Cyclopropene: A new simple synthesis and Diels-Alder reactions with cyclopentadiene and 1,3-diphenylisobenzofuran

Full text of DOI:10.1021/jo960728r

6462
J . Org. Chem. 1996, 61, 6462-6464
equal amounts of cyclopropene (1) and cyclopropyldi-
Cyclop r op en e: A New Sim p le Syn th esis
methylamine are formed contaminated with some di-
methyl ether and ethylene. Treatment with dilute
hydrochloric acid removed the amine from the gas stream
and 1 was separated from the other products by gas
chromatography. Alder-Rickert cleavage of the Diels-
Alder adduct formed from cycloheptatriene and dimethyl
acetylenedicarboxylate resulted only in the formation of
a polymer and trace amounts of 1.8 A simple approach
by Closs and Krantz9 based on the synthesis of 1-meth-
ylcyclopropene10 involved the addition of allyl chloride to
a suspension of sodium amide at 80 °C. Under the
conditions employed, 1 could readily escape the reaction
mixture.9 Though a number of variations were tried, the
yield of 1 never exceeded 10%.
The common feature of all previous attempts at cyclo-
propene (1) is either very laborious methods or un-
acceptable yields, from a preparative point of view. Over
the last 25 years we have developed in our laboratories
simple syntheses for substituted cyclopropenes on a
multigram scale.4a,5a,11 At this time we would like to
disclose our efforts toward an improved synthesis of
parent compound 1.
a n d Diels-Ald er Rea ction s w ith
Cyclop en ta d ien e a n d
1,3-Dip h en ylisoben zofu r a n
Paul Binger,*,† Petra Wedemann,†
Richard Goddard,† and Udo H. Brinker*,‡
Max-Plank-Institut fu¨r Kohlenforschung,
Kaiser-Wilhelm-Platz 1, 45470 Mu¨lheim an der Ruhr,
Germany, and State University of New York at Binghamton,
Department of Chemistry, P.O. Box 6016,
Binghamton, New York 13902-6016
Received April 22, 1996
Due to its short double bond of 1.296 Å1 and its
calculated strain energy of 54.5 kcal/mol,2 cyclopropene
(1) is a highly reactive molecule. While the increased
angular strain of the molecular σ framework contributes
to the destabilization of 1, it is release of ring strain
which drives its reactions. The synthesis of cyclopropene
(1), a potentially explosive gas (bp -36 °C), was first
reported in 1922 by Demjanov and Doyarenko.3 Even
at temperatures below -30 °C, 1 is said to oligomerize
rapidly via ene reactions.
Cyclopropenes are important building blocks for or-
ganic synthesis and their preparation and reactions have
been reviewed extensively.4 Lower boiling 3,3-disubsti-
tuted cyclopropenes can simply be obtained in a two-step
synthesis5 with overall yields as high as 80%.
When allyl chloride was dropped into a solution of
sodium bis(trimethylsilyl)amide12 in boiling toluene, ca.
40% of cyclopropene could be isolated in a trap kept at
-80 °C. Compared with the published procedure,9 under
these conditions allyl chloride seems to react more
rapidly, affording a quadrupled yield of 1. Furthermore,
as could be established by NMR spectroscopy at -80 °C,
the cyclopropene (1) collected as a colorless liquid is
nearly pure (>95%), containing only traces of allyl
chloride. Compound 1, prepared in this manner, was
found to be stable in toluene solution at -78 °C for at
least 1 week. Upon warming up, 1 begins to oligomerize
at -30 °C (NMR control).
When 1 was reacted with cyclopentadiene, no reaction
took place, as could be monitored by NMR spectroscopy
at -80o nor at -30 °C. At room temperature, however,
the Diels-Alder reaction afforded quantitatively endo-
tricyclo[3.2.1.02,4]oct-6-ene (2).8b,9
Higher boiling cyclopropenes could conveniently be
prepared via dehydrohalogenation of the corresponding
monobromocyclopropanes at ca. 40 °C.6 In contrast, for
the preparation of the parent compoundscyclopropene
(1)squite a variety of diverse synthetic methods has been
employed. Schlatter7a and Demjanov and Doyarenko7b
pyrolyzed cyclopropyltrimethylammonium hydroxide at
320 °C using platinized asbestos as the catalyst. About
† Max-Plank-Institut fu¨r Kohlenforschung.
‡ State University of New York at Binghamton.
(1) Stigliani, W. M.; Laurie, V. W.; Li, J . C. J . Chem. Phys. 1975,
62, 1890. Kasai, P. H.; Myers, R. J .; Eggers, D. F. J r.; Wiberg, K. B. J .
Chem. Phys. 1959, 30, 512. Dunitz, J . D.; Feldman, H. G.; Schomaker,
V. J . Chem. Phys. 1952, 20, 1708.
(2) von R.-Schleyer, P.; Williams, J . E.; Blanchard, K. R. J . Am.
Chem. Soc. 1970, 92, 2377.
(3) Demjanov, N. Y.; Doyarenko, M. N. Bull. Acad. Sci. USSR, 1922,
16, 297.
It is known that 1 and many substituted cyclopropenes4
add to dienes with predominant endo selectivity in
agreement with Alder’s “endo rule”.13 According to
(4) (a) Binger, P.; Bu¨ch, H. M. Top. Curr. Chem. 1987, 135, 77. (b)
Review: Halton, B.; Banwell, M. G. In The Chemistry of the Cyclopropyl
Group; Rappoport, Z., Ed., Wiley: New York, 1987; Chapter 21, 1223.
(c) Deem, M. L. Synthesis 1972, 675. (d) Wendisch, D. In Houben-Weyl,
Methoden der Organischen Chemie, 1971; Thieme: Stuttgart, Vol. 4/ 3,
pp 679. (e) Closs, G. L. In Advances in Alicyclic Chemistry; Hart, H.,
Karabatsos, G., Eds.; 1966; Vol. 1, p 53. (f) Carter, F. L.; Frampton, V.
L. Chem. Rev. 1964, 64, 497.
(5) (a) Binger, P. Synthesis 1974, 190. (b) Dijachenko, A. I.; Agre,
S. A.; Rudashevskaya, T. Y.; Shafran, R. M.; Nefedov, O. M. Izv. Akad.
Nauk. SSSR, 1984, 2820; Engl. Transl. 1984, 33, 2585.
(6) Binger, P., unpublished results.
(8) (a) Alder, K.; J acobs, G. Chem. Ber. 1953, 86, 1528. (b) Wiberg,
K. B.; Bartley, W. J . J . Am. Chem. Soc. 1960, 82, 6375.
(9) Closs, G. L.; Krantz, K. D. J . Org. Chem. 1966, 31, 638.
(10) Fisher, F.; Applequist, D. E. J . Org. Chem. 1965, 30, 2089.
(11) Ko¨ster, R.; Arora, S.; Binger, P. Liebigs Ann. 1973, 1219.
(12) Sodium bis(trimethylsilyl)amide was prepared according to the
following references: (a) Wannagat, U.; Niederpru¨m, H. Chem. Ber.
1961, 94, 1540. (b) Kru¨ger, C.; Rochow, E. G.; Wannagat, U. Chem.
Ber. 1963, 96, 2132.
(7) (a) Schlatter, M. J . J . Am. Chem. Soc. 1941, 63, 1733. (b)
Demjanov, N. J .; Dojarenko, M. Ber. Dtsch. Chem. Ges. 1923, 56, 2200.
(13) Alder, K.; Stein, G. Angew. Chem. 1937, 50, 510.
S0022-3263(96)00728-1 CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 18, 1996 6463
F igu r e 1. Compared with that for cyclopentadiene, the endo-activated complex for DPIBF with 1 does not profit from enhanced
SOI due to severely reduced electron density (1.7% each) at C3a and C7a. (Percentages represent the squares of LCAO coefficients
and reflect actual sizes of orbitals.)
Woodward and Hoffmann,14 the preferred endo stereo-
selectivity is the result of favorable secondary orbital
interactions (SOI) between the dienophile and the diene
which do not lead to bonds in the adduct as opposed to
primary interactions (PI) which do. Apeloig’s ab initio
calculations15 have recently provided evidence for the
dominant role of secondary orbital interactions in dictat-
ing the endo:exo ratio of the products resulting from 1
and dienes. As Wiberg8b had already reported some 35
years ago, the reaction of 1 with cyclopentadiene affords
exclusively endo-adduct 2. Though our AM1 calculations
predict the exo-adduct of 1 and cyclopentadiene to be
more stable than 2 by ca. 3 kcal/mol, Apeloig’s calcula-
tions15 reveal weaker steric repulsions in the endo-
activated complex, thus favoring the formation of the
higher energy endo-adduct 2 in agreement with experi-
ment.
obtained in adddition to a trans-diol. This diol results
from a proton-catalyzed cleavage of the ether bridge with
dilute sulfonic acid which was used for the washing of 1
during its preparation.17 Battiste and Sprouse,18 how-
ever, avoided the acid washing of 1 and isolated only one
adduct in 63% yield. They could clearly show by an
independent synthesis of 3 that the stereochemical
assignments of Geibel and Heindl17 were in error and
should be reversed. The endo isomer 4, however, could
not be detected. Finally, Cava and Narasimhan19 gener-
ated cyclopropene according to the method described
earlier.9 After a stream of 1 in nitrogen was passed
through a trap cooled in dry ice and then led into a
solution of DPIBF in benzene at 20 °C, again, only the
exo-adduct 3 could be isolated.
By our method, when 1, which had been kept at -80
°C, was added to a solution of DPIBF in toluene at -30
°C, after purification by flash chromatography followed
by HPLC, 72% of the exo-adduct 3 and 24% of the endo-
adduct 4 were isolated. The 1H NMR spectrum (200
MHz) of 3 in C6D6 agreed with the one reported in the
literature.18 The mass spectrum of the minor compound
4 revealed a M+ peak at m/e 310, like that of 3. The
proton NMR spectrum displayed three signals at higher
field representing four aliphatic hydrogen atoms (a
doublet of triplets at δ 0.07 and 1.14 for the geminal
methylene protons and a doublet of doublets at δ 2.47
ppm for the cyclopropyl methylidyne bridge hydrogens).
While the data pointed to the structure of 4, in order to
finally be absolutely certain about the stereochemical
assignments of 3 and 4, an X-ray structure determina-
tion20 of 4 was undertaken which proved the minor
component to be the endo-adduct 4.
The discrepancies concerning the exclusive formation
of endo-adduct 2 and the preponderant formation of exo-
adduct 3 may point to possible differences in the potential
energy surfaces for these Diels-Alder reactions. Orbital
coefficients of the LUMO of DPIBF obtained from AM1
calculations (Figure 1) show that the coefficients at C3a
The reaction of 1 with 1,3-diphenylisobenzofuran16
(DPIBF) had already been studied before.17-19 Geibel and
Heindl17 prepared 1 by applying the method of Closs and
Krantz.9 According to these authors, when 1 was reacted
with DPIBF in chloroform, 75% of 4 and 13% of 3 was
and C7a necessary for SOI15 with the πCH part of the
2
(14) Woodward, R. B.; Hoffmann, R. The Conservation of Orbital
Symmetry; Verlag Chemie: Weinheim, 1971.
HOMO (2B1) of 1 are severely diminished compared with
(15) Apeloig, Y.; Matzner, E. J . Am. Chem. Soc. 1995, 117, 5375.
(16) Wiersum, U. E. Aldrichimica Acta 1981, 14, 53.
(17) Geibel, K.; Heindl, J . Tetrahedron Lett. 1970, 2133.
(18) Battiste, M. A.; Sprouse, C. T., J r. Tetrahedron Lett. 1970, 4661;
Tetrahedron Lett. 1969, 3165.
(20) The authors have deposited atomic coordinates for this struc-
ture with the Cambridge Crystallographic Data Centre. The coordi-
nates can be obtained, on request, from the Director, Cambridge
Crystalographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ,
UK.
(19) Cava, M. P.; Narasimhan, K. J . Org. Chem. 1971, 36, 1419.

6464 J . Org. Chem., Vol. 61, No. 18, 1996
Notes
in 1 mL of toluene-d8. The NMR spectrum recorded at -80 °C
showed that no reaction had taken place (even after 24 h). Also,
after 2 h, at -30 °C there was no reaction. At room temperature,
however, endo-tricyclo[3.2.1.02,4]oct-6-ene (2) was formed quan-
titatively. Besides 2, the NMR showed the presence of excess
of cyclopentadiene and its dimer.
the corresponding orbitals of cyclopentadiene. This
undermines SOI arguments for a preferred endo-adduct
4 formation.
It is also interesting to compare our results with those
obtained from the reaction of cyclopropenone and DPIBF
by Breslow and co-workers.21 Here, the [4 + 2] cyclo-
addition affords only the exo-adduct. Recently Berson et
al.22 confirmed these findings by providing a crystal
structure of the exo-adduct. Furthermore, some evidence
was provided that at -30 °C the missing endo-isomer
converts to the exo-isomer through a ring-opening reac-
tion. Here, the preferred formation of the exo-adduct
seems to benefit from an attractive nucleophilic ether-
carbonyl interaction.
Rea ction of Cyclop r op en e (1) w ith 1,3-Dip h en ylisoben -
zofu r a n . A 0.9 g (3.3 mmol) portion of 1,3-diphenylisobenzo-
furan was dissolved at -30 °C in 40 mL of toluene. To the yellow
solution was added 0.2 g (5 mmol) of cyclopropene which had
been kept at -80 °C. After 1 h at this temperature, a light
decolorization had taken place and after further standing
overnight at 0 °C, a clear colorless solution resulted. The solvent
was removed in vacuo at room temperature to afford 1.18 g of a
colorless oil which consisted of 3 and 4 (ratio 72:24) and
oligomers of 1. Purification by flash chromatography using a
25 cm silica gel filled column, hexane:ether ) 5:1 as eluant, and
1 bar of argon pressure, gave 0.98 g of a highly viscous liquid
which consisted of 735 mg of 3 (72%) and 245 mg of 4 (24%).
HPLC separation on the 23.0 and 12.5 cm columns, respectively
(CH3CN and CH3CN:H2O ) 95:5, at 20 mL and 10 mL/min,
respectively) afforded 3 and 4 in a purity of 96% and 92%,
respectively.
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected. IR
spectra were recorded as KBr pellets on a FT spectrophotometer.
1H (and 13C) NMR spectra were acquired on instruments at 300
(75), 200 (50) and 400 (100) MHz, respectively. For the lH NMR
spectra, TMS served as an internal chemical shift reference. 13
C
exo-1a ,2,7,7a -Tetr a h yd r o-2,7-d ip h en yl-2,7-ep oxy-1H-cy-
clop r op a [b]n a p h th a lin e (3): mp ) 95 °C; lH NMR (300 MHz,
spectra were referenced to the center line of CDCl3 at 77.0 ppm.
Coupling constants are reported in hertz. Low resolution mass
spectra were obtained on either a spectrometer or by GC-MS
using a gas chromatograph and a mass selective detector.
Analytical gas chromatography was performed using a 15 m SE
54/G 124 glass capillary column (FID, H2). Flash chromatog-
raphy was done on a 2.5 cm (i.d. ) 4.5 cm) column using silica
gel (230-400 mesh). Preparative HPLC was performed using
either a 23.0 cm column (i.d. ) 2.6 cm; stationary phase:
LiChroprep Si 100-C18/A, 25-40 mm) or a 12.5 cm column (i.d.
) 2.0 cm; stationary phase: Nucleosil-7-100-C18/A, 95-26 mm).
Crystal structure analysis was done with an Enraf Nonius
CAD-4 Diffractometer. Combustion analyses were performed
by Dornis and Kolbe, Mu¨lheim/Ruhr, Germany.
Cyclop r op en e (1). In a 250 mL three-necked flask, equipped
with a 25 mL dropping funnel, water-cooled Dimroth condenser,
stirrer, an argon gas bubbler, and an inlet tube connected to a
cold trap, 31.1 g (0.17 mol) of sodium bis(trimethylsilyl)amide12
were dissolved in 100 mL of toluene. To this solution, at
vigorous reflux, was added 11.5 g (0.15 mol) of allyl chloride,
dropped over 20 min. Cyclopropene (1) escaped from the flask
and was condensed in the trap at -80 °C. After an additional
30 min at reflux, 3.4 mL (d ) 0.7 g/mL) (yield 40%) of
cyclopropene (1) was collected as a colorless liquid. The 1H NMR
spectrum recorded at -80 °C is identical with a published
spectrum and showed nearly pure 1 (>95%) with only traces of
allyl chloride.
C6D6) δ 0.69 (dt, H1, anti to oxygen bridge, J 1,1′ ) -5.3, J 1,1a
)
6.7), 1.46 (dd, H1a, H7a, J 1,1a ) 6.7, J 1a,1′ ) 3.6), 1.70 (H1′; syn
to oxygen bridge), (400 MHz, CDCl3), 6.9-7.1 (AA′ BB′, 4H, H3-
6) 7.25-7.7 (m, 10 H); 13C (50 MHz) 15.7 (t, C1), 25.4 (d, C1a,
7a), 88.7 (s, C2, 7), 119.3 (d), 126.0 (d), 126.7 (d) 128.0 (d), 128.4
(d), 136.6 (s), 150.9 (s); IR (KBr) 3060, 3002, 1603, 1495, 1454,
1448, 1369, 1309, 1056, 755, 698, cm-1; MS (m/e) 310 (M+), 292,
205 (100%), 165, 127, 105, 77, 51. Anal. Calcd. for C23H18O:
C, 89.00; H, 5.84. Found: C, 88.67; H, 5.83.
en d o-1a ,2,7,7a -Tet r a h yd r o-2,7-d ip h en yl-2,7-ep oxy-1H -
l
cyclop r op a [b]n a p h th a lin e (4): mp ) 142 °C; H NMR (300
MHz) δ 0.07 (dt, H1, syn to benzene ring, J 1,1′ ) -6.1, J 1,1a
)
3.3), 1.14 (dt, H1′, J 1′,1a ) 7.0), 2.47 (dd, H1a, H7a, J 1′,1a ) 7.0,
J 1,1a ) 3.3), 6.7-7.15 (AA′ BB′, 4H, H 3-6), 7.25-7.6 (m, 10 H);
13C NMR (75 MHz) δ 24.5 (t, C1), 27.2 (d, C1a, 7), 90.7 (s, C2,
7), 118.6 (d), 126.7 (d), 127.7 (d), 128.3 (d), 138.5 (s), 145.8 (s);
IR (KBr) 3070, 3048, 3027, 2999, 1602, 1494, 1458, 1448, 1368,
1320, 1076, 754, 695 cm-1; MS (m/ e) 310 (M+), 282, 206 (100%)
178, 126, 104, 71. Anal. Calcd for C23H18O: C, 89.00; H, 5.84.
Found: C, 88.73; H, 5.81.
Ack n ow led gm en ts. U.H.B. thanks the State Uni-
versity of New York at Binghamton for a sabbatical
leave and those at the Max-Planck-Institut fu¨r Kohlen-
forschung for their generous hospitality. We are grate-
ful to Murray G. Rosenberg for performing AM1 calcu-
lations on 2, its exo-adduct, 3, and 4.
Rea ction of Cyclop r op en e (1) w ith Cyclop en ta d ien e. In
an NMR tube, 0.2 mL (0.16 g, 4 mmol) of cyclopropene (1) was
added at -80 °C to 0.4 mL (0.32 g, 48 mmol) of cyclopentadiene
Su p p or tin g In for m a tion Ava ila ble: ORTEP plots of 4
(2 pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
masthead page for ordering information.
(21) (a) Breslow, R.; Oda, M. J . Am. Chem. Soc. 1972, 94, 4787. (b)
Oda, M.; Breslow, R.; Pecoraro, J . Tetrahedron Lett. 1972, 4419.
(22) Cordes, M. H. J .; de Gala, S.; Berson, J . A. J . Am. Chem. Soc.
1994, 116, 11161.
(23) According to AM1 calculations, exo-adduct 3 is 3.1 kcal/mol more
stable than endo-adduct 4. Rosenberg, M. G.; Brinker, U. H., unpub-
lished.
J O960728R