Stereoselective synthesis of α,α′-spirane-bridged dibenzyl ligands

Article abstract of DOI:10.1080/00397910500186250

Benzylation in the α,α′-positions in the benzospirane, 2,2′-spirobiindane in a cis,cis manner has been effected from the corresponding diketone. Initial Grignard reactions and subsequent water elimination provided a stereoisomeric mixture of α,α′- alkylid

Full text of DOI:10.1080/00397910500186250

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Stereoselective Synthesis of
α,α′‐Spirane‐Bridged Dibenzyl
Ligands
Guixian Hu a , Christian Rømming a & Kjell Undheim
a
a Department of Chemistry , University of Oslo ,
Oslo, Norway
Published online: 18 Aug 2006.
To cite this article: Guixian Hu , Christian Rømming & Kjell Undheim (2005)
Stereoselective Synthesis of α,α′‐Spirane‐Bridged Dibenzyl Ligands, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:17, 2277-2288
To link to this article: http://dx.doi.org/10.1080/00397910500186250
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Synthetic Communicationsw, 35: 2277–2288, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500186250
Stereoselective Synthesis
of a,a0-Spirane-Bridged Dibenzyl Ligands
Guixian Hu, Christian Rømming, and Kjell Undheim
Department of Chemistry, University of Oslo, Oslo, Norway
Abstract: Benzylation in the a,a0-positions in the benzospirane, 2,20-spirobiindane in a
cis,cis manner has been effected from the corresponding diketone. Initial Grignard
reactions and subsequent water elimination provided a stereoisomeric mixture of
a,a0-alkylidene intermediates, which were stereoselectively hydrogenated to cis,cis-
dibenzyl derivatives. The structure of intermediates in the reaction sequence has
been ascertained by X-ray analyses.
Keywords: a,a0-cis,cis-Dibenzylspiranes, a,a0-disubstituted 2,20-bisindanes, spirane
bridge, stereoselective hydrogenation
INTRODUCTION
The rigid framework in small-ring spiranes provides a potentially useful
scaffold for attachment of configurationally highly oriented coordinating
functions as ligands for metal complexation and for stereochemically con-
trolled attachment of pharmacophoric groups useful in medicinal chemistry.
The two rings in the spirane are interconnected through a common ring
atom and have an orthogonal relationship. Functional groups in the same
relative positions in the two rings will have a pseudo-orthogonal relationship.
Hence, functional groups in spiro rings are highly directed in space. From
our attempts to develop methods for the preparation of functionalized
spiranes,[1–3] we herein describe synthesis of C2-symmetrical derivatives of
Received in the U.K. February 14, 2005
Address correspondence to Kjell Undheim, Department of Chemistry, University of
Oslo, N-0315, Oslo, Norway. Tel.: 47 22 85 5521; Fax: 47 22 85 5507; E-mail: kjell.
undheim@kjemi.uio.no
2277

2278
G. Hu, C. Rømming, and K. Undheim
the spiro[4.4]nonane system that has been additionally rigidified by benzene-
ring annulation. The target molecules are derivatives of 2,20-spirobiindane.
A spirane-bridged structure as in the bisarene A and the dibenzyl
analogue B in Scheme 1 are reminiscent of certain ligands for metallocenes.
The benzene and benzyl substituents are situated in the a,a0 positions to be
close to the spirocenter (Scheme 1).
RESULTS AND DISCUSSION
The substrate for benzoannulated spiranes was 2,20-spirobiindan-1,10-dione
(1) (Scheme 2). A synthesis of the diketone 1 dates back to 1972.[4] Indirect
chiral syntheses have been described.[5,6] We have adapted a recent
procedure for the preparation of the racemate using 2-ethoxycarbonylinda-
none as substrate.[5] The latter was benzylated by ethyl 2-bromomethylbenzo-
ate and the benzylated product cyclized and decarboxylated under strongly
acidic conditions.
In our first exploratory work, we have used racemic substrates. Nucleo-
philic substitutions in spiranes in the most desireable a position next to the
spirocenter is complicated by the neo-effect from the spirocenter. A method
for carbylation in the a-oxo position has been found by initial formation of
enol triflate and a subsequent Pd-mediated cross-coupling reaction.[2,3] For
the spirobiindanone to be triflated, a proton must first be removed from the
methylene indanone carbon followed by a transmittance of the charge through
the benzene ring to generate an enolate oxygen, which is to be triflated.
However, we failed to isolate any triflate using LDA and agents for triflation.
Attempts to introduce substituted methylene substituents under Wittig con-
ditions were unsatisfactory. Subsequently, successful reactions were run with
Grignard reagents providing the corresponding alcohols. Water elimination
from the alcohols provided the desired alkylidene derivatives. TLC was
used to monitor the reaction with benzylmagnesium bromide. Excess
reagent resulted in complete transformation of the diketone substrate 1.
The product was a mixture of the mono adduct 2 (39%) and the diol 3
(51%). The products were readily separated by chromatography. Acid
catalysis by p-toluenesulfonic acid in benzene at room temperature led to
water elimination. From the monoadduct 2, the two stereomeric alkylidene
Scheme 1.

a,a0-Spirane-Bridged Dibenzyl Ligands
2279
Scheme 2.
derivatives 4 and 5 were obtained in high yield and were separated by chro-
matography. The (E)-form 4 was the major isomer. Their stereochemistry
was ascertained by a single crystal X-ray analysis (Fig. 1). The analysis was
carried out on the minor isomer, which was found to have the (Z)-configuration
as in structure 5. Full stereoselectivity in the generation of cis,cis-a,a0-diaryl-
spiranes has been achieved by way of catalytic hydrogenation of the corre-
sponding a,a0-dienospiranes.[2,3] An endocyclic double bond was saturated in

2280
G. Hu, C. Rømming, and K. Undheim
Figure 1. ORTEP plot of compound 5. Ellipsoids are shown at 50% probability. For
clarity the hydrogen atoms are omitted.
this process. In the present case the double bond to be saturated is exocyclic.
A stereoselective reduction of the double bonds for formation of the cis or
cis,cis isomer is required.
The cis,cis configuration, however, leads to a significant repulsive inter-
action and is thermodynamically the least favorable structure of the three geo-
metrical isomers. For steric reasons, on heterogenous hydrogenation the less
sterically shielded face of a spirane ring becomes associated with the metal
catalyst. A subsequent transfer of hydrogen from the metal to the double
bond forces the substituent into a cis position. The double bond saturation was
effected with a mixture of the alkylidene isomers 4 and 5 over 10% palladium
on charcoal and hydrogen pressure 6 bar in methanol. One product was seen.
Either stereoisomeric alkylidene 4 and 5 would be expected to coordinate to
the hydrogen-bearing catalyst at the less-shielded face. In this process the
benzyl group is forced into the spirane, the product being the cis-benzyl
derivative 6.
For the introduction of a second benzyl group, the ketone 6 was treated
with benzylmagnesium bromide as previously described. The product was a
stereoisomeric mixture of the alcohols 7a and 7b. Formation of product 7a
as the major isomer would suggest preferential addition of the Grignard
reagent to the less-shielded carbonyl face. The isomers could be separated
by chromatography. The relative configuration of the major isomer was estab-
lished by a single crystal X-ray analysis as the cis,cis isomer 7a. Water elim-
ination from the epimeric alcohols 7a and 7b was effected in an almost
quantitative manner by p-toluenesulfonic acid in benzene at room tempe-
rature. The product was a mixture of the two benzylidene isomers 8. No
attempt was made to separate the isomer mixture. The latter was hydrogenated
over 10% palladium on charcoal under pressure at room temperature. The
reduction product was homogenous. According to our postulate, hydrogen

a,a0-Spirane-Bridged Dibenzyl Ligands
2281
transfer was to take place at the surface of the catalyst at the less-shielded face
of the olefinic bond, thereby providing structure 9. The assignment of cis,cis
stereochemistry is consistent with C2-symmetry of the molecule in the 1H and
13C NMR spectra. The benzyl groups in structure 9 are stacked, one above the
other, to provide a sandwich-like structure (Scheme 3).
In a slight preparative variation for the synthesis of the dibenzyl deriva-
tive 9, the isomeric alkylidene ketones 4 and 5 were reacted with benzylmag-
nesium bromide. Water elimination from the Grignard adduct was again
effected with p-toluenesulfonic acid to provide the dibenzylidene product 11
as a complex stereoisomeric mixture. Catalytic hydrogenation of the isomer
mixture furnished one single product, which was identical with the product
from the stepwise process in Scheme 1 and therefore has been tentatively
assigned cis,cis-dibenzyl spirane 9 configuration.
The relative stereochemistry of compounds 5 and 7a was determined by
single-crystal X-ray analyses. The ORTEP plots of the crystal structures are
shown in Figs. 1 and 2.
CONCLUSION
Substitutions in the a,a0 positions in the benzospirane, 2,20-spiroindane in a
cis,cis manner has been effected from the corresponding diketone by way of
benzyl Grignard reactions, water elimination, and catalytic hydrogenation of
the stereoisomeric a,a0-dibenzylidene derivatives. The structure of selected
Scheme 3.

2282
G. Hu, C. Rømming, and K. Undheim
Figure 2. ORTEP plot of compound 7a. Ellipsoids are shown at 50% probability. For
clarity the hydrogen atoms are omitted.
intermediates in the reaction sequence has been ascertained by X-ray analyses.
The products are potential ligands for sandwich metal complexes.
EXPERIMENTAL
The mass spectra under electron-impact conditions were recorded at 70eV (EI).
The spectra are presented as m/z (%, rel. int). The 1H NMR and the 13C NMR
data were recorded at 200 MHz and 300 MHz and CDCl3 was used as the
solvent. Dry dioxane and dry THF were distilled from sodium and benzophe-
none. IR spectra were recorded on a Nicolet Magda 550 instrument.
X-Ray Crystallographic Analysis for Compounds 5 and 7a
X-ray data were collected on a Siemens SMART CCD diffractometer[7] using
˚
graphite monochromated MoKa radiation (l ¼ 0.71073 A). Data collection
method: v-scan, range 0.68, crystal-to-detector distance 5 cm. Data reduction
and cell determination were carried out with the SAINT and XPREP
programs.[7] Absorption corrections were applied by the use of the SADABS
program.[8] The structures were determined and refined using the SHELXTL
program package.[9] The nonhydrogen atoms were refined with anisotropic
thermal parameters; hydrogen atoms were located from difference Fourier
maps and refined with isotropic thermal parameters. The following crystal
structure data have been deposited at the Cambridge Crystallographic Data
Centre and allocated the deposition number CCDC 262929 for compound 5
and CCDC 262930 for compound 7a.

a,a0-Spirane-Bridged Dibenzyl Ligands
2283
Crystal Data for C15H24N2O3 (5)
˚
M ¼ 280.36, monoclinic, P21, a ¼ 6.147(1), b ¼ 14.671(1), c ¼ 8.650(1) A,
3
23
˚
.
b ¼ 97.90(1)8, V ¼ 772.7(1) A , Z ¼ 2, Dx ¼ 1.205 Mg m
,
m ¼
0.084 mm21, T ¼ 105(2) K, measured 13,417 reflections in the 2u range
4.8–56.68, Rint ¼ 0.023. 277 parameters refined against 3789 F2, R ¼ 0.030
for Io . 2s(Io) and 0.031 for all data.
Crystal Data for C31H28O (7a)
˚
M ¼ 416.53, triclinic, P-1, a ¼ 10.657(1), b ¼ 13.559(1), c ¼ 17.153(1) A,
3
˚
a ¼ 74.41(1)8, b ¼ 78.43(1)8, g ¼ 75.42(1)8, V ¼ 1704.1(1) A , Z ¼ 4,
Dx ¼ 1.210 Mg m23, m ¼ 0.071 mm21, T ¼ 105(2) K, measured 19,272
.
reflections in the 2u range 10.2–52.78, Rint ¼ 0.037. 801 parameters refined
against 8913 F2, R ¼ 0.045 for Io . 2s(Io) and 0.068 for all data.
10-Benzyl-10-hydroxy-2,20-spirobiindan-1-one (2) and 1,10-Dibenzyl-
2,20-spirobiindane-1,10-diol (3)
Benzylmagnesium bromide in diethyl ether (5 mmol, 5 mL) was added slowly
at room temperature to a solution of 2,20-spirobiindan-1,10-dione (496 mg,
2.0 mmol) in THF (10 mL) under argon. The reaction was monitored by
TLC and stopped when all the starting material had been consumed. The
reaction was quenched by addition of water (4 mL) and the mixture
extracted with diethyl ether (three times). The organic phase was dried
(Na2SO4), the solvent distilled off, and the residual material subjected to
flash chromatography on silica gel using hexane–EtOAc 5 : 1 for separation
and purification of the two main products:
10-Benzyl-10-hydroxy-2,20-spirobiindan-1-one (2) was a white crystalline
material; yield 264 mg (39%), mp 156–1598C (hexane–CH2Cl2). HRMS:
Found [M–H2O] 322.1346. Calc. for [C24H20O2–H2O]: 322.1358;
n
max(film)/cm21 3549 (s), 3414 (s), 3064 (m), 3028 (s), 2918 (s), 2842 (m),
1699 (vs), 1606 (s), 1464 (m), 1455 (m), 1328 (m), 1287 (s), 1083 (m), 747 (m),
701 (m); dH (300 MHz, CDCl3) 2.83 (d, 1H, J 15.5 Hz), 3.14 (d, 1H, J
17.1 Hz), 3.23–3.36 (m, 3H), 3.81 (d, 1H, J 17.1 Hz), 4.14 (s, 1H), 6.96–
7.64 (m, 13H); dC (75 MHz, CDCl3) 37.2, 43.0, 43.3, 65.1 (Cspiro), 86.5
(C–OH), 124.0, 124.8, 125.1, 126.7, 126.9, 127.3, 127.9, 128.0, 128.8,
131.4, 135.5, 136.1, 136.4, 139.8, 146.8, 152.9, 209.2 (C55O); m/z (EI) 340
(0.4%, Mþ), 322 ([M–H2O], 4), 250 (19), 249 (100), 231 (15), 221 (6), 202
(8), 115 (7), 91 (29).
1,10-Dibenzyl-2,20-spirobiindane-1,10-diol (3) was
yield 440 mg (51%). HRMS: Found [M–H2O] 414.1979. Calc. for
a
white solid;

2284
G. Hu, C. Rømming, and K. Undheim
[C31H28O2–H2O]: 414.1984, Found: [M-2H2O] 396.1895. Calc. for
[C31H28O2–2H2O]: 396.1878; nmax(film)/cm21 3412 (vs), 3061 (s), 3026
(vs), 2932 (s), 1707 (vs), 1609 (m), 1495 (s), 1454 (vs), 1361 (s), 1220 (s),
1030 (m), 772 (m), 705 (s); dH (300MHz, CDCl3) and dC (75 MHz, CDCl3).
The spectra showed that this was a mixture of two stereoisomers because
there were three C–OH peaks, two Cspiro peaks, and no peak for an oxo
group in the 13C NMR spectra, and some peaks from OH and spiro-system in
the 1H NMR spectra; m/z (EI) 414 (2.4%, [M–H2O]), 396 (9%, [M–2H2O]),
323 (100), 305 (14), 245 (11), 231 (49), 215 (13), 202 (19), 91 (91).
10-Benzylidene-2,20-spirobiindan-1-one (4) and (5)
pTsOH (18 mg) was added to a solution of 10-benzyl-10-hydroxy-2,20-spiro-
biindan-1-one (2) (240 mg, 0.70 mmol) in benzene (40 mL) and the solution
stirred at room temperature overnight. The solution was washed with water
(three times), dried (Na2SO4), and evaporated to dryness. The stereoisomers
4 and 5 were separated from the residual material by flash chromatography
on silica gel using hexane–CH2Cl2 1 : 2.
10-(E-Benzylidene)-2,20-spirobiindan-1-one (4) was a white crystalline
material; yield 120 mg (53%), mp 117–1208C (hexane–CH2Cl2). HRMS:
Found M 322.1367. Calc. for C24H18O: 322.1358; nmax(film)/cm21 3054 (m),
3021 (m), 2936 (m), 2905 (m), 2840 (w), 1705 (vs), 1604 (s), 1461 (s),
1430 (m), 1324 (m), 1273 (s), 1207 (m), 1153 (m), 916 (m),736 (s), 715 (s);
dH (300 MHz, CDCl3) 3.06 (d, 1H, J 16.3 Hz), 3.85 (d, 1H, J 17.32 Hz),
3.54 (d, 1H, J 17.3 Hz), 3.56 (d, 1H, J 16.3 Hz), 6.08 (s, 1H), 6.84–692 (m,
1H), 7.26–7.09 (m, 8H), 7.40 (t, 1H), 7.50 (d, 1H), 7.62 (t, 1H), 7.81
(d, 1H); dC (75 MHz, CDCl3) 42.2, 44.6, 60.6 (Cspiro), 121.9, 124.6, 125.0,
126.2, 126.4, 127.2, 127.8, 128.3, 128.5, 128.7, 128.8, 135.0, 136.3, 137.4,
138.4, 145.3, 147.9, 153.1, 206.9 (C55O); m/z (EI) 322 (100%, Mþ), 305
(12), 303 (11), 245 (27), 231 (44), 215 (23), 202(19), 118 (9), 91 (11).
10-(Z-Benzylidene)-2,20-spirobiindan-1-one (5) was a white crystalline
material; yield 84 mg (37%), mp 116–1188C (hexane–CH2Cl2). HRMS:
Found M 322.1360. Calc. for C24H18O: 322.1358; nmax(film)/cm21 3052 (m),
3019 (m), 2931 (m), 2842 (w), 1705 (vs), 1604 (s), 1493 (m), 1461 (s),
1430 (m), 1321 (m), 1275 (s), 1265 (s), 1321 (m), 1275 (s), 1265 (s), 1207
(m), 1152 (m), 760 (s), 732 (s), 696 (s); dH (300 MHz, CDCl3) 2.98 (d, 1H,
J 16.2 Hz), 3.18 (d, 1H, J 18.0 Hz), 3.48 (d, 1H, J 16.2 Hz), 3.48 (d, 1H,
J 18.0 Hz), ꢀ 6.9 (m, 5H), 7.19–7.34 (m, 6H), 7.53–7.67 (m, 3H); dC
(75 MHz, CDCl3) 43.9, 47.8, 59.8 (Cspiro), 121.0, 121.1, 121.9, 124.9, 125.3,
126.7, 127.2, 127.6, 127.9, 128.7, 129.1, 135.1, 136.97, 137.03, 142.3, 143.0,
146.4, 152.3, 208.0 (C55O); m/z (EI) 322 (100%, Mþ), 321 (18), 305 (10),
303 (11), 245 (28), 231 (47), 215 (17), 149 (7), 118 (10), 91 (10).

a,a0-Spirane-Bridged Dibenzyl Ligands
2285
cis-10-Benzyl-2,20-spirobiindan-1-one (6)
A solution of the crude stereoisomeric mixture of 10-benzylidene-2,20-spiro-
biindan-1-one (4 and 5) (160 mg, 0.5 mmol) in methanol (20 mL) was hydro-
genated over 10% palladium on charcoal (30 mg) at 6 bar at room temperature
overnight. The catalyst was removed by filtration, the solvent evaporated and
the product obtained from the residual material by flash chromatography on
silica gel using hexane–EtOAc 6 : 1. The product was a white crystalline
solid; 130 mg (81%), mp 118–1218C (hexane–CH2Cl2). HRMS: Found
M 324.1498. Calc. for C24H20O: 324.1514; nmax(film)/cm21 3071 (m), 3023
(m), 2916 (m), 2849 (m), 1704 (vs), 1606 (s), 1475 (m), 1293 (m), 740 (m),
620 (s); dH (300MHz, CDCl3) 2.94–2.86 (m, 3H), 3.08 (s, 2H), 3.42 (t, 1H),
3.64 (d, 1H, J 15.8Hz), 6.53 (d, 1H, J 7.5 Hz), 6.89–7.40 (m, 10H), 7.52–
7.60 (dt, 1H, J1 1.2, J2 7.4 Hz), 7.73 (d, 1H, J 7.5 Hz); dC (75 MHz, CDCl3)
37.6, 43.6, 41.6, 57.3, 60.6 (Cspiro), 124.0, 124.4, 124.8, 125.9, 126.3, 126.9,
127.5, 127.9, 129.4, 134.7, 137.0, 139.6, 141.1, 144.4, 152.1, 207.4 (CO).
1,10-Dibenzyl-2,20-spirobiindan-1-ol (7a) and (7b)
Benzylmagnesium bromide in diethyl ether (2.0 M, 0.5 mL) was added
dropwise to a solution of cis-10-benzyl-2,20-spirobiindan-1-one (6) (116 mg,
0.36 mmol) in THF (2 mL) under argon. The reaction mixture was stirred
at room temperature overnight and was quenched by the addition of
10% aqueous NH4Cl (4 mL). The mixture was extracted with diethyl ether,
the organic extracts dried (NaSO4) and evaporated, and the products
separated and purified by flash chromatography on silica gel using hexane–
EtOAc 6 : 1.
cis,cis-1,10-Dibenzyl-2,20-spirobiindan-1-ol (7a) was a white crystalline
material; yield 80 mg (54%), mp 159–1618C (hexane–CH2Cl2). HRMS:
Found [M–H2O]þ 398.2028. Calc. for [C31H28O–H2O]þ: 398.2035;
n
max(film)/cm21 3565 (m), 3061 (s), 3025 (vs), 2934 (s), 2850 (m), 1602 (m),
1495 (vs), 1454 (m), 1265 (m), 1080 (m), 733 (vs), 697(vs); dH (300 MHz,
CDCl3) 1.76 (s, 1H, OH), 2.65–3.1 (m, 5H), 3.43–3.58 (m, 4H), 6.40
(d, 1H, J 7.5 Hz), 6.64 (d, 1H, J 7.5 Hz), 6.97–7.35 (m, 16H); dC (75 MHz,
CDCl3) 37.6, 38.2, 44.3, 44.7, 56.9, 63.8 (Cspiro), 123.9, 124.5, 124.7,
124.9, 125.7, 126.0, 126.3, 126.5, 127.8, 128.0, 129.3, 131.3, 137.0, 140.7,
141.3, 141.4, 146.8, 147.4; m/z (EI) 398 (8%, [M–H2O]þ), 326 (26), 325
(100), 307 (8), 232 (8), 209 (5), 217 (17), 205 (7), 193 (10), 115 (8), 91 (35).
cis,trans-1,10-Dibenzyl-2,20-spirobiindan-1-ol (7b) was a white crystalline
material; yield 38 mg (25%), mp 178–1828C (hexane–CH2Cl2). HRMS:
Found [M–H2O]þ 398.2042. Calc. for [C31H28O–H2O]þ: 398.2035;
n
max(film)/cm21 3567 (s), 3063 (s), 3025 (vs), 2931 (s), 2848 (m), 1604 (m),

2286
G. Hu, C. Rømming, and K. Undheim
1495 (vs), 1474 (vs), 1453 (vs), 1341 (m), 1242 (m), 1080 (m), 1049 (m), 727
(vs), 700 (vs); dH (300 MHz, CDCl3) 2.15 (s, 1H, OH), 2.25 (d, 1H, J 14.9 Hz),
2.52–2.64 (m, 2H), 2.82 (d, 1H, J 14.9 Hz), 3.03 (d, 1H, J 13.0 Hz), 3.40–3.53
(m, 2H), 3.76 (d, 1H, J 13.0 Hz), 3.98 (d, 1H, J 13.0 Hz), 6.30–6.40 (m, 2H),
6.85–7.25 (m, 16H); dC (75 MHz, CDCl3) 37.2, 37.7, 41.3, 43.2, 52.9, 64.6
(Cspiro), 83.9 (C–OH), 123.5, 125.1, 125.5, 125.9, 126.3, 126.6, 127.4,
127.8, 128.1, 129.8, 131.2, 136.3, 139.3, 140.7, 141.6, 146.2, 147.2; m/z
(EI) 398 (8%, [M–H2O]þ), 326 (26), 325 (100), 307 (8), 232 (8), 209 (5),
217 (17), 205 (7), 193 (10), 115 (8), 91 (35).
cis-1-Benzyl-10-(E/Z-benzylidene)-2,20-spirobiindane (8)
pTsOH (15 mg) was added a solution of 1,10-dibenzyl-2,20-spirobiindan-1-ol
(7a 1 7b) (116 mg) in benzene (20 mL) and the solution stirred at room temp-
erature overnight. The reaction mixture was extracted with water (three
times), dried (Na2SO4), and evaporated, and the crude product purified by
flash chromatography on silica gel using hexane–CH2Cl2 1 : 2. The product
was a white solid; yield 112 mg (99%). HRMS: Found M 398.2024. Calc.
for C31H26: 398.203; nmax(film)/cm21 3061 (s), 3023 (s), 1931 (s), 2899 (s),
1599 (m), 1493 (s), 1472 (s), 1459 (s), 1440 (s), 1359 (w), 1218 (w), 1154
(w), 1069 (w), 1028 (w), 756 (s), 725 (m), 696 (vs); dH (300 MHz, CDCl3)
2.55–2.57 (dd, 1H, J1 10.5, J2 13.4Hz), 2.92 (d, 1H, J3 15.6Hz), 2.99–3.10
(m, 3H), 3.13–3.18 (dd, 1H, J4 4.96, J1 10.5Hz), 3.60 (d, 1H, J3 15.6Hz),
6.46 (d, 1H), 6.58 (s, 1H), 6.91–6.98 (m, 4H), 7.09–7.17 (m, 7H), 7.29–7.37
(m, 6H); dC (75MHz, CDCl3) 38.9, 42.9, 47.4, 56.7, 61.0, 125.5, 125.3,
125.0, 126.1, 126.17, 126.3, 126.4, 127.1, 127.3, 128.4, 128.5, 128.9, 129.0,
129.8, 138.6, 140.3, 141.0, 142.5, 145.5, 145.8; m/z (EI) 398 (85%, Mþ),
307 (73), 293 (27), 229 (55), 215 (90), 193 (69), 115 (22), 91 (100).
cis,cis-1,10-Dibenzyl-2,20-spirobiindane (9)
Method 1
cis-1-Benzyl-10-(E/Z-benzylidene)-2,20-spirobiindane (8) (112mg) in methanol
(20 mL) was hydrogenated at 6 bar H2 over 10% palladium on charcoal (20 mg)
at room temperature overnight. The catalyst was filtered off, the solvent evap-
orated, and the crude product purified by flash chromatography on silica gel
using hexane–CH2Cl2 5 : 2. The product was a white crystalline material;
yield 100 mg (88%), mp 199–2008C (benzene, .1858C sublimation).
Method 2
1,10-Bis(E/Z-benzylidene)-2,20-spirobiindane (11) (48 mg) in methanol (20 mL)
was hydrogenated at 6 bar H2 over 10% palladium on charcoal (14 mg) at

a,a0-Spirane-Bridged Dibenzyl Ligands
2287
room temperature overnight. The catalyst was filtered off, the solvent evapor-
ated, and the crude product purified by flash chromatography on silica gel
using hexane–CH2Cl2 5 : 2. The product was a white crystalline material as
previously; yield 100 mg (78%). HRMS: Found M 400.2200. Calc. for
C31H28: 400.2191; nmax(film)/cm21 3060 (s), 3020 (vs), 2934 (vs), 2924 (vs),
2904 (s), 2893 (s), 1602 (s), 1495 (s), 1473 (s), 1453 (s), 1074 (m), 1026
(m), 755 (s), 750 (s), 730 (s), 714 (vs); dH (300 MHz, CDCl3) 2.55 (dd, 2H,
J1 11.4, J2 13.0 Hz), 2.49 (d, 2H, J3 15.0 Hz), 2.95 (d, 2H, J3 15.0 Hz), 3.31
(dd, 2H, J4 2.5, J1 11.4 Hz), 3.65 (dd, 2H, J4 2.5, J2 13.0 Hz), 6.36 (d, 2H),
6.80–7.24 (m, 16H); dC (75 MHz, CDCl3) 37.4, 43.3, 52.8, 60.1, 125.2,
125.3, 126.1, 126.3, 128.1, 129.7, 140.2, 141.9, 147,0; m/z (EI) 400 (0.5%,
Mþ), 309 (66), 218 (33), 217 (100), 215 (14), 202 (12), 115 (8), 91 (52).
1-benzyl-10(E/Z-benzylidene)2,20-spirobiindan-1-ol (10)
Benzylmagnesium bromide in diethyl ether (1 M, 1.5 mL) was added dropwise
with stirring to solution of 10-(E/Z-benzylidene)-2,20-spirobiindan-1-one (4
and 5) (43 mg, 0.14 mmol) in THF (2 mL) under argon at room temperature.
The mixture was stirred at room temperature overnight. The reaction was
quenched by the addition of aqueous 10% NH4Cl (1.5 mL). The mixture
was extracted with diethyl ether, the organic phases combined, the solvent
evaporated, and the residual material subjected to flash chromatography on
silica gel using hexane–EtOAc 5 : 1. The product was a white foam; yield
52 mg (94%). HRMS: Found M 414.1983. Calc. for C31H26O: 414.1984; dH
(300 MHz, CDCl3) 2.29–3.79 (m, 7H), 6.07 (s, 0.6H), 6.29 (0.4H), 6.60
(d, 0.6H), 6.85–7.32 (m, 17.4H); dC (75 MHz, CDCl3). There were several
peaks between 144.9 and 120.3 from the carbons in the benzene rings and
the double bonds, 85.5 (C–OH from major isomer), 85.2 (C–OH from
minor isomer), 65.2 (Cspiro from the minor isomer), 64.7 (Cspiro from the
major isomer), 44.3 (from the major isomer), 43.2 (from the major isomer),
39.0 (from the major isomer); m/z (EI) 416 (0.3%, Mþ), 197 (45), 305
(100), 303 (78), 289 (65), 215 (74), 202 (87), 191 (57), 178 (42), 165 (56),
115 (38), 91 (98).
1,10-Bis(E/Z-benzylidene)-2,20-spirobiindane (11)
pTsOH (6 mg) was added to a solution of 1-benzyl-10(E/Z-benzylidene)2,20-spir-
obiindan-1-ol (10) (52 mg, 0.13 mmol) in benzene (20 mL). The mixture was
stirred at room temperature overnight. The solution was washed with water
(three times), dried (Na2SO4), and evaporated, and the product purified by flash
chromatography on silica gel using hexane–CH2Cl2 1 : 2. The product was a
white solid, yield 48 mg (96%). HRMS: Found M 396.1884. Calc. for C31H24:
396.1878; nmax(film)/cm21 3057 (s), 3021 (s), 2928 (s), 1598 (m), 1492 (s),
1470 (s), 1460 (s), 1443 (s), 11265 (m), 761 (vs), 734 (s), 718 (s), 694 (vs); dH

2288
G. Hu, C. Rømming, and K. Undheim
(300 MHz, CDCl3) 3.03–3.76 (m, 4H), 6.45–7.44 (m, 20H); dC (75 MHz,
CDCl3) for the major isomer: 49.3, 60.9, 123.7, 125.2, 125.6, 126.6, 127.3,
128.8, 129.0, 138.8, 139.9, 145.2, 150.6; m/z (EI) 396 (100%, Mþ), 305 (54),
303 (17), 280 (10), 159 (11), 149 (15), 105 (11),78 (14).
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