Mendeleev Commun., 2006, 16(1), 33–34
In the usual synthesis of these compounds, the temperature
Ph
of –35 °C is used. But at this temperature, trans-stilbene crys-
tallises and does not react. Therefore, the reaction was performed
at –15 °C.
The desired reaction product (compound 2) was separated by
thin-layer chromatography (TLC) (light petroleum–diethyl ether,
14:1) and its structure was established by IR and 1H NMR spec-
troscopy (Scheme 2).‡
NaOH, – Br–
(CoII)
Ph
2
O
(CoI)–
(CoIII)Cl
EtOH
NaBH4
O
O
Ph
Ph
Ph
Ph
HO
O
Ph
Br
Br+
NBS
3
1
(CoIII)Cl = Chloro-bis(dimethylglyoximato)-
(triphenylphosphine) cobalt(III)
Ph
Ph
Scheme 2
Ph
2
Scheme 3
Cyclisation of 1-bromo-1,2-diphenylethylprop-2-yn-1-yl ether
2 was carried out in the presence of cobaloxime in 10 N NaOH
and sodium borohydride in ethanol to form 2,3-diphenyl-
4-methylenetetrahydrofuran 3 in 50% yield, as an oil.§
We conclude that the method described does not require
vigorous reaction conditions and would be useful for the syn-
thesis of cyclopentane annulated α-methylene-γ-butyrolactones.
By analogy to the report of Tada et al.,9 it is believed that the
reaction takes the steps presented in Scheme 3, in which
cobaloxime(I) is prepared in situ via the reduction of chloro-
cobaloxime(III) by sodium borohydride and cobaloxime(I) thus
formed is oxidised by brominated product 2 to cobaloxime(II).
Since sodium borohydride easily reduces cobaloxime(II) to
cobaloxime(I), the cobaloxime can recycle in the reaction system.
In the cyclisation reaction, a small amount of cobaloxime was
used and no organocobalt intermediate was isolated. Final step
in the synthesis of α-methylene-β,γ-diphenyl-γ-butyrolactone
was carried out by oxidation of 2,3-diphenyl-4-methylenetetra-
hydrofuran 3 with an excess of CrO3·Py in dichloromethane,
which provided desired compound 4 as a white powder in 62.5%
yield. This product was characterised by IR and 1H NMR spectro-
scopy and mass spectrometry.¶
CrO3, Py
3
4
CH2Cl2
This work was supported in part by the Guilan University
Research Council.
References
1
2
3
T. K. Devon and A. L. Scott, Handbook of Naturally Occurring
Compounds, Academic Press, New York, 1972, vol. 2, 79.
A. F. Barrero, J. E. Oltra, A. Barragan and M. Alvarez, J. Chem. Soc.,
Perkin Trans. 1, 1998, 4107.
4
5
6
Only one stereoisomer of compound 4 was detected and
characterised. The coupling constant (J 7.65 Hz) of this com-
1
pound in H NMR spectra indicated a trans configuration for
7
8
the two hydrogen atoms adjacent to phenyl groups.
‡
Synthesis of 1-bromo-1,2-diphenylethylprop-2-yn-1-yl ether 2. To a
9
cold magnetically stirred solution (–15 °C) of N-bromosuccinimide
(0.7 g, 4 mmol) in propyn-2-ol (5 ml), a solution of trans-stilbene (0.54 g,
3 mmol) in carbon tetrachloride (20 ml) was added gradually for 2 h.
The reaction mixture was stirred for 2 h at 0 °C and then for 48 h at room
temperature. Sodium hydroxide (1 N, 5 ml) was added to the solution,
and the mixture was extracted with carbon tetrachloride (3×20 ml). The
organic phase was washed with 10 N NaOH. The solvent was evaporated
under reduced pressure to give a mixture of the product and by-products.
The mixture was separated by TLC (light petroleum–diethyl ether, 14:1)
to provide 1-bromo-1,2-diphenylethylprop-2-yn-1-yl ether 2 (0.67 g,
10 G. N. Schrauzer and J. Kohnle, Chem. Ber., 1964, 97, 3056.
1
2.14 mmol) in 80% yield. H NMR (CDCl3) d: 2.4 (t, 1H, J 2.18 Hz),
3.8 (dd, 1H, J 16 and 2.24 Hz), 4.1 (dd, 1H, J 16 and 2.24 Hz), 5.1 (dd,
2H, J 15.1 and 7.4 Hz), 7.3 (m, 10H). IR (CCl4, n/cm–1): 3250 (br. s),
3020 (w), 1076 (s), 750 (br. s), 700 (s), 645 (br. s).
§
Synthesis of 2,3-diphenyl-4-methylenetetrahydrofuran 3. To a mag-
netically stirred solution of 1-bromo-1,2-diphenylethylprop-2-yn-1-yl
ether 2 (0.63 g, 2 mmol) in ethanol (10 ml), 10 N sodium hydroxide
(0.2 ml) and sodium borohydride (76 mg, 2 mmol) were added, and the
mixture was warmed under an atmosphere of nitrogen up to 50 °C.
Chloro-bis(dimethylglyoximato)(triphenylphosphine)cobalt(III) [cobal-
oxime] (0.48 mg, 0.12 mmol) was added for 1.5 h at 50–60 °C. The
reaction mixture was stirred at the same temperature for 3 h. Ethanol
was evaporated under reduced pressure and a saturated solution of
sodium chloride (10 ml) was added. The mixture was extracted with
light petroleum–diethyl ether (4:1) (3×10 ml). The organic phase was
washed with saturated sodium chloride and evaporated in a vacuum.
The residue was purified by preparative TLC (a 7:1 mixture of light
petroleum and diethyl ether as an eluent) to give 2,3-diphenyl-
4-methylenetetrahydrofuran 3 as an oil (0.24 g, 1 mmol) in 50% yield.
1H NMR (CDCl3) d: 3.7 (dd, 1H, J 2.53 Hz), 4.75 (dd, 1H, J 13.3 and
2.2 Hz), 4.78 (d, 1H, J 2.5 Hz), 4.9 (d, 2H, J 9.6 Hz), 5.1 (dd, 1H,
J 2.53 Hz), 7.3 (m, 10H). IR (Neat, n/cm–1): 3000–3050 (br. s), 2580
(br. s), 1660 (br. s), 1050 (s), 750 (s), 700 (s).
Received: 9th August 2005; Com. 05/2561
¶
Synthesis of a-methylene-b,g-diphenyl-g-butyrolactone 4. To a solution
of pyridine (1 ml) in dichloromethane (10 ml), chromium trioxide (1 g,
10 mmol) was added, and the mixture was stirred for 20 min. Compound
3 (0.12 g, 0.5 mmol) was dissolved in dichloromethane (5 ml), added to
the reaction mixture, refluxed for 3 h and filtered. The residue was
washed with dichloromethane (3×10 ml), and the filtrate was washed
with saturated sodium bicarbonate, 2 N hydrochloric acid and passed
through a short silica gel column to remove chromium compounds. The
solvent was evaporated in a vacuum, and the residue was separated by
TLC (a 7:1 mixture of light petroleum and diethyl ether) to obtain product
4 as a white powder (0.08 g, 0.31 mmol) in 62.5% yield, mp 37 °C.
1H NMR (CDCl3) d: 4.00 (d, 1H, J 7.65 Hz), 5.40 (d, 1H, J 7.69 Hz),
5.47 (d, 1H, J 2.79 Hz), 6.5 (d, 1H, J 2.76 Hz), 7.3 (m, 10H). IR (CCl4,
n/cm–1): 3000–3050 (w), 2850–2900 (br. s), 1760 (s), 1645 (br. s), 1600
(br. s), 1130 (s), 750 (s), 700 (s). MS, m/z (%): 250 (3.4), 144 (55.3), 116
(100), 77 (7.2).
34 Mendeleev Commun. 2006
Tabatabaeian, Khalil
