Diazodiphenylmethane and monosubstituted butadienes: Kinetics and a new chapter of vinylcyclopropane chemistry

Article abstract of DOI:10.1002/hlca.200890081

Diazodiphenylmethane (DDM) undergoes cycloadditions to 1-substituted buta-1,3-dienes exclusively at the C(3)=C(4) bond. At room temperature, the N₂ loss from the initially formed 4,5-dihydro-3H-pyrazoles 2 is faster than the cycloaddition and furnishes the vinylcyclopropane derivatives 7 and 9 with structural retention at the C(1)=C(2) bond. 2-Substituted butadienes react with DDM at the C(3)=C(4) bond to give 12; isoprene, however, affords 3,4/1,2 products in the ratio of 86:14. DDM is a nucleophilic 1,3-dipole: 1-Cyanobutadiene reacts 400 times faster than 1-methoxybuta-1,3-diene (DMF, 40°). The log k₂ for the additions to six 1-substituted butadienes show a linear correlation with σ_p (Hammett) and ρ = +2.9; the log k₂ of five 2-substituted butadienes are linearly related to Taft's σ_I (ρ = +1.7). The structures of the vinylcyclopropanes 7, 9, and 12 are established by NMR spectra and oxidation. A cyclopropyl carbinyl cation is made responsible for the isomerization of 12, R = Ph, Me, by acetic acid to 4-substituted 1,1-diphenylpenta-1,3-dienes 25 and 29; TsOH at 200° converts 25 further to 9,10-dihydro-9-methyl-10-phenyl-9,10-ethanoanthracene (27). Thermal rearrangement of 7, 9, and 12 at 200-300° produces the 3- or 1-substituted 4,4-diphenylcyclopentenes 30 and 31. These give the same mass spectra as the vinylcyclopropanes, and an open-chain distonic radical cation is suggested as common intermediate. Besides spectroscopic evidence for the cyclopentene structures, hydrogenation and epoxidation are described; NMR data support the trans-attack by perbenzoic acid.

Full text of DOI:10.1002/hlca.200890081

Helvetica Chimica Acta – Vol. 91 (2008)
783
Diazodiphenylmethane and Monosubstituted Butadienes: Kinetics and a New
Chapter of Vinylcyclopropane Chemistry1)
by Akihiro Ohta, Klaus Dahl, Rainer Raab†, Jochen Geittner, and Rolf Huisgen*
Department Chemie und Biochemie der Ludwig-Maximilians-Universität, Butenandtstrasse 5 – 13,
D-81377 München
Dedicated to Emanuel Vogel, the discoverer of the vinylcyclopropane rearrangement, on the occasion of
his 80th birthday
Diazodiphenylmethane (DDM) undergoes cycloadditions to 1-substituted buta-1,3-dienes exclu-
sively at the C(3)¼C(4) bond. At room temperature, the N2 loss from the initially formed 4,5-dihydro-
3H-pyrazoles 2 is faster than the cycloaddition and furnishes the vinylcyclopropane derivatives 7 and 9
with structural retention at the C(1)¼C(2) bond. 2-Substituted butadienes react with DDM at the
C(3)¼C(4) bond to give 12; isoprene, however, affords 3,4/1,2 products in the ratio of 86 :14. DDM is a
nucleophilic 1,3-dipole: 1-Cyanobutadiene reacts 400 times faster than 1-methoxybuta-1,3-diene (DMF,
408). The log k2 for the additions to six 1-substituted butadienes show a linear correlation with sp
(Hammett) and r¼ þ2.9; the log k2 of five 2-substituted butadienes are linearly related to Taftꢀs sI (r¼
þ1.7). The structures of the vinylcyclopropanes 7, 9, and 12 are established by NMR spectra and
oxidation. A cyclopropyl carbinyl cation is made responsible for the isomerization of 12, R ¼ Ph, Me, by
acetic acid to 4-substituted 1,1-diphenylpenta-1,3-dienes 25 and 29; TsOH at 2008 converts 25 further to
9,10-dihydro-9-methyl-10-phenyl-9,10-ethanoanthracene (27). Thermal rearrangement of 7, 9, and 12 at
200 – 3008 produces the 3- or 1-substituted 4,4-diphenylcyclopentenes 30 and 31. These give the same
mass spectra as the vinylcyclopropanes, and an open-chain distonic radical cation is suggested as common
intermediate. Besides spectroscopic evidence for the cyclopentene structures, hydrogenation and
epoxidation are described; NMR data support the trans-attack by perbenzoic acid.
1. Introduction. – Diazomethane and diazodiphenylmethane are nucleophilic 1,3-
dipoles and preferably react with electrophilic C¼C bonds (Scheme 1). The rate
constant k2 (DMF, 258) for the 1,3-cycloadditions of diazomethane (DM) to ethyl
acrylate exceeds that of styrene 2500-fold, and that of butyl vinyl ether by a factor of 107
[2]; enamines are inert to DM.
Scheme 1
1
)
1,3-Dipolar Cycloadditions, Part 137; for Part 136, see [1].
ꢁ 2008 Verlag Helvetica Chimica Acta AG, Zürich

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The corresponding cycloadditions of diazodiphenylmethane (DDM) in DMF at 408
are slower than those of DM at 258, and cover a smaller range: ethyl acrylate is only 660
times faster than styrene and 104-fold ahead of hex-1-ene; vinyl ethers no longer react
[2]. Whereas the cycloadditions of DM usually allow the isolation of dihydropyrazoles,
those of DDM are accompanied by N2 loss and afford vinylcyclopropane derivatives.
In the 1970s, MO perturbation theory (PMO) offered the clue to a successful
description of reactivity and regiochemistry in concerted cycloadditions (for reviews,
see [3 – 5a]). Among the two frontier orbital (FMO) interactions, HO(diazome-
thane) – LU(dipolarophile) controls the energy of the transition structure (TS) to a
higher extent than the second HO – LU pair. In a simplified version of the perturbation
equation, log k2 should be linearly related to the reciprocal energy distance of the
controlling HO – LU pair [3]. Using the IP of DM for HO(diazomethane) and (IP À
E
p!p*) for LU(dipolarophile), the log k2 for the cycloadditions to numerous ethylene
and butadiene derivatives fulfilled such a linear relationship [6]. In an orthodox PMO
calculation, however, the interaction of all p-MOs of both cycloaddition partners must
be included [7][8].
The present state of the art is an ab initio calculation of TSs; its increasing
sophistication reflects the progress of quantum-chemical methods as well as that of
computer efficiency. As early as 1975, Leroy and Sana calculated cycloadditions of DM
at the STO-3G level [9]. In 1998, RHF and B3LYP calculations by Rastelli, Gandolfi
et al. [10] confirmed the concertedness; the calculated activation energies for the
additions of DM to substituted ethylenes showed an ꢂimpressive agreement both in trend
andabsolute values ꢀ with measured data. Recently, Ess and Houk demonstrated by
B3LYP calculations that the distortion energies of 1,3-dipoles (diazonium and nitrilium
betaines) constitute a substantial part of the activation energies for the concerted 1,3-
cycloadditions to ethylene and acetylene [11].
An experimental argument for concertedness rests on the high stereospecificity
observed for the cycloadditions of DM to methyl tiglate and methyl angelate. The
configurational retention of > 99.997% would burden the CÀC bond of a hypothetical
intermediate in a two-step process with a rotational barrier of > 7.2 kcal molÀ1 [12].
2. Results and Discussion. – 2.1. Site Selectivity, Regiochemistry, andProducts.
Diazodiphenylmethane (DDM) resembles diazomethane (DM) in its preference for
electrophilic cycloaddition partners, as mentioned above. However, the steric demands
of DDM exceed those of the parent DM. Monosubstituted buta-1,3-dienes offer a
model for separating, to some extent, steric and electronic effects on the cycloaddition
rate. Fortunately, 1-substituted butadienes accepted DM and DDM exclusively at the
C(3)¼C(4) bond.
In a previous contribution from our laboratory, the cycloadditions of DM to 1-
substituted buta-1,3-dienes 1 were studied [13]. The 4,5-dihydro-3-vinyl-3H-pyrazoles 2
were isolated in experiments with 1, R ¼ H, Me, MeO, whereas tautomerization to
dihydro-1H-pyrazoles 3 took place on workup after reactions of 1, R ¼ Ph, CO2Me, CN
(Scheme 2). In the HOMO and LUMO, DM has the larger atomic-orbital coefficient at
the C-atom, thus directing the addition to 1 which possesses in the LUMO the larger
coefficients at C(1) and C(4) [14]. The consistent site selectivity is more problematic
[15] and speaks for participating steric effects.

Helvetica Chimica Acta – Vol. 91 (2008)
785
Scheme 2
As an example of 2-substituted buta-1,3-dienes, 4, R ¼ Ph, was reacted with DM to
give the 3,4-cycloadduct 5, R ¼ Ph [13].
The cycloadditions of DDM to 1- and 2-substituted butadienes were attended by
elimination of N2. Most of the butadienes 1 were available as (E)-forms, the cyano
compound was 1(Z), and 1, R ¼ MeO, consisted of an (E)/(Z) mixture with a ratio of
60 :40. Products of N2 extrusion from the 4,5-dihydro-3H-pyrazoles 6 and 8 were the
1,1-diphenyl-2-vinylcyclopropanes 7 and 9, which, according to the NMR spectra,
occurred with retention of configuration at the former C(1)¼C(2) bond (Scheme 3).
The C(3)¼C(4) bond of 1 is definitely the reaction site, but, due to the rapid N2 loss,
there is no experimental evidence for the regiochemistry of cycloaddition. The
assumption of structures 6 and 8 rests on the analogy with the isolated DM cycloadducts
2 and 3.
The reactions of DDM with 1 were run at room temperature, and the butadienes 1,
R ¼ H, Me, Ph, MeO, served as solvent for the slow additions. These cycloadditions
Scheme 3

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competed with the self-decomposition of DDM which proceeds in DMF at 258 with a
half-life of 72 days. 1,3-Dipolar cycloadditions usually have large negative DS# values,
and, therefore, a lower temperature dependence of rate than the first-order decom-
position of DDM. We accepted reaction times of weeks and months to promote the
cycloaddition. The faster reactions with 1, R ¼ CO2Me, CN, were carried out with 1:1
stoichiometry in benzene.
Correspondingly, several 2-substituted buta-1,3-dienes 4 were reacted with DDM.
Isoprene (4, R ¼ Me) accepted the 1,3-dipole both at the C(3)¼C(4) and the
C(1)¼C(2) bond, and 12/13 86 :14 was observed. The cycloadditions with 4, R ¼ Ph, Cl,
MeO, took place only at the C(3)¼C(4) bond and provided 12 (Scheme 4).
Scheme 4
The yields of the vinylcyclopropane derivatives (see Table 2 below) amounted to
33 – 91%. Limiting factors were the decomposition of DDM in the reactions with the
ꢂslowꢀ dienes 1, R ¼ Me, MeO, and the oligomerization of 4, R ¼ Ph. The spectra and
the chemistry of the products will be dealt with in Sect. 2.3.
The intermediacy of the 4,5-dihydro-3H-pyrazoles of type 6 and 10 requires brief
consideration. An alternative to the concerted cycloaddition of DDM would be the
formation of a diazonium zwitterion 14 (or biradical) and ring closure after loss of N2;
the cycloadduct would be bypassed. However, the N2 extrusion from 4,5-dihydro-3H-
pyrazoles (1-pyrazolines) is known as ꢂBuchner – Curtius Cyclopropane Synthesisꢀ; the
first examples dealt with cycloadducts of diazoacetate (1888) [16]. According to van
Alphen [17], DDM and methyl citraconate afford 15, which cannot tautomerize to the
more stable dihydro-1H-pyrazole (2-pyrazoline), and N2 is eliminated above 1008.

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What determines the rate of N2 evolution from 4,5-dihydro-3H-pyrazoles? Various
kinetic studies of the thermolysis [18] suggest that conjugating substituents are already
effective in the TS of N2 loss. The initially formed trimethylene species, often described
as biradical, is stabilized by Ph, vinyl, or CO2Me groups. That makes the DDM
cycloadducts 6, 8, 10, and 11 prone to N2 extrusion; whether the loss of N2 is a one-step
or two-step process will not be discussed here. Interestingly, the perphenylated
compound 16 requires 48 h at 2408 for N2 elimination [19]; here, TS and product suffer
from steric hindrance of resonance.
2.2. Rate Constants of Diazodiphenylmethane Cycloadditions. The rates were
measured as pseudo-first-order reactions in the presence of ca. 10 equiv. of
dipolarophile in DMF at 408. The concentration of DDM was determined volumetri-
cally in withdrawn samples (N2 evolution with Cl3CCOOH). The high solubility of DM
in DMF was originally responsible for the choice of DMF as solvent. The k1y values
were corrected for k1 of self-decomposition. The rate constants of DDM additions at
408 are compared with those of DM at 258 in Table 1.
Table 1. Rate Constants k2 [ · 105 mÀ1 sÀ1] for the 1,3-Cycloadditions of Diazomethane [13] and
Diazodiphenylmethane to Butadiene and Its Monosubstituted Derivatives in DMF
Substituent R
H2C¼CHÀCH¼CHR
þ CH2N2 at 258
H2C¼CHÀCH¼CHR
þ Ph2CN2 at 408
H2C¼CHÀCR¼CH2
þ Ph2CN2 at 408
CNa)
Cl
33.0
2.22
CO2Me
H
Ph
Me
MeOc)
2570
21.4
21.0
2.43
1.34
11.4
0.78b)
0.58
0.10
0.08
0.78b)
0.71
0.25
0.76
r(Hammett)
þ 4.3
þ 2.2
r(Taft) þ 1.7
b
a) 98% (Z) and 2% (E). ) Statistical value 1ꢃ2 used for the plots of Figs. 1 and 2. c) 60% (E) and 40%
(Z).
In the reaction with (E)-1-phenylbuta-1,3-diene in DMF at 408, DM is 108 times
faster than DDM. The rate constants were measured at different temperatures, and the
Eyring parameters suggest that mainly the higher activation enthalpy is responsible for
the lower rate of DDM: DH# ¼ 16.1 ꢀ 0.8 kcal molÀ1 and DS# ¼ À31 ꢀ 3 e.u. for DDM,
compared with DH# ¼ 13.8 ꢀ 0.8 kcal molÀ1 and DS# ¼ À29 ꢀ 3 e.u. for DM. Remark-
ably, the entropies at 408 contribute 38% (DDM) and 40% (DM) to the activation free
energy. The data confirm an earlier experience that the dramatic differences in the rates
of diazoalkane cycloadditions (methyl diazoacetate and dimethyl diazomalonate were
also included) are controlled by variation of DH# [20].
The k2 values for the cycloadditions of DDM to the C(3)¼C(4) bond of 1-
substituted butadienes reveal a diminished substituent influence, compared with the k2
of DM reported in [13]. DM reacts with methyl buta-1,3-diene-1-carboxylate (1, R ¼
CO2Me) 1900 times faster than with 1-methoxybuta-1,3-diene (R ¼ MeO); this ratio
shrinks to 143 for DDM. Nevertheless, the k2 values of DDM stretch over a range of

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> 400. The log k2 for DDM, like those for DM, fit linear free energy correlations fairly
well, when plotted vs. sp (Hammett) (Fig. 1). This is reasonable, since both resonance
and inductive effects of substituents R are conducted through the butadiene system as
in p-substituted benzenes, virtually without steric impairment. The r values, 4.3 for DM
[13] and 2.9 for DDM, reflect the lower sensitivity of the latter. The configuration at the
C(1)¼C(2) bond of 1, (E) or (Z), appears to be of minor importance.
Fig. 1. Rate Constants k2 for the Cycloadditions of DDM to 1-SubstitutedButa-2,3-dienes (DMF, 408).
Plot of log k2 vs. sp (Hammett).
In 2-substituted butadienes 4, the C(1)¼C(2) bond profits from resonance and
inductive contributions of R, whereas only the I-effect reaches the C(3)¼C(4) bond.
As mentioned above, DDM cycloadditions take place at the C(3)¼C(4) bond of 4 with
the exception of isoprene, which furnishes 3,4- and 1,2-adduct in a ratio of 86 :14. The
five rate constants given in Table 1 cover the modest range of factor 9. The log k2 values
fit Taftꢀs inductive substituent constants sI [21][22] slightly better (Fig. 2) than
Hammettꢀs sm; coincidence may play a role, since steric effects of R are no longer
negligible.
We regard the analogy of DM and DDM in the rate phenomena as further
confirmation for assuming dihydro-3H-pyrazoles to be initial products of DDM
reactions (see Sect. 2.1).
As a 1,3-dipole, DDM is less nucleophilic than DM. Benzylic resonance distributes
the charge, and, in the language of MO theory, the phenyl conjugation decreases the
HOMO energy. Superimposed is the retardation of DDM reactions by steric hindrance.
In the framework of a highly successful concept of electrophileÀnucleophile
combinations (recent review: [23]), Mayr and co-workers [24] determined the kinetics
for the CÀC bond formation of aliphatic diazo compounds with benzhydryl-type
cations (CH2Cl2, 208) and assigned nucleophilicity parameters N: 10.48 (DM) and 5.29
(DDM) correspond to a decrease of 5 logarithmic units caused by the two Ph groups.

Helvetica Chimica Acta – Vol. 91 (2008)
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Fig. 2. Cycloadditions of DDM with 2-SubstitutedButa-1,3-dienes. Plot of log k2 (DMF, 408) vs. Taftꢀs
inductive substituent constants sI.
Since both reactants, DDM and carbocation, are sterically demanding, steric shielding
participates in the effect.
In the cycloadditions of DM and DDM with (E)-1-phenylbuta-1,3-diene (DMF,
408, kDM/kDDM ¼ 108), DDG# amounts to 2.9 kcal molÀ1, i.e., the retardation is smaller.
1,3-Dipoles are ambiphilic, i.e., both termini are nucleophilic and electrophilic [5b]; it is
the preponderance of nucleophilic character that is disclosed in the rate ratio kDM/kDDM
as well as in the substituent effects observed in cycloadditions to substituted butadienes.
2.3. Properties andSome Reactions of 1,1-Diphenyl-2-vinylcyclopropanes. The
structures of the vinylcyclopropanes were elucidated by NMR spectroscopy. The high-
field shifts of d(1H) and d(13C) are in accordance with a cyclopropane ring. The
1H-NMR parameters of 7, R ¼ Ph, given in formula 17 (see below) serve as an example.
They were confirmed by computer simulation (DAVINX [25]); the coupling constants
Jgem ¼ À5.0, Jcis ¼ 8.6, and Jtrans ¼ 5.8 Hz, are within the range of literature data for
cyclopropanes [26]. The chemical shifts of the olefinic H-atoms change more with
variation of R, and Jvic establishes the assignments of (E)- and (Z)-configurations
(Table 2).
Chemical confirmation came from oxidation with KMnO4, which, in the example of
7, R ¼ Ph, furnished 2,2-diphenylcyclopropane-1-carboxylic acid (18; 73%) and
PhCOOH (68%). The KMnO4 oxidation of 12, R ¼ Ph, stopped at the glycol 20,
which was cleaved by Pb(OAc)4 to give the cyclopropyl ketone 19.
Noteworthy is the sensitivity of 12, R ¼ Ph, to acid. In boiling AcOH, a conversion
to 1,1,4-triphenylpenta-1,3-diene (25) took place with 95% yield (Scheme 5). Besides
the spectroscopic characterization, the oxidation of 25 furnished benzophenone and
acetophenone. Catalytic hydrogenation converted 25 to 1,1,4-triphenylpentane (28).
Supposedly, 25 has the (E)-configuration at the C(3)¼C(4) bond. Compound 25 has

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Table 2. 2-Ethenyl-1,1-diphenylcyclopropanes as Products of Cycloadditions of DDM with Monosub-
stitutedButa-1,3-dienes
R
H
Yield [%]
79
M.p. (B.p. at 10À3 Torr)
1H-NMR Chemical shifts [ppm]
and coupling constants [Hz]
HÀC(1’)
HÀC(2’)
3J(1’,2’)
7
(93 – 958)
5.24
5.32
5.04
5.60
6.55
6.60
6.05
6.00
5.69
5.18
5.01
17.0 (E)
9.6 (Z)
15.2 (E)
15.8 (E)
12.6 (E)
6.3 (Z)
15.5 (E)
11.0 (Z)
17.2 (E)
10.7 (Z)
7
7
7
9
7
Me
Ph
MeO
MeO
CO2Me
CN
33
76
(95 – 1008)
60 – 61.58
(120 – 1308)
(120 – 1308)
66.5 – 67.58
66 – 678
4.73
5.46
4.25
3.83
6.28
5.23
5.41
31a)
16a)
90
9
13
91
11b)
Me
(100 – 1028)
HaÀC(2’)
HbÀC(2’)
2Jgem
12
12
12
12
Me
Ph
MeO
Cl
70b)
48
81
(100 – 1028)
149.5 – 150.58
52.0 – 52.58
(118 – 1218)
4.58
4.63
3.74
4.81
4.79
5.16
3.83
4.96
1.4
0.77
2.0
1.5
74
a) Mixture 7/9 74 : 26. b) Mixture 12/13 84 : 16.
been described twice, likewise with uncertain configuration [27][28], but with the same
melting point (122 – 1248).
Protonation at the terminal methylidene group of 12, R ¼ Ph, affords a carbocation
21, which profits from benzyl and cyclopropylcarbinyl resonance: ꢂthe cyclopropyl
group is equal to or better than a phenyl in stabilizing an adjacent carbocationic centerꢀ
[29]. The rearrangement of [cyclopropylcarbinyl]þ to [cyclobutyl]þ and [but-3-enyl]þ
has long been known [30]. Ring opening of 21 provides the diphenylmethyl cation 22,
which forms 25 by proton loss.
When diene 25 (or 12, R ¼ Ph) was treated with toluene-4-sulfonic acid at 2008,
another isomerization generated a hydrocarbon (55%), with a melting point 181 – 1828,
stable to peracid or H2/Pd. It turned out to be the bridgehead-substituted 9,10-dihydro-
9,10-ethanoanthracene 27. The 13C-NMR spectrum shows signals of two CH2 groups,
four signals for Ph, and six signals for two equivalent benzo rings, thus revealing a plane
1
of symmetry. The H-NMR spectrum displays an AA’BB’ pattern for the CH2 groups,

Helvetica Chimica Acta – Vol. 91 (2008)
791
Scheme 5
which was solved by calculation: the coupling constants, Jcis ¼ 10.6 and Jtrans ¼ 4.2, are in
accordance with other dibenzobicyclo[2.2.2]octadienes [31]. The base peak in the mass
spectrum of 27 is [M À CH2CH2]þ, i.e., the radical cation of methyl-phenyl-anthracene.
The interpretation in Scheme 5 foresees a sequence of two acid-induced cationic
cyclizations. The first leads to the 1,2-dihydronaphthalene derivative 23, which, in turn,
is protonated to give a new diphenyl-methyl-type cation 26. The latter undergoes a
second aromatic alkylation, which yields the 9,10-dihydroanthracene derivative 27 after
proton loss. It is noteworthy that all the acid-catalyzed conversions take place in the
manifold C23H20.
The major product obtained from DDM and isoprene (12, R ¼ Me) is likewise
sensitive to acid. Hot AcOH (even adsorption on silica gel was sufficient) effected the
analogous formation of 29 (Scheme 6).
Scheme 6

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Helvetica Chimica Acta – Vol. 91 (2008)
2.4. Thermal Rearrangements of the Vinylcyclopropanes to Cyclopentene Deriva-
tives. Compared to the classic rearrangements of organic chemistry, the thermal
isomerization of vinylcyclopropane and its derivatives to yield cyclopentenes is a late
discovery: it was observed by three groups in 1959/60 [32 – 34], but, 25 years later, a
review with 228 references [35] collected the publications on all-carbon systems,
neglecting, however, the rich harvest on hetero analogues. This flaring up of interest
was fanned by Woodward and Hoffmann who discussed the rearrangement as a [1.3]-
sigmatropic alkyl shift, but avoided a clear mechanistic conclusion [36]. In 2003,
Baldwin competently summarized the mechanistic contributions [37] (237 references).
Most of the substituted vinylcyclopropanes of Table 2 were subjected to the
rearrangement by heating to 3108 for 5 min. After high-vacuum distillation, the
cyclopentenes of type 30 and 31 were isolated in good yield (Table 3 and Scheme 7). In
many cases, milder conditions were sufficient, as shown by 91% yield of 30, R ¼ Ph,
after heating of 7, R ¼ Ph, for 10 min at 2008.
Scheme 7
Table 3. 4,4-Diphenylcyclopent-1-enes 30 and 31 by Thermal Isomerization of 2-Ethenyl-1,1-diphenyl-
cyclopropanes 7, 9, and 12 at 3108
R
Yield [%]
M.p. (B.p.
at 10À3 Torr)
1H-NMR Chemical shifts [ppm]
and coupling constants [Hz]
3-Substitutedcyclopentenes
HÀC(1)
HÀC(2)
J(1,2)
HÀC(3)
30
30
30
30
30
H
Me
Ph
CO2Me
CN
77
98
91
90
(100 – 1058)
(100 – 1058)
68 – 708
52.5 – 53.08
96.0 – 96.58
5.74
6.01
6.00
5.89
6.01
5.74
6.07
6.02
6.06
5.69
3.02
3.87
4.78
4.50
4.37
5.9
5.9
5.8
5.8
a
)
1-Substitutedcyclopentenes
HÀC(2)
HÀC(3)
HÀC(5)
31
31
Me
Ph
87
59
(100 – 1058)
93.5 – 94.08
5.51
6.27
3.09
3.32
3.16
3.51
a) Not determined.

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1
The H-NMR spectra of the cyclopentenes 30 reveal a high propensity for H,H-
coupling, like cyclopentene itself [38][39]; the latter still enjoys the bonus of symmetry.
The computer simulation [25] of the 600-MHz spectrum of 30, R ¼ Ph, showed, that
each of the five aliphatic H-atoms couples with the other four; the assignments in
formula 32A (Scheme 7) are based on several assumptions. The (Z)-ethylenic J(1,2) is
5.9 Hz, and the geminal J(5a,5b) is À 16.8 Hz. The three vicinal, three allylic, and two
homoallylic couplings are in the range of 1.7 – 2.3 Hz. With ten J values as variables, the
simulation becomes problematic.
The 1-substituted cyclopentenes 31 are blessed with a symmetry plane, as shown in
32B for the 1H-NMR parameters of 31, R ¼ Ph. Double-resonance experiments
disclosed that both homoallylic couplings, trans and cis, are identical (5J ¼ 1.7); for
5
cyclopentene, the parent compound, different homoallylic couplings, Jtrans ¼ 3.0 and
5Jcis ¼ 2.1, were reported [38][39].
Remarkably, the mass spectra of corresponding pairs of vinylcyclopropanes and
cyclopentenes are the same. Thus, the mass spectra of, e.g., 7, 9, and 30, R ¼ Ph,
recorded at room temperature, are virtually indistinguishable. We doubt that the
rearrangement is so fast on the level of the radical cation, but we rather tend to assume
that both initial radical ions rapidly afford one and the same open-chain species 33
(Scheme 8). This species is a distonic radical cation [40], in which charge and electron
spin are formally separated. With a carbocation of the diphenylmethyl type and an
allylic radical, 33 should be more stable than the initial cyclic radical cations. The rapid
move of one electron allows a certain distribution of cationic charge and spin density
between the termini.
The dashed lines in 33 denote fragmentation pathways a – f, and all of these were
.
.
observed. In the mass spectrum of 7, R ¼ Ph, the radicals phenyl and benzyl are lost
Scheme 8

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Helvetica Chimica Acta – Vol. 91 (2008)
from the benzylic terminus of 33, R ¼ Ph, as shown by 33, R ¼ p-tolyl. With the
cleavage of type a in 33, i.e., the ion [M À R]þ, all the fragmentation sequences
converge, regardless of the nature of R. The bond rupture b reaches in [M À CH2R]þ,
m/z 205, one of the most populous fragments. It represents loss of Me (77%) in the case
.
of 33, R ¼ H, whereas 33, R ¼ MeO, loses MeOCH2, and in the mass spectrum of 33,
R ¼ Ph or p-tolyl, m/z 205 constitutes the base peak.
The speculative formulae 34 – 36 contain conjugated diphenylmethyl cations and
may help to visualize the fragmentations a – c. The dehydrocyclization of diphenyl-
methyl to fluorenyl cations is well-known in mass spectrometry [41]. As the result of
cleavage e, more [fluorenyl]þ (m/z 165, 37) than [benzhydryl]þ (m/z 167) was observed,
e.g., 49% of 37 and 8% of Ph2CHþ from 33, R ¼ H. Thus, 39 appears more probable
than 36 for m/z 191, and [9-phenylindenyl]þ (38) is another alternative. The peak at m/z
115 ([indenyl]þ) occurs in all mass spectra of 7, 9, and 30, and so does m/z 178
(diphenylacetylene, phenanthrene) as product of cleavage d.
Chemical evidence for the cyclopentene structures came from the catalytic
hydrogenation of 30, R ¼ Me, Ph, and CO2Me, which provided the cyclopentanes 40
(Scheme 9). During the thermolysis of 7, R ¼ CO2Me, no shift of the C¼C bond into
conjugation occurred; the conversion of 30, R ¼ CO2Me, to 41 required catalysis by
MeONa. Perbenzoic acid converted 30 and 31 to the crystalline epoxides 42 – 44. Their
IR spectra show the strong as-stretching frequency CÀOÀC near 845 cmÀ1, character-
istic for oxiranes [26]. The 1H-NMR spectra reveal that the epoxide H-atoms, HÀC(1)
and HÀC(5) have a low propensity for coupling; 3J(1,5) < 1 Hz is not resolved, but only
diagnosed from an increased line width.
An epoxidation trans to the 3-substituent R of 30 is the less-hindered pathway.
1
There is H-NMR evidence for the exo-position of R ¼ Ph, CO2Me, at the oxabicyclo
system in compliance with 42. Only in the epoxidation of 30, R ¼ Me, both steric paths
were observed, as shown by 42/43 formed in the ratio of 74 :26. It is HbÀC(4) of 42,
rather than HaÀC(2) of 43, that couples with the oxirane HÀC(5). This assignment
rests on the reliability of Jvic,cis > Jvic,trans in cyclopentanes.
Scheme 9

Helvetica Chimica Acta – Vol. 91 (2008)
795
3. Conclusions. – The 1,3-dipolar cycloaddition of DDM to the C(3)¼C(4) bond of
1- or 2-substituted buta-1,3-dienes at room temperature offers a convenient and general
access to 1,1-diphenyl-2-vinylcyclopropanes substituted in 1’- or 2’-position (i.e., 7, 9,
and 10). The rapid N2 loss from the initially formed 4,5-dihydro-3H-pyrazoles exceeds
the rate of cycloaddition. Electron-releasing substituents in the butadienes slow down
the cycloaddition, and the first-order decomposition of DDM begins to compete.
DM cycloadditions are much faster; the dihydropyrazoles are isolable, and the N2
elimination requires heating [13]. A disadvantage is the formation of DM-bisadducts,
which are favored with butadienes bearing electron-attracting 1-substituents (CO2R,
CN). Diazophenylmethane stands in 1,3-dipolar activity in between, but closer to DM
[20]; its reactions with butadienes have not been studied so far.
The thermal ring expansion of the 1,1-diphenyl-2-vinylcyclopropanes to 4,4-
diphenylcyclopentenes 30 and 31 proceeds smoothly and appears to be free of major
side reactions.
We express our thanks to the Fonds der Chemischen Industrie, Frankfurt, for support. Dr. DavidS.
Stephenson deserves our gratitude for the computer simulation of 1H-NMR spectra. We owe special
thanks to Claudia Dubler, who competently dealt with the NMR spectra. Furthermore, we thank Sonja
Kosak for recording the mass spectra, and to Helmut Schulz for carrying out the elemental analyses.
Experimental Part
1. General. PLC is prep. layer chromatography on 20 ꢁ 20 cm glass plates, often with 2-mm siliga gel
Merck 60 PF254. IR Spectra were either taken from KBr disks with a Perkin-Elmer 125 instrument or
recorded with Perkin-Elmer BX II as ATR spectra (without KBr, attenuated total reflection); oop is out-
of-plane deformation, and str the stretching frequency. NMR spectra were recorded with Varian Systems
1
300, 400, or 600, some with Varian A60, and all 13C-NMR spectra were H-decoupled and used DEPT.
Solvent was acid-free CDCl3, if not otherwise stated. The MS are EI spectra at 70 eV, recorded on a MAT
95Q instrument. High resolutions (HR) were obtained with the program CMASS; small distortions of
m/z can occur when 13C or 37Cl isotope peaks were not fully separated. Intensities of isotope peaks are
given as, e.g., 13C % calc./% found, and HR as calc./found. Tentative assignments of frequently occurring
m/z peaks are given for 7, R ¼ H, and are not repeated later. Molecular mass with vapor pressure
osmometer in CHCl3 (Mechrolab).
2. Rate Measurements of Cycloadditions of Diazodiphenylmethane (DDM). 2.1. Anal. Method. The
solns. of DDM (50 ml) [42] and dipolarophile (20 ml) in carefully purified DMF [43] were thermostated
at 40.0 ꢀ 0.18. After combination of the two, the soln. was ca. 90 mm in DDM, and the concentration of
dipolarophile was nearly ten times larger. The soln. was briefly purged with N2, and 2-anilinonaphthalene
(0.4 g) was added as polymerization inhibitor [44]. After suitable reaction times, 5-ml samples were
withdrawn with an Inaltera syringe and injected through a rubber septum into a long-necked 50-ml flask.
The latter contained 2m Cl3CCOOH in MeOCH2CH2OH (15 ml) at 20.0 ꢀ 0.18 and was connected to a
double-walled gas buret (25 ml); water of 20.08 was pumped through the mantle. The N2 evolution was
completed by shaking the flask, until the gas volume remained constant (ca. 2 min). About 8 – 12 samples
were drawn to reach 65 – 80% conversion.
The rate constants of pseudo-first order were graphically evaluated from the N2 volumes, corrected
to 720 Torr/258; 8.1 · 10À7 sÀ1, i.e., the k1 of the DDM thermolysis at 408 (see below), was subtracted, an
important correction for the less reactive butadienes. The second-order-rate constant k2 resulted when
k1y(corr.) was divided by 0.95 [dipolarophile]o, i.e., the concentration at half-conversion. The k2 of two
independent runs rarely differed by more than 5%. The Eyring parameters for DDM þ 1-phenylbuta-1,3-
diene (Sect. 2.2) came from measurements at 258, 358, and 408 (k2 ¼ 0.15, 0.37, and 1.34 ꢁ 10À5 [mÀ1sÀ1]).

796
Helvetica Chimica Acta – Vol. 91 (2008)
2.2. Thermolysis of DDM in DMF. By the same method, the decomposition rate was measured in
0.132m DDM in DMFat 40.0 ꢀ 0.18; the N2 volumes fit the first-order law up to 65%. Two runs gave k1 ¼
8.0 and 8.1 · 10À7 sÀ1, which corresponds to t1/2 ¼ 239 h. Experiments at different temp. (k1 ¼ 1.11 · 10À7 at
24.88 and 25.1 · 10À7 at 50.08 [mÀ1 sÀ1]) provided DH# ¼ 23.1 kcal molÀ1 and DS# ¼ À13 e.u.
3. 2-Ethenyl-1,1-diphenylcyclopropane (7, R ¼ H). Buta-1,3-diene (12.5 g, 231 mmol) and DDM
(9.70 g, 49.9 mmol) were reacted in a thick-walled sealed glass tube at r.t.; after 2 weeks, the deep-red
color of the soln. was changed to orange. After cooling, the tube was opened, the N2 pressure was
relieved, and the excess of butadiene was removed. Distillation at 110 – 1158/10À3 Torr furnished 7, R ¼ H,
as a colorless liquid (8.71 g, 79%); when the residue was triturated with Et2O, benzophenone azine as
product of decomposition of DDM was obtained. Redistillation of 7, R ¼ H, from a microflask (b.p. 93 –
958/10À3 Torr) gave the anal. sample, n2D0 1.5915. IR (film): 694vs, 751s (arom. oop), 898s, 988m (vinyl
oop); 1445m, 1493s, 1600m (arom. breath. modes); 1631m, 1660m (C¼C str). 1H-NMR (300 MHz): 1.64
(dd, 2Jgem ¼ 5.1, 3Jtrans ¼ 5.8, HaÀC(3)); 1.72 (dd, 2Jgem ¼ 5.1, 3Jcis ¼ 8.6, HbÀC(3)); 2.44 (m, 6 lines visible,
3
2
4
3
2
HÀC(2)); 5.04 (ddd, J(Z) ¼ 9.6, Jgem ¼ 1.2, J(2’a,2) ¼ 2.4, HaÀC(2’)); 5.32 (ddd, J(E) ¼ 17.0, Jgem ¼ 1.2,
4J(2’b,2) ¼ 2.4, HbÀC(2’)); 5.24 (ddd, 3J(E) ¼ 17.0, 3J(Z) ¼ 9.7, 3J(1’,2) ¼ 8.6, HÀC(1’)); 7.2 – 7.5 (m, 10 arom.
H). 13C-NMR (75.5 MHz): 22.3, 31.1, 37.2 (C(3), C(2), C(1)); 113.9, 139.3 (C(2’), C(1’)); 126.0, 126.6 (2
arom. p-CH); 127.4, 128.4 (2ꢁ), 131.0 (8 arom. o,m-CH); 141.4, 146.7 (2 arom. Cq). MS: 220 (82, Mþ; HR
220.1248/220.1249; 13C 15.4/13.2), 219 (24, 34), 205 (47, [M À CH2 À H]þ, 13C 13.6/14.3, 35), 204 (27, [M À
CH2 À 2 H]þ, C16Hþ12 ), 203 (22), 192 (12, [M À CH2CH2]þ, C15Hþ12 perhaps Ph2C¼C¼CHþ2 or [methyl-
phenanthrene]þ), 191 (27, C15H1þ1, 38 or 39), 182 (26, C14H1þ4 13C 4.0/3.6, [diphenylethane]þ), 180 (11,
;
Ph2C¼CHþ2 ), 179 (17, C14H1þ1, [9-methylfluorenyl]þ), 178 (27, C14H1þ0, PhCꢂCPh or phenanthrene), 167
(8, [benzhydryl]þ), 165 (49, [9-fluorenyl]þ, 37; HR 165.0702/165.0697), 152 (11, C12Hþ8 , [biphenylene]þ),
142 (48, C11Hþ10, possibly PhÀCH¼CHÀC ꢂ CÀCH3þ or [methylnaphthalene]þ), 141 (30, C11Hþ9 , [1-
vinylinden-1-yl]þ or [naphthylmethyl]þ), 129 (100, C10Hþ9 ; 13C 11.1/12.6, PhÀCHþÀCH¼C¼CH2 or
[methylindenyl]þ), 128 (43, C10Hþ8 , [naphthalene]þ), 115 (31, C9Hþ7 , PhCHþÀCꢂCH or [1-indenyl]þ),
105 (42, C8Hþ9 , PhCHþÀCH¼CH2), 101 (16), 91 (42, C7H7þ, PhCHþ2 /[tropylium]þ), 77 (41, Phþ), 43 (26,
[isopropyl]þ). Anal. calc. for C17H16 (220.30): C 92.68, H 7.32; found: C 92.07, H 7.20.
4. 1,1-Diphenyl-2-[(E)-prop-1-enyl]cyclopropane (7, R ¼ Me). (E)-Piperylene (Fluka; 3.40 g,
49.9 mmol), DDM (10.7 g, 55 mmol), and 2-anilinonaphthalene (0.20 g) as polymerization [44] inhibitor
were dissolved in benzene (10 ml) and kept at r.t. for 2 months; N2 evolution and decolorization were
observed. Workup gave benzophenone azine (2.16 g), identified by mixed m.p. and IR spectrum.
Distillation at 95 – 1008/10À3 Torr afforded 7, R ¼ Me, (3.86 g, 33%); a redistilled colorless liquid showed
n2D0 1.5839. IR (film): 694vs, 743s (arom. oop), 950 þ 957s (trans-CH¼CH oop), 1440s, 1488s, 1574w, 1595s
(arom. ring vibr.), 1657w (C¼C str). 1H-NMR (60 MHz): 1.55 (dd, 3J ¼ 6.4, 4J ¼ 1.5, Me; superimposed
3
3
3
by m of CH2(3)); 2.23 (dt, J(2,3cis) ¼ 3J(2,1’) ¼ 8.7, J(2,3trans) ¼ 6.8, HÀC(2)); 4.73 (ddq, J(E) ¼ 15.2,
3J(2,1’) ¼ 8.7, 4J ¼ 1.4, HÀC(1’)); 5.60 (dq, 3J ¼ 15.2 and 6.4, HÀC(2’)). Anal. calc. for C18H18 (234.32): C
92.26, H 7.74; found: C 91.85, H 7.48.
5. 1,1-Diphenyl-2-[(E)-2-phenylethenyl]cyclopropane (7, R ¼ Ph). 5.1. Preparation. The soln. of
DDM (17.5 g, 90.0 mmol) and 2-anilinonaphthalene (0.20 g) in (E)-1-phenylbuta-1,3-diene (23.4 g,
180 mmol, [44]), were reacted at r.t., and the deep-red color vanished in 4 weeks. After distilling the
excess of 1, R ¼ Ph, at 758/10À3 Torr, the residue was subjected to column chromatography (CC; 100 g
silica gel) with petroleum ether (b.p. 40 – 558) and furnished 7, R ¼ Ph, as a colorless oil, which solidified.
Recrystallization from EtOH gave needles (20.3 g. 76%). M.p. 60 – 61.58. IR (ATR): 957s, 968m, 979m
(trans-CH¼CH oop); 1443m, 1493s, 1596m (arom. ring vibr.), 1638w (C¼C str). 1H-NMR (400 MHz):
The non-aromatic 5-H system was simulated by DAVINX [25] and provided 1.59 (HaÀC(3)); 1.73
(HbÀC(3)); 2.40 (HÀC(2)); 5.46 (HÀC(1’)); 6.55 (HÀC(2’)); 3J(2,3a) ¼ 5.84 (trans), 3J(2,3b) ¼ 8.64
3
(cis), 3J(2,1’) ¼ 9.61, 4J(2,2’) ¼ 0.70, 2J(3a,3b) ¼ À4.99, and J(E) ¼ 15.8; 7.10 – 7.42 (m, 15 arom. H).
13C-NMR (100 MHz): 22.9 (C(3)); 31.1 (C(2)); 37.6 (C(1)); 125.7, 127.1, 128.30, 128.34, 128.42, 131.0 (6
signals for 12 arom. o,m-CH, as expected for free Ph rotation); 125.85, 126.64, 126.68, 129.1, 131.6 (5
signals of lower intensity for C(1’), C(2’), and 3 arom. p-CH); 137.7, 141.3, 146.5 (3 arom. Cq). MS (258):
296 (47, Mþ; HR 296.1560/296.1563), 219 (9, [M À Ph]þ, C17Hþ15 ), 218 (29, [M À Ph À H]þ, C17H1þ4 ), 217
(15), 206 (38), 205 (100, [M À PhCH2]þ, C16H1þ3 ; HR 205.1014/205.1003, 35), 204 (31, [M À toluene]þ,
C16H1þ2 ), 203 (35), 192 (24, [M À styrene]þ, C15H1þ2 ), 191 (21, C15H1þ1 ), 178 (24, C14Hþ10 ), 167 (8, C13H1þ1 ),

Helvetica Chimica Acta – Vol. 91 (2008)
797
165 (37, C13Hþ9 , 37), 115 (35, C9Hþ7 ), 91 (41, C7H7þ ), 77 (8, Phþ). Anal. calc. for C23H20 (296.39): C 93.20, H
6.80; found: C 93.26, H 6.75.
5.2. KMnO4 Oxidation. The soln. of 7, R ¼ Ph, (593 mg, 2.0 mmol) in pyridine (20 ml) was treated at
50 – 558 with KMnO4 (4 mmol); the MnO2 was filtered and washed with Na2CO3; workup with HCl/Et2O
gave 350 mg of colorless crystals. In boiling H2O, 310 mg (73%) of 2,2-diphenylcyclopropane-1-
carboxylic acid (18), m.p. 167 – 1698, remained undissolved. After recrystallization from acetone/H2O,
m.p. 168 – 169.58; the identity with authentic 18 [45] was established by mixed m.p., and IR spectrum.
2
3
2
3
1H-NMR (60 MHz): 1.59 (dd, Jgem ¼ 4.8, Jcis ¼ 7.9, HaÀC(3)); 2.07 (dd, Jgem ¼ 4.8, Jtrans ¼ 5.6,
3
3
HbÀC(3)); 2.46 (dd, Jcis ¼ 7.9, Jtrans ¼ 5.6, HÀC(1)). Ether extracted from the aq. phase benzoic acid
(165 mg, 68%) in colorless needles, m.p. 118 – 1198 (mixed m.p.).
6. 2-[(E)-2-Methoxyethenyl]-1,1-diphenylcyclopropane (7, R ¼ MeO) andthe Corresponding ( Z)-
Isomer 9, R ¼ MeO. 6.1. Preparation. The homogenous mixture of 1-methoxybuta-2,3-diene [46] (12.60 g,
150 mmol; (E)/(Z) 60 :40, based on d(H) 3.51 and 3.47 for MeO), DDM (9.71 g, 50 mmol), and 2-
anilinonaphthalene (200 mg) slowly developed N2, but, even after 55 days at r.t. the red color of DDM
had not completely disappeared. The excess of 1-methoxybuta-2,3-diene was distilled at 12 Torr, the
brown residue digested with petroleum ether, polymeric material filtered, the soln. subjected to CC over
alumina (neutral, 40 g), and eluted with petroleum ether/Et2O 9 :1. Distillation at 120 – 1308 (bath)/10À3
Torr gave 5.85 g (47%) crude material. On renewed CC (silica gel, (100 g); eluant as before), the first
fraction furnished, after distillation at 1308/10À3 Torr, the mixture of 7 and 9, R ¼ MeO ((E)/(Z) 74 :26,
4.12 g, 33%). n2D0 1.5853. IR (film): 928s (olefin. oop); 1101s, 1121m, 1206s, (CÀOÀC str as and sy), 1651s
(C¼C str). 1H-NMR (300 MHz): 1.54, 1.71 (2m, HaÀC(3) and HbÀC(3) of (E) and (Z)); 2.32, 2.82 (2m,
(E)/(Z) 73 :27, HÀC(2)); 3.45, 3.74 (2s, (E)/(Z) 74 :26, Me); 3.83 (dd, 3J(Z) ¼ 6.2, 3J(1’,2) ¼ 9.6, HÀC(1’)
3
3
of (Z)); 4.25 (dd, J(E) ¼ 12.6, 3J(1’,2) ¼ 9.0, HÀC (1’) of (E), (E)/(Z) 73 :27); 6.05 (d, J(Z) ¼ 6.3,
HÀC(2’) of (Z)); 6.60 (d, J(E) ¼ 12.6, HÀC(2’) of (E)); 7.33 – 7.56 (m, 10 arom. H). 13C-NMR
3
(75.5 MHz, (E)/(Z) ratio from peak heights): 22.3, 22.8 (C(3) of (E) and (Z)); 26.4, 23.0 (C(2), (E)/(Z)
74 :26); 35.8, 36.6 (C(1), (E)/(Z) 74 :26); 56.0, 59.8 (MeO, (E)/(Z) 78 :22); 104.2, 107.3 (C(1’), (E)/(Z)
73 :27); 141.6, 141.9 (C(2’) of (E)/(Z)); arom. CH of (E) and (Z) assigned; 141.6, 147.02 (2 arom. Cq of
(E)); 141.9, 147.03 (2 arom. Cq of (Z)). MS: 250 (19, Mþ, C18H18Oþ; HR 250.1353/250.1347, 13C 3.8/3.9),
219 (18, [M À MeO]þ), 218 (33, [M À MeOH]þ), 217 (21), 205 (37, [M À CH2OMe]þ, C16H1þ3 ), 204 (16),
193 (32), 192 (58), 191 (31), 183 (25, Ph2C¼OHþ), 182 (52, C13H10Oþ; HR 182.0729/182.0716,
benzophenone), 180 (28), 178 (28), 167 (22), 165 (41), 115 (27), 105 (100, C6H5ÀCꢂOþ, HR 105.0339/
105.0313 (a shift of the O-function in the ring-opened Mþ is conceivable), 91 (50), 77 (55), 43 (16). Anal.
calc. for C18H18O (250.32): C 86.36, H 7.25; found: C 85.93, H 7.23.
6.2. Oxidation of 7, R ¼ MeO. The reaction with KMnO4 in acetone afforded 18 (61%). Colorless
crystals. M.p. 168 – 169.58; mixed m.p. without depression.
7. Methyl (E)-3-(2,2-Diphenylcyclopropyl)prop-2-enoate (7, R ¼ CO2Me). 7.1. Preparation. Methyl
(E)-buta-1,3-diene-1-carboxylate (5.60 g, 49.9 mmol) [47][48], DDM (10.68 g, 55 mmol), and 2-
anilinonaphthalene (200 mg) were dissolved in benzene (30 ml). After 3 weeks, the N2 evolution was
finished, and the red color had faded. Distillation at 160 – 1658 (bath)/10À3 Torr furnished 7, R ¼ CO2Me,
as a yellow oil (12.46 g, 90%), which solidified. M.p. 50 – 608. Recrystallization from MeOH gave
colorless prisms (11.60 g). M.p. 66.5 – 67.58. IR (ATR): 951s, 984s (olefin. oop); 1146vs, 1243s (CÀO);
1438s, 1493m, 1600w (arom. ring vibr.), 1644s (C¼C), 1714s (C¼O). 1H-NMR (300 MHz)2): 1.74 (t-like,
J ꢃ 5.3, HaÀC(3’)); 1.83 (dd, 3Jcis ¼ 8.5, 2Jgem ¼ 5.1, HbÀC(3’)); 2.41 (ddd, 3Jtrans ¼ 5.6, 3Jcis ¼ 8.5, 3J(2’,3) ¼
3
3
10.5, HÀC(2’)); 6.00 (d, J(E) ¼ 15.5, HÀC(2)); 6.28 (dd, 3J(3,2’) ¼ 10.5, J(E) ¼ 15.5, HÀC(3)); the
assignments of the non-aromatic H-atoms were confirmed by HSQCAD. 13C-NMR (75.5 MHz)2): 23.3
(C(3’)); 30.2 (C(2’)); 39.7 (C(1’)); 51.3 (MeO), 119.6 (C(3)); 126.3, 127.1 (arom. p-CH); 127.8, 128.45,
128.65, 130.5 (8 arom. o,m-CH); 140.5, 145.5 (2 arom. Cq); 150.4 (C(2)); 166.8 (C¼O). MS: 278 (45, Mþ;
HR 278.1302/278.1310; 13C 9.5/8.6), 246 (15, [M À MeO À H]þ, C18H14Oþ), 219 (36, [M À CO2Me]þ,
C17Hþ15 ), 218 (38, [M À HCO2Me]þ), 217 (41, C17H1þ3 ), 205 (10), 204 (31), 203 (33), 202 (33), 192 (15),
191 (16), 187 (23), 180 (17), 178 (20), 165 (45), 141 (25), 115 (26), 111 (43, C6H7Oþ2 ; HR 111.0444/
2
)
The nonsystematic C-atom numbering used for assignments corresponds to that indicated in the
Formulae.

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Helvetica Chimica Acta – Vol. 91 (2008)
111.0404), 98 (100, C5H6Oþ2 , HR 98.0366/98.0303, MeCꢂCÀCO2Meþ or H2C¼C¼CHÀCO2Meþ), 91
(62), 77 (13). Anal. calc. for C19H18O2 (278.33): C 81.98, H 6.52; found: C 82.05, H 6.57.
7.2. Oxidation of 7, R ¼ CO2Me. The reaction with KMnO4 in acetone produced 18 (88%).
M.p. 167 – 1698; mixed m.p. without depression and 1H-NMR spectrum confirmed the structure.
8. (Z)-3-(2,2-Diphenylcyclopropyl)prop-2-enenitrile (9, R ¼ CN). 8.1. Preparation. Buta-1,3-diene-1-
carbonitrile (Knapsack-Griesheim AG; (Z)/(E) 98 :2, 1.98 g, 24.7 mmol), DDM (5.34 g, 27.5 mmol), and
2-anilinonaphthalene (100 mg) in benzene (15 ml) reacted at r.t. in 10 d. Distillation at 1658 (bath)/10À3
Torr furnished a light-yellow oil (6.06 g) that solidified; recrystallization from MeOH gave 9, R ¼ CN
(5.50 g, 91%). Colorless prisms. M.p. 66 – 678. IR (ATR): 960s (C¼C oop); 1485s, 1493s, 1597m (arom.
1
2
breath. modes), 1613s (C¼C conj. str), 2112s (CꢂN conj. str). H-NMR (300 MHz)2): 1.79 (t, Jgem
ꢃ
3Jtrans ꢃ 5.3, HaÀC(3’)); 1.88 (dd, Jcis ¼ 8.5, Jgem ¼ 5.1, HbÀC(3’)); 2.88 (ddd, 3J(2’,3) ¼ 10.7, Jcis ¼ 8.6,
3
2
3
3Jtrans ¼ 5.4, HÀC(2’)); 5.23 (dd, J(Z) ¼ 11.0, 4J(2,2’) ¼ 0.5, HÀC(2)); 5.69 (t, J(Z) ꢃ J(3,2’) ꢃ 10.7,
HÀC( 3 )) ; 7.2 – 7.4 ( m, 10 arom. H). 13C-NMR (75.5 MHz)2): 23.4 (C(3’)); 28.9 (C(2’)); 40.4 (C(1’)); 97.2
(C(2)); 116.8 (CꢂN); 126.7, 127.2 (2 arom. p-CH); 127.7, 128.61, 128.73, 130.2 (8 arom. o,m-CH); 140.4,
144.6 (2 arom. Cq); 155.8 (C(3)). MS: 245 (55, Mþ), 244 (100, [M À H]þ; HR 244.1123/244.1104), 217 (15,
[M À CN À 2 H]þ, C17H1þ3 ), 205 (13, [M À CH2CN]þ, C16H1þ3 ), 203 (17), 202 (14), 192 (12, [M À
H2C¼CHCN]þ, C15H1þ2 ), 191 (13, C15Hþ11 ), 178 (18, C14Hþ10 ), 168 (87, C12H10Nþ), 167 (41, [M À Ph À
2 H]þ, C12H9Nþ; HR 167.0733/167.0714), 165 (40), 154 (15 [M À CH2Ph À H]þ, C11H8Nþ), 115 (15), 91
(18), 77 (6). Anal. calc. for C18H15N (245.31). C 88.13, H 6.16, N 5.71; found: C 87.97, H 6.18, N 5.98.
8.2. Oxidation of 9, R ¼ CN. The reaction with KMnO4 in aq. acetone afforded 18, m.p. 169.5 – 1708,
and showed the intact cyclopropane ring.
3
3
3
9. 2-(1-Methylethenyl)-1,1-diphenylcyclopropane (12, R ¼ Me) and1-Ethenyl-1-methyl-2,2-diphe-
nylcyclopropane (13, R ¼ Me). 8.1. Preparation. Isoprene (20.4 g, 300 mmol), DDM (11.65 g, 60 mmol),
and 2-anilinonaphthalene (0.2 g) were kept at r.t. for 50 d. A light-yellow liquid (11.36 g, 81%) was
distilled at 100 – 1028/10À3 Torr, nD20 ¼ 1.5829. TLC showed two spots, and the NMR signals of Me
established the two title compounds in the ratio 86 :14. IR (film): 881s, 1026m (olefin. oop), 1445s, 1493s,
1579w, 1597m (arom. ring vibr.), 1629w, 1648w (C¼C str). 1H-NMR (300 MHz) of 12, R ¼ Me: 1.49 (dd,
3
2
3
2Jgem ¼ 5.3, Jcis ¼ 8.7, HaÀC(3)); 1.64 (s, broadened, Me); 1.88 (dd, Jgem ¼ 5.3, Jtrans ¼ 6.5, HbÀC(3));
2
1
2.38 (t-like, HÀC(2)); 4.68, 4.79 (2d, Jgem ¼ 1.4, CH2(2’)); 7.15 – 7.60 (m, 10 arom. H). H-NMR of 13,
R ¼ Me2): 3 H of cyclopropane overlap with those of 12, R ¼ Me; 1.20 (s, Me); 5.01 (dd, J(Z) ¼ 10.6,
3
2Jgem ¼ 1.5, HaÀC(2’)); 5.18 (dd, J(E) ¼ 17.2, Jgem ¼ 1.5, HbÀC(2’)); 5.41 (dd, J(Z) ¼ 10.7, J(E) ¼ 17.2,
HÀC(1’)); 7.15 – 7.60 (m, 10 arom. H). 13C-NMR (75.5 MHz; assignments of 12 and 13 by signal height)
of 12, R ¼ Me: 18.8 (C(3)); 23.0 (Me); 33.6 (C(2)); 37.5 (C(1)); 111.7 (C(2’)); 125.97, 126.26 (2 arom. p-
CH); 127.94, 128.12, 128.35, 130.11 (8 arom. o,m-CH); 141.0, 142.9, 147.1 (C(1’) and 2 arom. Cq).
13C-NMR of 13, R ¼ Me2): 19.3 (Me); 27.1 (C(3)); 28.6 (C(2)); 43.5 (C(1)); 110.8 (C(2’)); 126.15, 126.21
(2 arom. p-CH); 128.25, 128.37, 129.64, 130.26 (8 arom. o,m-CH); 144.0, 144.1, 144.7 (C(1’) and 2 arom.
Cq). MS (12/13 86 :14): 234 (66, Mþ; HR 234.1404/234.1403), 219 (90, [M À Me]þ; 13C 16.9/15.9), 205 (50,
[M À CH2Me]þ), 191 (36, [M À CH2CH2Me]þ), 165 (45), 156 (25, [M À Ph À 2 H]þ), 143 (100, [M À
CH2Ph]þ; HR 143.0858/143.0843), 128 (38), 115 (42), 105 (11), 91 (76), 77 (17). Anal. calc. for C18H18
(234.32): C 92.26, H 7.74; found: C 92.31, H 7.89.
3
2
3
3
9.2. 4-Methyl-1,1-diphenylpenta-1,3-diene (29). a) The mixture of 12, R ¼ Me, and 13, R ¼ Me
(86 :14, 500 mg, 2.13 mmol) was refluxed in AcOH (10 ml) for 1 h; at 110 – 1158/10À3 Torr, a pale-yellow
oil (495 mg) was distilled which contained 29 and 13, R ¼ Me, 85 :15. 1H-NMR of 29 (60 MHz): 1.86, 1.73
(2s broadened, 2 Me); 5.95 (dq, 3J(2,3) ¼ 11.4, 4J(2,Me) ¼ 1.3, HÀC(3)); 6.92 (d, 3J(2,3) ¼ 11.6,
HÀC(2)); 7.1 – 7.5 (m, 10 arom. H). Anal. calc. for C18H18 (234.32): C 92.26, H 7.74; found: C 92.44, H
7.74.
b) Cyclopropanes 12, R ¼ Me, and 13, R ¼ Me, (86 :14) were subjected to CC (silica gel; petroleum
ether) and furnished after distillation a mixture of 29, 12, R ¼ Me, and 13, R ¼ Me, 69 :18 :13 (1H-NMR
analysis).
10. 1,1-Diphenyl-2-(1-phenylethenyl)cyclopropane (12, R ¼ Ph). 10.1. Preparation. The homogenous
mixture of 2-phenylbuta-1,3-diene [49] (19.53 g, 150 mmol), DDM (9.71 g, 50.0 mmol), and 2-
anilinonaphthalene (200 mg) was reacted at r.t. without solvent for 37 d; after 20 d, the crystallization
started. Trituration with a small amount of Et2O gave 12, R ¼ Ph (7.10 g, 48%) as prisms, m.p. 136 – 1478;

Helvetica Chimica Acta – Vol. 91 (2008)
799
after recrystallization from AcOEt, m.p. 149.5 – 150.58. The mother liquor contained oligomers of the
diene; only 1.58 g of 2-phenylbuta-1,3-diene was re-isolated by distillation. IR (ATR) of 12, R ¼ Ph: 895s
(C¼CH2 oop), 1442s, 1450m, 1492s, 1552w, 1599w (arom. breath. modes), 1625m (C¼CH2 str). 1H-NMR
(400 MHz): simulation of the 5 non-arom. H by DAVINX [25] led to 1.59 (HbÀC(3)); 1.92 (HaÀC(3));
2
3
3
2.72 (HÀC(2)); 4.63 (HaÀC(2’)); 5.16 (HbÀC(2’)); J(3a,3b) ¼ À5.29, J(2,3b) ¼ 8.74 (cis), J(2,3a) ¼
6.68 (trans), 4J(2,2’a) ¼ 1.20, 4J(2,2’b) ¼ 0.27, 2J(2’a,2’b) ¼ 0.77; 7.10 – 7.45 (m, 15 arom. H). 13C-NMR
(100 MHz): 19.7 (C(2)); 31.7 (C(3)); 38.8 (C(1)); 112.4 (C(2’)); 125.9, 126.23, 127.26 (3 arom. p-CH);
126.3, 127.43, 127.68, 128.16, 128.32, 130.7 (12 arom. o,m-CH); 140.2, 142.2, 144.6, 146.6 (C(1’) and 3 arom.
Cq). MS: 296 (Mþ, C23Hþ20 ; HR 296.1560/296.1548; 13C 5.6/5.9), 281 (14, [M À CH2 À H]þ, C22H1þ7 ), 219
(10), 218 (26, [M À Ph À H]þ, C17H1þ4 ), 205 (100, [M À CH2Ph], C16H1þ3 ; HR 205.1014/205.0999), 204 (28),
193 (24), 192 (21), 191 (37), 178 (25), 167 (12), 165 (26), 115 (48), 105 (43), 91 (32), 77 (11). Anal. calc.
for C23H20 (296.39): C 93.20, H 6.80; found: C 93.00, H 6.71.
10.2. Oxidation. 10.2.1. 1-(2,2-Diphenylcyclopropyl)-1-phenylethane-1,2-diol (20). Compound 12,
R ¼ Ph (1.19 g, 4.0 mmol), in pyridine (60 ml) was treated with KMnO4 (0.79 g) in H2O (30 ml) at 50 –
608 for 1 h. After reduction with NaHSO3, the neutral product (1.22 g) was purified by PLC (silica gel,
C6H6/MeOH 20 :1), and 20 (930 mg, 71%) was obtained. M.p. 104 – 1058. IR (ATR): 3419s (OH, assoc.),
2
3
3495s (OÀH, free). 1H-NMR (300 MHz): 1.15 (dd, Jgem ¼ 5.0; Jcis ¼ 9.6, HaÀC(3’)), shielded by
PhÀC(1)); 1.56 (s, tert-OH); 1.67 (br., t, 3J(2,OH) ¼ 6.1, prim-OH); 1.83 (dd, Jgem ¼ 5.1, Jtrans ¼ 6.9,
2
3
3
3
2
HbÀC(3’)); 2.26 (dd, Jcis ¼ 9.5, Jtrans ¼ 6.8, HÀC(1’)); 3.97, 4.08 (2 dd, Jgem ¼ 11.2, 3J(2,OH) ¼ 6.0,
CH2(2)); 7.15 – 7.45 (m, 15 arom. CH). 13C-NMR (75.5 MHz): 14.1 (C(3’)); 32.8 (C(1’)); 37.0 (C(2’)); 70.8
(C(2)); 76.6 (C(1)); 126.3, 126.9, 127.0 (3 arom. p-CH); 6 peaks for 12 arom. o,m-CH); 140.5, 143.4, 147.3
(3 arom. Cq). Anal. calc. for C23H22O2 (330.41): C 83.60, H 6.71; found: C 83.76, H 6.86.
10.2.2. (2,2-Diphenylcyclopropyl)(phenyl)methanone (19). Glycol 20 (330 mg, 1.0 mmol) and
Pb(OAc)4 (653 mg, 1.5 mmol) in benzene (25 ml) were heated at 608 for 4 h. Workup and recrystalliza-
tion from EtOH gave 19 (265 mg, 89%). M.p. 133 – 134.58 (133 – 1348 [50]). IR (KBr): 1665s (C¼O).
3
NMR (60 MHz): 1.71 (dd, HbÀC(3)); 2.55 (dd, HaÀC(3)); 3.48 (dd, HÀC(1)) with J(1,3b) ¼ 7.5 (cis),
3J(1,3a) ¼ 5.8 (trans), 2Jgem ¼ 4.5. Anal. calc. for C22H18O (298.36): C 88.56, H 6.08; found: C 89.02, H 6.37.
10.3. 1,1,4-Triphenylpenta-1,3-diene (25). Cyclopropane 12, R ¼ Ph (300 mg, 1.01 mmol), was
refluxed in AcOH (10 ml) for 3 h and distilled at 1908 (bath)/10À3 Torr: 25 (285 mg, 95%), m.p. 115 –
1208; colorless prisms from EtOH, m.p. 122 – 1248 ([27]: 121 – 1228; [28]: 122 – 1238). IR (ATR):
1440m, 1488m, 1596w (arom. ring vibr.), 1639w (C¼C str). UV (EtOH): 329 nm (log e ¼ 4.58), 244
(4.21), 207 (4.54), similar to (E,E)-1,4-diphenylbuta-1,3-diene [51] (EtOH): 330 (4.78), 232 (4.12), 207
(4.27). 1H-NMR (300 MHz): 2.34 (d, 3J ¼ 1.4, Me); 6.62 (dq, 3J(2,3) ¼ 11.5, 4J(3,5) ¼ 1.4, HÀC(3)); 7.10
þ
3
(d, J ¼ 11.5, HÀC(2)); 7.16 – 7.59 (m, 15 arom. H). MS: 296 (100, Mþ, C23H20 ; HR 296.1560/296.1548),
281 (42, [M À Me]þ), 268 (21), 205 (43), 203 (28), 202 (18), 167 (31), 165 (17), 115 (12), 105 (13), 91
(11), 77 (5). Anal. calc. for C23H20 (296.39): C 93.20, H 6.80; found: C 93.20, H 6.86.
10.4 Oxidation of 25. Compound 25 (87 mg, 0.29 mmol) and KMnO4 (326 mg) in acetone (10 ml)
were refluxed for 30 min, filtered, made alkaline, and extracted with Et2O. TLC (silica gel, petroleum
ether/Et2O 4 :1) of the neutral fraction showed the presence of benzophenone and acetophenone. The 2,4-
dinitrophenylhydrazones were separated by PLC (silica gel; petroleum ether/AcOEt 95 :5): that of
benzophenone (45%, m.p. 238 – 2398, mixed m.p.), and that of acetophenone (36%, m.p. 248 – 2498,
mixed m.p.).
10.5. Hydrogenation of 25. The soln. of 25 (520 mg, 1.75 mmol) in EtOH consumed 80.2 ml H2 in the
presence of Pd (10% on C). Distillation at 140 – 1508 (bath)/10À3 Torr furnished 1,1,4-Triphenylpentane
(28, 97%). Colorless oil. n2D0 1.5811. IR (film): 698vs, 744s, 759s (arom. oop), 1456s, 1494s, 1601m (arom.
ring vibr.). UV (EtOH): absorptions of Ph at 266.5 nm (log e ¼ 1.70), 264 (1.76), 259 (1.85), 248.5 (1.66),
241.5 (148). 1H-NMR (60 MHz, CCl4): 1.14 (d, 3J ¼ 7.0, Me); 1.70 (m, 2 CH2); 2.63 (sext., 3J ¼ 7.0,
HÀC(4)); 3.76 (t, 3J ¼ 7.1, H ÀC(1)); 7.07 (br. s, 15 arom. H). Anal. calc. for C23H24 (300.42): C 91.95, H
8.05; found: C 92.27, H 8.21.
10.6. 9,10-Dihydro-9-methyl-10-phenyl-9,10-ethanoanthracene (27). Compound 12 (300 mg,
1.01 mmol) and TsOH (100 mg) were heated to 200 – 2058 for 10 min, distilled at 180 – 2008 (bath)/
10À3 Torr, dissolved in Et2O, and washed with aq. Na2CO3. Removal of the ether left 27 (165 mg, 55%).
M.p. 178 – 1808. The anal. sample, colorless prisms, m.p. 181 – 1828 crystallized from petroleum ether. The

800
Helvetica Chimica Acta – Vol. 91 (2008)
same compound was obtained, when 25 was treated with TsOH at 2008. IR (ATR): 705vs, 740vs, 757vs,
781m (arom. oop); 1443m, 1453s, 1484w, 1498m, 1597w, br. (arom. breath. modes). UV (EtOH): fine
structure of benzene at 271 nm (log e ¼ 2.06), 263.5 (2.06), 257 (1.97), 251.5 (1.86). 1H-NMR (400 MHz):
2
2
1.68, 2.17 (AA’BB’ spectrum, which – on computer simulation [25] – provided JAA’ ¼ À11.2, JBB’
¼
À11.0, 3JAB ¼ 4.22 (trans), 3JAB ¼ 10.6 (cis), CH2(11) and CH2(12)); 2.04 (s, Me); 6.85 – 7.60 (m, 13 arom.
H). 13C-NMR (100.6 MHz): 18.4 (Me); 31.7 (C(12)); 35.8 (C(11)); 41.7 (C(9)); 52.1 (C(10)); 120.3, 123.3,
125.0, 125.6, 127.0, 128.1, 130.4 (13 arom. CH of C(1)ÀC(4), C(5)ÀC(8), and Ph, in accordance with Cs);
139.7, 145.6, 145.8 (5 arom. Cq). MS: 296 (1, Mþ, C23Hþ20 ), 281 (1, [M À Me]þ), 268 (100, [M À CH2CH2]þ,
C21Hþ16 ; HR 268.1248/268.1271; 13C 23.4/22.2), 252 (17, [268 À CH4]þ, C20Hþ12
;
13C 2.6/2.5), 126 (16,
C10Hþ6 ). Anal. calc. for C23H20 (296.39): C 93.20, H 6.80; found: C 92.82, H 6.78. Hydrocarbon 27 does not
react with H2 or PhCO3H.
11. 1,1-Diphenyl-2-[1-methoxyethenyl]cyclopropane (12, R ¼ MeO). 2-Methoxybuta-1,3-diene
(11.35 g, 135 mmol)) [52][53] and DDM (12.2 g, 62.8 mmol) reacted 90 h at 408 in the dark. Distillation
at 121 – 1238/10À3 Torr afforded 12, R ¼ MeO, in colorless crystals (14.2 g, 81%). M.p. 49 – 518.
Recrystallization from petroleum ether at À 158 gave anal. pure 12, R ¼ MeO. M.p. 52 – 52.58.
3
2
3
2
1H-NMR (60 MHz): 1.35 (dd, Jcis ¼ 9.0, Jgem ¼ À4.8, HaÀC(3)); 1.79 (dd, Jtrans ¼ 6.2, Jgem ¼ À4.8,
HbÀC(3)); 2.29 (dd, 3Jtrans ¼ 6.2, 3Jcis ¼ 9.0, HÀC(2)); 3.15 (s, MeO); 3.74, 3.83 (2d, 2Jgem ¼ 2.0, CH2(2’)).
Anal. calc. for C18H18O (250.32): C 86.36, H 7.25; found: C 86.46, H 7.29.
12. 2-(1-Chloroethenyl)-1,1-diphenylcyclopropane (12, R ¼ Cl). The soln. of DDM (13.55 g,
69.8 mmol) and 2-anilinonaphthalene (200 mg) in 2-chlorobuta-1,3-diene (33.6 g, 380 mmol) lost the
red color in 4 d at r.t., and the excess of the diene was distilled at 12 Torr. At b.p. 110 – 1208/10À3 Torr, 12,
R ¼ Cl (14.21 g, 74%), was obtained as a colorless oil. After fractional distillation at 118 – 1218/10À3 Torr,
the product showed n2D0 ¼ 1.5939. IR (film): 694vs, 743vs, 762s (arom. oop); 820m, 890s, br. (CÀCl str and
olefinic oop); 1018s, 1090s, 1141s (skeletal vibr.); 1440s, 1488s, 1592s (arom. ring vibr.), 1628s (C¼C str).
1H-NMR (60 MHz): 1.43 (dd, 3Jcis ¼ 8.7, 2Jgem ¼ 5.1, HaÀC(3)); 1.78 (t-like, HbÀC(3)); 2.51 (dd, 3Jtrans
¼
3
2
6.5, Jcis ¼ 8.7, HÀC(2)); 4.70, 4.80 (2d, Jgem ¼ 1.4, CH2(2’)); 7.0 – 7.8 (m, 10 arom. H). Anal. calc. for
C17H15Cl (254.75): C 80.15, H 5.94; found: C 80.31, H 5.92.
13. Rearrangement of Ethenylcyclopropanes to Cyclopentenes. 13.1. 4,4-Diphenylcyclopent-1-ene (30,
R ¼ H). Compound 7, R ¼ H (1.37 g, 6.22 mmol), was heated in a sealed tube to 300 – 3108 (metal bath)
for 5 min. Distillation at 100 – 1058 (bath)/10À3 Torr afforded 30, R ¼ H (1.27 g, 93%), as a pale-yellow
oil; the TLC showed a small impurity at the starting line. After redistillation, 30, R ¼ H (1.06 g, 77%), was
NMR-pure. n2D0 1.5767. IR (film): 1449s, 1487s, 1591s (arom. ring vibr.). 1H-NMR (60 MHz, CCl4; in
accordance with C2v symmetry): 3.02 (s, 4 H); 5.74 (s, 2 H, vic. and allyl. coupling unresolved); 7.10 (br. s,
10 H). Anal. calc. for C17H16 (220.30): C 92.68, H 7.32; found: C 92.16, H 7.15.
13.1.1. 3,3-Diphenyl-6-oxabicyclo[3.1.0]hexane (42, R ¼ H). The reaction of 30, R ¼ H, with 1.2
equiv. of PhCO3H in CHCl3 (see Sect. 13.3.2) furnished, after purification by CC, 42, R ¼ H (72%).
Colorless crystals. M.p. 56 – 578. IR (ATR): 696vs, 748s, 776s (arom. oop), 842s (CÀOÀC, oxirane [26]).
2
1H-NMR (300 MHz): 2.53 (d, Jgem ¼ 14.6, slightly broadened, J(1,2b) ¼ J(4b,5) ꢄ 0.6 by comparison of
2
line widths, HbÀC(2/4)); 3.16 (d, sharp, Jgem ¼ 14.5, HaÀC(2/4)); 3.68 (s, S J < 0.6 from line width,
HÀC(1/5)); 7.10 – 7.35 (m, 10 arom. H). 13C-NMR (75.5 MHz): 40.8 (C(2/4)); 52.3 (C(3)); 56.8 (C(1/5));
8 peaks for 12 arom. C, as expected for free rotation of both Ph. Anal. calc. for C17H16O (236.30): C 86.40,
H 6.83; found: C 86.15, H 6.69.
13.2. 3-Methyl-4,4-diphenylcyclopentene (30, R ¼ Me). Prepared from 7, R ¼ Me, as described in
Sect. 13.1, the rearrangement product 30, R ¼ Me, was obtained as a colorless oil (98%) after distillation
at 100 – 1058 (bath)/10À3 Torr. n2D0 1.5878. IR: 696vs, 727s, 745s, 759m (arom. and olefin. oop); 1443s, 1491s,
1578w, 1598m (arom. vibr.), 1661w (C¼C str.). 1H-NMR (300 MHz): 0.99 (d, 3Jvic ¼ 7.1, Me); 3.04, 3.71 (2
2
3
4
dq, Jgem ¼ 16.0, Jvic ꢃ Jallyl ꢃ Jhomoallyl ¼ 1.9 – 2.0, HaÀC(5), HbÀC(5)); 3.87 (m, 14 lines visible,
3
3J(3,Me) ¼ 7.1, H ÀC(3)); 6.01, 6.07 (2m, J(1,2) ¼ 5.9, HÀC(1), HÀC(2)); 7.34 – 7.60 (m, 10 arom. H).
13C-NMR (75.5 MHz): 17.0 (Me); 46.4 (C(5)); 47.0 (C(3)); 58.8 (C(4)); 128.0, 137.1 (C(1), C(2)); 6 peaks
for 10 arom. CH; 147.1, 150.8 (2 arom. Cq). MS: 234 (100, Mþ; HR 234.1404/234.1388), 219 (38, [M À
Me]þ), 205 (72, [M À Et]þ, C16H1þ3 ), 204 (19), 191 (12, C15H1þ1 ), 178 (15), 165 (25), 143 (52), 128 (20),
115 (21), 91 (39), 77 (10). Anal. calc. for C18H18 (234.32): C 92.26, H 7.74; found: C 92.34, H 7.85.

Helvetica Chimica Acta – Vol. 91 (2008)
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13.2.1. 2(exo)- and2( endo)-Methyl-3,3-diphenyl-6-oxabicyclo[3.1.0]hexane (42, R ¼ Me, and 43,
R ¼ Me). The reaction of 7, R ¼ Me, with PhCO3H (1.2 equiv.) was carried out, as described in
Sect. 13.3.2, and provided the crystalline 42, R ¼ Me, m.p. 107 – 1088, and the oily 43, R ¼ Me, in 74 :26
ratio.
Data of 42, R ¼ Me (exo). IR (KBr): 844s (CÀOÀC, oxirane). 1H-NMR (60 MHz): 0.61 (d, 3J ¼ 7.2,
Me); 2.67, 2.69 (perhaps AB, HaÀC(4), HbÀC(4)); 3.22 – 3.60 (m, 3 H, poorly resolved); 6.78 – 7.33 (m,
10 arom. H). Anal. calc. for C18H18O (250.32): C 86.36, H 7.25; found: C 86.29, H 7.23.
1
Data of endo-isomer 43, R ¼ Me. IR (film): 842s (CÀOÀC, oxirane). H-NMR (60 MHz): 0.84 (d,
2
3J ¼ 7.2, Me, deshielded by oxide function); 2.30 (dd, Jgem ¼ 15.2, 3J(4b,5) ¼ 1.7, HbÀC(4)); 2.98 (dq,
3
2
3J(2b,1) ¼ 1.7, J(2b,Me) ¼ 7.2, partial overlap, HbÀC(2)); 3.24 (d, J ¼ 15.2, HaÀC(4)); 3.30, 3.41 (2dd,
3J ¼ 1.7, J(1,5) ¼ 3.0, partial overlap, HÀC(1), HÀC(5)); 6.87 – 7.58 (m, 10 arom. H).
3
13.3. 3,4,4-Triphenylcyclopent-1-ene (30, R ¼ Ph). Compound 7, R ¼ Ph (7.00 g, 23.6 mmol), was
heated without solvent to 200 – 2108 for 10 min. Distillation at 190 – 2008 (bath)/10À3 Torr gave a pale-
yellow liquid, which solidified and was recrystallized from EtOH: 30, R ¼ Ph (6.38 g, 91%). Colorless
prisms. M.p. 68 – 708. IR (ATR): 1443s, 1451m, 1490s, 1577m, 1594m (arom. ring vibr.), 1630m (C¼C str).
1H-NMR (600 MHz): Simulation by DAVINX [25] afforded the chemical shifts for the 5 cycloaliphatic
H; precondition for d assignment in 32A is the deshielding by PhÀC(3): HbÀC(3) > HaÀC(5) >
HbÀC(5); coupling constants: 3J(1,2) ¼ 5.93, 4J(1,3) ¼ 1.66, 3J(1,5a) ¼ 1.72, 3J(1,5b) ¼ 2.22, 3J(2,3) ¼
2.28, 4J(2,5a) ¼ 1.99, 4J(2,5b) ¼ 1.56, 5J(3,5a) ¼ 2.05, 5J(3,5b) ¼ 1.28, 2J(5a,5b) ¼ À16.31. 13C-NMR
(100 MHz): 46.3 (C(5)); 59.6 (C(3)); 61.1 (C(4)); 129.5 (C(1)); 135.2 (C(2)); 125.3, 125.7, 126.0 (3
arom. p-CH); 6 peaks of double height for 12 arom. o,m-CH; 140.8, 145.4, 151.2 (3 arom. Cq). MS: similar
to 7, R ¼ Ph, Sect. 5.1.
13.3.1. Oxidation. Treatment of 30, R ¼ Ph, with KMnO4 (4.2 mol-equiv.) in boiling pyridine
furnished, after the usual workup, benzophenone (isolated as 2,4-dinitrophenylhydrazone) and
PhCOOH, both in poor yield.
13.3.2. 2(exo),3,3-Triphenyl-6-oxabicyclo[3.1.0]hexane (42, R ¼ Ph). In CHCl3 (20 ml), 30, R ¼ Ph
(593 mg, 2.0 mmol), were reacted with PhCO3H (2.2 mmol) at r.t. for 48 h. After washing with Na2CO3
and H2O, the solvent was evaporated, and the crystalline residue was subjected to CC (neutral alumina,
50 g). The first fraction eluted with petroleum ether/Et2O was unchanged 30, R ¼ Ph (150 mg), followed
(with Et2O alone) by 42, R ¼ Ph (430 mg, 92% of consumed 30). Colorless prisms (from MeOH).
M.p. 87 – 898. IR (ATR): 690vs, 703s, 740s, 751m (arom. oop), 848s (CÀOÀC as str, oxirane [26]).
2
1H-NMR (600 MHz; best assignments, not free of doubt): 2.92 (d, Jgem ¼ 14.5, HaÀC(4)); 3.10 (dd,
2Jgem ¼ 14.5, 3J(4b,5) ¼ 1.7, HbÀC(4)); 3.72 (d, J ¼ 2.8, signal width 3.7, HÀC(1)); 3.88 (t, J(4b,5) ꢃ
J(1,5) ꢃ 1.9, signal width 5.8, HÀC(5)); 4.61 (s, line width 2.0 (0.8 for CHCl3), HaÀC(2)); 6.80 – 7.38
(m, 15 arom. H). 13C-NMR (75.5 MHz): 39.3 (C(4)); 52.8 (C(2)); 57.3 (C(5)); 58.3 (C(3)); 60.5 (C(1)); 12
peaks for 18 arom. C show free rotation of 3 Ph. MS: 312 (6, Mþ; HR 312.1509/312.1513), 294 (5, [M À
H2O]þ), 207 (11, [M À C8H9]þ, C15H11Oþ; HR 207.0807/207.0789); 192 (51, C15H1þ2 ), 191 (15, 38), 180
(100, C14Hþ12, diphenylethene; HR 180.0936/180.0942; 13C 15.6/14.1), 179 (33), 178 (31), 165 (48, 37), 115
(33), 105 (14), 91(22), 82 (48, C5H7Oþ), 77 (16, Ph). Anal. calc. for C23H20O (312.39): C 88.42, H 6.45;
found: C 88.28, H 6.55.
13.3.3. 1,1,2-Triphenylcyclopentane (40, R ¼ Ph). In the presence of Pd (10% on C), 30, R ¼ Ph
(1.0 mmol), in EtOH (10 ml) consumed ca. 1 mmol of H2. Recrystallization from MeOH afforded 40,
1
R ¼ Ph. Needles. M.p. 81.5 – 82.58. H-NMR (100 MHz): 1.6 – 3.0 (m, 6 H); 4.00 (t, J ¼ 6.8, further split,
HÀC(2)); 6.60 – 7.55 (m, 15 arom. H). MS: 298 (100, Mþ; HR 298.1716/298.1729; 13C 25.6/25.7), 207 (19),
193 (100, [M À CH2CH2Ph]þ, C15H1þ3, possibly [9-ethylfluorenyl]þ), 180 (69), 179 (41), 167 (54), 165
(56), 129 (24), 115 (53), 91 (45), 82 (13), 77 (10). Anal. calc. for C23H22 (298.41): C 92.57, H 7.43; found: C
92.13, H 7.29.
13.4. Methyl 5,5-Diphenylcyclopent-2-ene-1-carboxylate (30, R ¼ CO2Me). After heating 7, R ¼
CO2Me (7.64 g, 27.4 mmol), in N2 atmosphere for 10 min at 310 – 3208, distillation at 175 – 1858/10À3
Torr gave a yellow oil, which crystallized after a while from MeOH/H2O 9 :1 and yielded 30, R ¼ CO2Me
(4.47 g). M.p. 50 – 52.58. CC (silica gel; petroleum ether/Et2O 95 :5) of the mother liquor afforded
another 2.39 g (together 90%). M.p. 52.5 – 538 (MeOH). IR (KBr): 701vs, 715s, 740s, 746s (arom. and
olefin. oop), 1170s (CÀO str), 1625w, 1644w (cis-CH¼CH str), 1735vs (C¼O). 1H-NMR (60 MHz,

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Helvetica Chimica Acta – Vol. 91 (2008)
simulation of aliph. 5-H system): 3.18 (s, MeO); 2.82, 3.52 (2 dq-like, HbÀC(4), HaÀC(4)); 4.50 (quint.-
like, HbÀC(1)); 5.89, 6.06 (sym, 14 lines, HÀC(3), HÀC(2)); coupling constants: 3J(1b,2) ¼ 2.10;
4J(1b,3) ¼ À2.13; 5J(1b,4b) ¼ 1.80; 5J(1b,4a) ¼ 1.77; 3J(2,3) ¼ 5.82; 4J(2,4b) ¼ À2.17; 4J(2,4a) ¼ À2.12;
2
3J(3,4b) ¼ 2.19; 3J(3,4a) ¼ 2.15; J(4a,4b) ¼ À16.05; 7.1 – 7.5 (m, 10 arom. H). Molecular mass (osmo-
metr., CHCl3): calc.: 278, found: 282. Anal. calc. for C19H18O2 (278.33): C 81.98, H 6.52; found: C 82.33, H
6.38.
13.4.1. Methyl 3,3-Diphenyl-6-oxabicyclo[3.1.0]hexane-2(exo)-carboxylate (42, R ¼ CO2Me). Ester
30, R ¼ CO2Me (3.53 mmol), and PhCO3H (4.30 mmol) in benzene (45 ml) were reacted at r.t. in the
dark for 1 week. Workup (see Sect. 13.3.2) rendered back olefin (0.98 mmol) and yielded 42, R ¼ CO2Me
(2.43 mmol, 95% of consumed 30). The oil crystallized after several weeks. M.p. 70 – 718 (MeOH/H2O
9 :1). IR (ATR): 694vs, 703vs, 748s, 767m (arom. oop); 830m, 846s, 851s (oxirane, as str); 1165s, 1188s
(CÀO str), 1730vs (C¼O). 1H-NMR (300 MHz): 2.86 (d, 2Jgem ¼ 14.1, HaÀC(4)); 3.19 (dd, 2Jgem ¼ 14.1,
3J(4b,5) ¼ 1.2, HbÀC(4)); 3.28 (s, MeO); 3.81 (s, broadened, some evidence of AB, HÀC(1) þ HÀC(5));
4.38 (s, HaÀC(2)); 7.1 – 7.3 (m, 10 arom. H). 13C-NMR (75.5 MHz): 39.7 (C(4)); 51.5, 53.9 (C(2), Me);
56.7 (C(3)); 57.3, 58.2 (C(1), C(5)); 8 peaks for 12 arom. C; 171.7 (C¼O). MS: 294 (27, Mþ; HR 294.0990/
294.0999), 262 (26, [M À MeOH]þ), 234 (30, [M À HCO2Me]þ, C17H14Oþ; HR 234.1041/234.1047), 217
(17), 207 (21), 192 (100, C15Hþ12 ), 191 (60, 38), 181 (33), 179 (55), 165 (55), 115 (57), 91 (32), 77 (22).
Anal. calc. for C19H18O3 (294.33): C 77.53, H 6.16; found: C 77.58, H 6.16.
13.4.2. Methyl 2,2-Diphenylcyclopentane-1-carboxylate (40, R ¼ CO2Me). Catalytic hydrogenation
(see Sect. 13.3.3) converted 30, R ¼ CO2Me, into 40, R ¼ CO2Me, which was purified by TLC (silica gel;
petroleum ether/Et2O 8 :2) and distillation at 125 – 1308 (bath)/10À3 Torr. Colorless oil (90%). n2D0
¼
1
1.5715. IR (film): 1162s (br., CÀO), 1725vs (C¼O). H-NMR (60 MHz): 1.30 – 2.56 (m, 5 H); 2.64 –
3
3.08 (m, 1 H), 3.20 (s, MeO); 3.79 (t-like, J ¼ 5.9, HÀC(1)); 7.0 – 7.4 (d-like, 10 arom. H). Anal. calc.
for C19H20O2 (280.35): C 81.39, H 7.19; found: C 81.79, H 7.45.
13.4.3. Methyl 5,5-Diphenylcyclopent-1-ene-1-carboxylate (41). MeONa (6.7 mmol) and 30, R ¼
CO2Me (2.12 mmol), in MeOH (30 ml) were refluxed for 1 h and worked up with 0.5n HCl and Et2O.
TLC (silica gel; petroleum ether/Et2O) furnished 41 (76%). Colorless oil. B.p. 145 – 1508 (bath)/10À3
1
Torr. n2D0 ¼ 1.5928. IR (film): 1109s (CÀO), 1620w (C¼C str), 1719s (C¼O). H-NMR (600 MHz, Cs
symmetry): 2.68 (dt, 3J(2,3) ¼ 2.7, 3J(3,4) ¼ 7.0; 2,3-coupling established by GDQCOSY, CH2(3)); 2.80 (t-
3
3
like, J(3,4) ¼ 6.9, broadened, CH2(4)); 3.66 (s, MeO); 7.20 (t, J(2,3) ¼ 2.7, HÀC(2)); 7.25 – 7.41 (m, 10
arom. H). 13C-NMR: 31.4 (C(3)); 45.5 (C(4)); 51.3 (MeO); 62.1 (C(5)); 126.2 (2 arom. p-CH); 127.9,
128.3 (8 arom. o,m-CH); 141.9 (C(1)); 146.4 (C(2)); 146.8 (2 arom. Cq); 164.9 (C¼O). MS: 278 (28, Mþ;
HR 278.1302/278.1289; 13C 5.9/5.5), 246 (26, [M À MeOH]þ), 219 (100, [M À CO2Me]þ), 218 (42), 204
(21), 141 (37), 91 (22). Anal. calc. for C19H18O2 (278.33): C 81.98, H 6.52; found: C 82.13, H 6.95.
13.5. 5,5-Diphenylcyclopent-2-ene-1-carbonitrile (30, R ¼ CN). Prepared from 9, R ¼ CN, at 300 –
3108, b.p. 130 – 1358/10À3 Torr, m.p. 96 – 96.58. IR (KBr): 1625w (C¼C str), 2245m (CꢂN). 1H-NMR
(60 MHz, simulation): 2.93 (HbÀC(4)); 3.36 (HaÀC(4)); 4.37 (HÀC(1)); 5.69 (HÀC(3)); 6.01
(HÀC(2)); coupling constants: 3J(1b,2) ¼ 2.17; 4J(1b,3) ¼ À2.31; 5J(1b,4b) ¼ 2.16; 5J(1b,4a) ¼ 2.02;
3J(2,3) ¼ 5.83; 4J(2,4b) ¼ À2.34; 4J(2,4a) ¼ À2.03; 3J(3,4b) ¼ 2.41; 3J(3,4a) ¼ 2.57; 2J(4a,4b) ¼ À16.76.
Anal. calc. for C18H15N (245.31): C 88.13, H 6.16, N 5.71; found: C 87.92, H 6.05, N 5.75.
13.6. 1-Methyl-4,4-diphenylcyclopentene (31, R ¼ Me). For preparation from 12, R ¼ Me, see
Sect. 13.1. Yield: 87%. Colorless liquid. B.p. 100 – 1058 (bath)/10À3 Torr. nD20 ¼ 1.5852. IR (film): 1650w
5
(C¼C str). 1H-NMR (300 MHz; s-plane): 1.89 (t-like, 4J(2,Me) ꢃ J(3,Me) ¼ 0.8, Me); 3.09, 3.16 (2m, 6
and 5 peaks visible, CH2(3) and CH2(5)); 5.51 (m, HÀC(2)); 7.2 – 7.4 (m, 10 arom. H). 13C-NMR
(75.5 MHz): 16.8 (Me); 47.0, 50.8 (C(3), C(5)); 55.7 (C(4)); 123.2 (C(2)); 125.6 (2 arom. p-CH); 127.7,
128.1 (8 arom. o,m-CH); 139.2 (C(1)); 150.5 (2 arom. Cq). MS: 234 (100, Mþ; HR 234.1404/234.1397),
fragments similar to MS of 12, R ¼ Me. Anal. calc. for C18H18 (234.32): C 92.26, H 7.74; found: C 92.65, H
7.85.
13.6.1. 1-Methyl-3,3-diphenyl-6-oxabicyclo[3.1.0]hexane (44, R ¼ Me). Compound 44, R ¼ Me, was
prepared as described in Sect. 13.3.2; yield after recrystallization: 72%. M.p. 86.5 – 87.58. IR (ATR): 843s
1
(CÀOÀC, oxirane), 1446s, 1491s, 1579w, 1591w (arom. ring vibr.). H-NMR (300 MHz): 1.53 (s, Me);
2
2
2.50 (d, Jgem ¼ 14.4, HbÀC(2)); 2.53 (dd, Jgem ¼ 14.4, 3J(4b,5) ¼ 1.7 (cis), HbÀC(4)); 3.03, 3.12 (2 d,
Jgem ¼ 14.3, HaÀC(2), HaÀC(4)); 3.44 (d, J(4b,5) ¼ 1.4, HÀC(5); 7.1 – 7.3 (m, 10 arom. H). 13C-NMR
3

Helvetica Chimica Acta – Vol. 91 (2008)
803
(75.5 MHz): 18.0 (Me); 41.2, 45.0 (C(2), C(4)); 53.0 (C(3)); 62.9 (C(5)); 64.0 (C(1)); 6 lines for 10 arom.
CH; 149.7, 150.9 (2 arom. Cq). MS: 250 (19, Mþ; HR 250.1353/250.1345; 13C 3.8/3.3), 207 (46, [M À
MeCO]þ), 192 (100, C15Hþ12 ), 191 (25), 180 (56, [diphenylethene]þ), 179 (37, C14H1þ1 ), 165 (54), 129
(45), 115 (42), 91 (37), 77 (19). Anal. calc. for C18H18O (250.32): C 86.36, H 7.25; found: C 86.60, H 7.20.
13.7. 1,4,4-Triphenylcyclopent-1-ene (31, R ¼ Ph). 13.7.1. Preparation. Thermal polymerization of 12,
R ¼ Ph (2.95 mmol), could be diminished by heating with 2-anilinonaphthalene (0.7 mmol) to give a
homogenous melt. After 5 min at 310 – 3208, the material was purified by TLC (silica gel; petroleum
ether/Et2O 99 :1) and furnished 31, R ¼ Ph, as the main product (0.70 g), which was recrystallized from
EtOH: colorless needles (59%). M.p. 93.5 – 948. IR (ATR): 1631w (C¼C str). 1H-NMR (400 MHz; d and
J values in 32B): 3.30 (q-like, broadened, J ꢃ 2.0, CH2(3)); 3.48 (q, sharp, J ¼ 1.8, CH2(5); 6.84 (structured
4
sept. by superposition of two t, 3J þ J ¼ 4.35, HÀC(2)); irradiation at 6.24 generates 2t at 3.30 and 3.48
with 5J(3,5)cis ¼ 5J(3,5)trans ¼ 1.79; the signal at 6.24 is converted to t, 3J(2,3) ¼ 1.69 when CH2(3) is
4
decoupled whereas t with 4J(2,5) ¼ 2.64 for HÀC(2) results on decoupling of CH2(5); thus, 3Jvic þ Jallyl
¼
4.33; 7.15 – 7.57 (m, 15 arom. H). 13C-NMR (75.5 MHz): 46.96, 47.14 (C(3), C(5)); 55.2 (C(4)); 124.2
(C(2), established by comparison of line heights and confirmed by a HSQCAD experiment); 136.2
(C(1)); 125.6, 125.8, 127.21, 127.24, 128.1, 128.4 (15 arom. CH); 141.1, 149.0 (3 arom. Cq).
13.7.2. 1(exo),3,3-Triphenyl-6-oxabicyclo[3.1.0]hexane (44, R ¼ Ph). The reaction of 31, R ¼ Ph,
with PhCO3H (1.3 equiv.), as described above, produced the epoxide44, R ¼ Ph, as leaflets (67%) after
recrystallization from EtOH. M.p. 129.5 – 1318. IR (ATR): 880m (CÀOÀC, oxirane), 1446m, 1492m,
1
2
3
1594w (arom. ring vibr.). H-NMR (400 MHz): 2.70 (dd, Jgem ¼ 14.7, J(4b,5) ¼ 1.5, HbÀC(4)); 3.06 (d,
2Jgem ¼ 14.2, HbÀC(2)); 3.21 (d, 2Jgem ¼ 14.7, HaÀC(4)); 3.36 (d, 2Jgem ¼ 14.3, HaÀC(2)); 3.69 (t, 3J(4b,5) ¼
3
0.8, HÀC(5)); 7.02 – 7.38 (m, 15 arom. H); GDQ-COSY shows J(4b,5) (calc. by simulation [25] to be
1.59) as the only vicinal coupling. 13C-NMR (100 MHz): 41.2, 42.3 (C(2), C(4)); 52.2 (C(3)); 65.7 (C(5));
66.1 (C(1)); 3 peaks for 3 arom. p-CH, 6 peaks for 12 o,m-CH, and 3 peaks for Cq. MS: 312 (36, Mþ; HR
312.1509/312.1492; 13C 9.2/10.3), 268 (14, [M À MeCHO]þ, C21Hþ16 ), 234 (14, [M À C6H6]þ), 207 (48,
[M À PhC2H4]þ, C15H11Oþ; HR 207.0807/207.0802), 192 (78), 191 (53); 180 (100, [diphenylethylene]þ),
178 (53), 165 (55), 105 (41), 91 (36), 77 (31). Anal. calc. for C23H20O (312.39): C 88.42, H 6.45; found:
C 88.31, H 6.73.
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ReceivedFebruary 26, 2008