Cycloaddition of (E)-N-[2-([2.2]paracyclophan-4-yl)ethylidene] methylamine-N-oxide with 2,3-diphenylcyclopropenones and dibenzoyl acetylene; synthesis of new paracyclophanylpyrroles

Article abstract of DOI:10.3184/030823407X236363

When N-[2-([2.2]paracyclophan-4-yl)ethylidene]methylamine-N-oxide (1) is treated with cyclopropenones 6a-c, the [2.2]paracyclophane-based pyrrole(-2-one, -thione and -ylidene malnonitrile) 7a-c are formed in good yields via formal [3π + 3π]cycloaddition. The reaction of 1 with dibenzoyl acetylene (12) afforded, via a Michael-type reaction, the stereoisomeric pyrrole 13. The reaction mechanism described the products formation is discussed.

Full text of DOI:10.3184/030823407X236363

JOURNAL OF CHEMICAL RESEARCH 2007
AUGUST, 451–454
RESEARCH PAPER 451
Cycloaddition of (E)-N-[2-([2.2]paracyclophan-4-yl)ethylidene]
methylamine-N-oxide with 2,3-diphenylcyclopropenones and dibenzoyl
acetylene; synthesis of new paracyclophanylpyrroles
Ashraf A. Aly
Chemistry Department, Faculty of Science, El-Minia University, 61519-El-Minia, Egypt
When N-[2-([2.2]paracyclophan-4-yl)ethylidene]methylamine-N-oxide (1) is treated with cyclopropenones 6a–c, the
[2.2]paracyclophane-based pyrrole(-2-one, -thione and -ylidene malnonitrile) 7a–c are formed in good yields via
formal [3p + 3p]cycloaddition. The reaction of 1 with dibenzoyl acetylene (12) afforded, via a Michael-type reaction,
the stereoisomeric pyrrole 13. The reaction mechanism described the products formation is discussed.
Keywords: paracyclophanyl-nitrone, cyclopropenones, dibenzoyl acetylene, pyrroles
Chiral paracyclophanyl substitutents are growing in
importance as ligands and auxiliaries in asymmetric synthesis,1
derivatives of this class of layered compounds reported
in the literature is increasing rapidly.2,3. For a long time,
paracyclophanyl derivatives were mostly studied because of
their unusual geometry, their steric, transannular, and ring
strain effects as well as the electronic interaction between
their aromatic rings.4,5 Recently, the stereochemical properties
of these systems especially their planar chirality have been the
focus of studies in this field. In particular, paracyclophanyl
derivatives carrying a nitrogen atom in the 4-position are of
growing interest as auxiliaries.6,7 These derivatives having
substituted amino functions have also been shown to be useful
as effective photoconductive components.8 Cycloaddition
reactions still play an important part in the synthesis of various
classes of polycyclic and/or heterocyclic compounds derived
and/or fused to the [2.2]paracyclophane moiety.9 Our initial
studies on the chemistry of (E)-N-[2-([2.2]paracyclophan-4-
yl)ethylidene]methylamine-N-oxide (1) were studied towards
dibenzoylethylene (2) and the corresponding paracyclo-
one dipolarophile to another,9b,10,11 we decided to reinvestigate
its chemical behaviour with other types of dipolarophiles such
as cyclopropenones and dibenzoyl acetylene.
Results and discussion
Nitrones are a well-studied class of 1,3-dipoles that react
with numerous unsaturated systems,14 among them 1,2-
dibenzoylacetylene,15 to yield the corresponding isoxazolidine
derivatives, usually under mild conditions and in good yield.
Diphenylcyclopropenone has been found to react with a wide
range of imines and other compounds containing the C=N
moiety, usually to form azacyclopentenones (pyrrolinones)
via a formal [2p + 3p]cycloaddition reactions.16-18 In view of
our previous results,10 we expected another pyridine skeleton
from the reaction between 1 and cyclopropenones 6a–c. To our
surprise, on heating the two compounds together, we in fact
obtained 1,5-dimethyl-3,4-diphenyl-5-([2.2]paracyclophan-
4-yl)-1,5-dihydropyrrol-2-(one, thione or propenylidene
malnonitrile) 7a–c in good yields along with diphenyl acetylene
(8) (Scheme 2). The structure elucidation of these unusual
phanyl-phenylpyridine
3
was obtained.10 Furthermore,
1
adducts rests primarily on their H and 13C NMR spectra,
aldehydic nitrone as in N[2.2(paracyclophan-4-yl)methyly-
lene]methylamine-N-oxide yielded various classes of
five-member heterocyclic rings (imidazole, isoxazole and
pyrrole derivatives of PC), when it was allowed to react
with various dipolarophiles.11 It has been shown that the
use of cyclopropenone chemistry is of systematic interest in
constructing a wide variety of heterocycles.12 Recently, Aly
et al. has reported on the synthesis of pyridazinethiones and
[1,2,4]triazolo[4,3-b]pyridazinethiones from the reaction of
thiosemicarbazides with 2,3-diphenylcyclopropenone.13 On
the basis that the reactivity of the target nitrone 1 is varied from
which were fully assigned by the techniques mentioned above.
During the course of reaction, thin layer analyses indicated
that the reaction was completed when one equivalent of
1 reacted with two equivalents from 6a–c (Scheme 2). The
proton signals of the paracyclophanyl moiety were analysed
by COSY H H, C H and NOE experiments. The points of
attachment of the paracyclophanyl and pyrrole follow from
the cross-peaks in the COSY H H and C H spectra. NOE
experiments were done between the two methyl groups
along with the methyl protons in position 5 and H-5' of the
paracyclophanyl moiety.
'
2
Me
3'
-
N
+
O
Ph
Me
7'
4'
5'
N
..
toluene
1'
N
OH
Me
+
PhCOCH=CHCOPh
PC
PC
9'
reflux, 3 d
12'
11'
15'
2
CH2
4
3 (70%)
1
= PC
Scheme 1
* Correspondent. E-mail: ashraf160@yahoo.com
PAPER: 07/4688

452 JOURNAL OF CHEMICAL RESEARCH 2007
Ph
Ph
X
toluene
N
Me
X
+
1
+
2
Ph
Me
reflux, 2-3 d
Ph
6a-c
6 and 7
7a-c (60-75%)
[3π + 3π]
Yield of 7 (%)
X
Ph
Ph
8
O
a
b
c
60
70
75
S
(5-10%)
C(CN)2
Ph
Ph
X
Ph
PC
Me
+
Ph
X
X
-
X
C
11a-c
O
N
O
_
O
Me
7a-c + 8
Ph
X
PC
N
Me
6a-c
Me
Ph
Ph
Ph
9a-c
10a-c
Scheme 2
Logically, it can be expected the formation of [3 + 3] cycloadducts
9a–c as a formal step from the reaction of 1 with 6a–c (Scheme
2). In the next step of the sequence, the oxygen with its bond
electrons in 9a–c could then attack the C = X of another molecule
of 6a–c forming the salt 10a–c (Scheme 2). Intramolecular
cyclisation process then occurred accompanied by loss of the X-
C=O 11a–c, thus generating the two isolated products 7a–c and
diphenyl acetylene (8) as shown in Scheme 2.
In a different manner, the reaction of nitrone 1 with
dibenzoyl acetylene (12) in refluxing toluene produced the
stereoisomeric pyrrole 13 in 70% yield (Scheme 3). Mass
spectra and elemental analysis established the molecular
formula of 13 as C35H31NO3. The IR spectrum of 13 did not
indicate the absorption of any hydroxyl or amino group (see
the experimental). However, a broad band at n = 1710–1685
cm-1 was assigned to the carbonyl groups. The 1H NMR
spectrum showed a singlet at d = 3.64 assigned to the NMe
protons. The other methyl protons present in the main nitrone
1 disappeared and a singlet at d = 4.20 related to the presence
of the CH2-pyrrole protons. NOE experiments confirmed the
proposed structure, since saturation of the CH2 of pyrrole
protons causes an enhancement of the ethano-bridge protons,
which are also enhanced during irradiation of the NMe protons.
COSY C H showed that the CH2 protons have a correlation
with C-5 (d = 80.0) and C-3 (d = 141.4). The carbonyl carbon
signals resonated in the 13C NMR spectrum of 13 at two
different values (d = 176.7 and 191.4). For the mechanism of
the formation of 13, we propose that the tautomer 4 initially
attacks the activated triple bond of the dipolarophile 12 in a
Michael-type reaction, thus resulting in the formation of the
salt 14. That intermediate would be found in tautomerism
as in 15 (Scheme 3). In previous consequences9b of similar
reactions such as the reaction between 1 and dimethyl
acetylenedicarboxylate, the final step involves elimination of
water. In our case, the reaction of 1 with dibenzoyl ethylene
proceeds by the regioselective rearrangement of benzoate
anion by the pathway shown in Scheme 3.
Conclusion
Nitrones derived from paracyclophanyl group still show
new chemistry towards various dipolarophiles in a different
reactivity compared to the classical aromatic system.
Therefore much work has to be done for more investigation of
the reactivity of nitrone 1 towards another diepolarophiles.
Me
Me
-
N
N
+
O
toluene
+
PhCO
COP h
COP h
O
COP h
Me
O
reflux, 8 h
12
Ph
13 (70%)
1
COP h
HC
-
C
COP h
+
COP h
+
N
Me
-
PC
N
O
PC
HO
Me
15
14
Scheme 3
PAPER: 07/4688

JOURNAL OF CHEMICAL RESEARCH 2007 453
J9a',9s' = –13.6, J9a',10a' = 10.8, J9a',10s' = 3.0, J9s',10a' = 5.0, J9s',10s' = 10.5,
J10a',10s' = –13.0 Hz; 13C NMR: δ = 25.8 (q, 5-Me), 27.4 (q, C-2'), 29.8
(q, 1-NMe), 33.4 (t, C-9'), 34.6 (t, C-10'), 35.0 (t, C-1'), 74.2 (s, C-5),
109.0 (s, C-3), 125.8, 127.4 (d, para Ph–H), 128.0, 128.2 (d, meta-2
Ph–CH), 129.0, 129.6 (d, ortho-2 Ph–CH), 131.2 (d, C-5'), 131.5 (d,
C-7'), 132.0 (d, C-12'), 133.2 (d, C-16'), 133.6 (d, C-13'), 134.4 (d,
C-15'), 136.7 (C-4), 138.0 (s, C-4'), 138.5 (d, C-8'), 139.0, 139.6 (Ph–C),
140.0 (s, C-6'), 140.2 (s, C-11'), 140.6 (s, C-14'), 141.8 (s, C-3'), 182.0
(C-2); IR nmax (KBr): 3050–3008 cm-1 (Ar-CH, s), 2940–2860 (aliph.-
CH, m), 1315, 1100 (s, C=S), 1610, 1130 (N–O, s); UV (CH3CN): lmax
(log e) 380 nm (3.8); m/z (%): 485 [M+] (100), 470 (16), 455 (18), 380
(22), 205 (40) 178 (22), 158 (20), 142 (24), 118 (60), 91 (20), 77 (40),
44 (32). Anal. Calcd for C34H31NS (485.70): C, 84.08; H, 6.43; N, 2.88;
S, 6.60 Found: C, 84.20; H, 6.40; N, 2.95; S, 6.52.
[1,5-Dimethyl-3,4-diphenyl-5-([2.2]paracyclophan-4-yl)-1,5-
dihydropyrrol-2-ylidene]malononitrile (7c): (0.31 g, 75%) obtained
as yellow crystals (methanol), Rf = 0.2 (toluene), m.p. 200°C;
1H NMR: δ = 1.52 (s, 3 H, 5-Me), 2.80 (s, 3 H, NMe), 2.90 (ddd,
1 H, 2'-Ha, ethano bridge), 3.00 (ddd, 1 H, 1'-Ha, ethano bridge), 3.10
(ddd, 1 H, 9'-Hs, ethano bridge), 3.18 (ddd, 1 H, 10'-Ha, ethano bridge),
3.20-3.25 (m, 2 H, 1'-Hs, 10'-H, ethano bridge), 3.32-3.36 (m, 1 H,
9'-Ha, ethano bridge) 3.40 (ddd, 1 H, 2'-Hs, ethano bridge), 6.38 (dd,
1 H, 12'-H, PC–H), 6.52 (dd, 1 H, 13'-H, PC–H), 6.60–6.66 (m, 3 H,
7'-, 15'-, 16'-H, PC–H), 6.75 (d, 1 H, 5'-H, PC–H), 6.90–7.00 (m, 1 H,
8'-H, PC–H), 7.08–7.16 (m, 5 H, Ph–H), 7.40-7.48 (m, 3 H, Ph–H),
7.60–7.66 (m, 2 H, Ph–H); JHH in the paracyclophane fragment: J5',7'
= 1.8, J7',8' = 8.0, J12',13' = 8.2, J12',16' = 2.1, J13',15' = 2.0, J15',16' = 8.0,
J1a',1s' = –13.0, J1a',2a = 10.5, J1a',2s' = 3.9, J1s',2a' = 4.0, J1s',2s' = 10.0,
J2a',2s' = –13.4, J9a',9s' = –13.6, J9a',10a' = 10.4, J9a',10s' = 3.0, J9s',10a' = 5.0,
J9s',10s' = 10.6, J10a',10s' = –13.2 Hz; 13C NMR: δ = 25.4 (q, 2-Me), 26.6
(q, C-2'), 32.4 (q, 1-NMe), 33.2 (t, C-9'), 34.9 (t, C-10'), 35.4 (t, C-1'),
48.0 (q, =C(CN)2), 73.8 (s, C-5), 113.0, 113.6 (q, CN), 118.0 (s, C-3),
127.0, 128.0 (d, para Ph–H), 128.3, 128.7 (d, meta-2 Ph–CH), 129.6,
129.8 (d, ortho-2 Ph–CH), 131.0 (d, C-5'), 131.4 (d, C-7'), 132.4
(d,C-12'),133.2(d,C-16'),133.6(d,C-13'),134.0(d,C-15'),134.6(C-4),
138.1 (s, C-4'), 138.8 (d, C-8'), 139.4, 139.8 (Ph–C), 140.0 (s, C-6'),
140.4 (s, C-11'), 140.5 (s, C-14'), 140.4 (s, C-3'), 185.0 (C-2); IR nmax
(KBr): 3090–3015 cm-1 (Ar–CH, s), 2960–2820 (aliph.-CH, m), 2220-
2210 (CN, vs), 1612, 1120 (N–O, s); UV (CH3CN): lmax (log e) 300
nm (3.2); m/z (%): 518 [M + 1] (26), 517 [M+] (80), 502 (14), 488 (22),
413 [M-C(CN)2] (100), 282 (34), 260 (22), 218 (50), 178 (36), 144
(20), 118 (20), 91 (32), 77 (62). Anal. Calcd for C37H31N3 (517.68): C,
85.85; H, 6.04; N, 8.12. Found: C, 86.00; H, 6.10; N, 8.08.
Experimental
General procedure
Melting points: Kofler hot stage, uncorrected. NMR: Bruker AM-400,
solvent: CDCl3, internal standards: TMS (δ = 0.00) for 1H, CDCl3
(δ = 77.05) for 13C. The results of NOE difference experiments are
given in the form: irradiated signal→ enhanced signal. The spin
systems of both CH2CH2 bridges in compounds 7a–c and 13 were
also fully analysed. Chromatography columns were packed with
silica gel 7714 (Merck). For preparative layer chromatography (PLC),
glass plates (20 cm x 48 cm) were covered with a slurry of silica gel
Merck PF254 and the solvents listed for development and air-dried.
Zones were detected by the quenching of indicator fluorescence upon
exposure to 254 nm UV light. Elemental analyses were performed
at the Institut für Anorganische und Analytische Chemie, Technische
Universität Braunschweig. MS: Finnigan MAT 8430 spectrometer at
70 eV. IR: Nicolet 320 FT-IR with KBr pellets and paraffin films.
(E)-N-[2-([2.2]Paracyclophan-4-yl)ethylidene]methylamine-N-oxide
(1) was synthesised by the procedure mentioned in ref. 9a. 2,3-
Diphenylcyclopropenone (6a) was bought from Fluka. 2,3-
Diphenylcyclopropen-1-thione (6b) and 2-(2,3-diphenylcycloprop-
2-enylidene)-malononitrile (6c) were prepared according to ref. 19,
whereas dibenzoyl acetylene (12) was prepared according to ref. 20.
Reaction of nitrone 1 with cyclopropenones 6a–c
(6): A mixture of 1 (279 mg, 1 mmol) and cyclopropenones 6a–c
(2 mmol) was heated at reflux in toluene (100 ml) for 2–3 d (the
reaction was followed by TLC analysis). The solvent was evaporated
in vacuo and the residue was column chromatographed on silica gel
with toluene to give 7a–c as the slowest migrating zones and 8 as the
fastest migrating zones. The products 7a–c were recrystallised from
the stated solvents.
1,5-Dimethyl-3,4-diphenyl-5-([2.2]paracyclophan-4-yl)-1,5-
dihydropyrrol-2-one (7a): (0.20 g, 60%), obtained as colourless
crystals, Rf = 0.3 (toluene), m.p. 240°C; 1H NMR (400 MHz, CDCl3)
1H NMR: δ = 1.62 (s, 3 H, 5-Me), 2.62 (s, 3 H, NMe), 2.80 (ddd,
1 H, 2'-Ha, ethano bridge), 2.85 (ddd, 1 H, 1'-Ha, ethano bridge),
2.92 (ddd, 1 H, 9'-Hs, ethano bridge), 3.20 (ddd, 1 H, 10'-Ha, ethano
bridge), 3.10-3.14 (ddd, 1 H, 1'-Hs, ethano bridge), 3.13 (ddd, 1 H,
10'-Hs, ethano bridge), 3.22-3.24 (m, 1 H, 9'-Ha, ethano bridge),
3.32 (ddd, 1 H, 2'-Hs, ethano bridge), 6.35 (dd, 1 H, 12'-H, PC–H),
6.52 (dd, 1 H, 13'-H, PC–H), 6.60 (m, 2 H, 7'-, 15'-H, PC–H), 6.73
(dd, 1 H, 16'-H, PC–H), 6.85 (d, 1 H, 5'-H, PC–H), 7.03–7.08 (m, 1
H, 8'-H, PC–H), 7.05 (td, 2 H, Ph–H), 7.10–7.13 (m, 2 H, Ph–H),
7.34 (dd, 2 H, Ph–H, J = 8.0, 1.2 Hz, Ph–H), 7.35–7.40 (m, 2 H,
Ph–H), 7.47–7.54 (m, 2 H, Ph–H); JHH in the paracyclophane
Reaction of nitrone 1 with dibenzoyl acetylene (12): A mixture of
1 (279 mg, 1 mmol) and 12 (234 mg, 1 mmol) was heated at reflux
in toluene (300 ml) for 8 h. The solvent was evaporated in vacuo and
the residue was applied on palates chromatography (silica gel) with
dichloromethane to give 13.
fragment: J5',7' = 1.7, J7',8' = 8.0, J12',13' = 8.0, J12',16' = 2.1, J13',15'
2.0, J15',16' = 7.8, J1a',1s' = –13.1, J1a',2a = 10.4, J1a',2s' = 3.9, J1s',2a'
=
=
4.1, J1s',2s' = 10.2, J2a',2s' = –13.6, J9a',9s' = –13.4, J9a',10a' = 10.6, J9a',10s'
= 3.0, J9s',10a' = 5.2, J9s',10s' = 10.5, J10a',10s' = –13.2 Hz; 13C NMR:
δ = 25.4 (q, 5-Me), 26.6 (q, C-2'), 29.4 (q, 1-NMe), 33.2 (t, C-9'),
34.9 (t, C-10'), 35.4 (t, C-1'), 73.8 (s, C-5), 108.6 (s, C-3), 125.0,
127.9 (d, para Ph–H), 128.1, 128.5 (d, meta-2 Ph–CH), 129.2,
129.3 (d, ortho-2 Ph–CH), 131.4 (d, C-5'), 131.6 (d, C-7'), 132.6 (d,
C-12'), 133.0 (d, C-16'), 133.7 (d, C-13'), 134.6 (d, C-15'), 136.8
(C-4), 138.1 (s, C-4'), 138.8 (d, C-8'), 139.4, 139.8 (Ph–C), 140.0 (s,
C-6'), 140.4 (s, C-11'), 140.6 (s, C-14'), 140.8 (s, C-3'), 171.2 (C-2);
IR nmax (KBr): 3060–3000 cm-1 (Ar-CH, s), 2960–2860 (aliph.-CH,
m), 1685 (C=O, vs), 1610, 1130 (N–O, s); UV (CH3CN): lmax (log e)
350 nm (3.2); m/z (%): 469 [M+] (86), 440 (12), 365 (50), 336 (8) 308
(10) 293 (14), 261 (12), 218 (74), 202 (10), 178 (16), 158 (20), 144
(24), 118 (100), 91 (22), 77 (42), 44 (28). Anal. Calcd for C34H31NO
(469.63): C, 86.96; H, 6.65; N, 2.98. Found: C, 86.80; H, 6.50; N,
3.05.
4-Benzoyl-1-methyl-2-([2.2]paracyclophan-4-yl)-2,3-dihydro-
pyrrol-2-yl benzoate (13): (0.36 g, 70%) obtained as colourless
needles (ethanol), Rf
= 0.3, (dichloromethane), mp 290°C;
1H NMR: δ = 2.70 (ddd, 1 H, 2'-Ha, ethano bridge), 2.83–2.90 (m, 2 H,
9'-Hs, 1'-Ha, ethano bridge), 3.10–3.16 (m, 2 H, 1'-Hs, 10'-Ha, ethano
bridge), 3.20–3.26 (m, 2 H, 9'-Ha, 10'-Hs, ethano bridge), 3.35 (ddd,
1 H, 2'-Hs, ethano bridge), 3.64 (s, 3 H, NMe), 4.20 (s, 2 H, CH2-
pyrrole), 6.400 (m, 1 H, 12'-H, PC–H), 6.52 (d, 4 H, 13'-, 7'-, 15'-,
16'-H, PC–H), 6.73 (dd, 1 H, 8'-H, PC–H), 6.78 (d, 1 H, 5'-H, PC–
H), 7.20–7.25 (m, 2 H, Ph-meta-H), 7.27-7.32 (m, 4 H, Ph–H), 7.37
(s, 1 H, pyrrole-2-H), 7.50–7.55 (m, 2 H, Ph-ortho-H), 7.82–7.85
(m, 2 H, Ph-ortho-H); 13C NMR: δ = 27.2 (t, C-2'), 33.2 (t, C-9'), 34.9
(t, C-10'), 35.4 (t, C-1'), 45.3 (q, NMe), 48.5 (CH2-2), 80.0 (s, C-5),
112.1 (d, C-3), 125.0, 127.9 (d, para Ph–H), 128.1, 128.5 (d, meta-
2 Ph–CH), 129.2, 129.3 (d, ortho-2 Ph–CH), 131.4 (d, C-5'), 131.6
(d, C-7'), 132.6 (d, C-12'), 133.0 (d, C-16'), 133.7 (d, C-13'), 134.6 (d,
C-15'), 138.1 (s, C-4'), 138.8 (d, C-8'), 139.4, 139.8 (Ph-C), 140.0 (s,
C-6'), 140.4 (s, C-11'), 140.6 (s, C-14'), 141.4 (s, C-3'), 142.7 (s, C-2),
176.7 (OCOPh), 191.4 (COPh); IR nmax (KBr): 3060–3000 cm-1
(Ar-CH, s), 2960–2860 (aliph.-CH, m), 1710–1685 (C=O, vs), 1610
(C=N, s); UV (CH3CN): lmax (log e) 270 nm (2.8); m/z (%): 513
[M+] (100), 495 (14), 466 (8), 408 (14), 390 (16), 363 (14), 303 (10),
286 (12), 133 (20), 105 (60), 91 (18), 77 (40), 57 (18). Anal. Calcd
for C35H31NO3 (513.64): C, 81.84; H, 6.08; N, 2.73. Found: C, 81.70;
H, 6.18; N, 2.70.
1,5-Dimethyl-3,4-diphenyl-5-([2.2]paracyclophan-4-yl)-1,5-
dihydropyrrol-2-thione (7b): Obtained (0.32 g, 66%) as pale yellow
1
crystals (ethanol), Rf = 0.6, toluene, m.p. 280°C; H NMR: δ = 1.60
(s, 3 H, 5-Me), 2.70 (s, 3 H, NMe), 2.69 (ddd, 1 H, 2'-Ha, ethano
bridge), 2.80 (ddd, 1 H, 1'-Ha, ethano bridge), 2.90 (ddd, 1 H, 9'-Hs,
ethano bridge), 3.20 (ddd, 1 H, 10'-Ha, ethano bridge), 3.30 (ddd, 1
H, 1'-Hs, ethano bridge), 3.13 (ddd, 1 H, 10'-Hs, ethano bridge), 3.22–
3.24 (m, 1 H, 9'-Ha, ethano bridge), 3.32 (ddd, 1 H, 2'-Hs, ethano
bridge), 6.30 (dd, 1 H, 12'-H, PC–H), 6.50 (dd, 1 H, 13'-H, PC–H),
6.54 (dd, 1 H, 7'-H, PC–H), 6.65 (m, 1 H, 15'-H, PC–H), 6.70 (dd,
1 H, 16'-H, PC–H), 6.83 (d, 1 H, 5'-H, PC–H), 7.03–7.08 (m, 1 H, 8'-H,
PC–H), 7.10 (td, 2 H, Ph–H), 7.15–7.18 (m, 2 H, Ph–H), 7.36 (dd,
2 H, Ph–H, J = 8.0, 1.2 Hz, Ph–H), 7.40–7.50 (m, 2 H, Ph–H), 7.52–
7.56 (m, 2 H, Ph–H); JHH in the paracyclophane fragment: J5',7' = 1.6,
J7',8' = 7.8, J12',13' = 8.0, J12',16' = 2.1, J13',15' = 1.8, J15',16' = 7.8, J1a',1s' = –
12.8, J1a',2a = 10.6, J1a',2s' = 4.0, J1s',2a' = 4.0, J1s',2s' = 10.2, J2a',2s' = –13.5,
Prof Dr Ashraf A Aly thanks DAAD foundation for its
financial support.
Received 7 June 2007; accepted 23 July 2007
Paper 07/4688 doi: 10.3184/030823407X236363
PAPER: 07/4688

454 JOURNAL OF CHEMICAL RESEARCH 2007
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(a) A.A. Aly, H. Hopf and L. Ernst, Eur. J. Org. Chem. 2000, 3021;
(b) A.A. Aly, S. Ehrhardt, H. Hopf, I. Dix and P.G. Jones, Eur. J. Org.
Chem., 2006, 335.
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PAPER: 07/4688