A Formal [3 + 2] Alkene Addition to Benzhydrol Cations. A Practical and Mild Methodology for the Synthesis of Substituted 1-Arylindanes and Related Compounds

Article abstract of DOI:10.1081/SCC-120027710

We report the single step synthesis of several 1-arylindanes in good yield via a formal [3 + 2] atom cycloaddition. The success of this formal cycloaddition relies on the Lewis acid activation of a bibenzylic alcohol in the presence of an alkene. The cati

Full text of DOI:10.1081/SCC-120027710

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A Formal [3 + 2] Alkene Addition to Benzhydrol
Cations. A Practical and Mild Methodology for the
Synthesis of Substituted 1‐Arylindanes and Related
Compounds
Beatriz Lantaño a , Jose M. Aguirre b , Liliana Finkielsztein a , Elba N. Alesso a , Ernesto
Brunet c & Graciela Y. Moltrasio a
a Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Universidad
de Buenos Aires, Junín 956 (1113), Buenos Aires, Argentina
b Departamento de Ciencias Básicas, Universidad Nacional de Luján, Luján, Argentina
c Departamento de Química Orgánica, Universidad Autónoma de Madrid, Cantoblanco,
Madrid, España
Version of record first published: 16 Aug 2006.
To cite this article: Beatriz Lantaño , Jose M. Aguirre , Liliana Finkielsztein , Elba N. Alesso , Ernesto Brunet & Graciela
Y. Moltrasio (2004): A Formal [3 + 2] Alkene Addition to Benzhydrol Cations. A Practical and Mild Methodology for the
Synthesis of Substituted 1‐Arylindanes and Related Compounds, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 34:4, 625-641
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 4, pp. 625–641, 2004
A Formal [3 1 2] Alkene Addition to
Benzhydrol Cations. A Practical and
Mild Methodology for the Synthesis
of Substituted 1-Arylindanes and
Related Compounds
Beatriz Lantan˜o,1 Jose M. Aguirre,2 Liliana Finkielsztein,1
Elba N. Alesso,1 Ernesto Brunet,3
and Graciela Y. Moltrasio1,
*
1
´ ´
Departamento de Quımica Organica, Facultad de Farmacia y
´
Bioquımica, Universidad de Buenos Aires, Buenos Aires, Argentina
´
2
´
Departamento de Ciencias Basicas, Universidad Nacional de Lujan,
´
Lujan, Argentina
3
´ ´ ´
Departamento de Quımica Organica, Universidad Autonoma de Madrid,
Cantoblanco, Madrid, Espan˜a
ABSTRACT
We report the single step synthesis of several 1-arylindanes in good yield
via a formal [3 þ 2] atom cycloaddition. The success of this formal
*
´ ´
Correspondence: Graciela Y. Moltrasio, Departamento de Quımica Organica,
´ ´
Facultad de Farmacia y Bioquımica, Junın 956 (1113), Universidad de Buenos Aires,
Buenos Aires, Argentina; E-mail: gmoltra@ffyb.uba.ar.
625
DOI: 10.1081/SCC-120027710
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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626
Lantan˜o et al.
cycloaddition relies on the Lewis acid activation of a bibenzylic alcohol
in the presence of an alkene. The cation generated from the alcohol can be
trapped by the alkene to afford a new benzylic cation which can then
undergoes cyclization leading to 1-arylindanes with three stereogenic
centres.
Key Words: Styrenes; Stilbenes; Indanes; Cycloadditions.
INTRODUCTION
The dihydroindene ring system is a structural subunit found in a large
number of naturally occurring compounds.[1] In addition, there are several
synthetic compounds with this skeleton that show a broad range of biological
activities.[2]
Regio- and stereoselective synthesis of highly substituted dihydroindenes
has received considerable attention. As part of our program to develop routes
to synthesize natural products containing the dihydroindene ring system, we
report here our results using a formal [3 þ 2] cycloaddition of benzhydrol
cations with alkenes.
This synthetic strategy affords the advantage, over others already in use,
of the considerable molecular complexity that may be achieved in the final
compounds.
Previous work has already demonstrated that benzylic cations react with
alkenes in the presence of Lewis acids to render 2,3-dihydro(1H)indenes, via a
formal [3 þ 2] cycloaddition.[3] Up to now, the success of such formal
cycloaddition relied on selective Lewis acid activation of a quinone methide
or benzylic alcohol, both substituted in p-position with an hydroxyl group and
in m-position by a methoxy or methyl group, in the presence of a nucleophilic
alkene.
The proposed mechanism for the formal [3 þ 2] cycloaddition[3] (Sch. 1)
is similar to the dimerization of isosafrol and other styrenes in acid medium
reported by McMillan and coworkers in 1969 (Sch. 2).[4]
Scheme 1.

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Formal [3 1 2] Alkene Addition to Benzhydrol Cations
627
Scheme 2.
We hereby report the synthesis of several dihydroindenes in a single step
via the reaction of bibenzylic cations, generated from benzhydrols 1 or 2
(Sch. 3) with alkenes. As these benzhydrols render a remarkably stable
bibenzylic cation, their reactivity was assayed with nucleophilic alkenes such
as styrenes,[3] and with other relatively electron-poor alkenes such as stilbenes
and diphenylacetylene.
RESULTS AND DISCUSSION
Benzhydrols 1 and 2 were prepared in good yield using a very well known
technique,[5] starting from the corresponding aldehyde and the Grignard
reagent derived from bromobenzene (Sch. 3). SnCl4 was chosen as catalyst
for cycloaddition reactions. Experimental conditions were mild to moderate
(08–408C; time: 30–180 min) and the solvent employed throughout was
methylene chloride.
Given the similarity of this formal [3 þ 2] cycloaddition to the process of
styrene dimerization,[3] we first chose several styrenes (3, 6 and 8) to react
with the bibenzylic cation (Sch. 4).
In contrast to the observations reported by Angle and Arnaiz,[3] the
reaction of benzhydrols 1 and 2 with styrene 3 afforded two pairs of indane
diastereoisomers (4a, 4b and 5a, 5b) respectively with acceptable yield,
indicating that, under those conditions (30 minutes, 08C), the reaction between
Scheme 3.

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628
Lantan˜o et al.
Scheme 4.
the styrene and the benzhydrolic cations is faster than the dimerization of
styrene itself.[6]
The reaction between (E)-b-methyl styrene 6 and alcohol 1, had a similar
outcome[3] but gave better yields, rendering indanes 7a, and 7b.
Under the same conditions, the reaction of benzhydrols 1 and 2 with
a-methyl styrene 8 led in good yield to indanes 9 and 10.
An attempt was made to assay the reactivity of benzhydrols 1 and 2 with
the less nucleophilic compounds, such as (E) and (Z) stilbenes 11 and 12, in
each case, benzhydrols 1 and 2 afforded single diastereomers 13 and 14
(Sch. 5), respectively, though under more severe conditions than used for the
reaction with styrenes (reflux, 3 h).

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Formal [3 1 2] Alkene Addition to Benzhydrol Cations
629
Scheme 5.
To rule out isomerization of (Z)-stilbene to (E)-stilbene, the former was
treated with SnCl4 at reflux during 3 hours, after which no isomerization had
occurred (1H NMR). This finding supports the formality of the [3 þ 2]
cycloaddition and its non-concerted, stepwise mechanism, in which the
second intermediate planar carbocation (Sch. 2) allows for the formation of
the most stable product, regardless of the configuration of the starting stilbene.
The reactivity of these benzhydrols was then assayed with molecules
presenting the styrene system in a more rigid environment. For this purpose,
alkenes 15, 16 and 17 were chosen (Sch. 6).
Scheme 6.

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Lantan˜o et al.
Scheme 7.
In the case of indene (15), tetracyclic compounds 18 and 19 were
obtained, which are epimers. Results proved to be similar with 1,2-dihydro-
naphthalene (16), giving compounds 20 and 21. Alkene 17, however, only
afforded compounds 22 and 23 starting from alcohols 1 or 2, respectively.
The formal cycloaddition was briefly examined with alkyne 24 (Sch. 7).
Formation of regioisomers 25a, 25b, and 26a, 26b have obtained starting from
1 and 2 respectively. These were the only cases, in our studies, in which
regioisomers were formed.
STEREOCHEMICAL ASSIGNMENT
Stereochemical assignment of the cycloadducts was obtained from NMR
experiments (1H, 13C, HMBC (heteronuclear multiple bond correlation)),
HMQC (heteronuclear multiple quantum correlation),[7] NOE and NOESY.
Table 1 provides the values of the coupling constants J1–2 and J2–3 for the
obtained 1,2,3-trisubstituted dihydro(1H)indenes 7a, 7b, 13 and 14.
Table 1. Selected coupling constants (Hz)
for 1,2,3-trisubstituted indanes.
Compd.
J1–2
J2–3
7a
7b
13
14
8.1
10.3
10.0
9.9
9.9
10.3
10.0
9.9

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631
Table 2. Selected chemical shifts (ppm) and coupling constants (Hz) of bi-indanes.
Comp.
Ha
Hb
Hc
Hd
He
Ja–c Jb–c Ja–b Jc–d Jc–e
19a
19b
20a
20b
2.62
3.22
2.67
3.26
2.52
3.01
2.57
3.07
3.70
3.38
3.75
3.40
4.76
4.03
4.78
4.08
4.65
4.72
4.69
4.76
9.0
2.8
9.2
3.1
7.4 16.7 8.2
7.7 16.2 6.7
7.9 16.7 7.9
7.9 16.2 6.1
7.7
7.7
7.9
7.5
From the values in Table 1, it may be readily appreciated that the J values
of the compounds fall into two groups: 8.1 Hz and those ranging from 9.9 to
10.3 Hz, which led us to assign the r-1, c-2, t-3 configuration to compound 7a
and r-1, c-3, t-2 to compounds 7b, 13 and 14.[8]
In the case of 1,3-disubstituted indanes 4 (R55H) and 5 (R55Me), con-
figurational assignment is straightforward due to symmetry. Isomer 5a bears a
C2 axis, which makes H-2a and H-2b isochronous (d 2.57), whereas these
protons in 5b, without that axis, are not (d 2.05 and 2.98 respectively). In the
case of isomers 4 that symmetry does not exist but chemical shifts of H-2a and
H-2b should behave in a similar fashion. Coupling constants agreed with those
measured for analogue compounds without substituents in the aromatic
ring.[9,10]
The values of d and J observed for 1,3,3 trisubstituted indanes 9 and 10
are similar to those found by Brook and coworkers[11] for trisubstituted
indanes without substituents in the aromatic ring, who assigned the geometry
of the compounds on steric grounds. Thus, analogously, the r-1, t-3-biphenyl
configuration was assigned to compounds 9a and 10a and the r-1,
Figure 1. NOEs data of compounds 20a and 20b.

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Lantan˜o et al.
Figure 2. 1H-NMR and 13C-NMR chemical shifts and NOESY data of compound 22.
c-3-biphenyl to compounds 9b and 10b. It may be inferred from H-2b
chemical shifts in compounds 9 (9a d 2.62 ppm, 9b d 2.82 ppm) and 10 (10a d
2.64 ppm, 10b d 2.78 ppm) that the phenyl moiety exerts a greater shielding
effect than the methyl group.[10] Stereoisomers 18 and 19 presented similar
values of chemical shifts and coupling constants (Table 2) as those found by
Kuck and coworkers[12] for compounds with the same type of carbon skeleton,
but without substituents, therefore the configuration was assigned by
comparison.
Stereochemical assignment for the products 20a and 20b was carried out
by observing the coupling constants between the bridgehead protons (J 6.1 Hz
in 20a and J 7.5 Hz in 20b) that indicate a cis ring fusion. Additionally, Fig. 1
shows the NOEs found in 1D difference experiments after careful assignment
of proton signals by various 2D-NMR techniques. All values are only
compatible with the configurations r-1-phenyl, t-2, t-3 for 20a and r-1-phenyl,
c-2, c-3 for 20b.
Structure determination of compound 22, obtained from benzhydrol 1 and
alkene 17, by the usual 2D-NMR techniques allowed us to assign the values of
protons and carbon atoms. In the 1H NMR spectrum, the bibenzylic hydrogen
atom at d 4.25 ppm and its neighbour methine at d 2.76 ppm presented a J
10.6 Hz, which is only compatible with an anti arrangement. Figure 2 shows
some NOESY data, which point to a cis fusion of the 5- and 6-membered rings
so that, the two phenyl substituents at 1,3 positions of the indane moiety are in
a syn arrangement. NOE was observed between the protons at d 2.76 and d
7.10 ppm, as well as between those at d 2.76 and d 7.33 ppm, thus confirming
the cis configuration between the two phenyl substituents and the cis ring
linkage. The lack of NOE between the hydrogen atoms at d 4.25 and 7.10 ppm
indicates that H-1 and 3-phenyl should be in an anti arrangement.

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Formal [3 1 2] Alkene Addition to Benzhydrol Cations
633
Figure 3. Conformation predicted by computational calculation of compound 22.
Besides, the shape of most stable conformation predicted by computa-
tional calculation employing the semiempiric method AM1 (Austin Model
1)[13] (Fig. 3), is in good agreement with that deduced from NMR data.
Finally, the structure and configuration of compound 23, obtained from
benzhydrol 2 and alkene 17, was assigned by comparison with compound 22.
CONCLUSION
The reaction of benzhydrol cations with diverse alkenes allows to obtain
complex indane structures in good yield. It should be highlighted that the
skeleton of the type of compounds 20, 21, 22 and 23 has not yet been described
in the literature, and that benzhydrol cations can react with a wider spectrum
of alkenes.
EXPERIMENTAL SECTION
NMR spectra were recorded (CDCl3) on a Bruker AC 300 or Avance 500
spectrometers. Shifts reported are relative to internal standard Si(Me)4 and
coupling constants are reported in Hz (s: singlet, bs: broad singlet, d: doublet,
t: triplet, q: quartet, dd: double doublet, dt: double triplet, m: multiplet). Mass

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Lantan˜o et al.
spectra were recorded on a VG Auto Spec (Micromass Inst.) or a ZAB SEQ
(VG, Fisons) spectrometer (FABþ, matrix: glycerol) and are reported as
percent relative intensity to the base peak. Preparative thin layer chromatog-
raphy (p-Tlc) was done on Merck Silica Gel 60 GF254; and analytical Tlc was
performed on Merck aluminum sheets Silica Gel 60 F254. THF and CH2Cl2
were distilled from sodium/benzophenone and CaH2, respectively. Melting
points are uncorrected and were determined in a Thomas Hoover apparatus.
The products were isolated by quenching the reaction mixture with a solution
of NaCO3H 5%, separate the organic layer, extract the aqueous layer several
times with the organic solvent, dry the combined organic extracts over
Na2SO4, and remove the solvent under reduced pressure.
4-(Hydroxyphenylmethyl)-2-methoxyphenol (1). Phenylmagnesium
bromide (58 mmol in 29 mL of THF) was added dropwise to a stirred
solution of vanillin (5 mL, 19.7 mmol) at 08C for 15 min and then allowed to
warm to room temperature. After the solution was stirred for 2 h. at room
temperature, CH3OH (5 mL) was added. Aqueous workup (H2O, AcOH,
ether) afforded 3.89 g (86%) of 1 as white crystals (recrystallization: ether–
hexane, 80%) mp: 84–868C. dH 2.35 (1H, s, OH), 3.84 (3H, s, OCH3), 5.64
(1H, s, ArCHAr), 5.77 (1H, s, OH), 6.82 (1H, dd, J: 1.6 and 8.2, Ar), 6.87 (1H,
d, J: 8.2, Ar), 6.90 (1H, d, J: 1.6, Ar), 7.24–7.39 (5H, m, Ar), dC 56.6, 76.0,
109.7, 114.8, 120.4, 127.1, 128.2, 129.1, 136.6, 144.6, 145.8, 147.3.
(3,4-Dimethoxyphenyl)phenylmethan-1-ol (2). The same procedure
described for the preparation of 1 was carried out with 3,4-dimethoxy
benzaldehyde (4.34 g, 26.2 mmol) and PhMgBr (56 mmol in 28 mL of THF).
Recrystallization (ethanol) afforded 6.05 g (95%) of 2 as white crystals; mp:
94–958C. dH 2.32 (1H, s, OH), 3.84 (3H, s, OCH3), 3.85 (3H, s, OCH3), 5.79
(1H, s, ArCHAr), 6.81 (1H, d, J: 8.3, Ar), 6.87 (1H, d, J: 1.3, Ar), 6.91 (1H, dd,
J: 8.3 and 1.3, Ar), 7.26–7.39 (5H, m, Ar); dC 55.8, 55.9, 76.2, 109.7, 110.9,
118.9, 126.4, 127.5, 128.4, 136.5, 143.8, 148.4, 149.0.
General Procedure for the Formal [3 1 2] Cycloaddition of a
Benzhydrol and an Alkene in the Presence of SnCl4
(1R/S,3S/R)-6-Methoxy-1,3-diphenylindan-5-ol (4a) and (1R/S,3R/
S)-6-methoxy-1,3-diphenylindan-5-ol (4b). Styrene 3 (0.09 g, 0.92 mmol)
and SnCl4 (0.19 g, 0.75 mmol) were sequentially added to a solution of alcohol
1 (0.13 g, 0.58 mmol) in CH2Cl2 (10 mL) at 08C. The resulting solution was
stirred for 30 min at 08C and then poured into a rapidly stirred solution of
NaHCO3 5%. Aqueous workup (NaHCO3, CH2Cl2) followed by p-Tlc
(CHCl3) afforded 0.07 g (40%) of 4a and 4b as a 1 : 2.6 (4a/4b) inseparable
mixture (clear oil). Found: C, 83.6; H, 6.38. C22H20O2. Calcd: C, 83.5; H, 6.4.

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Mayor diastereomer 4b: dH 2.05 (1H, dt, J: 10.7 and 12.4, CH2), 2.94 (1H, dt,
J: 7.2 and 12.4, CH2), 3.75 (3H, s, OCH3), 4.28 (2H, m, J: 10.7 and 6.8,
ArCHAr), 5.51 (1H, s, OH), 6.43 (1H, s, Ar), 6.52 (1H, s, Ar), 7.13–7.39
(10H, m, Ar); dC 48.4, 50.4, 50.6, 56.1, 106.9, 110.5, 126.4, 127.8, 128.2,
128.3, 128.4, 128.5, 138.2, 139.8, 144.5, 144.8, 144.9, 145.9. Minor
diastereomer 4a: dH 2.55 (2H, m, CH2), 3.79 (3H, s, OCH3), 4.47 (2H, m, J:
7.0, ArCHAr), 5.56 (1H, s, OH), 6.58 (1H, s, Ar), 6.66 (1H, s, Ar), 7.13–7.39
(10H, m, Ar); dC 47.0, 49.6, 50.0, 56.0, 107.1, 110.8, 126.2, 127.7, 128.2,
128.3, 128.4, 128.5, 137.8, 139.3, 145.1, 145.4, 145.8, 146.1.
(1R/S,3S/R)-5,6-Dimethoxy-1,3-diphenylindane (5a) and (1R/S,3R/
S)-5,6-dimethoxy-1,3-diphenylindane (5b). General procedure was carried
out with alcohol 2 (0.14 g, 0.58 mmol), styrene 3 (0.09 g, 0.92 mmol) and
SnCl4 (0.19 g, 0.75 mmol). p-Tlc (CHCl3) afforded: 0.08 g (42%) of 5a and 5b
as a 1 : 3 (5a/5b) inseparable mixture (clear oil). Found: C, 83.5; H, 6.8.
C23H22O2. Calcd: C, 83.6; H, 6.7. Mayor diastereomer 5b: dH 2.05 (1H, dt, J:
10.7 and 12.5, CH2), 2.98 (1H, dt, J: 7.2 and 12.5, CH2), 3.76 (6H, s, OCH3),
4.33 (2H, dd, J: 10.5 and 7.2, ArCHAr), 6.49 (2H, s, Ar), 7.15–7.40 (10H, m,
Ar); dC 48.7, 50.7, 56.1, 107.6, 126.5, 128.2, 128.3, 138.8, 144.8, 148.6. Minor
diastereomer 5a: dH 2.57 (2H, t, J: 7.0, CH2), 3.80 (6 H, s, OCH3), 4.52 (2H, t,
J: 7.0, CH2), 6.63 (2H, s, Ar), 7.15–7.40 (10H, m, Ar); dC 47.4, 50.0, 55.9,
107.7, 126.2, 127.7, 128.5, 138.4, 147.7, 148.7.
(1R/S,2S/R,3S/R)-6-Methoxy-2-methyl-1,3-diphenylindan-5-ol (7a)
and (1R/S,2R/S,3R/S)-6-methoxy-2-methyl-1,3-diphenylindan-5-ol (7b).
General procedure was carried out with alcohol 1 (0.13 g, 0.58 mmol), styrene
6 (0.11 g, 0.92 mmol) and SnCl4 (0.19 g, 0.75 mmol). p-Tlc (CHCl3) afforded
0.15 g (80%) of 7a and 7b as a 1 : 1.3 (7a/7b) mixture (clear oil). p-Tlc (9 : 1
hexane : ethyl acetate) allowed the separation of 7a (clear oil) and 7b (clear
oil). Found: C, 83.5; H, 6.8. C23H22O2. Calcd: C, 83.6; H, 6.7. Mayor
diastereomer 7b: dH 1.07 (3H, d, J: 6.3, CH3), 2.29 (1H, m, J: 6.3 and 10.3,
CHCH3), 3.75 (3 H, s, OCH3), 3.80 (1H, d, J: 10.3, ArCHAr), 3.81 (1H, d, J:
10.3, ArCHAr), 5.51 (1H, s, OH), 6.42 (1H, s, Ar), 6.48 (1H, s, Ar), 7.27–7.36
(10H, m, Ar); dC 14.9, 54.5, 56.0, 57.0, 107.2, 110.6, 126.5, 128.3, 128.4,
137.7, 137.9, 142.2, 143.6, 145.1, 146.1. Minor diastereomer 7a: dH 0,68 (3H,
d, J: 7.0, CH3), 2.73 (1H, m, J: 7.0, 8.1, and 9.9, CHCH3), 3.81 (3H, s, OCH3),
3.87 (1H, d, J: 9.9, ArCHAr), 4.40 (1H, d, J: 8.1, ArCHAr), 5.55 (1H, s, OH),
6.53 (1H, s, Ar), 6.68 (1H, s, Ar), 6.94 (2H, d, J: 8.1, Ar), 7.16–7.36 (8H, m,
Ar); dC 15.5, 50.4, 56.2, 58.4, 58.2, 106.9, 110.4, 126.2, 126.4, 128.0, 128.8,
128.9, 137.8, 139.4, 143.4, 143.7, 144.9, 145.9.
(1R/S,3S/R)-6-Methoxy-3-methyl-1,3-diphenylindan-5-ol (9a) and
(1R/S,3R/S)-6-methoxy-3-methyl-1,3-diphenylindan-5-ol (9b). General
procedure was carried out with alcohol 1 (0.13 g, 0.58 mmol), styrene 8
(0.11 g, 0.92 mmol) and SnCl4 (0.19 g, 0.75 mmol). p-Tlc (CHCl3) afforded

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Lantan˜o et al.
0.092 g (50%) of 9a and 9b as a 1 : 1.6 (9a/9b) inseparable mixture (yellow
solid). Found: C, 83.4; H, 6.6. C23H22O2. Calcd: C, 83.6; H, 6.7. Mayor
diastereomer 9b dH 1.75 (3H, s, CH3), 2.22 (1H, dd, J: 10.7 and 12.3, CH2),
2.82 (1H, dd, J: 6.8 and 12.3, CH2), 3.77 (3H, s, OCH3), 4.10 (1H, dd, J: 6.8
and 10.7, ArCHAr), 5.63 (1H, s, OH), 6.42 (1H, s, Ar), 6.86 (1H, s, Ar),
7.12–7.43 (10H, m, Ar); dC 28.9, 48.8, 50.9, 55.5, 56.1, 107.0, 109.8, 125.8,
126.9, 128.0, 128.3, 128.4, 128.5, 137.9, 142.7, 144.9, 145.0, 146.0, 148.7.
Minor diastereomer 9a dH 1.64 (3H, s, CH3), 2.35 (1H, dd, J: 10,3 and 12.7,
CH2), 2.62 (1H, dd, J: 7.7 and 12.7, CH2), 3.76 (3H, s, OCH3), 4.43 (1H, dd,
J: 8.6 and 9.2, ArCHAr), 5.54 (1H, s, OH), 6.43 (1H, s, Ar), 6.49 (1H, s,
Ar), 7.12–7.43 (10H, m, Ar); dC 26.3, 49.5, 51.1, 55.9, 56.1, 107.2, 110.0,
125.8, 126.9, 128.0, 128.3, 128.4, 128.5, 136.7, 142.6, 144.8, 145.0, 146.1,
149.0.
(1R/S,3S/R)-5,6-Dimethoxy-1-methyl-1,3-diphenylindane (10a) and
(1R/S,3R/S)-5,6-dimethoxy-1-methyl-1,3-diphenylindane (10b). General
procedure was carried out with alcohol 2 (0.14 g, 0.81 mmol), styrene 8
(0.09 g, 0.75 mmol) and SnCl4 (0.19 g, 0.75 mmol). p-Tlc (CHCl3) afforded
0.12 g (60%) of 10a and 10b as a 1 : 1 (10a/10b) inseparable mixture (white
solid). Found: C, 83.6; H, 6.6. C24H24O2. Calcd: C, 83.7; H, 7.0. Diastereomer
10b dH 1.80 (3H, s, CH3), 2.24 (1H, dd, J: 10.5 and 12.3, CH2), 2.78 (1H, dd, J:
7.0 and 12.3, CH2), 3.75 (3H, s, OCH3), 3.76 (3H, s, OCH3), 4.1 (1H, dd, J: 6.8
and 10.3, ArCHAr), 6.46 (1H, s, Ar), 6.77 (1H, s, Ar), 7.10 (2H, dd, J: 1.3 and
8.3, Ar), 7.19–7.36 (8H, m, Ar). Diastereomer 10a d 1.66 (3H, s, CH3), 2.33
(1H, dd, J: 10.1 and 12.7, CH2), 2.64 (1H, dd, J: 7.5 and 12.9, CH2), 3.77 (3H,
s, OCH3), 3.90 (3H, s, OCH3), 4.4 (1H, dd, J: 7.7 and 9.9, ArCHAr), 6.42 (1H,
s, Ar), 6.46 (1H, s, Ar), 7.19–7.36 (8H, m, Ar), 7.43 (2H, dd, J: 1.3 and 8.4,
Ar). dC of the mixture of diastereomers 10a and 10b: d 26.2, 28.8, 48.8, 49.5,
51.0, 51.3, 55.8, 55.9, 56.0, 56.3, 106.8, 107.5, 107.7, 125.8, 126.4, 127.0,
128.1, 128.3, 128.4, 137.2, 138.4, 141.8, 144.1, 144.7, 145.0, 148.5, 148.8,
148.9, 149.2.
(1R/S, 2R/S, 3R/S)-6-Methoxy-1,2,3-triphenylindan-5-ol (13). Trans-
stilbene 11 (0.17 g, 0.93 mmol) and SnCl4 (0.19 g, 0.75 mmol) were
sequentially added to a solution of alcohol 1 (0.13 g, 0.58 mmol) in CH2Cl2
(10 mL) at 08C. The resulting solution was stirred for 30 min at 08C, 1 h at
room temperature. p-Tlc (CHCl3) afforded 0.12 g (50%) of 13 (yellow oil).
Cis-stilbene 12 (0.17 g, 0.93 mmol) and SnCl4 (0.19 g, 0.75 mmol) were
sequentially added to a solution of alcohol 1 (0.13 g, 0.58 mmol) in CH2Cl2
(10 mL) at room temperature. The resulting solution was stirred for 180 min at
408C. p-Tlc (CHCl3) afforded 0.04 g (20%) of 13 (yellow oil). Found: C, 85.6;
H, 6.2. C28H24O2. Calcd: C, 85.7; H, 6.1. dH 3.45 (1H, t, J: 10.0, CHAr), 3.77
(3H, s, OCH3), 4.5 (2H, d, J: 10.0, ArCHAr), 5.62 (1H, s, OH), 6.49 (1H, s, Ar),
6.59 (1H, s, Ar), 7.07 (2H, dd, J: 1.7 and 7.5, Ar), 7.13–7.32 (13H, m, Ar),

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Formal [3 1 2] Alkene Addition to Benzhydrol Cations
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7.77 (3H, s, OCH3); dC 56.2, 58.2, 58.6, 68.2, 107.1, 110.6, 126.5, 126.6,
128.3, 128.4, 128.5, 128.6, 136.5, 138.2, 140.8, 142.9, 143.3, 146.3.
(1R/S,3R/S)-5,6-Dimethoxy-1,2,3-triphenylindane (14). The same
procedure described for the preparation of 13 was carried out with alcohol 2
(0.14 g, 0.58 mmol), stilbene 11 (0.17 g, 0.93 mmol) and SnCl4 (0.19 g,
0.75 mmol). p-Tlc (CHCl3) afforded 0.12 g (51%) of 14 (clear oil). The same
procedure described for the preparation of 14 was carried out with alcohol 2
(0.14 g, 0.58 mmol), stilbene 12 (0.17 g, 0.93 mmol) and SnCl4 (0.14 g,
0.5 mmol). p-Tlc (CHCl3) afforded 0.04 g (25%) of 14. Found: C, 85.5; H, 6.3.
C29H26O2. Calcd: C, 85.7; H, 6.4. dH 3.45 (1H, t, J: 9.9, CHAr), 3.79 (6H, s,
OCH3), 4.56 (2H, d, J: 9.9, CHAr2), 6.56 (2H, s, Ar), 7.09 (2H, dd, J: 1.6 and
7.7, Ar), 7.16–7.33 (13H, m, Ar); dC 56.1, 58.6, 68.6, 107.6, 126.5, 126.6,
128.3, 128.5, 137.1, 140.8, 143.2, 148.9.
(5R/S, 5aR/S, 10bS/R)-3-Methoxy-5-phenylindano[1,2-a]indan-2-ol
(18a) and (5aR/S,5S/R,10bS/R)-3-methoxy-5-phenylindano[1,2-a]indan-
2-ol (18b). General procedure was carried out with alcohol 1 (0.11 g,
0.46 mmol), indene 15 (0.08 g, 0.74 mmol) and SnCl4 (0.15 g, 0.6 mmol).
p-Tlc (CHCl3) afforded 0.10 g (66%) of 18a and 18b as a 1 : 2 (18a/18b)
inseparable mixture (white solid). (Found: C, 84.3; H, 6.3. C23H20O2. Calcd:
C, 84.1; H, 6.1). Mayor diastereomer 18b dH 3.01 (1H, dd, J: 16.1 and 2.8,
CH2), 3.22 (1H, dd, J: 16.1 and 7.7, CH2), 3.38 (1H, m, J: 2.8 and 7.7,
CH2CHCHAr), 3.72 (3H, s, OCH3), 4.03 (1H, d, J: 6.7, ArCHAr), 4.72 (1H, d,
J: 7.7, ArCHAr), 5.5 (1H, s, OH), 6.41 (1H, s, Ar), 7.15 (1H, s, Ar), 7.20–7.41
(9H, m, Ar); dC 34.0, 49.9, 53.2, 55.9, 56.2, 108.1, 110.3, 123.8, 124.4, 126.4,
126.5, 126.7, 128.4, 128.8, 135.2, 137.3, 142.1, 143.3, 144.9, 145.3, 146.1.
Minor diastereomer 18a dH 2.52 (1H, dd, J: 8.9 and 16.7, CH2), 2.62 (1H, dd,
J: 7.4 and 16.7, CH2), 3.70 (1H, m, overlaps with OCH3, CH2CHAr), 3.79
(3H, s, OCH3), 4.65 (1H, d, J: 7.7, ArCHAr), 4.76 (1H, d, J: 8.2, ArCHAr),
5.61 (1H, s, OH), 6.67 (1H, s, Ar), 7.03 (1H, s, Ar), 7.0–7.5 (9H, m, Ar); dC
37.3, 55.3, 55.4, 56.1, 57.9, 107.6, 109.9, 124.5, 125.1, 126.5, 126.8, 126.9,
128.3, 128.6, 137.3, 137.6, 143.4, 143.8, 145.3, 145.5, 146.3.
(5R/S, 5aR/S, 10bS/R)-2,3-Dimethoxy-5-phenylindano[1,2-a]indane
(19a) and (5aR/S,5S/R,10bS/R)-2,3-dimethoxy-5-phenylindano[1,2-a]
indane (19b). General procedure was carried out with alcohol 2 (0.09 g,
0.38 mmol), indene 15 (0.08 g, 0.74 mmol) and SnCl4 (0.15 g, 0.6 mmol).
p-Tlc (CHCl3) afforded 0.10 g (76%) of 19a and 19b as a 1 : 1 (19a/19b)
inseparable mixture (clear oil). Found: C, 84.2; H, 6.6. C24H22O2. Calcd: C,
8.4; H, 6.5. Diastereomer 19b. dH 3.07 (1H, dd, J: 3.1 and 16.2, CH2), 3.26
(1H, dd, J: 7.9 and 16.2, CH2), 3.40 (1H, m, J: 3.1, 6.1, 7.5 and 7.9,
CH2CHCHAr), 3.74 (3H, s, OCH3), 4.0 (3H, s, OCH3), 4.08 (1H, d, J: 6.1,
ArCHAr), 4.76 (1H, d, J: 7.4 Hz, ArCHAr), 6.46 (1H, s, Ar), 7.10 (1H, s, Ar),
7.26–7.44 (9H, m, Ar); dC 37.4, 55.5, 56.0, 56.1, 57.9, 107.1, 108.3, 124.3,

ORDER
REPRINTS
638
Lantan˜o et al.
125.2, 126.5, 126.6, 126.8, 128.2, 128.7, 136.7, 137.9, 142.5, 143.9, 145.4,
148.9. Diastereomer 19a. dH 2.57 (1H, dd, J: 9.2 and 16.7, CH2), 2.67 (1H, dd,
J: 7.9 and 16.7, CH2), 3.75 (1H, m, overlaps with OCH3, CH2CH), 3.81 (3H, s,
OCH3), 3.95 (3H, s, OCH3), 4.69 (1H, d, J: 7.9, ArCHAr), 4.78 (1H, d, J:
7.9 Hz, ArCHAr), 6.72 (1H, s, Ar), 6.97 (1H, s, Ar), 7.01–7.55 (9H, m, Ar); dC
34.1, 50.0, 53.2, 55.6, 56.1, 107.3, 108.7, 123.7, 124.6, 126.4, 126.5, 128.2,
129.2, 135.7, 136.4, 141.9, 143.5, 145.0, 148.7, 148.9.
(4bR/S,9S/R,9aS/R)-7-Methoxy-9-phenyl-10,11,4b,9a-tetrahydro-
benzo[c]fluoren-6-ol (20a) and (4bR/S,9R/S,9aS/R)-7-methoxy-9-
phenyl-10,11,4b,9a-tetrahydrobenzo[c]fluoren-6-ol (20b). General pro-
cedure was carried out with alcohol 1 (0.13 g, 0.58 mmol), dihydronaphtalene
16 (0.12 g, 0.92 mmol) and SnCl4 (0.19 g, 0.75 mmol). p-Tlc (80 : 20 hexane:
ethyl acetate) afforded 0.08 g (41%) of 20a and 20b as a 1.6 : 1 (20a/20b)
(clear oil). Found: C, 84.3; H, 6.6. C24H22O2. Calcd: C, 84.2; H, 6.5. Mayor
diastereomer 20a. dH 1.79 (1H, m, CHCH2CH2), 1.95 (1H, m, CHCH2CH2),
2.80 (3H, m, CHArCHCH2, CHCH2Ar), 3.75 (3H, s, OCH3), 4.12 (1H, d, J:
5.7, ArCHAr), 4.41 (1H, d, J: 7.5, ArCHAr), 5.55 (1H, s, OH), 6.52 (1H, s,
Ar), 7.03 (1H, s, Ar), 7.10–7.45 (9H, m, Ar); dC 25.9, 27.6, 45.9, 49.5, 55.7,
56.0, 107.8, 110.8, 125.8, 126.0, 126.3, 128.0, 128.5, 128.7, 129.3, 136.2,
137.1, 137.4, 138.6, 144.7, 144.8, 145.9. Minor diastereomer 20b dH 1.1 (1H,
m, CHCH2CH2), 1.3 (1H, m, CHCH2CH2), 2.60 (2H, m, CHCH2CH2Ar),
2.80 (1H, m, CHArCHCH2), 3.79 (3H, s, OCH3), 4.31 (1H, d, J: 5.7 Hz,
ArCHAr), 4.63 (1H, d, J: 6.1, ArCHAr), 5.53 (1H, s, OH), 6.69 (1H, s, Ar),
6.90 (1H, s, Ar), 7.08 (1H, d, J: 7.5 Hz, Ar), 7.18 (1H, d, J: 7.2, Ar), 7.26–7.46
(7H, m, Ar); dC 21.3, 28.9, 46.7, 47.3, 54.5, 56.3, 108.1, 110.5, 125.7, 126.1,
126.6, 128.2, 128.9, 129.7, 130.1, 134.0, 136.3, 137.2, 139.1, 140.0, 144.5,
145.3.
(4bR/S,9S/R,9aS/R)-6,7-dimethoxy-9-phenyl-10,11,4b,9a-tetrahy-
drobenzo[c]fluorene (21a) and (4bR/S,9R/S,9aS/R)-6,7-dimethoxy-9-
phenyl-10,11,4b,9a-tetrahydrobenzo[c]fluorene (21b). General procedure
was carried out with alcohol 2 (0.14 g, 0.58 mmol), dihydronaphtalene 16
(0.12 g, 0.92 mmol) and SnCl4 (0.19 g, 0.75 mmol). p-Tlc (80 : 20 hexa-
ne : ethyl acetate) afforded 0.10 g (54%) of 21a and 21b as a 1.5 : 1 (21a/21b)
(clear oil). m/z (EI) 356.1884 (Mþ, 356 C25H24O2) requires 356.1776, 356
(100), 227 (17) and 91 (13%). Mayor diastereomer 21a dH 1.79 (1H, m, J: 4.9,
5.1 and 13.3, CHCH2CH2Ar), 1.95 (1H, m, J: 4.9, 5.1, 7.9 and 13.3,
CHCH2CH2Ar), 2.80 (3H, m, J: 5.1, 7.4 and 7.9, CHArCHCH2, CH2Ar), 3.73
(3H, s, OCH3), 3.87 (3H, s, OCH3), 4.13 (1H, d, J: 5.4, ArCHAr), 4.42 (1H, d,
J: 7.4, ArCHAr), 6.54 (1H, s, Ar), 6.94 (1H, s, Ar), 7.11–7.33 (8H, m, Ar),
7.42 (1H, d, J: 7.7, Ar); dC 26.2, 27.8, 46.3, 49.5, 55.9, 56.0, 56.1, 108.1 108.6,
125.9, 126.0, 126.3, 127.9, 128.5, 128.9, 129.0, 136.5, 136.8, 137.4, 137.6,
137.8, 148.4, 148.5. Minor diastereomer 21b dH 1.09 (1H, dd, J: 3.6 and 13.1,

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Formal [3 1 2] Alkene Addition to Benzhydrol Cations
639
CHCH2CH2), 1.29 (1H, m, J: 6.7 and 11.0, CHCH2CH2Ar), 2.60 (2H, m, J:
4.1 and 6.1, CH2CH2Ar), 2.85 (1H, m, CHArCHCH2), 3.76 (3H, s, OCH3),
3.92 (3H, s, OCH3), 4.33 (1H, d, J: 5.9, ArCHAr), 4.64 (1H, d, J: 6.2,
ArCHAr), 6.70 (1H, s, Ar), 6.78 (1H, s, Ar), 7.20–7.47 (9H, m, Ar), dC 21.8,
29.4, 47.1, 48.0, 54.9, 56.5, 56.6, 108.1, 109.3, 126.1, 126.5, 127.0, 128.6,
129.6, 130.1, 130.3, 135.1, 136.9, 137.8, 139.0, 140.3, 148.4, 148.5.
(4bS/R,9S/R,9aS/R)-7-methoxy-9,4b-diphenyl-10,11,4b,9a-tetrahy-
drobenzo[c]fluoren-6-ol (22). General procedure was carried out with
alcohol 1 (0.10 g, 0.46 mmol), 1-phenyl-3,4-dihydronaphtalene 17 (0.15 g,
0.74 mmol) and SnCl4 (0.15 g, 0.6 mmol). p-Tlc (CHCl3) afforded 0.08 g
(40%) of 22 (white solid); mp: 180–1828C (see Fig. 2).
(4bS/R,9S/R,9aS/R)-6,7-Dimethoxy-9,4b-diphenyl-10,11,4b,9a tet-
rahydrobenzo[c]fluorene (23). General procedure was carried out with
alcohol 2 (0.11 g, 0.64 mmol), 1-phenyl-3,4-dihydronaphtalene 17 (0.15 g,
0.74 mmol) and SnCl4 (0.15 g, 0.6 mmol). p-Tlc (CHCl3) afforded 0.1 g (51%)
of 23 (white solid); mp: 210–2128C m/z (CI) 418.1933 (Mþ, 418. C30H26O2
requires 418.1997), 418 (100), 341(58), 327 (23). HRMS calcd. for C30H26O2
found: 418.1977. dH 1.7 (1H, m, J: 3.6 and 13.8, CHCH2CH2), 1.8 (1H, m,
CHCH2CH2), 2.70 (1H, dt, J: 3.6 and 10.8, CHArCHCH2), 2.9 (1H, m, J: 5.9,
7.9 and 17.2, CH2CH2Ar), 3.25 (1H, m, J: 6.1, 12.9 and 16.9, CH2CH2Ar),
3.71 (3H, s, OCH3), 3.86 (3H, s, OCH3), 4.25 (1H, d, J: 10.8, CHAr2), 6.42
(1H, s, Ar), 6.93 (1H, s, Ar), 7.05–7.38 (14H, m, Ar); dC 18.2, 25.7, 51.2, 56.0,
56.3, 58.7, 62.0, 107.8, 109.2, 125.9, 126.0, 126.3, 126.6, 127.7, 128.5, 128.7,
128.9, 129.1, 130.8, 136.9, 138.5, 139.5, 141.8, 143.4, 148.5, 148.9, 149.9.
6-Methoxy-1,2,3-triphenylinden-5-ol 25a and 4-methoxy-1,2,3-tri-
phenylinden-5-ol (25b). General procedure was carried out with alcohol 1
(0.11 g, 0.5 mmol), diphenylacetylene 24 (0.09 g, 0.5 mmol) and SnCl4
(0.17 g, 0.65 mmol). The reaction was carried out at 08C during 150 min. p-Tlc
(CHCl3) afforded 0.09 g (47%) of 25a and 25b as a 1 : 1.6 (25a/25b) mixture.
The separation of the regioisomers was made by p-Tlc (CHCl2). Diastereomer
25a, white solid, mp: 67–698C, dH 3.70 (3 H, s, OCH3), 5.03 (1H, s, CH), 5.41
(1H, s, OH), 6.51 (1H, s, Ar), 6.77 (1H, s, Ar), 7.05–7.10 (5H, m, Ar), 7.18–
7.30 (5H, m, Ar), 7.35–7.41 (5H, m, Ar); dC 55.8, 57.7, 110.1, 114.4, 121.4,
123.8, 125.7, 126.7, 127.4, 127.8, 128.7, 129.3, 129.5, 131.3, 135.6, 137.0,
140.5, 144.2, 144.7, 145.6, 146.5, 148.2, m/z (CI) 390.1622 (Mþ, 390.
C28H22O2 requires 390.1620), 390 (100), 313 (17) and 213 (14%).
Diastereomer 25b, white solid, mp: 65–678C, dH 3.83 (3H, s, OCH3), 5.01
(1H, s, CH), 5.57 (1H, s, OH), 6.76 (1H, d: J: 6.8, Ar), 6.86 (1H, d, J: 7.9, Ar),
7.01–7.18 (10H, m, Ar), 7.36–7.42 (5H, m, Ar), dC 55.7, 57.1, 102.1, 104.2,
126.7, 127.5, 127.6, 127.8, 128.3, 128.4, 128.8, 129.6, 129.7, 129.9, 129.9,
130.0, 130.1, 136.9, 140.5, 144.0, 144.1, 144.4, m/z (CI) 390.1625 (Mþ, 390.
C28H22O2) requires 390.1620, 390 (100), 313 (6), 267 (15%).

ORDER
REPRINTS
640
Lantan˜o et al.
5,6-Dimethoxy-1,2,3-triphenylindene 26a and 4,5-dimethoxy-1,2,3-
triphenylindene 26b. General procedure was carried out with alcohol 2
(0.11 g, 0.46 mmol), diphenylacetylene 24 (0.13 g, 0.74 mmol) and SnCl4
(0.15 g, 0.6 mmol). p-Tlc (CHCl3) afforded 0.11 g (60%) of 26a and 26b as a
1 : 1 (26a/26b) inseparable mixture (white solid). Found: C, 86.0; H, 5.96.
C28H24O2. Calcd: C, 85.7; H, 6.1. Spectroscopic data of the mixture of
regioisomers 26a and 26b: dH 3.71 (3H, s, OCH3), 3.80 (3H, s, OCH3), 3.82
(3H, s, OCH3), 3.83 (3H, s, OCH3), 5.02 (1H, s, ArCHAr), 5.05 (1H, s,
ArCHAr), 6.56 (1H, d, J: 1.8, Ar), 6.73 (1H, s, Ar), 6.80 (3H, m, Ar), 7.02–
7.29 (19H, m, Ar), 7.38–7.42 (10H, m, Ar); dC 54.6, 55.2, 57.0, 57.1, 104.2,
107.9, 110.9, 111.3, 119.7, 123.0, 124.8, 125.6, 125.9, 126.6, 127.0, 127.1,
127.4, 127.8, 128.3, 128.5, 128.7, 128.8, 131.0, 134.9, 135.2, 139.4, 139.7,
140.2, 143.6, 143.8, 144.8, 147.0. MS (FAB, glycerol) 405 (M þ 1).
ACKNOWLEDGMENTS
This work was supported by grants from the Consejo Nacional de
´ ´
Investigaciones Cientifıcas y Tecnicas (CONICET) and Universidad de
Buenos Aires.
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Received in the USA August 14, 2003

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