Tetrahydronaphthalene derivatives by amberlyst 15-promoted friedel-crafts cyclizations

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Organic Preparations and Procedures
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Tetrahydronaphthalene Derivatives by
Amberlyst® 15-Promoted Friedel-Crafts
Cyclizations
Richard A. Bunce a & Andrew N. Cox a
a Department of Chemistry , Oklahoma State University , Stillwater,
Oklahoma, USA
Published online: 03 Feb 2010.
To cite this article: Richard A. Bunce & Andrew N. Cox (2010) Tetrahydronaphthalene Derivatives
by Amberlyst® 15-Promoted Friedel-Crafts Cyclizations, Organic Preparations and Procedures
International: The New Journal for Organic Synthesis, 42:1, 83-93, DOI: 10.1080/00304940903523553
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Organic Preparations and Procedures International, 42:83–93, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print
DOI: 10.1080/00304940903523553
Tetrahydronaphthalene Derivatives by AmberlystꢀR
15-Promoted Friedel-Crafts Cyclizations
Richard A. Bunce and Andrew N. Cox
Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma,
USA
A recent project required the preparation of a series of 1,1-disubstituted-1,2,3,4-tetrahydro-
naphthalene derivatives. These compounds are known to be both retinoic acid receptor
(RAR) antagonists and retinoic X receptor (RXR) agonists. As RAR antagonists, these
materials have been investigated for the treatment of dermatological diseases, such as
psoriasis and eczema.1 As RXR agonists, these agents have been co-administered with
protein kinase A activators in efforts to control hyperproliferative diseases, such as leukemia
and breast cancer.2 Finally, studies are also underway to exploit these RXR agonists to
ameliorate diabetes, atherosclerosis and hypercholesteremia.3
AmberlystꢀR 15 is a sulfonated polystyrene resin that has been used for a large num-
ber of transformations promoted by strong acids.4 In the current work, we planned to use
this resin in a Friedel-Crafts-type ring closure of 1,1-disubstituted-4-arylbutanols. Past
reports have described the use of sulfuric acid5 and polyphosphoric acid6 for these cycliza-
tions but extensive work-up and purification schemes were often required. AmberlystꢀR 15
offers the advantage that the reaction proceeds cleanly without the need for tedious isolation
procedures. Reactions performed using this reagent require only filtration of the resin and
removal of the solvent.
A series of substrates was prepared to assess the possibility of carrying out these
cyclizations using AmberlystꢀR 15. Starting from 4-arylbutanoic acid derivatives 1–3,7
8
˚
esterification with CH3OH and H2SO4 in the presence of 3-A molecular sieves proceeded
in 85–90% yield to give 4–6. The trifluoromethyl-substituted ester 7 was prepared according
to a literature procedure.9 Treatment of 1 equivalent of each ester with 3 equivalents of (a)
CH3MgBr or (b) PhMgBr in ether gave the required tertiary alcohols 8a–11a in 90–93%
yields and 8b–11b in 74–82% yields, respectively. The cyclizations to give 12a–15a and
12b–14b were carried out by reacting 0.25 g of each alcohol in PhH10 with 0.25 g of
AmberlystꢀR 15 for 0.5–8 h. Filtration and concentration of the crude reaction mixture
Received August 28, 2009; in final form October 1, 2009.
Andrew N. Cox was a NSF-REU student during Summer 2009. Current address: Department of
Chemistry, Louisiana Tech University, Ruston, LA 71270.
Address correspondence to Richard A. Bunce, Department of Chemistry, Oklahoma State Uni-
versity, Stillwater, OK 74078-3071. E-mail: rab@okstate.edu
83

84
Bunce and Cox
Scheme 1
Synthesis of 1,1,7-trisubstituted 1,2,3,4-tetrahydronaphthalenes.
under vacuum gave the cyclized products in spectroscopically pure form. The synthesis
and cyclization of our alcohol substrates are summarized in Scheme 1.
Reaction of the methyl-substituted tertiary alcohols generally proceeded faster than
those substituted by phenyl. This presumably reflects the greater steric hindrance and
lower reactivity of the more stabilized diphenyl-substituted carbocation intermediates. Al-
though alkenes were not observed from the dimethyl precursors, exposure of diphenyl
substrates 8b–10b to AmberlystꢀR 15 in refluxing PhH for 0.5–1 h produced insepara-
ble mixtures of 4-aryl-1,1-diphenylbutenes 16b–18b (major) and 1,1-diphenyl-1,2,3,4-
tetrahydronaphthalenes 12b–14b (minor). Extending the reaction time to 8 h, however,
resulted in clean conversion of these mixtures to the cyclized products11 suggesting that
ring closure occurs predominantly via alkenes 16b–18b in the diphenyl series. Finally,
substrate 11b gave a nearly quantitative yield of alkene 19b, with virtually none of the
tetrahydronaphthalene 15b, even after prolonged reaction.
The substituents on the aromatic ring were chosen to evaluate the ease of cyclization for
electron-rich and electron-poor rings. To our surprise, the reaction proceeded smoothly for
all of the alcohols studied except 11b (X = CF3, R = Ph), which failed to cyclize due to the
hindered nature of the carbocation and the inductively deactivated aromatic ring at C4. In this
case, the alkene dehydration product 19b was isolated in 96% yield after 0.5 h at reflux. More
forcing conditions (1.00 g of AmberlystꢀR 15, PhH, reflux, 72 h) produced an inseparable
mixture of 19b with small amounts of 15b (< 5%) and several decomposition products.

Tetrahydronaphthalene Derivatives by Friedel-Crafts Cyclizations
85
In addition to the cyclization of alkenes 16b–18b, produced as intermediates in the reac-
tion of 8b–10b, we explored the ring closure of several other selected alkenes (Scheme 2).
Ketone 2012 was converted to 5-phenyl-2-methylpentene (21) by Wittig olefination and
methyl (E)-3-methyl-6-phenyl-2-hexenoate (22) using the Wadsworth-Emmons procedure.
Both of these substrates permitted reaction via a tertiary carbocation and gave excellent
yields of 12a and 23, respectively. In an effort to define the limitations of the current pro-
cedure, aldehyde 2413 was converted to methyl (E)-6-phenyl-2-hexenoate (25) to evaluate
a substrate that would require closure on a secondary carbocation. In this case, treatment
with AmberlystꢀR 15 using our standard protocol for 72 h gave a complex product mixture
containing recovered starting material and ketone 26 as the major components. This out-
come likely arises from the greater difficulty in generating the less stabilized carbocation
and suggests that cyclizations using this method may be limited to closures proceeding
through tertiary carbocations.
Scheme 2
Cyclization of selected alkenes.
In conclusion, we report a convenient method for the preparation of 1,1-disubstituted-
1,2,3,4-tetrahydronaphthalenes using AmberlystꢀR 15. Although a number of the com-
pounds prepared have been previously reported, the current procedure gives comparably
high yields and is operationally much simpler to perform in the laboratory. The procedure
works well for systems proceeding through a tertiary carbocation, but is unsatisfactory for
cyclizations involving less stabilized intermediates.
Experimental Section
All reactions were run in dry glassware under N2. The saturated NaCl, saturated NH4Cl
and 5% NaHCO3 used in work-up procedures refer to aqueous solutions. Reactions
were monitored by thin layer chromatography (TLC) on silica gel GF plates (Analtech
21521). Preparative separations were performed by one of the following methods: (1) flash
chromatography14 (FC) on silica gel (grade 62, 60–200 mesh) containing UV-active phos-
phor (Sorbent Technologies UV-05) packed into quartz columns or (2) preparative thin layer
chromatography (PTLC) on 20 cm × 20 cm silica gel GF plates (Analtech 02015). Band

86
Bunce and Cox
elution for all chromatographic separations was monitored using a hand-held UV lamp.
Melting points were uncorrected. IR spectra were run as thin films on NaCl disks. 1H and
13C NMR spectra were measured in CDCl3 at 300 MHz and 75 MHz, respectively, using
(CH3)4Si as the internal standard; coupling constants (J) are given in Hz. Mass spectra
(EI/DP) were obtained at 70 eV.
General Procedure for the Conversion of Acids to Methyl Esters: Methyl
4-Phenyl-butanoate (4)
The procedure of Eisenbraun and co-workers was used.8 To a solution of 6.00 g (36.6 mmol)
of 1 in 100 mL of anhydrous CH3OH was added 2 mL of concentrated H2SO4 and
the mixture was heated under reflux such that the condensed CH3OH passed through a
˚
Soxhlet cup containing 25–30 g of 3-A molecular sieves. After 12 h, the reaction was
cooled, concentrated, diluted with saturated NaCl solution and extracted with ether (3x).
The combined ether layers were washed with saturated NaCl (1x), dried (MgSO4) and
concentrated to give a colorless oil, which was distilled in vacuu to afford 5.62 g (86%) of
pure 4, bp 87–88◦C (1.5 mm Hg) [lit.15 bp 123–124◦C (13 mm Hg)]. IR: 1739 cm−1; 1H
NMR: δ 7.28 (m, 2 H), 7.19 (m, 3 H), 3.66 (s, 3 H), 2.65 (t, J = 7.1 Hz, 2 H), 2.33 (t, J
= 7.1 Hz, 2 H), 1.96 (quintet, J = 7.1 Hz, 2 H); 13C NMR: δ 173.9, 141.3, 128.4, 128.3,
125.9, 51.5, 35.1, 33.3, 26.4.
Methyl 4-(4-Chlorophenyl)butanoate (5)16
This compound (5.46 g, 85%) was isolated as a colorless oil from 6.00 g (30.2 mmol) of
2,7 bp 115–117◦C (1.5 mm Hg). IR 1736 cm−1; 1H NMR: δ 7.24 (d, J = 8.2 Hz, 2 H), 7.10
(d, J = 8.2 Hz, 2 H), 3.66 (s, 3 H), 2.62 (t, J = 7.1 Hz, 2 H), 2.32 (t, J = 7.1 Hz, 2 H), 1.93
(quintet, J = 7.1 Hz, 2 H); 13C NMR: δ 173.7, 139.7, 131.7, 129.8, 128.4, 51.5, 34.4, 33.2,
26.3.
Anal. Calcd for C11H13ClO2: C, 62.12; H, 6.12. Found: C, 62.23; H, 6.15.
Methyl 4-(4-Methoxyphenyl)butanoate (6)
This compound (5.78 g, 90%) was isolated as a colorless oil from 6.00 g (30.9 mmol) of
3, bp 120–122◦C (1.5 mm Hg) [lit.17 bp 105–110◦C (0.25 mm Hg)]. IR: 2840, 1737 cm−1
;
1H NMR: δ 7.09 (d, J = 8.2 Hz, 2 H), 6.83 (d, J = 8.2 Hz, 2 H), 3.78 (s, 3 H), 3.66 (s,
3 H), 2.59 (t, J = 7.1 Hz, 2 H), 2.31 (t, J = 7.1 Hz, 2 H), 1.92 (quintet, J = 7.1, 2 H);
13C NMR: δ 174.0, 157.8, 133.4, 129.3, 113.7, 55.2, 51.4, 34.1, 33.3, 26.7.
General Procedure for Grignard Addition to the Esters: 2-Methyl-5-phenyl-2-pentanol
(8a)
These reactions were carried out by reacting 1 eq of the ester with 3 eq of the Grignard
reagent. Methylmagnesium bromide was prepared from 2.39 g (16.5 mmol) of CH3I and
0.60 g (25.0 mmol) of Mg in 50 mL of anhydrous ether. To this reagent was slowly added
a solution of 1.00 g (5.62 mmol) of 4 in 10 mL of dry ether. The reaction was warmed to
reflux for 15 min, then cooled and quenched with 10 mL of saturated NH4Cl. The mixture

Tetrahydronaphthalene Derivatives by Friedel-Crafts Cyclizations
87
was transferred to a separatory funnel and the aqueous phase was extracted with ether
(3x). The combined ether layers were washed with saturated NaCl (1x), dried (MgSO4)
and concentrated under vacuum to afford 0.93 g (93%) of 8a as a colorless oil. This oil
was spectroscopically pure and used directly in the cyclization reaction. The spectral data
matched those previously reported.18
2-Methyl-5-(4-chlorophenyl)-2-pentanol (9a)
This compound 0.90 g (90%) was isolated as a colorless oil from 1.00 g (4.71 mmol) of
5. IR: 3375 cm−1; 1H NMR: δ 7.24 (d, J = 8.2 Hz, 2 H), 7.11 (d, J = 8.2 Hz, 2 H), 2.59
(t, J = 7.1 Hz, 2 H), 1.67 (m, 2 H), 1.51 (s, 1 H), 1.48 (m, 2 H), 1.19 (s, 6 H); 13C NMR:
δ 140.8, 131.4, 129.7, 128.3, 70.8, 43.2, 35.6, 29.2 (2 C), 26.1; MS: m/z 197, 199 (ca 3:1,
M+−CH3).
Anal. Calcd for C12H17ClO: C, 67.76; H, 8.00. Found: C, 67.82; H, 8.01.
2-Methyl-5-(4-methoxyphenyl)-2-pentanol (10a)19
This compound 0.91 g (91%) was isolated as a colorless oil from 1.00 g (4.81 mmol) of
6. IR: 3395, 2841 cm−1; 1H NMR: δ 7.10 (d, J = 8.2 Hz, 2 H), 6.82 (d, J = 8.2 Hz, 2 H),
3.78 (s, 3 H), 2.56 (t, J = 7.1 Hz, 2 H), 1.65 (m, 2 H), 1.51 (s, 1 H), 1.48 (m, 2 H), 1.19 (s,
6 H); 13C NMR: δ 157.6, 134.5, 129.2, 113.7, 70.9, 55.2, 43.4, 35.4, 29.2 (2 C), 26.4; MS:
m/z 193 (M+−CH3).
Anal. Calcd for C13H20O2: C, 75.00; H, 9.62. Found: C: 75.07; H, 9.66.
2-Methyl-5-(4-trifluoromethylphenyl)-2-pentanol (11a)
This compound 0.90 g (90%) was isolated as a colorless oil from 1.00 g (4.07 mmol) of
7.9 IR: 3378 cm−1; 1H NMR: δ 7.53 (d, J = 8.2 Hz, 2 H), 7.29 (d, J = 8.2 Hz, 2 H), 2.67
(t, J = 7.7 Hz, 2 H), 1.72 (m, 2 H), 1.52 (s, 1 H), 1.50 (m, 2 H), 1.21 (s, 6 H); 13C NMR: δ
146.5, 128.7, 128.1, 125.2 (q, J = 3.7 Hz), 124.3 (q, J = 270.2 Hz), 70.8, 43.2, 36.1, 29.2
(2 C), 25.9; MS: m/z 231 (M+−CH3).
Anal. Calcd for C13H17F3O: C, 63.41; H, 6.91. Found: C, 63.54; H, 6.94.
1,1,4-Triphenylbutanol (8b)
These reactions were carried out by reacting 1 eq of the ester with 3 eq of phenylmagnesium
bromide. This compound (1.36 g, 80%) was prepared from 1.00 g (5.62 mmol) of 4 and
was purified by FC on a 30 cm × 2.5 cm column eluted with 10–15% ether in hexanes
to give a white solid, mp 72–73◦C (lit.20 mp 72–73◦C). IR: 3556, 3467 cm−1; 1H NMR: δ
7.50–7.10 (complex, 15 H), 2.63 (t, J = 7.7 Hz, 2 H), 2.30 (m, 2 H), 2.07 (s, 1 H), 1.63 (m,
2 H); 13C NMR: δ 146.9, 142.1, 128.4, 128.2, 128.1, 126.8, 126.0, 125.7, 78.2, 41.3, 36.0,
25.4; MS: m/z 284 (M+−H2O).

88
Bunce and Cox
1,1-Diphenyl-4-(4-chlorophenyl)butanol (9b)
This compound (1.20 g, 76%) was prepared from 1.00 g (4.71 mmol) of 5 and was purified
by FC on a 30 cm × 2.5 cm column eluted with 10–15% ether in hexanes to give a white
solid, mp 77–79◦C. IR: 3565, 3470 cm−1; 1H NMR: δ 7.40–7.17 (complex, 12 H), 7.04 (d,
J = 8.2 Hz, 2 H), 2.59 (t, J = 7.7 Hz, 2 H), 2.27 (m, 2 H), 2.06 (s, 1 H), 1.60 (m, 2 H);
13C NMR: δ 146.8, 140.5, 131.5, 129.7, 128.3, 128.1, 126.8, 125.9, 78.1, 41.1, 35.3, 25.2;
MS: m/z 318, 320 (ca 3:1, M+−H2O).
Anal. Calcd for C22H21ClO: C, 78.45; H, 6.24, Found: C: 78.47; H, 6.24.
1,1-Diphenyl-4-(4-methoxyphenyl)butanol (10b)
This compound (1.31 g, 82%) was prepared from 1.00 g (4.81 mmol) of 6 and was purified
by FC on a 30 cm × 2.5 cm column eluted with 10–15% ether in hexanes to give a white
solid, mp 67–68◦C. IR: 3556, 3480, 2839 cm−1; 1H NMR: δ 7.40–7.16 (complex, 10 H),
7.04 (d, J = 8.2 Hz, 2 H), 6.80 (d, J = 8.2 Hz, 2 H), 3.77 (s, 3 H), 2.57 (t, J = 7.7 Hz, 2 H),
2.28 (m, 2 H), 2.07 (s, 1 H), 1.59 (m, 2 H); 13C NMR: δ 157.7, 147.0, 134.1, 129.3, 128.1,
126.8, 126.0, 113.7, 78.2, 55.2, 41.2, 35.0, 25.6; MS: m/z 314 (M+−H2O).
Anal. Calcd for C23H24O2: C, 83.13; H, 7.23. Found: C, 82.99; H, 7.20.
1,1-Diphenyl-4-(4-trifluoromethylphenyl)butanol (11b)
This compound (1.12 g, 74%) was prepared from 1.00 g (4.07 mmol) of 79 and purified by
FC on a 30 cm × 2.5 cm column eluted with 10–15% ether in hexanes to give a white solid,
mp 63–65◦C. IR 3559, 3466, 1328 cm−1; 1H NMR: δ 7.49 (d, J = 8.2 Hz, 2 H), 7.39–7.17
(complex, 12 H), 2.67 (t, J = 7.7 Hz, 2 H), 2.29 (m, 2 H), 2.07 (s, 1 H), 1.63 (m, 2 H);
13C NMR: δ 146.8, 146.2, 128.7, 128.4, 128.2, 126.9, 125.2 (q, J = 3.7 Hz), 78.1, 41.2,
35.8, 25.1 (the quartet of the CF3 carbon and 1 aromatic carbon were obscured); MS: m/z
352 (M+− H2O).
Anal. Calcd for C23H21F3O: C, 74.59; H, 5.68. Found: C; 74.66; H, 5.70.
ꢀR
General Procedure for the Cyclization with Amberlyst 15: 1,1-Dimethyl-1,2,3,4-
tetrahydronaphthalene (12a)
ꢀR
To a solution of 0.25 g (1.40 mmol) of 8a in 5 mL of PhH was added 0.25 g of Amberlyst
15 (dry, hydrogen form) and the mixture was heated under reflux for 0.5 h. The mixture
was cooled, filtered through a thin layer of anhydrous MgSO4 in a small fritted funnel, the
MgSO4 was washed with ether, and the solvent was removed under vacuum to afford 0.20
g (91%) of 12a as a colorless oil. This compound was spectroscopically pure, and the data
matched those previously reported.18
1,1-Dimethyl-7-chloro-1,2,3,4-tetrahydronaphthalene (13a)
This compound (0.21 g, 90%) was isolated as a colorless oil from 0.25 g (1.18 mmol)
1
of 9a after 0.5 h at reflux. IR: 1593, 1394, 1368 cm−1; H NMR: δ 7.27 (d, J = 2.2 Hz,
1 H), 7.02 (dd, J = 8.2, 2.2 Hz, 1 H), 6.96 (d, J = 8.2 Hz, 1 H), 2.70 (t, J = 6.4 Hz, 2 H),

Tetrahydronaphthalene Derivatives by Friedel-Crafts Cyclizations
89
1.78 (m, 2 H), 1.63 (m, 2 H), 1.26 (s, 6 H); 13C NMR: δ 147.7, 134.5, 131.2, 130.4, 126.6,
125.4, 38.8, 34.1, 31.7, 30.1, 19.5 (2 C); MS: m/z 194, 196 (ca 3:1, M+).
Anal. Calcd for C12H15Cl: C, 74.04; H, 7.71. Found: C, 74.12; H, 7.75.
1,1-Dimethyl-7-methoxy-1,2,3,4-tetrahydronaphthalene (14a)21
This compound (0.21 g, 92%) was isolated as a colorless oil from 0.25 g (1.20 mmol) of
10a after 0.5 h at reflux. IR: 2841, 1381, 1366 cm−1; 1H NMR: δ 6.97 (d, J = 8.2 Hz, 1 H),
6.87 (d, J = 2.2 Hz, 1 H), 6.65 (dd, J = 8.2, 2.2 Hz, 1 H), 3.78 (s, 3 H), 2.69 (t, J = 6.0 Hz,
2 H), 1.78 (m, 2 H), 1.64 (m, 2 H), 1.27 (s, 6 H); 13C NMR: δ 157.7, 147.0, 129.8, 128.4,
112.1, 110.9, 55.2, 39.2, 34.1, 31.8, 29.9, 19.8 (2 C); MS: m/z 190 (M+).
Anal. Calcd for C13H18O: C, 82.11; H, 9.47. Found: C, 82.01; H, 9.44.
1,1-Dimethyl-7-trifluoromethyl-1,2,3,4-tetrahydronaphthalene (15a)
This compound (0.20 g, 86%) was isolated as a colorless oil from 0.25 g (1.02 mmol) of
11a after 3 h at reflux. IR: 1619, 1389, 1360, 1332 cm−1; 1H NMR: δ 7.55 (s, 1 H), 7.29
(d, J = 8.2 Hz, 1 H), 7.12 (d, J = 8.2 Hz, 1 H), 2.79 (t, J = 6.0 Hz, 2 H), 1.82 (m, 2 H),
1.68 (m, 2 H), 1.29 (s, 6 H); 13C NMR: δ 146.5, 140.2, 129.5, 128.2, 124.6 (q, J = 270.6
Hz), 123.4 (q, J = 4.0 Hz), 121.9 (q, J = 3.7 Hz), 38.9, 34.0, 31.7, 30.7, 19.3 (2 C); MS:
m/z 228 (M+).
Anal. Calcd for C13H15F3: C, 68.42; H, 6.58. Found: C, 68.47; H, 6.60.
1,1-Diphenyl-1,2,3,4-tetrahydronaphthalene (12b)
This compound (0.22 g, 95%) was isolated as a white solid from 0.25 g (0.83 mmol) of
8b after 8 h at reflux, mp 120–122◦C (lit.22 mp 125◦C). The spectral data matched those
previously reported.22
1,1-Diphenyl-7-chloro-1,2,3,4-tetrahydronaphthalene (13b)
This compound (0.22 g, 93%) was isolated as a white solid from 0.25 g (0.74 mmol) of 9b
after 8 h at reflux, mp 134–136◦C. IR: 1594, 1499 cm−1; 1H NMR: δ 7.30–7.20 (complex,
7 H), 7.10–7.02 (complex, 5 H), 6.64 (d, J = 1.6 Hz, 1 H), 2.81 (t, J = 6.6 Hz, 2 H), 2.59
(m, 2 H), 1.63 (m, 2 H); 13C NMR: δ 147.5, 144.8, 135.7, 130.9, 130.7, 130.6, 129.3, 127.9,
126.4, 126.2, 53.7, 38.0, 28.7, 18.8; MS: m/z 318, 320 (ca 3:1, M+).
Anal. Calcd for C22H19Cl: C, 82.89; H, 5.97. Found: C, 82.87; H, 5.96.
1,1-Diphenyl-7-methoxy-1,2,3,4-tetrahydronaphthalene (14b)
This compound (0.22 g, 94%) was isolated as a white solid from 0.25 g (0.75 mmol) of
10b after 12 h at reflux, mp 108–109◦C. IR: 2833, 1609, 1493 cm−1; 1H NMR: δ 7.29–7.16
(complex, 7 H), 7.07 (d, J = 7.1 Hz, 4 H), 6.73 (dd, J = 8.2, 2.7 Hz, 1 H), 6.21 (d, J = 2.7
Hz, 1 H), 3.56 (s, 3 H), 2.79 (t, J = 6.6 Hz, 2 H), 2.59 (m, 2 H), 1.61 (m, 2 H); 13C NMR: δ
156.9, 148.6, 143.9, 130.0, 129.5, 129.4, 127.7, 125.9, 116.7, 112.0, 55.0, 53.9, 38.2, 28.4,
19.1; MS: m/z 314 (M+).
Anal. Calcd for C23H22O: C, 87.90; H, 7.01. Found: C, 87.78; H, 6.98.

90
Bunce and Cox
1,1-Diphenyl-4-trifluoromethylphenyl-1-butene (19b)
When this reaction was attempted on 0.25 g (0.68 mmol) of 11b, 0.23 g (96%) of alkene
19b was isolated as a white solid after 0.5 h of reflux, mp 66–68◦C. Refluxing for 72 h
gave a small amount of the tetrahydronaphthalene product, but it was inseparable from the
alkene. The spectral data for 19b were: IR: 1619, 1495, 1324 cm−1; 1H NMR: δ 7.50 (d,
J = 8.2 Hz, 2 H), 7.36–7.17 (complex, 11 H), 7.04 (dd, J = 7.7, 1.6 Hz, 1 H), 6.07 (t, J
= 7.7 Hz, 1 H), 2.79 (t, J = 7.7 Hz, 2 H), 2.44 (q, J = 7.7 Hz, 2 H); 13C NMR: δ 145.7,
142.8, 142.4, 139.8, 129.7, 128.8, 128.3, 128.2, 128.1, 127.8, 127.1, 127.02, 127.00, 125.2
(q, J = 3.7 Hz), 124.4 (q, J = 272.4 Hz), 35.9, 31.2; MS: m/z 352 (M+).
Anal. Calcd for C23H19F3: C, 78.41; H, 5.40. Found: C, 78.29; H, 5.35.
2-Methyl-5-phenylpentene (21)
To a stirred slurry of 2.40 g (6.72 mmol) of triphenylphosphonium bromide in 40 mL of
anhydrous THF at −78◦C was slowly added 4.00 mL of 1.7 M n-butyllithium in hexanes
(6.80 mmol) to give a bright yellow solution of the ylide. Stirring was continued for 15 min,
and a solution of 0.81 g (5.00 mmol) of 2010 in 2 mL of dry THF was added dropwise. The
reaction was stirred for 2 h with gradual warming to −25◦C and the reaction was poured
into 50 mL of saturated NH4Cl solution and extracted with ether (3x). The combined ether
layers were washed with saturated NaCl solution (1x), dried (MgSO4) and concentrated
under vacuum. The crude product was filtered through a plug of silica gel with pentane
and concentrated to give 0.70 g (88%) of 21 as a colorless oil. The spectral data for this
compound matched those reported previously.23
1,1-Dimethyl-1,2,3,4-tetrahydronaphthalene (12a)
ꢀR
To a solution of 0.25 g (1.56 mmol) of 18 in 5 mL of PhH was added 0.25 g of Amberlyst
15 and the mixture was heated under reflux for 0.5 h. Filtration of the mixture through
a thin layer of MgSO4 and concentration under vacuum afforded 0.23 g (92%) of 12a
as a colorless oil. This compound was spectroscopically pure and the data matched those
reported previously.18
Methyl (E)-3-Methyl-6-phenyl-2-hexenoate (22)24
The general procedure of Balsevich25 was used. Sodium hydride (0.28 g, 60% in mineral oil,
7.00 mmol) was washed with hexanes (3x) to remove the mineral oil and 8 mL of anhydrous
THF was added. The resulting slurry was stirred and treated at 22◦C with a solution of
1.28 g (7.02 mmol) of trimethyl phosphonoacetate in 2 mL of anhydrous DMSO added
dropwise over 20 min. The mixture was stirred for 15 min to give a tan solution of the
anion. To this anion was added a solution of 1.00 g (6.17 mmol) of 2012 in 3 mL of dry THF
and the reaction was stirred for 24 h at 22◦C. The crude reaction mixture was diluted with
petroleum ether and washed with 5% NaHCO3 solution (4x). The combined petroleum
ether washes were dried (MgSO4) and concentrated to give a tan oil, which was purified by
FC on a 40 cm × 2 cm column eluted with 2% ether in hexane. The major band afforded
1.15 g (85%) of (E)-22. IR: 1718, 1648 cm−1; 1H NMR: δ 7.28 (t, J = 7.7 Hz, 2 H), 7.18

Tetrahydronaphthalene Derivatives by Friedel-Crafts Cyclizations
91
(overlapping d and t, J ≈ 7.7 Hz, 3 H), 5.68 (s, 1 H), 3.68 (s, 3 H), 2.61 (t, J = 7.7 Hz, 2 H),
2.17 (t, J = 7.1 Hz, 2 H), 2.16 (s, 3 H), 1.80 (quintet, J = 7.7 Hz, 2 H); 13C NMR: δ 167.2,
160.0, 141.7, 128.3 (2 C), 125.9, 115.3, 50.8, 40.3, 35.2, 29.7, 29.0; MS: m/z 218 (M+).
Anal. Calcd for C14H18O2: C, 77.06; H, 8.26. Found: C, 77.16; H, 8.30.
Methyl ( )-2-(1-Methyl-1,2,3,4-tetrahydronaphthalen-1-yl)acetate (23)26
To a solution of 0.25 g (1.15 mmol) of (E)-22 in 5 mL of PhH was added 0.25 g of
ꢀR
Amberlyst 15 and the mixture was heated under reflux for 1 h. Filtration of the mixture
through a thin layer of MgSO4 and concentration under vacuum afforded 0.22 g (89%) of
23 as a colorless oil. (Note: A mixture of E and Z alkenes can also be used in the reaction.)
This compound was spectroscopically pure and gave the following data: IR: 1736 cm−1
;
1H NMR: δ 7.26 (d, J = 7.1 Hz, 1 H), 7.17–7.01 (complex, 3 H), 3.59 (s, 3 H), 2.77 (t, J
= 4.9 Hz, 2 H), 2.68 (d, J = 14.3 Hz, 1 H), 2.60 (d, J = 14.3 Hz, 1 H), 2.06 (m, 1 H),
1.82 (m, 2 H), 1.64 (m, 1 H), 1.40 (s, 3 H); 13C NMR: δ 172.1, 143.5, 136.4, 129.2, 126.4,
125.8, 125.7, 51.2, 47.1, 36.4, 35.7, 30.4, 29.5, 19.3; MS: m/z 203 (M+−CH3).
Anal. Calcd for C14H18O2: C, 77.06; H, 8.26. Found: C, 77.21; H, 8.29.
Methyl (E)-6-phenyl-2-hexenoate (25)
A 100-mL PhH solution of 1.00 g (6.77 mmol) of 2413 and 6.74 g (20.2 mmol) of
(methoxycarbonylmethylene)triphenylphosphorane27 was heated under reflux for 12 h,
then cooled and concentrated under vacuum. The residue was filtered through a 6 cm x 6
cm plug of silica gel in a sintered glass frit. FC of this material on a 30 cm × 2.5 cm column
eluted with 5% ether in hexane gave two bands: band 1, 0.10 g (0.47 mmol, 7%) of (Z)-25
contaminated with a small amount of the E isomer; band 2, 1.04 g (5.14 mmol, 76%) of
(E)-25. The spectral data for (E)-25 were: IR: 1725, 1656 cm−1; 1H NMR: δ 7.28 (t, J =
7.7 Hz, 2 H), 7.18 (overlapping t and d, J ≈ 7.7 Hz, 3 H), 6.99 (dt, J = 15.9, 7.1 Hz, 1 H),
5.84 (d, J = 15.9 Hz, 1 H), 3.72 (s, 3 H), 2.64 (t, J = 7.7 Hz, 2 H), 2.23 (q, J = 7.1 Hz, 2
H), 1.79 (quintet, J = 7.7 Hz, 2 H); 13C NMR: δ 167.0, 149.1, 141.6, 128.4, 128.3, 125.9,
121.2, 51.4, 35.1, 31.5, 29.6; MS: m/z 204 (M+).
Anal. Calcd for C13H16O2: C, 76.47; H, 7.84. Found: C, 76.55; H, 7.87.
( )-6,7,8,8a-Tetrahydroacenaphthalen-1(2H)-one (26)
To a solution of 0.25 g (1.23 mmol) of (E)-25 in 5 mL of PhH was added 0.25 g of
ꢀR
Amberlyst 15 and the mixture was heated under reflux for 72 h. Filtration of the mixture
through a thin layer of MgSO4 and concentration under vacuum afforded the crude product
as a colorless oil. The product was a complex mixture. Purification by PTLC using 5–10%
ether in hexanes afforded two major bands: band 1: 71 mg (28%) of recovered starting
material; band 2: 20 mg (10%) of 23, mp 99–100◦C (lit.28 mp 100–101.5◦C). IR: 1707
cm−1; 1H NMR: δ 7.52 (dd, J = 8.2, 1.6 Hz, 1 H), 7.28 (m, 2 H), 3.14 (apparent sextet, J
= 6.0 Hz, 1 H), 3.04–2.72 (complex, 3 H), 2.32 (dd, J = 17.6, 6.0 Hz, 1 H), 2.24 (m, 1 H),
2.14 (m, 1 H), 1.95 (m, 1 H), 1.37 (m, 1 H); 13C NMR: δ 205.7, 156.0, 135.6, 135.2, 133.1,
127.8, 120.5, 45.6, 36.5, 28.2, 25.9, 22.8; MS: m/z 172 (M+).
Anal. Calcd for C12H12O: C, 83.72; H, 6.98. Found: C, 83.59; H, 7.01.

92
Bunce and Cox
Acknowledgments
A. N. C. thanks the 2009 NSF-REU program at Oklahoma State University (CHE-0649162)
for support. Funding for the 300 MHz NMR spectrometer of the Oklahoma Statewide
Shared NMR Facility was provided by NSF (BIR-9512269), the Oklahoma State Regents
for Higher Education, the W. M. Keck Foundation, and Conoco, Inc. Finally, the authors
wish to thank the OSU College of Arts and Sciences for funds to upgrade our departmental
FT-IR and GC-MS instruments.
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Tetrahydronaphthalene Derivatives by Friedel-Crafts Cyclizations
93
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