Design and synthesis of novel propellanes by using claisen rearrangement and ring-closing metathesis as the key steps

Article abstract of DOI:10.1002/chem.200501366

Novel hexacyclic caged compounds are prepared by a combination of Claisen rearrangement and ring-closing metathesis (RCM). Additionally, a Grignard reaction in conjugation with RCM produced intricate hexacyclic caged molecules.

Full text of DOI:10.1002/chem.200501366

DOI: 10.1002/chem.200501366
Design and Synthesis of Novel Propellanes by Using Claisen Rearrangement
and Ring-Closing Metathesis as the Key Steps
[
a]
Sambasivarao Kotha* and Mirtunjay Kumar Dipak
Abstract: Novel hexacyclic caged compounds are prepared by a combination of
Claisen rearrangement and ring-closing metathesis (RCM). Additionally, a
Grignard reaction in conjugation with RCM produced intricate hexacyclic caged
molecules.
Keywords: cage
Claisen rearrangement · metathesis ·
polycycles
compounds
·
Introduction
Caged polycyclic molecules play an important role in the
[1]
design and synthesis of natural and non-natural products.
Lack of conformational mobility, their molecular symme-
[
2a]
try, and their intricate molecular structure prompted us to
synthetically investigate these compounds. They are also
[2b]
useful building blocks for high-energy materials.
In con-
nection with our interest in the preparation of annulated
polyquinane we have prepared diallylated tetracyclic dione,
Inspection of the molecular models revealed that the pres-
ence of the C1ÀC7 bond in pentacyclic system 3 (Scheme 2)
4
,11 5,9
3,6-diallyltetracyclo[6.3.0.0 .0 ]undecan-2,7-dione (1) by
would force the two allyl groups in close proximity; howev-
using fragmentation methodology, which involves a four-
step sequence starting with 1,3-cyclopentadiene and 1,4-ben-
[3–5]
zoquinone.
It was anticipated that the two allyl groups
present in 1 would undergo ring-closing metathesis (RCM)
to generate a new novel pentacyclic system 2 (Scheme 1).
Scheme 2. Retrosynthetic analysis of hexacyclic propellane.
Scheme 1. Nonparticipation of allyl groups in RCM under G-Iand G-II
conditions.
er, the two allyl groups are far apart in tetracyclic system 1,
which is not suitable for RCM. It appears that the transan-
nular “proximity effect” between the two carbonyl groups in
1 is responsible for hemiketal formation instead of the ex-
pected diol during the allyl and vinyl Grignard addition se-
However, we observed that even under forcing reaction con-
ditions compound 1 failed to give a RCM product with
[6,7]
[1b]
Grubbs first- and second-generation catalysts.
quence.
Results and Discussion
[
a] Prof. S. Kotha, M. K. Dipak
Indian Institute of Technology
Bombay, Powai, Mumbai-400 076 (India)
Fax : (+91)22-2572-3480
As a result of the conformation of pentacyclic system 3, in
which the two allyl groups are much closer in space, we rea-
soned that this system may undergo RCM to generate a new
E-mail: srk@chem.iitb.ac.in
4446
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 4446 – 4450

FULL PAPER
[8]
hexacyclic propellane, system 4. Retrosynthetic analysis of
(Scheme 2) indicates that the required diallylated pentacy-
4
clic dione 3 could be obtained from [2+2] photocycloaddi-
tion of adduct 10, produced by Diels–Alder (DA) cycloaddi-
tion of 2,3-diallyl-1,4-benzoquinone with 1,3-cyclopenta-
diene (Scheme 3).
Scheme 4. [2+2] photocycloaddition, RCM with G-I, Pd-catalyzed hydro-
A
H
R
N
genation and RCM with G-I, IBX-mediated dehydrogenation (IBX = o-
iodoxybenzoic acid), [6+2] or [2+2] photocycloaddition, and Pd-cata-
lyzed hydrogenation.
cloaddition gave compound 14, reported by the Kushner
[15]
et al.
The initial observation that the tetracyclic system 1 did
not undergo RCM could be turned into an exciting opportu-
nity to design new caged systems, for example, a double
Grignard reaction (GR) with allyl magnesium bromide
Scheme 3. Base-catalyzed allylation of 1,4-hydroquinone, o-Claisen rear-
rangement, MnO
tadiene.
2
oxidation, and Diels–Alder reaction with 1,3-cyclopen-
[16,17]
would be expected to give 15. RCM
of this tetrallylated
Thus, the preparation of diallyl benzoquinone 9 begin
derivative 15 in principle can generate the hexacyclic system
16 with two new additional rings (Scheme 5).
[9]
with 1,4-hydroquinone (5). Diallylation of hydroquinone
followed by Claisen rearrangement gave two rearranged al-
lylated hydroquinones 7 and 8 in a 1:1 ratio which could be
[10]
separated by column chromatography.
Oxidation of the
2
,3-diallylated derivative 7 with MnO gave 2,3-diallyl-1,4-
2
benzoquinone (9) in 66% isolated yield after column chro-
matography. Cycloaddition of 9 with freshly cracked 1,3-cy-
clopentadiene at 0–108C produced low melting DA adduct
1
0. The structure of the DA adduct has been established
Scheme 5. Allyl Grignard addition to 1 followed by RCM.
1
based on high field H NMR spectroscopy (400 MHz) and is
further supported by C NMR spectral data (100 MHz, d=
1
3
3
0.7, 48.2, 48.7, 48.9, 116.6, 133.3, 135.1, 148.6, 198.1 ppm).
The stereochemistry of the DA product was expected to
To prepare the hexacyclic caged system 16, the diallyl
dione 1 was treated with the excess amount of allyl magnesi-
um bromide, generating triallyated hemiketal 17 instead of
the tetrallylated derivative 15. The proximity of the carbonyl
groups is responsible for hemiketal formation. In view of
be endo and this assumption has been confirmed by the pho-
tochemical behavior of the DA adduct, which undergoes a
smooth [2+2] photocycloaddition upon exposure to light.
The pentacyclic system 3 has displayed the required number
of signals in the C NMR spectrum (100 MHz, d=30.2,
[11]
[18]
earlier observations this result is not surprising. The struc-
13
ture of pentacyclic hemiketal derivatives 17 and 19
1
3
41.4, 41.5, 43.7, 54.1, 55.6, 118.6, 132.7, 213.0 ppm).
(Scheme 6) has been firmly established by C NMR spectral
Having prepared the pentacyclic dione 3, the stage was
set for RCM. Exposure of compound 3 to Grubbs first-gen-
[6]
eration catalyst produced hexacyclic propellane 4 in 90%
yield after column chromatography. Additional proof of the
structure has been obtained by its chemical conversion to
the known hexacyclic system 11 (Scheme 4). The spectral
properties of the compound obtained by this route are iden-
[12]
tical to that in the reported data. Alternatively, compound
1 was also prepared by another sequence involving the in-
1
termediates 12 and 13.
Thus, the DA adduct 10 underwent RCM
[13]
to generate
the tetracyclic derivative 12 in 70% yield. IBX-mediated de-
[14]
hydrogenation
followed by [2+2] (or [6+2]) photocy-
Scheme 6. Allyl and vinyl Grignard addition to 1 followed by RCM.
Chem. Eur. J. 2006, 12, 4446 – 4450
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4447

S. Kotha and M. K. Dipak
data. In particular, the presence of a signal at d=115.6 ppm
Conclusion
13
in the C NMR spectrum of 17 indicates the carbon atom
attached to two oxygen atoms. Molecular models indicate
that the formation of the hemiketal did not aid in bringing
the two initial allyl groups closer (Figure 1). RCM of triallyl
compound 17 gave 18 as a sole product.
We have shown that Claisen rearrangement in combination
with RCM provides a useful method for the synthesis of
hexacyclic caged propellanes such as 4, which is suitable for
[19]
studying stereoelectronic effects. This methodology opens
up a new route to novel caged compounds of higher order
ring systems for example; compound 1 may be an ideal can-
didate to study the cross-metathesis reaction. A Grignard re-
action in combination with RCM gave access to polycyclic
caged ether derivatives (e.g. 18 and 20). These two ap-
proaches clearly demonstrate that RCM in combination
with other carbon–carbon bond-forming processes, such as
Claisen rearrangement and the Grignard reaction, provide
exciting opportunities to create novel molecular frames. We
have also demonstrated that the presence of suitably dis-
posed olefinic moieties at appropriate distance is necessary
for the success of RCM. The strategy demonstrated here has
distinct advantages. The cycloaddition reaction and RCM
protocol have mostly been employed without the need for
protecting groups. Expansion of these strategies to other in-
tricate molecular frames will be reported in near future.
Along similar lines, addition of vinyl magnesium bromide
produced 20 from the corresponding hemiketal derivative
19 (Scheme 6). Later on, it was found that the optimization
by ChemDraw and distances between allyl-bearing carbon
atoms in 1, 3, and 17 were measured by Rasmol visualiza-
tion software (Figure 1). The distance between the allyl-
bearing carbon atoms in 1 (d =3.16 Š) is approximately
1
double the distance between the allyl-bearing carbon atoms
in 3 (d =1.57 Š). Even in hemiketal 17 (d =3.06 Š) this
3
17
distance has not decreased as much as that between the two
allyl groups present in 1. Participation of the allyl group in
ring formation in 3 and 17 clearly shows that the large sepa-
ration of allyl groups in 1 is responsible for our observa-
tions.
Experimental Section
General: Reactions involving organometallic species were carried out
under nitrogen by using oven-dried glassware and syringes. THF and
Et
2
O were distilled from sodium/benzophenone under nitrogen immedi-
. TLC was
ately prior to use. Dichloromethane was distilled over P
2
O
5
performed by using (10”5 cm) glass plates coated with Acmeꢁs silica gel
GF254 (containing 13% calcium sulphate as a binder). Flash-column
chromatography was performed by using Aceme silica gel (100–200
mesh). Solvents were concentrated at reduced pressure on a Büchi R-114
1
13
rotary evaporator. H NMR (300, 400 MHz) and C NMR (75, 100 MHz)
spectra were recorded at room temperature on Varian VXR 300 instru-
1
ments or AX 400 with TMS (d=0.0 ppm, H NMR spectra) and CDCl
(
3
1
3
d=77.0 ppm, C NMR spectra) as internal standards. IR spectra were
recorded on a Nicolet Impact-400 FTIR spectrometer. HRMS were de-
termined on a Micromass Q-Tof spectrometer.
Materials: Vinyl magnesium bromide (1m solution in THF) and Grubbs
first-generation catalyst were purchased from Aldrich, Milwaukee
(
USA).
,5-Diallyltricyclo[6.2.1.0 ]undeca-4,9-diene-3,6-dione (10): Cyclopenta-
diene (0.2 mL, 0.34 mmol) was added dropwise to a cooled solution of
,3-diallyl-1,4-benzoquinone 9 (60 mg, 0.32 mmol) at 08C in methanol
15 mL). At the end of the reaction (3.5 h, TLC monitoring), the solvent
2
,7
4
2
(
was evaporated under reduced pressure and the residue was purified by
silica gel column chromatography (3% EtOAc/petroleum ether) to give
1
0 (66 mg, 81.4% yield) as a thick yellow liquid. R
f
=0.45 (petroleum
): d=1.42–1.52 (dd, J
), 3.06–3.20 (m, 4H; 2”CH
ÀCH=CH
.24–3.26 (m, 2H; 2”CH bridge head), 3.52 (s, 2H; 2”CH ring junction),
.01–5.08 (m, 4H; 2”CH ), 5.66–5.76 (m, 2H; 2”CH
ÀCH=CH ÀCH=
), 6.00 ppm (s, 2H; CH=CH); C NMR (100 MHz, CDCl ): d=30.7,
8.2, 48.7, 48.9, 116.6, 133.3, 135.1, 148.6, 198.1 ppm; IR (neat): n˜ =3079
1
ether/EtOAc 9:1); H NMR (400 MHz, CDCl
3
1
=
J
3
5
2
=9.7 Hz, 2H; bridge CH
2
2
2
),
2
2
2
1
3
CH
4
2
3
(
9
C
=CH
15 cm
2
st), 2992 (=CH st), 1664 (C=O conjugated), 1608 (C=C st),
À1
(HC=CH d); HRMS (QTOF ES+): m/z: calcd for
+
17
H
18
O
2
Na: 277.1204; found: 277.1215 [M+Na] .
2
,6 3,10 5,9
1
,7-Diallylpentacyclo[5.4.0.0 .0 .0 ]undeca-8,11-dione (3): Tricyclic
dione 10 (125 mg, 0.49 mmol) was dissolved in dry EtOAc (500 mL) and
irradiated in a Pyrex immersion well by using an 125 W UV lamp (home-
made) for 1.5 h under nitrogen at RT. At the conclusion of the reaction
Figure 1. Distance between allyl-bearing carbon atoms in 1, 3, and 17,
d =3.16, d =1.57, and d17 =3.06 Š.
1 3
4448
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 4446 – 4450

Propellanes
FULL PAPER
[
15]
(
TLC monitoring), the solvent was evaporated under reduced pressure
to give 14 (46.8 mg, 78%) as an off-white solid. M.p. 110–1118C (lit.
m.p. 111–1128C).
and the residue was purified by silica gel column chromatography (5%
EtOAc/petroleum ether) to give 3 (80 mg, 80%) as a white crystalline
Triallyl pentacyclic hemiketal 17: A solution of tetracyclic dione 1
105 mg, 0.41 mmol) in diethyl ether (8 mL) was added dropwise to fresh-
ly prepared allyl magnesium bromide (327 mg, 2.45 mmol) in ether
10 mL) over a period of 10–15 min at RT under nitrogen. At the end of
the reaction (8 h, TLC monitoring), the mixture was quenched with satu-
rated aqueous NH Cl solution at 08C, and the resulting aqueous layer
was extracted with EtOAc (3”25 mL). The combined organic layers
were washed with brine, dried over anhydrous Na SO , and the solvent
1
solid. R
f
=0.39 (petroleum ether/EtOAc 9:1); m.p. 80–818C; H NMR
(
(
400 MHz, CDCl
3
): d=1.90–2.00 (dd, JAB =12.0, 11.0 Hz, 2H; bridge
), 2.18–2.26 (dd, J=9.0, 8.9 Hz, 2H; 2”CH bridge head), 2.47–2.55
ÀCH=CH
), 2.90 (s,
H; 2”CH, ring junction), 5.00–5.10 (m, 4H; 2”CH ), 5.50–
ÀCH=CH
); C NMR (100 MHz, CDCl ): d=
CH
2
(
(
m, 2H; 2”CH bridge), 2.74–2.79 (m, 4H; 2”CH
2
2
2
5
3
3
2
2
4
1
3
.60 ppm (m, 2H; 2”CH
0.2, 41.4, 41.5, 43.7, 54.2, 55.6, 118.6, 132.7, 213.0 ppm; IR (KBr): n˜ =
069 (=CH st), 2970 (=CH st), 1751 (C=O), 1636 (C=C st), 924 cm
2
2
ÀCH=CH
2
3
2
4
À1
evaporated under reduced pressure. The resulting residue was purified by
silica gel column chromatography (4% EtOAc/petroleum ether) to give
(
HC=CH d); HRMS (QTOF ES+): m/z: calcd for C17H O : 255.1385;
19 2
+
found: 255.1397 [M+H] .
1
f
7 (85.5 mg, 70%) as a white solid. R =0.71 (petroleum ether/EtOAc
4
,9 4,14 9,13
1
Hexacyclo[10.2.1.0 .0 .0 ]pentadeca-6-ene-3,10-dione (4): Grubbs
first-generation catalyst (10 mg, 5 mol%) was added to a solution of dia-
llyl pentacyclic dione 3 (100 mg, 0.39 mmol) in dry dichloromethane
4:1); m.p. 95–968C; H NMR (400 MHz, CDCl ): d=1.50–1.60 (m, 2H;
3
2”CH attached to the allyl-bearing carbon atoms), 1.60–1.90 (m, 2H;
bridge CH ), 2.00–2.20 (m, 2H; 2”CH bridge head), 2.30–2.50 (m, 8H;
2
(
15 mL) under argon at RT. At the end of the reaction (4 h, TLC moni-
3”CH ÀCH=CH , 2”CH bridge), 2.50–2.60 (m, 2H; 2”CH bridge adja-
2
2
toring), the solvent was evaporated by using a water bath and the residue
was purified by silica gel column chromatography (8% EtOAc/petroleum
cent to C=O), 3.30 (d, J=8.0 Hz, 1H; OH), 4.94–5.10 (m, 6H; 3”CH À
2
1
3
CH=CH ), 5.60–6.01 ppm (m, 3H; 3”CH -CH=CH );
2
2
2
C NMR
ether) to give 4 (80 mg, 90%) as a white crystalline solid. R
f
=0.25 (pe-
troleum ether/EtOAc 9:1); m.p. 109–1108C; H NMR (400 MHz, CDCl ):
d=1.81–1.89 (m, 2H; 2”CH bridge head), 1.90–2.04 (dd, J = J
), 2.30–2.40 (d, J=16 Hz, 2H; 2”CH bridge),
.60–2.70 (m, 4H; 2”CH
ÀCH=CH), 2.90 (d, J=1.6 Hz, 2H; 2”CH
(100 MHz, CDCl ): d=34.9, 35.1, 37.6, 39.1, 45.1, 46.0, 46.4, 46.5, 51.30,
51.34, 57.7, 60.6, 93.0, 115.6, 115.8, 116.3, 117.1, 135.4, 137.8, 138.5 ppm;
3
1
3
1
2
=
IR (KBr): n˜ =3134 (OH hemiketal), 1638 (C=C st), 1403 (ÀOÀ hemike-
À1
1
2
1 Hz, 2H; bridge CH
2
tal), 910 cm
(CÀH d); HRMS (QTOF ES+): m/z: calcd for
+
2
C H O Na: 321.1833; found: 321.1831 [M+Na] .
2
0
26
2
bridge adjacent to carbonyl group), 5.90 ppm (t, J=3 Hz, 2H; CH=CH);
Monoallyl hexacyclic hemiketal 18: Grubbs first-generation catalyst
6 mg, 5 mol%) was added to a solution of 17 (23 mg, 0.076 mmol) under
1
3
3
C NMR (100 MHz, CDCl ): d=23.8, 41.1, 43.0, 43.5, 51.9, 54.8, 126.1,
(
2
1
2
12.8 ppm; IR (KBr): n˜ =2930 (=CH st), 1741 (C=O), 1725 (C=C st),
argon at RT. At the end of the reaction (after 5 h, TLC monitoring), the
solvent was evaporated, and the resulting residue was purified by silica
gel column chromatography (5% EtOAc/petroleum ether) to give 18
À1
094 cm (HC=CH d); HRMS (QTOF ES+): m/z: calcd for C15
15 2
H O :
+
27.1072; found: 227.1068 [M+H] .
4
,9 4,14 9,13
Hydrogenation of hexacyclo[10.2.1.0 .0 .0 ]pentadeca-6-ene-3,10-
(
4
1
f
16 mg, 77%) as an off-white solid. R =0.60 (petroleum ether/EtOAc
dione (4): Palladium/charcoal (10%, 300 mg) was added to a solution of
1
:1); m.p. 58–598C; H NMR (400 MHz, CDCl
3
): d=1.60 (s, 2H), 1.70–
4
(11.3 mg, 0.05 mmol) in EtOAc (10 mL) under hydrogen (1 atm) at RT.
À
.90 (m, 2H), 1.90–2.10 (m, 2H; bridge CH
2
), 2.30–2.50 (m, 8H; 2”CH
2
At the end of the reaction (3 h, TLC monitoring), the reaction mixture
was filtered off by using a Celite pad. The solvent then evaporated under
reduced pressure and the residue was purified by silica gel column chro-
matography (5% EtOAc/petroleum ether) to give 11 (8 mg, 90%) as an
À
CH=CH, 2”CH
bridge adjacent to C O), 3.20 (s, 1H; OH), 5.00–5.10 (m, 2H; CH
CH
(
2
CH=CH
À
2
, 2”CH bridge), 2.60–2.70 (m, 2H; 2”CH
À
CH=
); C NMR
2
13
2
), 5.70–5.90 ppm (m, 3H; 2”CH=CH, CH
2
À
CH=CH
2
3
100 MHz, CDCl ): d=30.5, 34.0, 35.1, 37.7, 45.0, 46.7, 47.3, 48.3, 51.1,
[
12]
off-white solid. M.p. 67–688C (lit. m.p. 708C).
5
1.6, 60.5, 61.5, 91.6, 115.9, 116.2, 125.5, 129.2, 138.7 ppm; IR (KBr): n˜ =
1
13
À1
H and C NMR spectroscopic chemical shift values matched with litera-
3116 (OH hemiketal), 1638 (C=C st), 1400 (ÀOÀ hemiketal), 916 cm
[
12]
ture values.
(CÀH d); HRMS (QTOF ES+): m/z: calcd for C H O Na: 293.1517;
1
8
22
2
+
found: 293.1526 [M+Na] .
1
,4,4a,5,8,9a-Hexahydro-1,4-methanoanthracene-9,10-dione (12): Grubbs
first-generation catalyst (15 mg, 5 mol%) was added to a solution of tri-
cyclicdione 10 (160 mg, 0.62 mmol) in dry dichloromethane (15 mL)
under nitrogen and stirred at RT for 3.5 h. At the end of the reaction
Diallyl-monovinyl pentacyclic hemiketal 19: Vinyl magnesium bromide
(6 equiv, 1m solution in THF) was added dropwise to a solution of 1
(105 mg, 0.41 mmol) in dry THF (8 mL). Initially the addition was carried
out at RT, but after 3 h the reaction mixture was heated up to 508C for
the next 10 h. At the end of the reaction (TLC monitoring) the reaction
(
4 h, TLC monitoring), the solvent was evaporated and the residue was
purified by silica gel column chromatography (5% EtOAc/petroleum
ether) to give 12 (98 mg, 70%) as a white crystalline solid. R =0.35 (pe-
troleum ether/EtOAc 9:1); m.p. 126–1288C; H NMR (300 MHz, CDCl ):
d=1.40–1.50 (m, 2H; bridge CH ), 2.90 (m, 4H; 2”CH ), 3.20
dd, J=2.0, 1.0 Hz, 2H; 2”CH bridge head), 3.50 (dd, J=2.0, 1.0 Hz,
f
was quenched with a concentrated aqueous solution of NH Cl at 08C,
4
1
3
and the resulting aqueous layer was extracted with EtOAc (3”25 mL).
ÀCH=CH
2
2
2
The combined organic layers were then washed with brine and dried
over anhydrous Na SO . The solvent was evaporated under reduced pres-
(
2
4
2
2
4
H; 2”CH ring junction), 5.70 (s, 2H; CH=CH), 6.00 ppm (t, J=2.0 Hz,
sure and the resulting residue was purified by silica gel column chroma-
tography (5% EtOAc/petroleum ether) to give 19 as a white solid
1
3
H; norbornene CH=CH); C NMR (100 MHz, CDCl
3
): d=24.6, 48.1,
8.9, 49.6, 122.6, 135.3, 145.6, 198.3 ppm; HRMS (QTOF ES+): m/z:
(65 mg, 56%). R =0.65 (petroleum ether/EtOAc 4:1); m.p. 110–1118C;
f
+
1
calcd for C15
H
15
O
2
: 227.1077; found: 227.1072 [M+H] .
H NMR (400 MHz, CDCl ): d=1.60–1.70 (m, 2H), 1.70–2.00 (m, 2H;
3
[
14]
À
IBX-mediated dehydrogenation of 12: IBX (2 equiv) was added to a
solution of 12 (80 mg, 0.35 mmol) in DMSO under nitrogen and heated
at 60–658C. At the end of the reaction (3 h, TLC monitoring), the mix-
ture was extracted with EtOAc (3”10 mL) and the combined organic
bridge CH
2
), 2.1–2.4 (m, 6H; 2”CH bridge, 2”CH
2
CH=CH
2
), 2.50–
2.60 (m, 2H), 2.71–2.75 (m, 2H), 3.0 (s, 1H; OH), 4.92–5.12 (m, 4H; 2”
CH
2
ÀCH=CH ), 5.06–5.07 (dd, J = J =1.83 Hz, 1H; CH=CHH), 5.23–
2
1
2
5.28 (dd, J
CH=CH
(100 MHz, CDCl
1
2 2
= J = 1.53 Hz, 1H; CH=CHH), 5.61–5.90 (m, 2H; 2”CH
À
1
3
layers were washed with brine and dried over anhydrous MgSO
4
. Once
2
), 5.94–6.02 ppm (dd,
J
1
=
J
2
= 17.4 Hz, 1H); C NMR
dry, the solvent was evaporated under reduced pressure and the residue
was purified by silica gel column chromatography (5% EtOAc/petroleum
ether) to give 13 (67 mg, 85%) as a white crystalline solid. M.p. 116–
3
): d=34.9, 36.7, 37.6, 45.1, 46.6, 46.7, 46.8, 51.3, 52.7,
58.9, 60.4, 93.5, 112.3, 115.8, 115.9, 116.2, 137.9, 138.6, 138.7 ppm; IR
(KBr): n˜ =3119 (OH hemiketal), 1638 (C=C st), 1400 (ÀOÀ hemiketal),
[
15]
À1
1
178C (lit. m.p. 117–1188C).
[2+2] Photocycloaddition of 13: Dehydrogenated product 13 (60 mg,
.27 mmol) dissolved in EtOAc (150 mL) was irradiated in a Pyrex im-
911 cm (CÀH d); HRMS (QTOF ES+): m/z: calcd for C19
24 2
H O Na:
+
3
07.1674; found: 307.1672 [M+Na] .
ACHTREUNG
0
Monoallyl hexacyclic hemiketal 20: Grubbs first-generation catalyst
(5 mg, 5 mol%) was added to a solution of 19 (23 mg, 0.080 mmol) under
argon at RT. At the end of the reaction (after 5 h, TLC monitoring), the
solvent was evaporated by using a water bath and the resulting residue
was purified by silica gel column chromatography (6% EtOAc/petroleum
mersion well by using an 125 W UV lamp (homemade) for 5 h under
argon at RT. At the end of the reaction (TLC monitoring), the solvent
was evaporated under reduced pressure and the residue obtained was pu-
rified by silica gel column chromatography (5% EtOAc/petroleum ether)
Chem. Eur. J. 2006, 12, 4446 – 4450
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4449

S. Kotha and M. K. Dipak
ether) to give 20 (15.6 mg, 76%) as a white crystalline solid. R
f
=0.58
[7] M. Scholl, S. Ding, C. W. Lee, R. H. Grubbs, Org. Lett. 1999, 1, 953–
956.
1
(
petroleum ether/EtOAc 4:1); m.p. 98–998C; H NMR (400 MHz,
CDCl
3
): d=1.60 (brd, J=2.0 Hz, 2H), 1.90–2.08 (m, 2H), 2.12–2.24 (m,
), 5.70–
CH=CH); C NMR (100 MHz,
[8] a) D. Ginsburg, Propellanes Structure and Reactions, Verlag Chemie,
Weinheim, 1975; b) D. Ginsburg, Propellanes Structure and Reac-
tions (Sequel I), Department of Chemistry, Technion, Haifa, 1981;
c) D. Ginsburg, Propellanes Structure and Reactions (Sequel II), De-
partment of Chemistry, Technion, Haifa, 1985.
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[10] a) S. Kotha, K. Mandal, Tetrahedron Lett. 2004, 45, 9603–9605;
b) S. K. Chattopadhyay, B. K. Pal, S. Maity, Chem. Lett. 2003, 32,
2
5
H), 2.40–2.80 (m, 8H), 5.00–5.20 (m, 2H; 2”CH
.90 ppm (m, 3H; CH
2
ÀCH=CH
2
1
3
ÀCH=CH
2
,
2
3
CDCl ): d=35.2, 37.0, 37.9, 45.4, 46.1, 46.5, 48.0, 51.2, 52.7, 59.8, 60.0,
1
03.5, 116.0, 116.7, 132.7, 133.0, 138.8 ppm; IR (KBr): n˜ =3129 (OH hem-
À1
iketal), 1638 (C=C st), 1399 (ÀOÀ hemiketal), 905 cm (CÀH d); HRMS
(
20 2
QTOF ES+): m/z: calcd for C17H O Na: 279.1361; found: 279.1365
+
[
M+Na] .
1
190–1191.
[
[
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Acknowledgements
We thank the DST, New Delhi for the financial support and SAIF,
Mumbai for recording the spectroscopic data. M.K.D. thanks C.S.I.R.,
New Delhi for the award of the research fellowship. We thank Dr. E.
Manivannan for some initial experimentation.
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Received: November 3, 2005
Please note: Minor changes have been made to this manuscript since its
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4450
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Chem. Eur. J. 2006, 12, 4446 – 4450