscopy.
After 1.5 h, the reaction was complete and trans-2 (62%), cis-2
(23%), and 4 (6%) were seen.
Reaction of cis-1 (100 mg, 0.438 mmol) and HOAc (38 µL,
0.66 mmol) in either MeOH or CHCl3 followed by purification
by preparative TLC (silica gel, 5:1 pentane:CH2Cl2) gave 4 as
a yellow oil (Rf 0.25). 1H NMR (300 MHz, CDCl3) δ 7.65
(d, J ) 8.3 Hz, 2H), 7.55 (d, J ) 8.3 Hz, 4H), 7.38 (t, J ) 7.2
Hz, 2H), 7.22-7.31 (m, 5H), 7.17 (tt, J ) 7.2, 1.2 Hz, 2H), 6.62
(d, J ) 3.3 Hz, 1H), 6.49 (d, J ) 3.6 Hz, 2H), 6.32 (d, J ) 3.3
Hz, 1H), 6.11 (d, J ) 3.3 Hz, 2H), 3.17 (t, J ) 5.7 Hz, 1H),
3.00 (d, J ) 5.7 Hz, 2H). 13C {1H} NMR (75 MHz, CDCl3)
δ 153.1, 152.9 (2C), 152.8, 151.2 (2C), 131.1 (2C), 131.0, 128.9
(2C), 128.7 (4C), 127.3, 127.1 (2C), 123.72 (2 C), 123.70 (4 C),
109.4 (2C), 107.9, 106.3, 106.1 (2C), 25.7 (2C), 23.3. HRMS
(EI) calcd for C33H24O3 (M+) 468.1725, found 468.1714.
trans-2 (55 mg, 55%) and cis-2 coeluted (Rf 0.39) and were
further separated by recrystallization from acetone to give
yellow solids. trans-2 (decomposition at 208-210 °C before
melting) was obtained in a pure state. 1H NMR (300 MHz,
CDCl3) δ 7.73 (d, J ) 7.2 Hz, 4H), 7.40 (t, J ) 7.5 Hz, 4H),
7.27 (tt, J ) 7.5, 1.2 Hz, 2H), 6.93 (s, 2H), 6.71 (d, J ) 3.6 Hz,
2H), 6.45 (d, J ) 3.6 Hz, 2H). 13C {1H} NMR (75 MHz, CDCl3)
δ 153.7, 152.9, 130.80, 128.9 (2 C), 127.7, 124.01 (2 C), 114.7,
111.6, 107.76. HRMS (ESI) calcd for C22H16O2 (M+) 312.1150,
found 312.1142.
Solutions of cis-2 completely isomerized to trans-2 in CDCl3
over a few hours or quite rapidly in the presence of light. All
NMR data for cis-2 were obtained from a ∼1:1 mixture with
trans-2. For cis-2: 1H NMR (300 MHz, CDCl3) δ 7.73
(d, J ) 7.7 Hz, 4H), 7.37 (t, J ) 8.4 Hz, 4H), 7.26 (tt, J ) 7.0,
1.2 Hz, 2H), 6.98 (d, J ) 3.3 Hz, 2H), 6.77 (d, J ) 3.3 Hz, 2H),
6.25 (s, 2H). 13C {1H} NMR (75 MHz, CDCl3) δ 153.9, 152.4,
130.78, 129.0 (2 C), 127.8, 123.99 (2 C), 113.9, 113.6, 107.78.
HRMS (EI) calcd for C22H16O2 (M+) 312.1150, found 312.1158.
5-Isopropylamino-1-phenyl-trans,trans-2,4-pentadien-
1-one (5) and 3-Isopropylamino-1-phenyl-4-pentyn-1-one
(6). A solution of cis-1, from deprotection of cis-3 (50 mg, 0.219
mmol), and isopropylamine (37 µL, 0.44 mmol) in CHCl3
(5 mL) was stirred at room temperature for 5 h under N2.
Solvent and excess isopropylamine were evaporated under
reduced pressure. 1H NMR spectroscopy of the crude material
showed compounds 5, 6, and trans-1 in 66%, 29%, and 5%
yields, respectively. Preparative TLC (silica gel, 2:1 EtOAc:
hexane) led to the isolation of 5 (30 mg, 64%, Rf 0.54) as an
oily brown solid and trans-1 (Rf 0.89). Compound 6 readily
decomposed during purification so it was identified by proton
NMR from a mixture of species.
1-Phenyl-cis-2-penten-4-yn-1-one (cis-1). A solution of
cis-3 (250 mg,1.09 mmol) and anhydrous KF (0.43 g, 7.3 mmol)
in MeOH (10 mL) was stirred at room temperature for 2 h.
Et2O (200 mL) was added and the solution was washed with
water (2 × 40 mL), dried (MgSO4), and concentrated on a
rotary evaporator to give cis-1 (0.154 g, 90%, >95% cis-1 by
NMR) as a yellow-brown oil. This oil was chromatographed
(10) (a) Hoffman, R. V.; Shechter, H. J. Am. Chem. Soc. 1971, 93,
5940. (b) Hoffman, R. V.; Orphanides, G. G.; Shechter, H. J. Am. Chem.
Soc. 1978, 100, 7927. (c) Hoffman, R. V.; Shechter, H. J. Am. Chem.
Soc. 1978, 100, 7934.
2580 J. Org. Chem., Vol. 70, No. 7, 2005