Oxidation of aryl- and diarylcyclopropanes in a pentasil zeolite: Ring opening with deprotonation or net hydrogen migration

Article abstract of DOI:10.1002/(SICI)1099-0690(200002)2000:3<467::AID-EJOC467>3.0.CO;2-B

Incorporation of trans-1,2-diphenylcyclopropane (1) and its 3,3-D2- isotopomer into the channels of a redox-active pentasil zeolite (Na-ZSM-5) resulted in the formation of exo,exo-1,3-diphenylallyl radical (2^.) and its 2-D1 isotopomer, respectively. This conversion requires oxidation, ring opening, and deprotonation, in an unspecified sequence. The allyl radical 2^. is also formed upon incorporation of trans-1,3-diphenylpropene (3). A comparison with the solution photochemistry, in the presence or absence of added base, shows the conversion of 1 into 2^. to be a zeolite-specific reaction. Incorporation of arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated trans-propenylbenzene radical cations 10^.+ (R = H, OCH3); the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three different isotopomers of 10^.+) (R = OCH3).

Full text of DOI:10.1002/(SICI)1099-0690(200002)2000:3<467::AID-EJOC467>3.0.CO;2-B

FULL PAPER
Oxidation of Aryl- and Diarylcyclopropanes in a Pentasil Zeolite: Ring
Opening with Deprotonation or Net Hydrogen Migration
Torsten Herbertz,[a] Prasad Sreeramachandra Lakkaraju,*[a] Florian Blume,[b]
Matthias Blume,[a] and Heinz Dieter Roth*[a]
Keywords: Zeolites / Radical cations / Ring opening / Electron transfer / Oxidation
Incorporation of trans-1,2-diphenylcyclopropane (1) and its
3,3-D2-isotopomer into the channels of redox-active
comparison with the solution photochemistry, in the presence
or absence of added base, shows the conversion of 1 into 2•
a
pentasil zeolite (Na-ZSM-5) resulted in the formation of
exo,exo-1,3-diphenylallyl radical (2•) and its 2-D1
isotopomer, respectively. This conversion requires oxidation,
ring opening, and deprotonation, in an unspecified
sequence. The allyl radical 2• is also formed upon
to be
a
zeolite-specific reaction. Incorporation of
arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated
trans-propenylbenzene radical cations 10•+ (R = H, OCH3);
the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three
different isotopomers of 10•+ (R = OCH3).
incorporation
of
trans-1,3-diphenylpropene
(3).
A
vealed no evidence for their existence (as unsolvated spec-
ies).[4f] However, species of this type have been reported in
solid matrices.[6b,6c] In at least two cases, the conversion of
type A to type P radical cations proceeds as a sigmatropic
shift, clearly eliminating TM type intermediates in solu-
tion.[8][9] Thus, sabinene radical cation (S•ϩ) undergoes a
[1,3]-sigmatropic shift whereas α-thujene radical cation
(T•ϩ) rearranges by competing [1,3]- and homo[1,5]-sigma-
tropic shifts.
Introduction
The structure and reactivity of cyclopropane radical cat-
ions have attracted much attention;[1][2] the spin density dis-
tributions of many derivatives have been delineated, and
many intra- and intermolecular reactions have been studied
in gas phase,[3] solution,[1e,2] or solid matrices. Vertical ion-
ization of the parent cyclopropane from a degenerate pair
of in-plane eЈ orbitals (s and a) generates a doubly degener-
2
ate EЈ state, which undergoes first-order JahnϪTeller dis-
2
2
tortion to two nondegenerate electronic states, A1 and B2
(C2v symmetry).[4] These components relax to structures
with one (“trimethylene”; type A) or two lengthened CϪC
bonds (“π-complex”; type B).[1e,5] Structures of type A are
established for many cyclopropane radical cations;[1e,5,6]
structure type B is less common.[5c,7]
In this paper, we report results pertinent to the structure
and reactivity of cis- and trans-1,2-diphenylcyclopropane,
cis-, trans-1. CIDNP studies have shown that cis- and trans-
1•ϩ have significant spin density on the benzylic carbon
atoms and sizeable hyperfine coupling constants (hfcs) for
benzylic and geminal 1H nuclei.[5] The doubly benzylic
C1ϪC2 bond retains a significant degree of bonding interac-
tion, as documented by the failure of either radical cation
to undergo geometric isomerization. The observation that
no polarized isomerization products are observed with
chloranil as acceptor/sensitizer, requires that the lifetimes of
cis- and trans-1•ϩ with respect to isomerization must be
greater than their spin lattice relaxation times (T1 values of
doublet species typically fall into the microsecond
range).[10] This assignment was recently confirmed by fast,
time-resolved optical spectroscopy.[11] On the other hand,
Some radical cations of type A are known to rearrange
to propene radical cations (P); bifunctional trimethylene
radical cations (TM) are potential intermediates in this con-
version. Detailed theoretical calculations have, so far, re-
[a]
Department of Chemistry, Rutgers University, Wright-Rieman
Laboratories,
610 Taylor Road, New Brunswick, NJ 08854-8087, USA
Fax: (internat.) ϩ 1-732/445-5312
E-mail: roth@rutchem.rutgers.edu
[b]
Department of Chemistry, Georgian Court College,
Lakewood, NJ 08701, USA,
Fax: (internat.) ϩ 1-732/905-8571
E-mail: Lakkaraju@Georgian.edu
Eur. J. Org. Chem. 2000, 467Ϫ472
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/0203Ϫ0467 $ 17.50ϩ.50/0
467

T. Herbertz, P. S. Lakkaraju, F. Blume, M. Blume, H. D. Roth
FULL PAPER
the ESR spectra of the radical cations, cis- or trans-1•ϩ
,
have so far been elusive.
In an attempt to characterize trans-1•ϩ by its EPR spec-
trum, we incorporated trans-1 into the channels of pentasil
zeolite (Na-ZSM-5). This attempt is based on the fact that
radical cations can be generated by incorporating appropri-
ate precursors with redox potentials, Eox ϭ 1.65 V, at ambi-
ent temperatures into the zeolite.[12][13] In some cases (for-
mation of iminoxyls from oximes), the zeolite played the
dual role of one-electron oxidant and proton acceptor.[14]
In others, it promoted more complex conversions (p-propyl-
anisole to p-propenylanisole radical cation).[15] Model con-
siderations indicate that trans-1 might fit into the zeolite
˚
channels (ID ഠ 5.5 A), whereas the cis isomer appears too
bulky. The oxidation potential of trans-1 (Eox ϭ 1.17 V vs.
Ag/Agϩ, ca. 1.5 V vs. SCE)[16] is sufficiently low for oxi-
dation by the zeolite.
Figure 1. Top: X-band EPR spectrum generated by incorporation
of trans-1,2-diphenyl-cyclopropane (trans-1) into the channels of
pentasil zeolite (Na-ZSM-5); the spectrum is identified as that of
exo,exo-1,3-diphenylallyl radical (2•); (bottom): second-order simu-
lated spectrum, an envelope of two Gaussian simulations, 1) a tri-
plet of septets with A2H ϭ 11.5 G and A6H ϭ 3.0 G, and a line-
width, FWHH ϭ 2.3 G, and 2) a broad line, FWHH ϭ 17 G; the
two spectra are simulated with relative intensities of 1:2; the two
components of the experimental spectrum have slightly different
centers (g factors); the simulation program[17] only allows for the
addition of isocentric spectra, resulting in a slight mismatch bet-
ween simulation and experiment.
Results and Discussion
Zeolite-Induced Conversions of trans-1
Incorporation of trans-1 into Na-ZSM-5 produced a
strong, long-lived EPR spectrum (Figure 1). The observed
evenly spaced multiplet indicates the presence of two
strongly coupled nuclei (A ϭ 11.5 G) and six more weakly show pronounced changes upon deuterium incorporation.
coupled nuclei (A ϭ 3.0 G); the spectrum can be simulated In analogy to p-propenylanisole radical cation,[14] species
1
satisfactorily with these data (Figure 1, bottom). A spec- 3•ϩ should have three strongly coupled H nuclei (A ഠ 10
trum with only one pair of strongly coupled nuclei is incom- G) when generated from perprotio-trans-1, but only one
patible with the structure established for trans-1•ϩ by the such nucleus when generated from trans-1-3-D2. Given the
CIDNP results; it rules out a simple one-electron oxidation hfc pattern of typical cyclopropyl radicals (Aα ഠ 7 G, Aβ ഠ
of trans-1 and suggests a significant chemical conversion on 24 G),[18] deuterium incorporation would produce 4• with
the internal surfaces of the zeolite. The identity of the two greatly diminished α-coupling.
strongly coupled nuclei hold the key to the nature of the
paramagnetic intermediate formed.
One species compatible with all features of the EPR spec-
trum is a 1,3-diphenylallyl radical (2•). This intermediate
In order to establish the identity of the strongly coupled could be formed by ring opening of the cyclopropane rad-
nuclei, an isotopomer, trans-1-3-D2, was studied; incorpor- ical cation, trans-1•ϩ, with deprotonation. Structure 2• re-
1
ation of this material into Na-ZSM-5 gave rise to an EPR adily explains why the H nuclei originating at the second-
spectrum essentially identical to that obtained from trans- ary cyclopropane carbons fail to show hyperfine coupling;
1
1•ϩ. Accordingly, the rearrangement must place the second- one H nucleus is lost by deprotonation, the other ends up
ary cyclopropane carbon atom (with the geminal deuterium in the nodal plane of the singly occupied molecular or-
label) into a position without appreciable hyperfine coup- bital (SOMO).
ling. This finding identifies the benzylic protons as the
Additional support for the identity of the intermediate as
strongly coupled nuclei. The range of structures to be con- a ring-opened species is derived from incorporation of
sidered for the intermediate is significantly limited by the trans-1,3-diphenylpropene (3) into the zeolite; trans-3 pro-
1
presence of six H nuclei with intermediate coupling. This duced a spectrum identical to that obtained from trans-1;
finding requires a fully delocalized species in which both clearly, the same species is generated from trans-1 and trans-
phenyl groups (2 ortho- plus 1 para-1H each) participate in 3. Since ring-opening of trans-1•ϩ is much more plausible
delocalizing the unpaired spin. Intermediates, in which the than ring-closure of trans-3•ϩ, the free radical 2• (and not
electron spin is delocalized onto only one phenyl group, 4•) is the logical species formed from the two precursors.
formed, e.g., by hydrogen shift (3•ϩ) or hydrogen abstrac- Only the stereochemistry of this species remains to be as-
tion (4•), are excluded also because their EPR spectra must signed.
468
Eur. J. Org. Chem. 2000, 467Ϫ472

Oxidation of Aryl- and Diarylcyclopropanes in a Pentasil Zeolite
FULL PAPER
The key to structure and stereochemistry of 2• lies in the observed; apparently nucleophilic capture is faster than iso-
known spectra of endo,exo- (Aendo ϭ 9.4 G; Aexo ϭ 14 G; merization.
A
o,p ϭ 2.3 G) and exo,exo-diarylallyl radicals (Aendo ϭ 10.2
G; Ao,p ϭ 2.9 G).[19] The hyperfine coupling of the species
observed in the zeolite (A ϭ 11.5 G) are closer to those
of the exo,exo-diarylallyl species; particularly, the hyperfine
coupling is closer to the 10.2 G measured for the endo-1H
nuclei and quite different from the 14.0 G assigned to the
exo-1H nuclei.[19] Accordingly, we identify the spectrum
(Figure 1) as that of the exo,exo-1,3-diphenylallyl radical,
exo,exo-2•, and the major splitting as that of 2 endo-1H
atoms. As trans-1•ϩ is converted into 2• the secondary
cyclopropane carbon atom is rehybridized with depro-
tonation and becomes the nodal center of the allyl SOMO;
the remaining 1H nucleus lies in the nodal plane; no signifi-
cant hyperfine coupling can be expected.
Irradiation of singlet-excited acceptors, 1,4-dicyanonaph-
thalene, 9-cyanophenanthrene (9-CNP), or 9,10-dicy-
anoanthracene in the presence of cis- or trans-1 resulted in
the slow conversion into the geometric isomers. CIDNP ef-
fects observed during these reactions were ascribed to the
formation of a ring-opened triplet (biradical) species,
formed by recombination of triplet radical ion pairs.[5a,5b,16]
This assignment was confirmed recently on the basis of fast
time-resolved optical spectroscopy.[11]
Under conditions similar to those used for the oxidative
conversion of trans-1, we also incorporated cis-1 and trans-
1-methyl-2-phenylcyclopropane (5), into ZSM-5. Incorpor-
ation of cis-1 failed to generate an EPR spectrum; this re-
sult is likely caused by the failure of the bulky substrate to
be incorporated into the zeolite. Incorporation of trans-5
generated a broad EPR spectrum (g ϭ 2.0027) showing that
trans-5 is oxidized on ZSM-5. However, the spectrum
showed no features that would reveal the identity of the
resulting species.
The 9-CNP-sensitized reaction of trans-1 in the presence
of 2-propanol as nucleophile formed an 2-propanol adduct
[R ϭ CH(CH3)2] and resulted in slow geometric isomeriz-
ation. In addition, this reaction produced minor quantities
of trans- and cis-1,3-diphenylpropenes, trans- and cis-3, for-
mally generated by a sigmatropic shift. Addition of a strong
base (2,6-di-tert-butylpyridine) likewise produced the cis
isomer, but failed to give rise to deprotonation with ring
opening. Overall, the electron-transfer photochemistry of
trans-1 in solution fails to produce any evidence for the
ring-opened, deprotonated free radical 2•.
Mechanistic Considerations
The overall transformation of trans-1 to 2• on the zeolite
requires three net changes: electron transfer, deprotonation,
and ring opening. In view of the demonstrated redox reac-
Solution Photochemistry of trans-1
The solution photochemistry of cyclopropane derivatives, tivity of Na-ZSM-5[12][13] and the oxidation potential of
including trans-1, has been studied in detail;[5a,5b,11,16,22] we trans-1 (Eox ഠ 1.5 V vs. SCE),[16] one-electron oxidation
have carried out additional reactions to probe pathways rel- might appear to be a reasonable first step. However, the
evant to the zeolite-induced conversions under consider- recent realization that Na-ZSM-5 contains Lewis and
ation. The electron-transfer photochemistry of trans-1 pro- Brønsted acid site[24] suggests that protonation, yielding a
vided little evidence for the deprotonation at C-2 with ring 1,3-diphenylpropyl carbenium ion, 8ϩ, must also be con-
opening observed in the zeolite. The salient results of these sidered; this species should be readily deprotonated. As for
experiments are described below.
the oxidation product, the significant electrostatic fields in-
Perhaps the best known photochemical reaction of cyclo- side the zeolite channels may favor the ring-opened bifunc-
propane derivatives, including 5, occurs upon irradiation of tional species, 1•ϩ-TM, even though it has been eliminated
(singlet) photo-sensitizers (p-dicyanobenzene) in the pres- specifically in solution.[5,11,16] The mechanism for the con-
ence of alcoholic nucleophiles (methanol). This reaction version of trans-1 to 2• has to accommodate the key fact
typically results in ring-opened products bearing either an that the benzylic protons of 1 remain adjacent to the phenyl
alkoxy group (e.g., 6, R ϭ CH3) or an alkoxy and a p- groups; there does not appear to be any random D vs. H
cyanophenyl group (e.g., 7); these products are formed by exchange. Some reactions of the potential primary inter-
the well-established nucleophilic capture of the correspond- mediates (Scheme 1) have precedent, others can be excluded
ing radical cation by the alcohol with ring-opening.[8,9,22,23] unambiguously. The enforced close contact between zeolite
In the reaction of trans-1, no isomerization products were and substrate must play a major role in the conversion, par-
Eur. J. Org. Chem. 2000, 467Ϫ472
469

T. Herbertz, P. S. Lakkaraju, F. Blume, M. Blume, H. D. Roth
FULL PAPER
topomer of 9b (9b-2,2-D2) gave rise to a particularly inter-
esting spectrum (Figure 2, bottom).
Scheme 1. Potential intermediates in the conversion of trans-1ϩ•
to 2•
ticularly the strong electrostatic fields in the zeolite interior.
Although a [1,3]-hydride shift generating 3•ϩ has pre-
cedent in some vinylcyclopropane radical cations[8,9,20] and
in the solution reaction of trans-1•ϩ (formation of trans-
and cis-3 in the 9-CNP sensitized reaction), the involvement
of 3•ϩ is incompatible with the EPR data obtained from
trans-1-3-D2. A [1,3]-D shift in trans-1•ϩ-3-D2 would form
3•ϩ-2,3-D2, which is expected to lose Hϩ (not Dϩ). The
spectrum of the resulting 2•-2,3-D2 should have only one
strongly coupled 1H, not two as the EPR spectrum ob-
tained from trans-1-3-D2 (cf. Figure 1, top).
Figure 2. X-band EPR spectrum generated upon incorporation of
anisylcyclopropane (9b, top) and anisylcyclopropane-D2 (9b-D2,
bottom) into pentasil zeolite (Na ZSM-5); the top spectrum is iden-
tified as that of anethole radical cation (10b•ϩ) whereas the bottom
one is a superposition of three isotopomers, 10b•ϩ-D2, -D1, and
-D0; the “wings” of the -D0 isotopomer are marked by asterisks
(*), the two central lines of the -D1 isotopomer are denoted by
pound signs (#)
This spectrum has the same overall width as the per-pro-
tio species; however, two changes are obvious: The upfield
and downfield wings are less intense and the “valleys” be-
tween the five lines are “filled in”. Changes of this nature
can be acommodated by the presence of two isotopomers,
10b•ϩ-D2 (represented by the three central lines) and 10b•ϩ
-
D1 (represented by four lines in the “valleys”), in addition
to the -D0 isotopomer (represented by the five principal
lines). The presence of three isotopomers of 10b•ϩ unam-
biguously rules out any specific reaction, such as a sigma-
tropic shift.
Since the starting material and the allyl radical, exo,exo-
2•, are formally related by a conrotatory distortion of trans-
1•ϩ towards exo,exo-2•, we have considered this process
with simultaneous transfer of a proton to the zeolite matrix.
However, this mechanism is rendered unlikely in the light
of results observed upon incorporation of phenyl (9a, R ϭ
H) or anisylcyclopropane (9b, R ϭ OCH3).
Two of the isotopomers, 10b•ϩ-D2 and 10b•ϩ-D1, are re-
adily explained by protonation with ring opening followed
by deprotonation and oxidation. The third species requires
an additional (random) H vs. D exchange. In the light of
ZSM-5-Induced Conversion of 9
Sequestering 9a or 9b into ZSM-5 resulted in strong EPR
spectra, showing quintets (g ϭ 2.0032 ± 0.0002; A ϭ
11.2 G, 4 H; e.g., Figure 2, top; R ϭ OCH3). These spectra
were identified, by analogy with the known spectra of ane-
thol radical cation, 10b•ϩ, as those of 1-arylpropene radical
cations 10a,b•ϩ in which the allylic methyl protons and the
olefinic β-proton are the strongly coupled nuclei.[15] An iso-
470
Eur. J. Org. Chem. 2000, 467Ϫ472

Oxidation of Aryl- and Diarylcyclopropanes in a Pentasil Zeolite
FULL PAPER
ation, due likely to free radicals or radical ions on its external sur-
face. The loaded zeolite was collected by filtration, washed with
hexane, and dried under vacuum (0.001 Torr). Some of the color-
ation was removed by washing, suggesting that the corresponding
radicals were removed from the external surface of the zeolite. The
dried zeolite samples were transferred to an EPR tube and their
spectra recorded with a Bruker ESP 300 EPR spectrometer.
these results, the formation of exo,exo-diphenylallyl radical
2• upon incorporation of trans-1 in Na-ZSM-5 clearly is a
zeolite-specific reaction.
Conclusion
The “spontaneous” ring opening with deprotonation of
Photo Reactions: Acetonitrile solutions, containing 0.2  donor
trans-1 on Na-ZSM-5 zeolite is a novel conversion without and 0.2  acceptor, in the presence or absence of base and/or nucle-
ophile in 5-mm NMR tubes, were irradiated in a Rayonet RPR-
100 photoreactor equipped with 16 RPR-3000 lamps. The reaction
progress was monitored by gas chromatography with a GC/MS sys-
tem (HP 5890 series II Plus GC interfaced with a HP 5972 mass-
selective detector), using a 30 m ϫ 0.25 mm ϫ 0.25 µm HP-5 capil-
lary column (crosslinked methyl silicone on fused silica). The ident-
ity of the products was established by comparison of retention
times and MS spectral features with those of independently synthe-
sized samples.
precedent or analog in solution. The structure assigned to
2• rests firmly on the generation of identical EPR spectra
from two different precursors (the cyclic trans-1 and its iso-
topomer, and the acyclic trans-3) and on the satisfactory
simulation, using the hyperfine coupling constants corre-
sponding to a known exo,exo-bisaryl radical. Radical cat-
ions often are generated in zeolites; the restrictive environ-
ment increases their stability because it protects them from
external reagents and prevents dimerization; these features
facilitate the study of otherwise unstable intermediates by
conventional spectroscopic techniques at ambient tempera-
tures.
The results reported here provide further evidence that
the interaction of organic substrates with redox- as well as
acid-base-active zeolites may result in interesting, complex,
and occasionally specific conversions. We are pursuing the
oxidation/dehydrogenation of a range of targets containing
strained-ring as well as unsaturated functions. Although the
incorporation of trans-5 failed to yield evidence for a
specific radical or radical cation, the oxidation/rearrange-
ment of cyclopropane compounds upon incorporation into
ZSM-5 is not limited to trans-1. Related reactions have been
observed for several mono-arylcyclopropanes as well as for
1-benzyl-2-phenylcyclopropane.
trans-1,2-Diphenylcyclopropane (trans-1): trans-1 was prepared by a
modified Simmons-Smith[30] addition of methylene (from CH2I2)
to trans-stilbene in 1,4-dioxane. Similarly, addition of methylene-
D2 (from CD2I2) to trans-stilbene furnished trans-1,2-diphenyl-
1
cyclopropane-3-D2 (trans-1-3-D2); H-NMR analysis of trans-1-3-
D2 indicated > 95% of deuterium incorporation. CD2I2 was pre-
pared from CH2I2 by base-catalyzed deuterium exchange (D2O,
NaOMe, NaI)[31] in 1,4-dioxane. Ϫ The following modified Sim-
monsϪSmith[30] procedure is intended for the conversion of 0.1
mol of olefin: 19.6 g (0.3 mol) of zinc dust, 1.0 g (0.01 mol) of
CuICl and 0.1 mol of olefin were suspended in 150 mL of 1,4-
dioxan, freshly distilled from potassium. A reflux condenser was
capped with a balloon, the suspension was magnetically stirred and
heated to the boiling point of the solvent. After the addition of ca.
5 mL of CH2I2, an induction period of 15Ϫ30 min was required
before the reaction became self-sustaining. The color changed from
a dull gray to dark purple. The progress of the reaction was fre-
quently checked by GC/MS. Additional CH2I2 and zinc dust were
added until complete conversion of the olefin. After complete con-
version, the mixture was cooled to room temperature and filtered
through silica gel to remove the sludge-like zinc residue. The filter
cake was then washed with ca. 100 mL of pentane and/or ethyl
ether, and the filtrate is washed repeatedly with water and dried
with anhydrous potassium carbonate. The combined pentane/ether
layers were concentrated by evaporation or distillation; further
purification by column chromatography with pentane on silica gel
leads to moderate yields (ca. 50%) of pure cyclopropanation prod-
ucts.
Experimental Section
General Remarks, Materials, and Solvents: The electron acceptor/
sensitizer, 9-cyanophenanthrene (Aldrich, 97%), the nucleophile, 2-
propanol (Fisher), and the hindered base, 2,6-di-tert-butylpyridine
(Aldrich, 97%) were used as received. For the preparation of EPR
samples, hexane (Aldrich, anhydrous, 95%) and 2,2,4-trimethylpen-
tane (Aldrich, anhydrous, 99.8%), were used, from SureSeal bottles,
as received. Acetonitrile (Fisher, A.C.S. certified) was distilled un-
der nitrogen from calcium hydride immediately prior to the photo-
reaction. The donor/substrates were synthesized by adapted litera-
ture procedures. Ϫ Na-ZSM-5 was synthesized by hydrothermal
crystallization of silica and alumina gels in aqueous basic medium
(NaOH) without a template according to a literature procedure.[25]
Although the chemical analysis of the resulting zeolite was consist-
ent with the Naϩ form, the pyridine adsorption-desorption method
showed the presence of Brønsted acid sites (pyridinium ion,
1550 cmϪ1) and Lewis acid sites (coordinated Lewis adduct, 1450
cmϪ1).[26Ϫ29]
cis-1,2-Diphenylcyclopropane (cis-1): cis-1 was isolated from a com-
mercially available mixture of cis- and trans-1 (Wiley Organics, Co-
shocton, Ohio, USA) by column chromatography on silica gel
(200Ϫ400 mesh, doped with AgNO3), eluted with petroleum ether
(bp < 65°C).
cis- and trans-1,3-Diphenylpropene (3): A mixture of these com-
pounds was prepared by dehydration of 1,3-diphenylpropan-2-ol[32]
or, in better yields, by base-catalyzed aldol condensation of phenyl-
acetaldehyde.[33]
Preparation of EPR Samples: Pentasil zeolite (Na-ZSM-5; Si/Al 15)
was thermally activated by calcination at 500°C for 12 h and stored
under argon. EPR samples were prepared by stirring ca. 1.5 mg of
appropriate substrates with 70 mg of the zeolite in 10 mL of 2,2,4-
trimethylpentane for 2 h. The incorporation of the substrates was
essentially complete judging by their depletion in the supernatant
liquid. Upon mixing the reagents the zeolite developed light color-
trans-1-Methyl-2-phenylcyclopropane (trans-5): trans-5 was pre-
pared by a modified Simmons-Smith[25] addition of methylene
(from CH2I2) to trans-1-phenylpropene in 1,4-dioxane.
Anisylcyclopropane (9b and 9b-D2): 9b and 9b-D2 were prepared by
a modified Simmons-Smith[30] addition of methylene (from CH2I2)
to p-methoxystyrene in 1,4-dioxane. Similarly, addition of methyl-
Eur. J. Org. Chem. 2000, 467Ϫ472
471

T. Herbertz, P. S. Lakkaraju, F. Blume, M. Blume, H. D. Roth
FULL PAPER
[4f]
1985, 63, 3283; Can. J. Chem. 1983, 61, 2310. Ϫ
P. Du, D.
ene-D2 (from CD2I2) to p-methoxystyrene furnished anisylcyclop-
ropane-2-D2; 1H-NMR analysis of 9b-2-D2 indicated > 95% of
deuterium incorporation.
A. Hrovat, W. T. Borden, J. Am. Chem. Soc. 1988, 110, 3405.
[4g] K. Krogh-Jespersen, H. D. Roth, J. Am. Chem. Soc. 1992,
114, 8388Ϫ8394.
Ϫ
[5] [5a]
H. D. Roth, M. L. M. Schilling, J. Am. Chem. Soc. 1980,
Photo Reaction of trans-1,2-Diphenylcyclopropane (trans-1): Ir-
radiation of acetonitrile solutions containing 0.2  9-cyanophen-
anthrene (9-CNP) and 0.2  of trans-1 produced cis-1 as the sole
product (cis-trans isomerization of the donor); ca. 10% conversion
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[5b]
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Support of this work by the National Science Foundation through
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