Studies in the Cycloproparene Series: Oxygen Transfer to 1-Diphenylmethylidene-1H-cyclopropabenzene

Article abstract of DOI:10.1071/CH99063

Oxygen transfer from dimethyldioxirane to 1-diphenylmethylidene-1H-cyclopropabenzene (8b) proceeds to give the corresponding epoxy derivative (7b), the simplest and most stable oxaspiropentene yet recorded. The compound has been characterized spectroscopi

Full text of DOI:10.1071/CH99063

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Volume 52, 1999
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Aust. J. Chem., 1999, 52, 647–652
.
Studies in the Cycloproparene Series:
Oxygen Transfer to 1-Diphenylmethylidene-
1H -cyclopropabenzene
Peter T. Bickers,A Brian Halton,A,B Andrew J. KayA,C and
Peter T. NorthcoteA
A
School of Chemical and Physical Sciences, Victoria University of Wellington,
P.O. Box 600, Wellington, New Zealand.
B
Author to whom correspondence may be addressed.
Present address: Industrial Research Ltd, Grace eld Research Centre,
C
P.O. Box 31-310, Lower Hutt, New Zealand.
Oxygen transfer from dimethyldioxiran to 1-diphenylmethylidene-1H -cyclopropabenzene (8b) proceeds
to give the corresponding epoxy derivative (7b), the simplest and most stable oxaspiropentene yet
recorded. The compound has been characterized spectroscopically prior to ring expansion and
rearrangement to the cyclobutenone (9b) above 20 C; this is the sole product isolated when the
reaction is performed at or above room temperature. If the oxygenation reaction is performed under
conditions other than strictly anhydrous, the rearrangement (7b) → (9b) competes with protonation of
the oxygen atom and sequential opening of the three-membered ring to provide the hydroxyethanone
(11b) via the diol (10b).
Despite major advances in the chemistry of the
recently by vacuum gas–solid reaction and it is even
less stable; it has provided a 1H n.m.r. spectrum
at 105 C and been intercepted from addition of
2 mol. equiv. of cyclopentadiene.8 In comparison to
these simple hydrocarbons, their oxygen-substituted
analogues (Scheme 1) have received surprisingly little
attention. Saturated oxaspiropentanes are recognized
4
cycloproparenes,1
many simple aspects of their
behaviour remain to be explored, and the existence and
stabilities of a range of conceptually simple derivatives
have yet to be assessed. In this context we have
reported already on the ease with which the alkyli-
denecycloproparenes undergo oxidation under both
acidic and neutral conditions.5 However, controlled
oxygen transfer has been applied previously only to
the cyclopropa[b]naphthalene derivative (8a) where-
upon the rst oxaspiropentene, the naphtho-annelated
derivative (7a), was characterized.6 We now report
upon comparable experiments involving the simpler
cyclopropabenzene derivative that lead to the homol-
ogous oxaspiropentene (7b), the second, simplest, and
most stable derivative of the ring system so far known.
Oxygen atom transfer to the bridge of (8b) is not
observed.
While spiropentene (1) is well recognized as a reac-
tive molecule (strain energy c. 375 kJ mol 1) that
polymerizes in the condensed phase at low temperature,
it has been characterized spectroscopically at 0 C and
trapped by Diels–Alder addition to cyclopentadiene
and furan.7 Spiropentadiene (2) was prepared more
Under rule A-21.3, IUPAC names the parent compound as bicyclo[4.1.0]hepta-1,3,5-triene. For convenience in making comparison
with the higher homologues the term 1H -cyclopropabenzene is employed throughout the discussion. [Editor’s note. Under the
1998 IUPAC recommendation FR-0, ‘no restriction is placed on when fusion nomenclature may be applied’; this means that
1H -cyclopropabenzene is now allowed as a formal name.]
Manuscript received 24 May 1999
᭧ CSIRO 1999
0004-9425/99/070647$ 05.00
10.1071/CH99063

648
P. T. Bickers et al.
as cyclobutanone equivalents par excellence,9 but the
alkene homologues 1-oxaspiro[2.2]pentene (3) and 1-
oxaspiro[2.3]hexene (4) have been neither recorded nor
intercepted. The simplest spiro-fused oxiran to contain
unsaturation appears to be 1-oxaspiro[2.4]hept-4-ene
(5),10 but the smaller and more highly strained
benzo-fused 1-oxaspiro[2.3]hex-4-ene (6) has also been
prepared recently;11 epoxides (5) and (6) are stable
compounds at room temperature.
either a hydroxy or a halogen substituent at the 1-
5
position has been isolated,2 it is expected that (10)
will undergo easy bond cleavage to provide (11) as
the nal product of reaction with the release of the c.
1
285 kJ mol
of strain energy3 of the cycloproparene
ring system.5 While it is possible for diol (10) to
eliminate water with concomitant ring expansion to
give cyclobutarenone (9), this last product has never
been observed under the acidic reaction conditions
employed.5,6 Not surprisingly, the behaviour of (7)
di ers from that of the isolable cyclobutarene homo-
logue (6). This compound reacts with aqueous HCl
to give chloro alcohol (12) and diol (13) (Scheme 3)
with retention of the cyclobutarene ring skeleton; diol
(13) was the minor product of reaction.11
Adam and his coworkers have made dimethyldioxiran
a convenient and easily accessible reagent for use in the
organic chemistry laboratory.14,15 When treated with
an excess of this reagent at 0 C the pale yellow solution
of (8b)16 lost its colour, and when the mixture was
allowed to warm to room temperature conventional
workup a orded the cyclobutenone (9b) in modest
(30%) yield, but at 50 C this is doubled to almost
60%. The sample is identical to one previously prepared
by a di erent route in these laboratories.17 Under the
neutral conditions of the reaction, epoxide (7b) is
presumed to be the initial product that undergoes
cyclopropylcarbinyl–cyclobutyl ring expansion (path a,
Scheme 4). However, this contrasts with the behaviour
of (8b) with dienes in Diels–Alder cycloadditions where
only a norcaradiene product is formed from reaction
across the bridge bond.18 It is the cyclopropanaphtha-
lene homologue (8a) that reacts with dienes by way
of the exocyclic double bond.19 These observations
suggest, therefore, that the oxygen transfer to ole n
(8b) could be to the bridge and not the exocyclic double
bond. Such addition would a ord the tricyclic oxiran
(14b) (path b, Scheme 4) which is expected to undergo
ring expansion to the oxacyclobutabenzene (15b) by
The formally simple cycloproparenes can be trans-
formed1,3,12 into a range of stable, coloured, crystalline
1-alkylidene-1H -cycloproparenes, e.g. (8), that are of
special interest because of their novel physicochemical
properties.13 Previously we found6 that epoxidation
of 1-diphenylmethylidene-1H -cyclopropa[b]naphthalene
(8a) with dimethyldioxiran yields the highly strained
oxaspiropentene (7a) (Scheme 2) that is stable below
0 C. Under the acidic conditions of peroxy acid epox-
idation only products of ring opening were recorded.5
Thus the reactions of both (8a) and (8b) with m-
chloroperoxybenzoic acid give the corresponding hydrox-
yethanone (11a) and (11b), respectively, in high yield
(71 and 83%). The formation of these compounds
under the acidic conditions is easily rationalized as
proceeding via the epoxides (7a,b) that are protonated
and then open in either direction to give the diols
(10a,b) (Scheme 2). As no cycloproparene carrying
The authors of the 1998 communication10 claim use of 1-oxaspiro[2.4]hept-4-ene but do not provide data for it. The 1985
paper10 provides data only for 4-methyl-1-oxaspiro[2.4]hept-4-ene.

Studies in the Cycloproparene Series
649
way of a bicyclobutane–cyclobutene rearrangement as
is observed for (16), the product of dihalocarbene
addition to parent cyclopropabenzene.20 The results of
the present study are inconsistent with such a pathway
but compatible with oxygen transfer to the exocyclic
double bond of (8b) to give oxiran (7b).
The typically shielded cyclopropabenzenyl C 2/5 atoms
(C 2/7 for the naphtho compounds) are deshielded in
comparison to those of the substrate alkene (8b) to
a similar extent as are those for (7a) compared with
(8a) [(8a)/(7a) 108 1/114 9; (8b)/(7b) 111 8/116 5
ppm]. The quaternary 13C n.m.r. resonances at 70 1
and 71 5 match closely those recorded for the oxiranyl
carbons of (7a) (71 0 and 71 7 ppm), and, when
comparison is made with the n.m.r. data of the isolable
oxiran (6) and its derived diol (13) (Fig. 1), it becomes
clear that high- eld chemical shifts recorded from oxy-
gen transfer to both (7a) and (7b) are consistent with
those recorded for (6) and not the ring-opened diol (13).
The three benzylic oxiranyl carbon atoms resonate in
the range 70 1–72 2 ppm whereas that of the benzylic
alcohol (13) is at 85 2 ppm and those of benzpinacol
[Ph2C(OH)C(OH)Ph2] are at 83 11 ppm.23 These are
some 12–13 ppm down eld of the resonances recorded
for (7a) and (7b) and therefore substantiate further
the argument that diol (10) (Scheme 2) is not involved
in the formation of ketone (9).
Fig. 1. N.m.r. resonances (in ppm) for selected quaternary
carbon atoms bonded to oxygen.
Oxiran (7b) appears to be more stable than its
naphtho analogue (7a) for there is little change in its
n.m.r. spectra even after standing at 10 C for more
than an hour—(7a) exhibits6 an onset of rearrangement
at 0 C which is some 50% complete after 8 h. After
almost 1 h at 20 C evidence for decomposition of (7b)
This last fact is substantiated by repetition of
the oxygen transfer employing perdeuterated reagent
[prepared from an excess of (D6)acetone and used
directly in this solvent21,22] at c. 30 C in the cavity
of an n.m.r. spectrometer. After c. 50 min at this
temperature oxygen transfer was >90% complete as
judged by the presence of only a very weak n.m.r.
resonance for the substrate C 2/5 atoms at 111 8 ppm.
After 1 h at 10 C reaction was complete, and 1H
and 13C n.m.r. spectra obtained were of the primary
product of oxygen transfer only. The data (Experi-
mental section) are fully compatible with epoxidation
occurring at the exocyclic double bond of (8b) to give
the benzo-fused oxaspiropentene (7b) with the same
symmetrical aromatic frame and nine distinct 13C
resonances. The 1H n.m.r. spectrum displayed a well
separated AA0 component of an AA0BB0 pattern in the
range 7 65–7 70 ppm with the remaining resonances
appearing as a complex multiplet from 7 41–7 54 ppm.
1
becomes evident in the H spectrum with new signals
appearing in the 7 8–8 2 ppm range; after only 5
min at 35 C these signals become clear. However, it
is only from heating at 50 C for a further 30 min
that the 13C spectrum shows convincing evidence for
signi cant change with new signals at
122 6 and
125 3 of similar intensity to that of C 2/5 of the
epoxide (7b) at 116 5. A further period of heating
for 1 h at this temperature essentially completes the
process and the major product of reaction is identi ed
as the cyclobutenone (9b) from its spectroscopic data
(see above). The changes recorded in the 13C spectra
in proceeding from (8b) → (7b) → (9b) are shown in
Fig. 2.
1
The H n.m.r. spectrum of (9b) recorded above dis-
plays signals extraneous to both itself and its precursor

650
P. T. Bickers et al.
(7b). Noteworthy is the presence of a singlet at 6 2 and
a multiplet in the range 7 92–7 96 in a 1 : 2 ratio that is
consistent with hydroxyethanone (11b); integration indi-
cates that (11b) is present to the extent of c. 10%. This
product is known5 to result from reaction of (7b) with
m-chloroperoxybenzoic acid and aqueous workup, but
we have now found, as expected, that it is formed in
74% yield when (7b) (generated as described above)
reacts with aqueous sulfuric acid and in 53% yield
with water alone (see Experimental section). In the
acid-catalysed reaction (1 h at room temperature) none
of cyclobutenone (9b) was detected while in the slower
Fig. 2. 13C n.m.r. spectra of cycloproparene (8b) (upper), oxiran (7b) (centre) and cyclobutenone (9b) (lower). Correlations
from (8b) are for the eight methylidenecyclopropabenzene carbon atoms.

Studies in the Cycloproparene Series
651
as cream crystals (20 C: 32 mg, 30%; 50 C: 61 mg, 57%), m.p.
104–105 C (lit.17 104–105 C). 1H n.m.r. 7 26, apparent tt,
Jave 7 2, 1 7 Hz, 2H, H 12; 7 35 m, 4H, H 11/13; 7 45, m, 4H,
H 10/14; 7 59 apparent dt, Jave 7 6, 1 1 Hz, 1H, H 5; 7 65,
apparent td, Jave 7 7, <1 Hz, 1H, H 4; 7 83, td, J 7 6, 1 2
Hz, 1H, H 3; 8 16, dt, J 7 6, 1 0 Hz, 1H, H 2. 13C n.m.r.
81 4, C 8; 122 6, C 5; 125 3, C 2; 127 5, C 10/14; 127 9, C 12;
129 4, C 11/13; 131 1, C 4; 137 4, C 3; 142 5, C 9; 146 8, C 6;
159 1, C 1; 190 2, C 7. Con rmation of the H 2–H 5 resonances
has been obtained from TOCSY experiments which correlate
H 2 at 8 16 ppm in sequence with the 7 83 (H 3), 7 65 (H 4),
and 7 59 ppm (H 5) resonances, in that order with increasing
mixing times.
uncatalysed hydrolysis (14 h at room temperature) this
ketone was isolated but only in 9% yield. As discussed
above, the conversion of (7b) into hydroxyethanone
(11b) must proceed by way of diol (10b) (Scheme 2).
The appearance of cyclobutenone (9b) only from the
uncatalysed aqueous hydrolysis is therefore much more
consistent with a slow thermal rearrangement from
(7b) competing with hydrolysis to (10b), rather than
with complete hydrolysis to diol (10b) and subsequent
partial conversion into ketone (9b) (Scheme 2).
Experimental
(b) 3 0,3 0-Diphenylspiro[bicyclo[4.1.0]hepta-1,3,5-triene-
7,2 0-oxiran] (7b)
General methods have been described previously.24 1H and
13C n.m.r. spectra were recorded for (D6)acetone solutions on a
Varian Associates Unity Inova 300 instrument with the chemical
shifts ( ) referenced25 to the residual methyl signal at 2 04(5)
To cycloproparene (8b) (15 mg, 0 06 mmol) in (D6)acetone
(100 l) contained in an n.m.r. tube sealed with a septum
cap and at 90 C was added, by syringe, the solution of
(D6)dimethyldioxiran (600 l, 0 06 mmol). The solution was
monitored by variable-temperature n.m.r. spectroscopy, and
after 10 min at 30 C changes in the 1H spectrum were evident.
After a further 50 min at this temperature oxygen transfer was
complete to >90% as judged from the 13C spectrum. Warming
to 10 C for 50 min resulted in spectra fully compatible
with the presence of the title epoxide (7b) only (see Fig. 2).
1H n.m.r. 7 41–7 54, complex m, 12H; 7 65–7 70, AA0 of
AA0BB0, 2H, H 3/4. 13C n.m.r. 70 1, C 7 or C 30; 71 5, C 30
or C 7; 116 4(5), C 2/5; 128 1, C 1/6; 128 4, 4 CH; 129 1,
C para; 129 2, 4 CH; 134 3, C 3/4; 138 9, C ipso. An HSQC
experiment in a separate run established the H–C connectivities
quoted.
and the central line of its 13C septet resonance at
29 8.
Short- and long-range 1H–13C correlations were determined
with gradient-enhanced inverse-detected HSQC and HMBC exper-
iments, and the data now provided for the known compounds
(8b), (9b) and (11b) are unpublished. The one-dimensional
TOCSY experiments were performed with shaped-pulse-selective
excitation and spin lock mixing times of 15–60 ms.
7-Diphenylmethylidenebicyclo[4.1.0]hepta-1,3,5-triene (8b)
The compound was prepared according to literature
methods.16 1H n.m.r.
7 30, br t, J 7 3 Hz, 2H, H 12;
7 38–7 41, BB0 of AA0BB0, 2H, H 2/5; 7 44, br t, J 6 5 Hz,
4H, 2 H 11/13; 7 58–7 61, AA0 of AA0BB0, 2H, H 3/4; 7 65,
br d, J 8 5 Hz, 4H, 2 H 10/14. 13C n.m.r.
111 7, C 8;
At 0 C the spectra were still of epoxide (7b) after 10 min, but
warming to 20 C and holding this temperature for 70 min gave
111 8, C 2/5; 114 1, C 7; 127 5, 2 C 12; 128 4, 2 C 10/14;
129 5, 2 C 11/13; 133 2, C 1/6; 134 9, C 3/4; 140 8, 2 C 9.†
a
1H spectrum which showed changes that became clear after 5
min at 35 C; these were, however, almost undetectable in the
13C mode. Heating to 50 C for 30 min resulted in a 13C n.m.r.
spectrum that displayed signals of almost the same intensity for
C 2/5 of epoxide (7b) ( 116 5) and C 2 and C 5 of cyclobutene
(9b) ( 125 3 and 122 6, respectively). After a further 60
min at this temperature the reaction was complete and the
spectroscopic data matched those for ketone (9b) described
above. Extraneous signals in this last 1H n.m.r. spectrum have
been assigned to hydroxytriphenylethanone (11b) (see below)
and account for c. 10% of the product mixture.
Dimethyldioxiran
Dimethyldioxiran was prepared from acetone [or (D6)acetone]
according to the method of Adam et al.14,15 employing the
monopersulfate 2KHSO5.KHSO4.K2SO4. The ltered solution
so obtained was assumed14 to be c. 0 1 M and was used within
48 h of its preparation. The 1H n.m.r. spectrum of the solution
of the labelled reagent in (D6)acetone at 0 C displayed a water
proton signal commensurate with that recorded for the labelled
solvent alone.
(c) 2-Hydroxy-1,2,2-triphenylethanone (11b)
Reactions of 7-Diphenylmethylidenebicyclo[4.1.0]hepta-1,3,5-
triene (8b) with Dimethyldioxiran
Ole n (8b) was allowed to react with dimethyldioxiran as
described in (a) above at 20 C for 60 min. This was followed
by two separate procedures: (i) the addition of sulfuric acid;
(ii) the addition of ice-cold water.
(i) The addition of sulfuric acid (0 5 ml, 2 M) at the
same temperature and then stirring for a further 60 min to
attain room temperature, followed by conventional workup and
recrystallization (hexane), a orded the -hydroxy ketone (11b)
as colourless needles (84 mg, 74%), m.p. 85–86 5 C (lit.26
86–87 C), identical to a sample prepared previously in these
laboratories.5 1H n.m.r. 6 03, br s, OH; 7 29–7 40, complex
m, 8H; 7 41–7 52, complex m, 5H; 7 94, br d, J 8 4 Hz,
2H. 13C n.m.r. 86 4, Ph2C(OH); 128 2(4), 4 CH; 128 2(7),
(a) 8,8-Diphenylbicyclo[4.2.0]octa-1,3,5-trien-7-one (9b)
Ole n (8b) (100 mg, 0 39 mmol) and anhydrous potas-
sium carbonate were placed in a round-bottomed ask (25 ml)
equipped with a magnetic stirring bar and the whole mixture
was cooled to 0 C. To the ask, purged with dry nitrogen,
was added dimethyldioxiran (10 ml, c. 1 0 mmol) and after
5–10 min the initially bright yellow solution became colourless.
In one reaction the contents were warmed to room tempera-
ture and stirred for several hours, while in a second run the
mixture was stirring at 50 C for 2 h. The resultant mixture
was cooled to room temperature, ltered through anhydrous
potassium carbonate, and the ltrate dried (Na2SO4/K2CO3,
3 : 1), ltered through Celite (30–80 mesh), and concentrated
in vacuum to a cream-coloured solid. Radial chromatography
(1 : 1 dichloromethane/light petroleum elution) gave a cream-
coloured oil which on trituration a orded the title compound
2
CH; 128 6, 2 CH; 128 8, 4 CH; 131 4, 2 CH; 133 0, CH
para; 137 0, C ipso; 144 5, 2 C ipso; 200 9, PhCO.
(ii) The addition of ice-cold water (0 5 ml) and then stirring
for 14 h, during which time room temperature was attained,
followed by conventional workup, a orded cyclobutenone (9b)
Formal von Baeyer nomenclature is employed in this section so that 1H -cyclopropabenzene becomes bicyclo[4.1.0]hepta-1,3,5-triene;
the atom numbers C 2/5 referred to in the text are the same under both naming systems.
† Atoms C 9–C 14 and H 10–H 14 belong to the phenyl groups. (C 8 is the methylidene carbon.)

652
P. T. Bickers et al.
12
(8 mg, 7 5%), m.p. 103–105 C (lit.5 104–105 C), as the
most mobile component from radial chromatography (1 : 1,
Halton, B., Cooney, M. J., Boese, R., and Maulitz, A. H.,
J. Org. Chem., 1998, 63, 1583; Halton, B., Kay, A. J.,
Zhi-mei, Z., Boese, R., and Haumann, T., J. Chem. Soc.,
Perkin Trans. 1, 1996, 1445; Halton, B., Cooney, M. J.,
Davey, T. W., Forman, G. S., Lu, Q., Boese, R., Blaser,
D., and Maulitz, A. H., J. Chem. Soc., Perkin Trans. 1,
1995, 2819.
Halton, B., Pure Appl. Chem., 1990, 62, 541; Halton, B.,
Lu, Q., and Melhuish, W. H., J. Photochem. Photobiol.,
A: Chem., 1990, 52, 205.
Adam, W., Hadjiarapoglou, L. P., Curci, R., and Mello,
R., in ‘Organic Peroxides’ (Ed. W. Ando) pp. 195–219
John Wiley: Chichester 1992), and references cited therein;
Adam, W., and Schuhmann, R. M., Liebigs Ann. Chem.,
1996, 635; Adam, W., Makosza, M., Saha-Moller, C. R.,
and Zhao, C.-G., Synlett, 1998, 1335.
Crandall, J. K., Batal, D. J., Sebesta, D. P., and Lin, F.,
J. Org. Chem., 1991, 56, 1153.
Halton, B., Randall, C. J., and Stang, P. J., J. Am. Chem.
Soc., 1984, 106, 6108; Halton, B., Randall, C. J., Gainsford,
G. J., and Stang, P. J., J. Am. Chem. Soc., 1986, 108,
5949.
Buckland, S. J., Halton, B., Mei, Q., and Stang, P. J.,
Aust. J. Chem., 1987, 40, 1375.
Halton, B., Kay, A. J., McNichols, A. T., Stang, P. J.,
Boese, R., Haumann, T., Apeloig, Y., and Maulitz, A. H.,
Tetrahedron Lett., 1993, 34, 6151.
McNichols, A. T., Stang, P. J., Halton, B., and Kay, A. J.,
Tetrahedron Lett., 1993, 34, 3131.
Kagabu, S., and Saito, K., Tetrahedron Lett., 1988, 29, 675.
Baumstark, A. L., and McCloskey, C. J., Tetrahedron Lett.,
1987, 28, 3311.
Chenault, H. K., and Danishefsky, S. J., J. Org. Chem.,
1989, 59, 4249.
Datum taken from the Victoria University of Wellington,
CHEM371 Laboratory Manual, 1999.
Cooney, M. J., and Halton, B., Aust. J. Chem., 1996, 49,
533.
Gottlieb, H. E., Kotlyar, V., and Nudelman, A., J. Org.
Chem., 1997, 62, 7512.
Eastham, J. F., Hu aker, J. E., Raaen, V. F., and Collins,
C. J., J. Am. Chem. Soc., 1956, 78, 4323.
dichloromethane/light petroleum elution), and the title
-
hydroxy ketone (11b) as the second component (60 mg, 53%)
identical to the sample described in (i) above.
Acknowledgments
13
14
Financial assistance from the Victoria University
of Wellington Science Faculty Grants Committee and
the New Zealand Lottery Grants Board (the former
Lottery Science Distribution Committee) for assistance
with instrument purchase is gratefully acknowledged.
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Note Added in Proof
10
Tannis, S. P., Johnson, G. M., and McMills, M. C., Tetra-
The synthesis and spectroscopic characterization of
oxaspiropentene (3) have been reported since submis-
sion of this paper—see Billups, W. E., Saini, R. K.,
and Daniels, A. D., Org. Lett., 1999, 1, 115.
hedron Lett., 1988, 29, 4521; Tannis, S. P., McMills, M. C.,
and Herrinton, P. M., J. Org. Chem., 1985, 50, 5887.
Frimer, A. A., Weiss, J., Gottlieb, H. E., and Wolk, J. L.,
J. Org. Chem., 1994, 59, 780.
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