1780 J . Org. Chem., Vol. 67, No. 6, 2002
Chakraborti et al.
(327 mg, 1.5 mmol) in NMP (2 mL) was treated with Na (92.00
mg, 4.0 mmol) at 90 °C for 15 min under N2. 2-Naphthyl
tosylate (745 mg. 2.5 mmol) in NMP (3 mL) was added, and
the mixture was heated at 90 °C for 2 h. The cooled reaction
mixture was made alkaline with 5% aqueous NaOH (25 mL)
and extracted with Et2O (3 × 15 mL) to separate any neutral
component (GCMS of these combined ethereal extracts showed
the presence of PhSTs). The aqueous part was acidified in the
cold (ice bath) with 6 N HCl and extracted with Et2O (3 × 15
mL). The combined Et2O extracts were washed with brine (15
mL), dried (Na2SO4), and concentrated under vacuo to afford
a brown solid which on passing through a column of silica gel
(230-400, 1 g) and elution with 5% EtOAc-hexane (200 mL)
afforded the product (360 mg, 100%) which was in full
agreement with mp and spectral data (IR, 1H NMR, and
GCMS) of an authentic sample of 2-naphthol.
stituent react at a faster rate than those having no such
substitution. Excellent selectivity has been achieved in
the deprotection of methyl esters over aryl methyl ethers,
aryl esters over aryl alkyl ethers, and aryl esters over
alkyl esters during intramolecular competitions.
Exp er im en ta l Section
Gen er a l. The aryl methyl ethers, alkyl esters, and aryl
esters were either available commercially or prepared by
standard procedures.1-3 Solvents were distilled before use.
DMPU, DMEU, HMPA, sulfolane, Ph2S2, (2-NH2-C6H4)2S2,
Me2S2, [Et2NC(dS)S]2, Li, LiH, KOBut, and KH were pur-
chased from Aldrich. DMF, NMP, Na, K, and NaH were
purchased from S. d. fine chemicals, India.
Gen er a l P r oced u r e for Dep r otection . Rep r esen ta tive
P r oced u r e for Dep r otection of Ar yl Alk yl Eth er s. The
magnetically stirred solution of Ph2S2 (327 mg, 1.5 mmol) in
NMP (2 mL) was treated with Na (92.00 mg, 4.0 mmol) under
reflux for 15 min under N2. 2-Methoxynaphthalene (395.4 mg,
2.5 mmol) in NMP (3 mL) was added, and the mixture was
heated under reflux for 30 min. The cooled reaction mixture
was made alkaline with 5% aqueous NaOH (25 mL) and
extracted with Et2O (3 × 15 mL) to separate any neutral
component (GCMS of these combined ethereal extracts showed
the presence of PhSMe). The aqueous part was acidified in
the cold (ice bath) with 6 N HCl and extracted with Et2O (3 ×
15 mL). The combined Et2O extracts were washed with brine
(15 mL), dried (Na2SO4), and concentrated under vacuo to
afford a brown solid which on passing through a column of
silica gel (230-400, 1 g) and elution with 5% EtOAc-hexane
(200 mL) afforded the product (340 mg, 93%) which was in
Selective Dep r otection in In tr a m olecu la r Com p eti-
tion . Selective Dep r otection of Meth yl Ester s in In -
tr a m olecu la r Com p etition betw een Meth yl Ester s a n d
Ar yl Alk yl Th ioeth er s. The magnetically stirred solution of
Ph2S2 (327 mg, 1.5 mmol) in NMP (2 mL) was treated with
Na (92.00 mg, 4.0 mmol) at 90 °C for 15 min under N2. Methyl
thiophenoxyaceate (455 mg. 2.5 mmol) in NMP (3 mL) was
added, and the mixture was heated at 90 °C for 15 min. The
cooled reaction mixture was made alkaline with saturated
aqueous NaHCO3 (25 mL) and extracted with Et2O (3 × 15
mL) to separate any neutral component (GCMS of these
combined ethereal extracts showed the presence of PhSMe).
The aqueous part was acidified in the cold (ice bath) with 6 N
HCl and extracted with Et2O (3 × 15 mL). The combined Et2O
extracts were washed with brine (15 mL), dried (Na2SO4), and
concentrated under vacuo to afford a light yellow solid which
on passing through a column of silica gel (60-120, 10 g) and
elution with 10% EtOAc-hexane afforded the product (400 mg,
97%) which was in full agreement with mp and spectral data
1
full agreement with mp and spectral data (IR, H NMR, and
GCMS) of an authentic sample of 2-naphthol.
Rep r esen ta tive P r oced u r e for Dep r otection of Alk yl
Ester s. The magnetically stirred solution of Ph2S2 (327 mg,
1.5 mmol) in NMP (2 mL) was treated with Na (92.00 mg, 4.0
mmol) at 90 °C for 15 min under N2. Methyl benzoate (340.4
mg, 2.5 mmol, 0.31 mL) in NMP (3 mL) was added, and the
mixture was heated at 90 °C for 15 min. The cooled reaction
mixture was made alkaline with saturated aqueous NaHCO3
(25 mL) and extracted with Et2O (3 × 15 mL) to separate any
neutral component (GCMS of these combined ethereal extracts
showed the presence of PhSMe). The aqueous part was
acidified in the cold (ice bath) with 6 N HCl and extracted with
Et2O (3 × 15 mL). The combined Et2O extracts were washed
with brine (15 mL), dried (Na2SO4), and concentrated under
vacuo to afford a light yellow solid which on crystallization
(5% EtOAc-hexane) afforded the product (305 mg, 100%)
which was in full agreement with mp and spectral data (IR,
1H NMR, and GCMS) of an authentic sample of benzoic acid.
Rep r esen ta tive P r oced u r e for Dep r otection of Ar yl
Ester . The magnetically stirred solution of Ph2S2 (327 mg, 1.5
mmol) in NMP (2 mL) was treated with Na (92.00 mg, 4.0
mmol) at 90 °C for 15 min under N2. 2-Naphthyl benzoate (620
mg. 2.5 mmol) in NMP (3 mL) was added, and the mixture
was heated at 90 °C for 15 min. The cooled reaction mixture
was made alkaline with 5% aqueous NaOH (25 mL) and
extracted with Et2O (3 × 15 mL) to separate any neutral
component (GCMS of these combined ethereal extracts showed
the presence of PhSCOPh). The aqueous part was acidified in
the cold (ice bath) with 6 N HCl and extracted with Et2O (3 ×
15 mL). The combined Et2O extracts were washed with
saturated aqueous NaHCO3 (2 × 15 mL), to separate any
benzoic acid formed as a result of partial hydrolysis of
PhSCOPh, and brine (15 mL), dried (Na2SO4), and concen-
trated under vacuo to afford a brown solid which on passing
through a column of silica gel (230-400, 1 g) and elution with
5% EtOAc-hexane (200 mL) afforded the product (360 mg,
100%) which was in full agreement with mp and spectral data
1
(IR, H NMR, and GCMS) of an authentic sample of thiophe-
noxyacetic acid.
Select ive Dep r ot ect ion of P h en olic E st er s in In t r a -
m olecu la r Com p etition betw een P h en olic Ester s a n d
Ar yl Alk yl Eth er s. The magnetically stirred solution of Ph2S2
(327 mg, 1.5 mmol) in NMP (2 mL) was treated with Na (92.00
mg, 4.0 mmol) at 90 °C for 15 min under N2. 3-Methoxy-4-ben-
zoyloxybenzaldehyde (640 mg. 2.5 mmol) in NMP (3 mL) was
added, and the mixture was heated at 90 °C for 15 min. After
the usual workup and purification, the phenolic product was
isolated (380 mg, 100%) and was in full agreement with mp
1
and spectral data (IR, H NMR, and GCMS) of an authentic
sample of vanillin. Deprotection of the corresponding acetate
in an analogous manner resulted in a 95% yield of vanillin.
No cleavage of the methyl ether was observed in either
occasion.
Selective Dep r otection of Ar yl Ester s in In tr a m olecu -
la r Com p etition betw een Alk yl a n d Ar yl Ester s. The
magnetically stirred solution of Ph2S2 (327 mg, 1.5 mmol) in
NMP (2 mL) was treated with Na (92.00 mg, 4.0 mmol) at 90
°C for 15 min under N2. Methyl 4-acetoxybenzoate (485 mg,
2.5 mmol) in NMP (3 mL) was added and the mixture was
heated at 90 °C for 15 min. After the usual workup and
purification, the phenolic product 2 was isolated (342 mg, 90%)
1
and was in full agreement with mp and spectral data (IR, H
NMR, and GCMS) of an authentic sample of methyl 4-hy-
droxybenzoate. Deprotection of methyl 4-benzoyloxybenzoate,
ethyl 4-acetoxybenzoate, ethyl 4-benzoyloxybenzoate, propyl
4-acetoxybenzoate, and propyl 4-benzoyloxybenzoate in an
analogous manner resulted the corresponding phenolic esters
in 80, 87, 100, 95, and 90% yields, respectively. No appreciable
amount of alkyl ester cleavage could be detected in each
occasion.
1
(IR, H NMR, and GCMS) of an authentic sample of 2-naph-
Ack n ow led gm en t. L.S. thanks CSIR, New Delhi,
for the award of senior research fellowship.
thol.
Rep r esen ta tive P r oced u r e for Dep r otection of Ar yl
Su lfon a te Ester s. The magnetically stirred solution of Ph2S2
J O010611P