Deoxygenation of diarylmethanols with dilute mineral acid

Article abstract of DOI:10.1139/V10-090

A new mild and efficient method for the deoxygenation of diarylmethanols is reported. The reaction employs catalytic hydrochloric acid in ethanol at reflux for 48 h. This reaction works on a variety of diarylmethanol substrates and mitigates the need for expensive and toxic reagents such stannanes and silanes used in alternative procedures. In addition, this reaction can be used in tandem with the deprotection of acid-sensitive silyl ether protecting groups in a one-pot procedure.

Full text of DOI:10.1139/V10-090

1003
Deoxygenation of diarylmethanols with dilute
mineral acid
Kyle A. Hope-Ross and John F. Kadla
Abstract: A new mild and efficient method for the deoxygenation of diarylmethanols is reported. The reaction employs
catalytic hydrochloric acid in ethanol at reflux for 48 h. This reaction works on a variety of diarylmethanol substrates and
mitigates the need for expensive and toxic reagents such stannanes and silanes used in alternative procedures. In addition,
this reaction can be used in tandem with the deprotection of acid-sensitive silyl ether protecting groups in a one-pot proce-
dure.
Key words: deoxygenation, diarylmethanols, reduction, silyl ether deprotection.
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Resume : On rapporte une nouvelle methode douce et efficace de desoxygenation des diarylmethanols. La reaction fait ap-
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pel a une quantite catalytique d’acide chlorhydrique, dans l’ethanol au reflux, pendant 48 h. La reaction donne de bons re-
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sultats avec une variete de substrats diarylmethanols et elle attenue le besoin pour des reactifs toxiques et dispendieux, tels
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les stannanes et les silanes utilises dans des methodes alternatives. De plus, cette reaction peut etre utilisee en tandem
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avec la deprotection d’ethers silyles sensibles aux acides utilises comme groupes protecteurs dans des methodes monoto-
pes.
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Mots-cles : desoxygenation, diarylmethanols, reduction, deprotection d’ether silyle.
one reported deoxygenation involves treatment of the alco-
Introduction
hol with triflic acid followed by triethyl silane.11
Diarylmethane is a reoccurring structural motif in numer-
ous natural products, including alangifolioside,1 itoside K,2
mastigophorene C,3 and terrestrols F–H4 (2–4, 5a–5c,
Fig. 1).
Herein, we report a new mild and efficient deoxygenation
of diaryl methanols to their corresponding diaryl methanes.
This method uses dilute mineral acid in ethanol and pro-
ceeds without the use of silanes or toxic heavy metals. A va-
riety of substrates were examined, and it was found that the
reaction proceeds exclusively for diarylmethanols, but not
for the other secondary alcohols examined.
A possible synthetic route towards these natural products
is the deoxygenation of diarylmethanols, which could be
achieved in a number of ways, including the Grignard reac-
tion.5 As such, the deoxygenation of secondary alcohols is
an important transformation in synthetic organic chemistry.
Unfortunately, few conditions for this transformation, which
are both mild and widely applicable, have been reported.
Perhaps the most well-known example is the Barton–
McCombie reaction, developed in 1975.6 In this reaction
the alcohol is converted to a thiocarbonyl derivative that,
upon treatment with tributylstannane and the radical initiator
AIBN (azobisisobutyronitrile), affords the corresponding hy-
drocarbon.7 Unfortunately, this reaction involves the homo-
lytic cleavage of the C–O bond, and because of the radical
nature of the reaction, this somewhat limits the substrate
scope. Additionally, the use of stoichiometric amounts of
toxic heavy metals such as tin limits the industrial applica-
tions of such reactions.
Experimental
All chemicals were purchased from Sigma-Aldrich and
used without further purification unless otherwise noted.
Solvents were purchased from Fisher Scientific and used as
received. All reactions were monitored by TLC, which was
˚
performed on Merck Alumafoil 60 A TLC plates with an
UV indicator. Flash chromatography was performed on
˚
60 A, 70–230 mesh silica gel purchased from Fisher Scien-
tific. 1H and 13C NMR spectra were recorded using a
300 MHz Bruker Avance Ultrashield NMR spectrometer
(300.13 and 75.03 MHz, respectively) and referenced to
CDCl3 (7.28 ppm). IR spectra were recorded using a
PerkinElmer Spectrum One FT-IR spectrometer. Melting
points were determined using a Mel-Temp melting point ap-
paratus and are uncorrected. Boiling points were determined
using differential scanning calorimetry (DSC) (TA Instru-
ments Q1000) at 101.1 kPa according to ASTM E1782.12
More recently, variants of this reaction have been re-
ported using silanes8 or dialkyl phosphites9 as hydrogen do-
nors, and trialkyl boron–oxygen or peroxides as radical
initiators.10
For the specific case of diarylmethanols (benzhydrols),
Received 24 September 2009. Accepted 14 June 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on
20 September 2010.
K.A. Hope-Ross and J.F. Kadla.1 Advanced Biomaterials Chemistry Laboratory, Department of Wood Science, University of British
Columbia, Vancouver, BC V6T 1Z4, Canada.
1Corresponding author (e-mail: john.kadla@ubc.ca).
Can. J. Chem. 88: 1003–1008 (2010)
doi:10.1139/V10-090
Published by NRC Research Press

1004
Can. J. Chem. Vol. 88, 2010
Fig. 1. Natural products containing the diarylmethane (1) moiety: alangifolioside (2), itoside K (3), mastigophorene C (4), and terrestrols F–
H (5a–5c).
General procedure for the attempted deoxygenation of
aryl methanols 6, 7, and 8
cooling to room temperature, the reaction mixture was
poured into a saturated solution of NaHCO3 (25 mL), added
to water (150 mL), and extracted with CH2Cl2 (3 Â
100 mL). The combined organics were washed with water
(200 mL), dried over MgSO4, filtered, and the solvent re-
moved in vacuo. Crystallization from hexanes afforded 8 as
a white powdery solid. Yield: 0.24 g, 90%; mp 136–139 8C
To a solution of aryl methanol (0.50 g) in ethanol
(50 mL) at 0 8C was added concentrated HCl (1.0 mL) as a
solution in ethanol. The solutions were heated to reflux for
48–120 h, and the reactions were monitored by TLC
(hexanes / ethyl acetate, 3:1). After cooling to room temper-
ature, the reaction mixture was poured into a saturated solu-
tion of NaHCO3 (25 mL), mixed well, and extracted with
CH2Cl2 (2 Â 100 mL). The combined organics were washed
with water (200 mL), dried over MgSO4, filtered, and sol-
vent removed in vacuo to afford the starting materials quan-
titatively.
1
(hexanes) (lit.13 134–138 8C). H NMR (300 MHz, CDCl3)
d: 7.27 (d, J = 8.28 Hz, 2H), 6.82 (d, J = 8.79 Hz, 2H),
4.86 (q, J = 6.37 Hz, 1H), 4.82 (s, 1H), 1.72 (s, 1H), 1.53
1
(d, J = 6.38 Hz, 3H). H NMR spectrum is in agreement
with that previously reported.13
1-[4-(tert-Butyl-dimethylsilanoxy)phenyl]ethanol (7) was
prepared according to the literature.13 Yield: 1.38 g, 91%.
1H NMR (300 MHz, CDCl3) d: 7.22 (d, J = 8.20 Hz, 2H),
6.80 (d, J = 8.20 Hz, 2H), 4.82 (m, 1H), 1.76 (s, 1H), 1.47
(d, J = 6.28, 3H), 0.98 (s, 9H), 0.21 (s, 6H). 13C NMR
(75 MHz, CDCl3) d: 158.82, 138.35, 126.43, 119.86, 70.07,
Diphenylmethanol (10)
To a solution of benzophenone (2.50 g, 13.72 mmol) in
freshly distilled THF (50 mL) was added sodium borohy-
dride (1.00 g, 27.44 mmol). The solution was heated to re-
flux for 18 h. After cooling to room temperature, the
reaction mixture was poured into water (125 mL) and ex-
tracted with CH2Cl2 (2 Â 200 mL). The combined organics
were washed with water (200 mL), dried over MgSO4, fil-
tered, and the solvent removed in vacuo to afford 10 as a
white crystalline solid. Yield: 2.23 g, 88%: mp 65–68 8C
1
25.81, 25.11, –4.21. H NMR and 13C NMR spectra are in
agreement with those previously reported.13
4-(1-Hydroxyethyl)phenol (8)
To a solution of 1-[4-(tert-butyl-dimethylsilanoxy)phenyl]-
ethanol (7, 0.50 g, 1.98 mmol) in ethanol (50 mL) at 0 8C
was added concd. HCl (1.0 mL) as a solution in ethanol
(9.0 mL). The reaction was heated to reflux for 48 h. After
(CH2Cl2) (lit.14 65–66 8C). H NMR (300 MHz, CDCl3) d:
1
7.43–7.26 (m, 10H), 5.87 (d, J = 3.41 Hz, 1H), 2.25 (d, J =
3.49 Hz, 1H). 13C NMR (75 MHz, CDCl3) d: 143.81,
Published by NRC Research Press

Hope-Ross and Kadla
1005
1
128.51, 127.59, 126.55, 76.29. H NMR and 13C NMR spec-
[4-(tert-Butyl-dimethylsilanoxy)phenyl]-4-(hexadecyloxy)-
phenylmethanol (12c) was prepared in a method analogous
to 12a. Yield: 3.54 g, 50%; bp 450 8C (determined from
tra are in agreement with those previously reported.14
1
Diphenylmethane (11)
DSC). H NMR (300 MHz, CDCl3) d: 7.27 (d, J = 8.21 Hz,
2H), 7.23 (d, J = 8.48 Hz, 2H), 6.87 (d, J = 8.67 Hz, 2H),
6.81 (d, J = 8.53 Hz, 2H), 5.77 (d, J = 3.39 Hz, 1H), 3.95 (t,
J = 6.55 Hz, 2H), 2.07 (d, J = 3.58 Hz, 1H), 1.78 (quin., J =
6.89 Hz, 2H), 1.54–1.23 (m, 26H), 0.99 (s, 9H), 0.94–0.87
(m, 3H), 0.20 (s, 6H). 13C NMR (75 MHz, CDCl3) d:
158.57, 155.01, 136.88, 136.10, 127.77, 127.70, 119.92,
114.37, 75.50, 68.03, 31.93, 29.69, 29.66, 29.60, 29.58,
29.40, 29.36, 29.29, 26.05, 25.67, 22.70, 18.19, 14.12, –4.42.
Anal. calcd. for C35H58O3Si: C, 75.75; H, 10.53. Found: C,
75.71; H, 10.46.
To
a solution of diphenylmethanol (10, 1.00 g,
5.43 mmol) in ethanol (50 mL) at 0 8C was added concd.
HCl (1.0 mL) as a solution in ethanol (9.0 mL). The solu-
tion was heated to reflux for 72 h. After cooling to room
temperature, the reaction mixture was poured into a satu-
rated solution of NaHCO3 (25 mL) and water (100 mL) was
added. The material was extracted with CH2Cl2 (2 Â
100 mL), washed with water (200 mL), dried over MgSO4,
filtered, and the solvent removed in vacuo to afford a clear,
colourless oil that crystallized on standing. Yield: 0.64 g,
72%; mp 24–26 8C (CH2Cl2) lit.15 25–26 8C. 1H NMR
(300 MHz, CDCl3) d: 7.26–7.30 (m, 4H), 7.18–7.21 (m,
6H), 3.98 (s, 2H). 13C NMR (75 MHz, CDCl3) d: 141.31,
4-(4-(Octyloxy)benzyl)phenol (13a)
To a solution of [4-(tert-butyl-dimethylsilanoxy)phenyl]-
4-(octyloxy)phenylmethanol (12a, 1.00 g, 2.26 mmol) in
ethanol (50 mL) at 0 8C was added concd. HCl (1.0 mL) as
a solution in ethanol (10 mL). The solution was heated to
reflux for 48 h. After cooling to room temperature, the reac-
tion mixture was poured into a saturated solution of
NaHCO3 (25 mL), mixed well, and extracted with hexanes
(3 Â 50 mL) and ether (50 mL). The combined organics
were washed with water (200 mL), dried over MgSO4, fil-
tered, and the solvent removed in vacuo. Crystallization
from 5% ether in petroleum ether afforded 13a as a white,
powdery solid. Yield: 0.56 g, 79%; mp 70–73 8C (5% ether
129.07, 128.66, 126.29, 42.11. H NMR and 13C NMR spec-
1
tra are in agreement with those previously reported.15
[4-(tert-Butyl-dimethylsilanoxy)phenyl]-4-
(octyloxy)phenylmethanol (12a)
To a solution of 1-bromo-4-(octyloxy)benzene (1.46 g,
5.12 mmol) in freshly distilled THF (60 mL) at –78 8C
under an Ar atmosphere was added tert-butyl lithium
(6.02 mL of a 1.7 mol/L solution in pentane, 10.24 mmol)
dropwise. After the mixture was allowed to stir for 1 h, a
solution of 4-(tert-butyl-dimethylsilanoxy)benzaldehyde
(1.21 g, 5.12 mmol) in freshly distilled THF (10 mL) was
added dropwise. The solution was warmed to room temper-
ature and stirred for 20 h. The reaction mixture was
quenched with brine (10 mL) and extracted with a 50:50
mixture of ether / petroleum ether (3 Â 80 mL). The com-
bined organic fractions were washed with water (3 Â
100 mL), dried over MgSO4, filtered, and the solvent re-
moved in vacuo. Flash chromatography (ether / petroleum
ether, 10:1) afforded 12a as a clear, light orange oil. Yield:
1
in petroleum ether). H NMR (300 MHz, CDCl3) d: 7.07 (t,
J = 8.22 Hz, 4H), 6.83 (d, J = 8.52 Hz, 2H), 6.76 (d, J =
8.42 Hz, 2H), 3.94 (t, J = 6.60 Hz, 2H), 3.86 (s, 2H), 1.78
(quin., J = 6.93 Hz, 2H), 1.52–1.21 (m, 10 H), 0.90 (t, J =
5.97 Hz, 3H). 13C NMR (75 MHz, CDCl3) d: 157.48,
153.75, 133.93, 133.45, 129.94, 129.70, 115.24, 114.50,
68.07, 40.13, 31.83, 29.37, 29.33, 29.25, 26.07, 22.66,
14.10. Anal. calcd. for C21H28O2: C, 80.73; H, 9.03; O,
10.24. Found: C, 80.31; H, 9.02; O, 10.67.
1
1.33 g, 59%; bp 435 8C (determined from DSC). H NMR
4-(4-(Dodecyloxy)benzyl)phenol (13b) was prepared in a
(300 MHz, CDCl3) d: 7.28 (d, J = 8.34 Hz, 2H), 7.23 (d,
J = 8.43 Hz, 2H), 6.87 (d, J = 8.63 Hz, 2H), 6.81 (d, J =
8.51 Hz, 2H), 5.77 (s, 1H); 3.96 (t, J = 6.51 Hz, 2H), 1.79
(quin., J = 6.80 Hz, 2H), 1.53–1.20 (m, 10H), 1.00 (s, 9H),
0.91 (m, 3H), 0.20 (s, 6H). 13C NMR (75 MHz, CDCl3) d:
158.57, 155.01, 136.88, 136.10, 127.77, 127.70, 119.92,
114.37, 75.50, 68.03, 31.92, 29.66, 29.63, 29.60, 29.58,
29.40, 29.34, 29.28, 26.05, 25.67, 22.69, 18.18, 14.12, –4.42.
Anal. calcd. for C31H50O3Si: C, 74.73; H, 10.10. Found: C,
74.71; H, 9.96.
method analogous to 13a. Yield: 0.50 g, 68%; mp 80–83 8C
1
(5% ether in petroleum ether). H NMR (300 MHz, CDCl3)
d: 7.07 (t, J = 8.20 Hz, 4H), 6.83 (d, J = 8.59 Hz, 2H), 6.76
(d, J = 8.48 Hz, 2H), 3.94 (t, J = 6.54 Hz, 2H), 3.86 (s, 2H),
1.78 (quin., J = 6.52 Hz, 2H), 1.51–1.21 (m, 14 H), 0.90 (t,
J = 6.51 Hz, 3H). 13C NMR (75 MHz, CDCl3) d: 157.48,
153.73, 133.95, 133.46, 129.94, 129.70, 115.25, 114.52,
68.09, 40.14, 31.93, 29.67, 29.64, 29.61, 29.59, 29.42,
29.35, 29.34, 26.07, 22.70, 14.12. Anal. calcd. for
C25H36O2: C, 81.47; H, 9.85; O, 8.68. Found: C, 81.40; H,
9.81; O, 8.79.
[4-(tert-Butyl-dimethylsilanoxy)phenyl]-4-(dodecyloxy)-
phenylmethanol (12b) was prepared in a method analogous
to 12a. Yield: 3.53 g, 56%; bp 443 8C (determined from
4-(4-(Hexadecyloxy)benzyl)phenol (13c) was prepared in
1
a method analogous to 13a. Yield: 0.60 g, 78%; mp 83–
DSC). H NMR (300 MHz, CDCl3) d: 7.27 (m, 2H), 7.23
1
90 8C (5% ether in petroleum ether). H NMR (300 MHz,
(d, J = 10.04 Hz, 2H), 6.87 (d, J = 8.16 Hz, 2H), 6.81 (d,
J = 7.98 Hz, 2H), 5.77 (s, 1H), 3.95 (t, J = 6.33 Hz, 2H),
2.07 (s, 1H), 1.78 (quin., J = 7.02 Hz, 2H), 1.51–1.21 (m,
18H), 0.99 (s, 9H), 0.90 (t, J = 6.42 Hz, 3H), 0.20 (s, 6H).
13C NMR (75 MHz, CDCl3) d: 158.57, 155.01, 136.88,
136.10, 127.77, 127.70, 119.92, 114.37, 75.50, 68.03, 31.92,
29.68, 29.64, 29.60, 29.58, 29.40, 29.35, 29.29, 26.05,
25.67, 22.70, 18.18, 14.12, –4.42. Anal. calcd. for
C27H42O3Si: C, 73.25; H, 9.56. Found: C, 73.21; H, 9.46.
CDCl3) d: 7.07 (t, J = 8.20 Hz, 4H), 6.80 (dd, J1 = 8.66 Hz,
J2 = 2.00 Hz, 4H), 4.56 (s, 1H), 3.94 (t, J = 6.58 Hz, 2H),
3.86 (s, 2H), 1.78 (quin., J = 6.58 Hz, 2H), 1.37 (m, 26H);
0.90 (t, J = 6.58 Hz, 3H). 13C NMR (75 MHz, CDCl3) d:
157.5, 153.7, 134.0, 133.4, 129.9, 129.7, 115.2, 114.5, 68.0,
40.1, 31.9, 29.7 (3), 29.6 (4), 29.4 (3), 29.3, 26.1, 22.7, 14.1.
Anal. calcd. for C29H44O2: C, 82.02; H, 10.44; O, 7.53.
Found: C, 82.05; H, 10.48; O, 7.47.
Published by NRC Research Press

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Can. J. Chem. Vol. 88, 2010
4-[Hydroxyl(4-(octyloxy)phenyl)methyl]phenol (14a)
To a solution of [4-(tert-butyl-dimethylsilanoxy)phenyl]-
(4-(octyloxy)phenyl)methanol (12a, 2.50 g, 5.65 mmol) in
freshly distilled THF (20 mL) at 0 8C was added a solution
of tributyl ammonium fluoride trihydrate (TBAF, 3.57 g,
11.30 mmol) in freshly distilled THF (20 mL). The solution
was allowed to stir for 1 h, warmed to room temperature,
and then stirred for 2 h. The reaction mixture was poured
into water (50 mL), mixed well, and then separated. The
aqueous phase was extracted with a 50:50 mixture of
ether / petroleum ether (2 Â 100 mL), and the combined or-
ganics were washed with water (250 mL), dried over
MgSO4, filtered, and the solvent removed in vacuo. Crystal-
lization from 5% ether in petroleum ether afforded 14a as a
white, powdery solid. Yield: 1.02 g, 55%; mp 81–86 8C (5%
a method analogous to 4-(4-(octyloxy)benzyl)phenol. Yield:
0.18 g, 79%; mp 83–90 8C (ether / petroleum ether). 1H
NMR (300 MHz, CDCl3) d: 7.07 (t, J = 8.20 Hz, 4H), 6.80
(dd, J1 = 8.66 Hz, J2 = 2.00 Hz, 4H), 4.56 (s, 1H), 3.94 (t, J =
6.58 Hz, 2H), 3.86 (s, 2H), 1.78 (quin., J = 6.58 Hz, 2H),
1.37 (m, 26H), 0.90 (t, J = 6.58 Hz, 3H). 13C NMR
(75 MHz, CDCl3) d: 157.5, 153.7, 134.0, 133.4, 129.9,
129.7, 115.2, 114.5, 68.0, 40.1, 31.9, 29.7 (3), 29.6 (4),
29.4 (3), 29.3, 26.1, 22.7, 14.1. Anal. calcd. for C29H44O2:
C, 82.02; H, 10.44; O, 7.53. Found: C, 82.05; H, 10.48; O,
7.47.
Bis(4-(dodecyloxy)phenyl)methanol (15)
A solution of 4,4’-bis(dodecyloxy)benzophenone (0.30 g,
0.55 mmol) and sodium borohydride (0.046 g, 1.20 mmol)
in ethanol (40 mL) was allowed to reflux for 1 h. After
cooling to room temperature, the reaction mixture was
poured into water (100 mL) and extracted with CH2Cl2
(2 Â 100 mL). The combined organics were washed with
water (2 Â 200 mL), dried over MgSO4, filtered, and the
solvent removed in vacuo. Crystallization from hexanes af-
forded 15 as a white powdery solid. Yield: 0.23 g, 76%;
mp 37–39 8C (hexanes). 1H NMR (300 MHz, CDCl3) d:
7.28 (d, J = 8.55 Hz, 4H), 6.88 (d, J = 8.55 Hz, 4H), 5.78
(d, J = 3.40 Hz, 1H), 3.95 (t, J = 6.58 Hz, 4H), 2.06 (d, J =
3.40 Hz, 1H), 1.78 (quin. J = 6.58 Hz, 4H), 1.52–1.19 (m,
36 H); 0.90 (t, J = 6.58 Hz, 6H). 13C NMR (75 MHz,
CDCl3) d: 158.55, 136.16, 127.71, 114.39, 75.46, 68.04,
31.92, 29.66, 29.63, 29.60, 29.58, 29.40, 29.35, 29.28,
26.05, 22.69, 14.12. Anal. calcd. for C37H61O3: C, 80.23; H,
11.10; O, 8.67. Found: C, 80.31; H, 11.03; O, 8.66.
1
ether in petroleum ether). H NMR (300 MHz, CDCl3) d: 7.
27 (d, J = 8.44 Hz, 2H), 7.25 (d, J = 8.37 Hz, 2H), 6.87 (d,
J = 8.71 Hz, 2H), 6.81 (d, J = 8.62 Hz, 2H), 5.78 (s, 1H),
4.77 (s, 1H), 3.95 (t, J = 6.57 Hz, 2H), 1.78 (quin., J =
6.57 Hz, 2H), 1.52–1.24 (m, 10H), 0.90 (t, J = 6.72 Hz,
3H). 13C NMR (75 MHz, CDCl3) d: 158.60, 154.86, 136.58,
136.05, 127.99, 127.72, 115.22, 114.42, 75.41, 68.05, 31.81,
29.35, 29.27, 29.23, 26.05, 22.65, 14.09. Anal. calcd. for
C21H28O3: C, 76.79; H, 8.59; O, 14.61. Found: C, 77.38; H,
7.80; O, 14.82.
4-[Hydroxy(4-(hexadecyloxy)phenyl)methyl]phenol (14c)
was prepared in a method analogous to 14a. Yield: 0.53 g,
50%; mp 95–101 8C (5% ether in petroleum ether). 1H
NMR (300 MHz, CDCl3) d: 7.28 (d, J = 8.11 Hz, 2H), 7.26
(d, J = 8.66 Hz, 2H), 6.87 (d, J = 8.49 Hz, 2H), 6.81 (d, J =
8.32 Hz, 2H), 5.78 (s, 1H), 4.69 (s, 1H), 3.95 (t, J =
6.51 Hz, 2H), 1.78 (quin., J = 6.53 Hz, 2H), 1.54–1.20 (m,
26H), 0.90 (t, J = 6.57 Hz, 3H). 13C NMR (75 MHz, CDCl3)
d: 158.59, 154.84, 136.58, 136.05, 128.39, 127.92, 115.22,
114.46, 75.41, 68.07, 31.81, 29.35, 29.29, 29.25, 26.06,
22.66, 14.10. Anal. calcd. for C29H44O3: C, 79.04; H, 10.06;
O, 10.89. Found: C, 78.43; H, 10.47; O, 11.10.
Bis(4-(dodecyloxy)phenyl)methane (16)
To a solution of bis(4-(dodecyloxy)phenyl)methanol (15,
0.25 g, 0.45 mmol) in ethanol (50 mL) at reflux was added
a solution of concd. HCl (0.5 mL) in ethanol (9.5 mL). The
solution was allowed to reflux for 48 h. After cooling to
room temperature, the reaction mixture was poured into a
saturated solution of NaHCO3 (25 mL) and mixed well.
Water (100 mL) was added and the mixture was extracted
with petroleum ether (150 mL) and ether (100 mL). The
combined organics were washed with water (200 mL), dried
over MgSO4, filtered, and the solvent removed in vacuo to
afford bis(4-(dodecyloxy)phenyl)methane as a waxy white
solid. Yield: 0.20 g, 83%; mp 30–33 8C (petroleum
4-(4-(Octyloxy)benzyl)phenol (13a)
To a solution of 4-[hydroxyl(4-(octyloxy)phenyl)methyl]-
phenol (14a, 0.20 g, 0.61 mmol) in ethanol (50 mL) 8C was
added concd. HCl (0.5 mL) as a solution in ethanol
(9.5 mL). The solution was allowed to stir for 1 h and then
heated to reflux for 48 h. After cooling to room temperature,
the reaction mixture was poured into a saturated solution of
NaHCO3 (25 mL), mixed well, and then extracted with pe-
troleum ether (3 Â 50 mL) and ether (50 mL). The com-
bined organics were washed with water (200 mL), dried
over MgSO4, filtered, and the solvent removed in vacuo to
afford 4-(4-(octyloxy)benzyl)phenol as a white powdery
solid. Yield: 0.17 g, 90%; mp 70–73 8C (ether / petroleum
1
ether / ether). H NMR (300 MHz, CDCl3) d: 7.08 (d, J =
8.59 Hz, 4H), 6.83 (d, J = 8.59 Hz, 4H), 3.94 (t, J =
6.57 Hz, 4H), 3.87 (s, 2H), 1.78 (quin., J = 6.56 Hz, 4H),
1.51–1.22 (m, 36H), 0.91 (t, J = 6.57 Hz, 6H). 13C NMR
(75 MHz, CDCl3) d: 157.46, 133.54, 129.68, 114.44, 68.02,
40.14, 31.92, 29.66, 29.63, 29.60, 29.59, 29.41, 29.34,
29.33, 26.07, 22.69, 14.12. Anal. calcd. for C37H61O2: C,
82.62; H, 11.43; O, 5.95. Found: C, 82.65; H, 11.48; O,
5.87.
1
ether). H NMR (300 MHz, CDCl3) d: 7.07 (t, J = 8.22 Hz,
4H), 6.83 (d, J = 8.52 Hz, 2H), 6.76 (d, J = 8.42 Hz, 2H),
3.94 (t, J = 6.60 Hz, 2H), 3.86 (s, 2H), 1.78 (quin., J =
6.93 Hz, 2H), 1.52–1.21 (m, 10 H), 0.90 (t, J = 5.97 Hz,
3H). 13C NMR (75 MHz, CDCl3) d: 157.48, 153.75, 133.93,
133.45, 129.94, 129.70, 115.24, 114.50, 68.07, 40.13, 31.83,
29.37, 29.33, 29.25, 26.07, 22.66, 14.10. Anal. calcd. for
C21H28O2: C, 80.73; H, 9.03; O, 10.24. Found: C, 80.01; H,
9.46; O, 10.53.
Results and discussion
In our efforts towards the acidic hydrolysis of silyl ether
protecting groups,16 we discovered an unexpected result: in
addition to cleavage of the silicon–oxygen bond, we also ob-
served deoxygenation of the diarylmethanol (Scheme 1).
4-(4-(Hexadecyloxy)benzyl)phenol (13c) was prepared in
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Hope-Ross and Kadla
1007
Table 1. Deoxygenation of secondary alcohols using HCl/EtOH.
Scheme 1. Attempted acidic hydrolysis of silyl ether protecting groups. Reagents and conditions: HCl, EtOH, reflux 48 h.
To further probe the generality of this reaction, we tested
a number of substrates including secondary alcohols and di-
arylmethanols with different substitution patterns, with and
without silyl ether protecting groups. Table 1 outlines the
substrates examined and the results, including reaction time
and yield. It was found that the reaction does not proceed
for primary alcohols or secondary alcohols not bearing two
aryl functionalities, nor was the presence of the silyl protect-
ing group required. The reaction proceeds in good yields
(68%–90%) for substrates displaying a variety of substitu-
tion patterns.
Conclusions
A new mild and efficient method for the deoxygenation of
diarylmethanols has been developed. This reaction mitigates
Published by NRC Research Press

1008
Can. J. Chem. Vol. 88, 2010
(9) Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. C. Tetrahedron
Lett. 1991, 32 (49), 7187. doi:10.1016/0040-4039(91)80472-
I.
the need to use radical conditions or toxic heavy metals em-
ployed in the Barton–McCombie deoxygenation.
(10) Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. C. Tetrahedron
Lett. 1992, 33 (17), 2311. doi:10.1016/S0040-4039(00)
74198-0.
(11) Waterlot, C.; Coutourier, D.; De Backer, M.; Rigo, B. Can.
J. Chem. 2000, 78 (9), 1242. doi:10.1139/cjc-78-9-1242.
(12) Standard Test Method for Determining Vapor Pressure by
Thermal Analysis; ASTM Standard E1782 [Online]; ASTM
International: West Conshohocken, PA, 2008. doi:10.1520/
E1782-08. Available from www.astm.org.
(13) Noji, M.; Ohno, T.; Fuji, K.; Futaba, N.; Tajima, H.; Ishii,
K. J. Org. Chem. 2003, 68 (24), 9340. doi:10.1021/
jo034255h. PMID:14629155.
(14) Kuriyama, M.; Shimazawa, R.; Shirai, R. J. Org. Chem.
2008, 73 (4), 1597. doi:10.1021/jo7020983. PMID:
18186645.
Acknowledgements
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support.
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