Efficient method for the preparation of carboxylic acid alkyl esters or alkyl phenyl ethers by a new-type of oxidation-reduction condensation using 2,6-dimethyl-1,4-benzoquinone and alkoxydiphenylphosphines

Article abstract of DOI:10.1246/bcsj.76.1645

A new-type of oxidation-reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1) having primary, bulky secondary or tertiary alkoxy groups, a mild quinone-type oxidant such as 2,6-dimethyl-1,4-benzoquinone (DMBQ) and carboxylic acids or phenols. Generally, alkoxydiphenylphosphines were prepared easily from chlorodiphenylphosphine (2) and alcohols in the presence of pyridine, and were isolated by distillation. On the other hand, the phosphines 1 were also prepared in situ from N,N-dimethylaminodiphenylphosphine (3a) and primary or secondary alcohols while primary, bulky secondary or tertiary alkoxydiphenylphosphines were alternatively formed in situ by adding 2 to the "BuLi-treated alcohols in order to perform the above reactions by a one-pot procedure from alcohols and nucleophiles. The reaction of thus formed 1, DMBQ and carboxylic acids or phenols afforded the corresponding alkylated products, including hindered secondary and tertiary alkylated ones, in good to high yields at room temperature. In the case of using chiral secondary alcohols, the corresponding carboxylic acid alkyl esters were obtained as well in high yields with perfect inversion of stereochemistry by S_N2 replacement.

Full text of DOI:10.1246/bcsj.76.1645

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1645–1667 (2003) 1645
Efficient Method for the Preparation of Carboxylic Acid Alkyl Esters or
Alkyl Phenyl Ethers by a New-Type of Oxidation–Reduction Conden-
sation Using 2,6-Dimethyl-1,4-benzoquinone and Alkoxydiphenylphos-
phines
#
ꢀ;
Taichi Shintou, Wataru Kikuchi, and Teruaki Mukaiyama
Center for Basic Research, The Kitasato Institute, 6-15-5 Toshima, Kita-ku, Tokyo 114-0003
(Received February 28, 2003)
A new-type of oxidation–reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl
phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1) having primary, bulky secondary
or tertiary alkoxy groups, a mild quinone-type oxidant such as 2,6-dimethyl-1,4-benzoquinone (DMBQ) and carboxylic
acids or phenols. Generally, alkoxydiphenylphosphines were prepared easily from chlorodiphenylphosphine (2) and al-
cohols in the presence of pyridine, and were isolated by distillation. On the other hand, the phosphines 1 were also pre-
pared in situ from N,N-dimethylaminodiphenylphosphine (3a) and primary or secondary alcohols while primary, bulky
n
secondary or tertiary alkoxydiphenylphosphines were alternatively formed in situ by adding 2 to the BuLi-treated al-
cohols in order to perform the above reactions by a one-pot procedure from alcohols and nucleophiles. The reaction of
thus formed 1, DMBQ and carboxylic acids or phenols afforded the corresponding alkylated products, including hin-
dered secondary and tertiary alkylated ones, in good to high yields at room temperature. In the case of using chiral sec-
ondary alcohols, the corresponding carboxylic acid alkyl esters were obtained as well in high yields with perfect inver-
sion of stereochemistry by SN2 replacement.
Preparation of carboxylic acid esters or phenyl ethers are
among the best-established, most fundamental, and most im-
portant procedures in organic synthesis.1 Direct formation
of carboxylic esters from the corresponding carboxylic acids
and alcohols is generally performed by shifting the equilibrium
in favor of the desired ester according to one of the following
methods:ffi) to use a large excess amount of carboxylic acids or
alcohols or to remove the formed water from the reaction mix-
ture as an azeotrope mixture with a solvent such as benzene or
xylene by using catalysts such as sulfuric acid,1e sulfonic acid,
hydrochloric acids, Nafion-H,1f zirconium oxide sulfate ion,1g
etc;ffl) to use dehydrating agents such as 1-methyl-2-halopyr-
idinium salts,1h dicyclohexylcarbodiimide,1i,1j 2,4,6-trichloro-
benzoyl chloride,1k and 2-methyl-6-nitrobenzoic anhydride,1l
etc. Of these esterification methods, preparation of bulky sec-
ondary or tertiary alkyl esters is known to be more difficult
compared with the preparation of primary ones. For the syn-
thesis of carboxylic esters from the corresponding carboxylic
acids and hindered alcohols, most of all the methods have
some problems:1 for example, long reaction time, need of a
large excess amount of carboxylic acids or alcohols, severe re-
action conditions with strong acids or bases, side reactions, or
poor yields of the desired products.
oxidants. The important point of this concept is that the reac-
tion proceeded under ‘‘mild and neutral’’ conditions without
having any assistance from acids or bases. The first examples
of this type of condensation were reported from our laboratory
concerning acylation reactions by using combinations of di-
phenylmercury and tributylphosphine (in 1963),2 trans-1,2-di-
benzoylethylene and tributylphosphine (in 1964),3 and 2,20-di-
pyridyl disulfide and triphenylphosphine (in 1970).4 In 1967,
preparation of phosphoric esters was also carried out by using
triethyl phosphite and diethyl azodicarboxylate (DEAD) in the
presence of alcohols.5 Mitsunobu developed this concept to an
efficient alkylation method by using a combination of triphen-
ylphosphine and DEAD, and achieved a condensation reaction
between alcohols and various nucleophiles (Mitsunobu reac-
tion), which is now known very widely.6 Recently, Tsunoda
et al. reported an alkylating reaction by using alcohols and cy-
anomethylenetributylphosphorane or N,N,N0,N0-tetramethyl-
azodicarboxamide (TMAD)7 which works out well likewise.
The search for a convenient and useful new-type of oxida-
tion–reduction condensation has been a matter of our contin-
ued interest ever since the reaction was first reported. In most
cases of the current oxidation–reduction condensation, triphen-
ylphosphine is employed as a reductant. Acylations proceeded
smoothly to afford the desired products in high yields while the
yields of alkylations using bulky secondary or tertiary alcohols
stayed generally low, which was probably because of the in-
complete formation of the key intermediates, phosphonium
alkoxides. Since the alkoxy part of alkoxydiphenylphosphine
had been introduced in advance, it was thought to have be-
The fundamental concept of oxidation–reduction condensa-
tion is to perform dehydration condensation by removing H2O
as 2[H] and [O] using a combination of weak reductants and
# Kitasato Institute for Life Sciences, Kitasato University, 5-9-1
Shirokane, Minato-ku, Tokyo 108-8641
Published on the web August 15, 2003; DOI 10.1246/bcsj.76.1645

1646 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Scheme 1.
Scheme 2.
haved more effectively in the formation of the important inter-
mediate phosphonium salt. In our another point of view, al-
koxydiphenylphosphine would form the key intermediate,
phosphonium salt, more smoothly by an interaction even with
weaker oxidizing agents such as quinone because of the intro-
duction of one alkoxy group in place of phenyl group of tri-
phenylphosphine, and the subsequent alkylation reaction via
the oxidation–reduction process would proceed effectively.
Quinone compounds have long been anticipated as effective
oxidants in this type of condensation; however, no successful
examples have been shown to date. The intermediate phos-
phonium salt was in turn converted to so-called penta-valent
phosphorus by catching one hydrogen atom up with a nega-
tively charged oxygen of the formed quartery phosphonium
salt (4) from carboxylic acids or phenols. At the same time,
thus formed nucleophilic species such as carboxylates or phe-
nolates attacked the alkyl group to form an alkylated product
and diphenylphosphinic acid 4-hydroxyphenyl ester (5)
(Scheme 1). Then, with the consideration that the combination
of Ph2POR and quinones would work well in the oxidation–re-
duction condensation, benzylation of benzoic acid (6a) with
benzyloxydiphenylphosphine (1a) was tried first by using
1,4-benzoquinone in toluene, and the desired product (7a)
was obtained in 32% yield. The result prompted us to work
further on this new-type of oxidation–reduction condensation
by using a combination of alkoxydiphenylphosphine and
DMBQ, and the reaction successfully afforded various carbox-
ylic acid alkyl esters or alkyl phenyl ethers including bulky al-
kyl groups in good to high yield after screening various qui-
nones (Scheme 2).8–10
Results and Discussion
Synthesis of Alkoxyphosphines (Scheme 3, 1a–i) and
Aminodiphenylphosphines (Scheme 3, 3a–e). Alkoxydi-
phenylphosphines such as methoxydiphenylphosphine (1b)
and ethoxydiphenylphosphine (1c) have been employed in
peptide syntheses or Arbuzov reactions as useful phosphorus
compounds.11 Alkoxydiphenylphosphines having a primary,
secondary, or tertiary alkoxy group were generally isolated
by distillation. Alkoxydiphenylphosphines (1a–f) having a
primary or secondary alkoxy group are prepared easily from
2 and alcohols by using a base such as pyridine. Similarly,
Scheme 3.

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1647
Table 1. Effect of Solvent on Benzylation of 6a
benzyloxydialkylphosphines such as benzyloxydiisopropyl-
phosphine (1h) and benzyloxycyclohexylphosphine (1i) were
prepared from alkylchlorophosphine and benzyl alcohol; t-bu-
toxydiphenylphosphine (1g) was also prepared from 2 and po-
tassium t-butoxide in 31% yield. Alkoxydiphenylphosphines
were alternatively in situ formed by treating aminodiphenyl-
phosphines (3a–e),12 prepared from 2 and the corresponding
amines or 1-(trimethylsilyl)-2-pyrrolidinone,13 with primary
or secondary alcohols.
Esterification of Carboxylic Acids by a New-Type of Ox-
idation–Reduction Condensation Using Quinones and
Alkoxydiphenylphosphines. In the first place, benzylation
of 6a with 1.0 equivalent of 1a was tried by using 1.0 equiv-
alent of 1,4-benzoquinone in toluene, and the desired ester
(7a) was obtained in 32% yield within 3 h (Table 1, entry
1). When the reaction was tried under the same conditions
in half the quantity of toluene, 7a was obtained in 43% yield
(Table 1, entry 2). Next, after screening the effect of several
other solvents such as acetonitrile, diethyl ether, and dichloro-
methane on the above model reaction, it was found that no sig-
nificant difference due to the nature of solvent was observed
(Table 1, entries 2–5). However, careful observation indicated
that a more concentrated solution could be available when di-
Entry Solvent/mL Yield/% Entry Solvent/mL Yield/%
1
2
3
4
Toluene/3.0
Toluene/1.5
CH3CN/1.5
Et2O/1.5
32
43
40
41
5
6
7
8
CH2Cl2/1.5
CH2Cl2/1.0
CH2Cl2/0.5
CH2Cl2/0.25
43
56
75
47
chloromethane was used because of its high solubility. When
the concentration was 1.2 mol dmꢁ3 in dichloromethane, 7a
was obtained in 75% yield under the above conditions
(Table 1, entry 7). Thus, dichloromethane was used as the
most preferable solvent for this condensation.
When benzylation of 6a with 1.0 equivalent of 1a was tried
in the absence of quinone type oxidant such as 1,4-benzoqui-
none in dichloromethane, the reaction hardly took place, as ex-
pected (Table 2, entry 1). When the well-known oxidant such
as trans-1,2-dibenzoylethylene or DEAD mentioned above
was used together, 7a was obtained within 3 h under the above
Table 2. Screening of Quinone Derivatives on Benzylation of 6a
Entry
1
Quinone
none
Yield/%
N.R.
Entry
7
Quinone
Yield/%
75
Entry
13
Quinone
Yield/%
19
2
55
8
90
14
77
3
4
5
6
73
9
10
11
12
66
12
45
70
15
16
19
32
N.R.
N.R.
N.R.

1648 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Table 3. Effect of Substituents of Phosphine on Benzylation
of 6a
Table 4. Benzylation of Various Carboxylic Acids with 1a
and DMBQ
Entry
1
RCOOH
Product
Yield/%
98
Entry
R
R2POBn/equiv. Time/h Yield/%
1
2
3
4
5
6
7
iPr
cyclohexyl 1i
1h
1.0
1.0
1.0
1.1
1.3
1.1
1.1
3
3
3
3
3
0.5
1
60
57
90
97
97
98
97
6a
6b
6c
7a
Ph
Ph
Ph
Ph
Ph
1a
1a
1a
1a
1a
2
3
7b
7c
98
95
4
5
6d
6e
7d
7e
95
93
conditions in 55% or 73% yields, respectively (Table 2, entries
2 and 3). It is interesting to note that the carboxylic esters
were not obtained when more powerful oxidizing agents such
as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetra-
chloro-1,4-benzoquinone (p-chloranil), and 2,6-dichloro-1,4-
benzoquinone were used (Table 2, entries 4–6) while the yield
of 7a was 75% when a milder oxidant such as 1,4-benzoqui-
none was used (Table 2, entry 7). After screening several qui-
none derivatives, 7a was obtained in 90% yield under mild
condition when DMBQ was used (Table 2, entries 8–16).
Next, it was thought that the present reaction might be im-
proved by replacing two phenyl groups contained in the above-
mentioned 1a by two electron-donating alkyl groups. It was
known that chlorodialkylphosphines were generally prepared
by treating phosphorus trichloride with the corresponding alkyl
Grignard reagents.14 However, preparation of chlorodialkyl-
phosphine having alkyl groups such as methyl or n-butyl group
was not successful due to the extreme unstability of the pro-
duced phosphines. In the case of secondary alkyl groups such
as isopropyl or cyclohexyl group, the corresponding chloro-
dialkylphosphines were successfully isolated and were con-
verted to 1h or 1i; employment of thus prepared 1h and 1i af-
forded the desired ester in 60% and 57% yields, respectively
(Table 3, entries 1 and 2).
6
7
6f
7f
89
89
6g
7g
8
9
6h
6i
7h
7i
86
90a)
10
6j
7j
89a)
11
12
6k
6l
7k
7l
95
93
a) No epimerization was observed by HPLC using Daicel
CHIRALPAK AF.8
benzyl esters were exclusively obtained in high yields with
no epimerizations (Table 4, entries 9 and 10). Carboxylic
acids having a chlorine atom at ꢀ-position such as chloroacetic
acid and trichloroacetic acid, also afforded the desired prod-
ucts in excellent yields (Table 4, entries 11 and 12).
In order to extend the scope of the present reactions, alkyla-
tion of several carboxylic acids using DMBQ and alkoxydi-
phenylphosphines such as 1c, 1d, 1e, 1f, and 1g was next tried
(Table 5). Esterifications of several aromatic and aliphatic car-
boxylic acids smoothly proceeded to afford the corresponding
carboxylic acid alkyl esters in good to high yields under mild
conditions when alkoxydiphenylphosphines having primary or
secondary alkoxy groups were used (Table 5, entries 1–4 and
6–11). In the case of using alkoxydiphenylphosphine that has
a t-butyl group, the desired product was obtained in 73% yield
when the reaction was carried out in refluxing dichloromethane
for 3 h (Table 5, entry 5).
Thus, an efficient method for esterification of various car-
boxylic acids was established via the present new-type of ox-
idation–reduction condensation by combined use of alkoxydi-
phenylphosphines having primary, secondary or tertiary
alkoxy group and DMBQ.
Etherification of Phenols by a New-Type of Oxidation–
Reduction Condensation Using Quinones and Alkoxy-
diphenylphosphines. Benzylation of phenol with 1.1 equiv-
alents of 1a was examined by using 1.0 equivalent of 1,4-ben-
zoquinone in dichloromethane, and the desired product was
Benzyloxydiphenylphosphine afforded the ester effectively
in 90% yield by treating 1a, DMBQ, and 6a (Table 3, entry
3). The reaction proceeded rapidly (0.5 h) at room temperature
and the ester was obtained in over 98% yield when 1.1 equiv-
alents of 1a was used (Table 3, entries 3–7).
The benzylation of various carboxylic acids was then tried
by using 1.1 equivalents of 1a and 1.0 equivalent of DMBQ
in dichloromethane (Table 4). As a result, benzylation of var-
ious carboxylic acids smoothly proceeded to afford the corre-
sponding carboxylic acid benzyl esters in high yields under
mild conditions. When benzoic acids having electron-donat-
ing or electron-withdrawing groups were used, the desired
products were obtained in excellent yields (Table 4, entries
1–4). The reactions of primary and tertiary aliphatic carboxyl-
ic acids also gave the corresponding carboxylic esters in high
yields (Table 4, entries 5–7). When a heterocyclic compound
such as tetrahydrofuran-2-carboxylic acid was used, the corre-
sponding ester was obtained in 86% yield under the above con-
ditions (Table 4, entry 8). In the cases of N-t-butoxycarbonyl-
L-valine and N-t-butoxycarbonyl-D-valine, the corresponding

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1649
Table 5. Alkylations of Several Carboxylic Acids with Alkoxydiphenylphosphines and DMBQ
Comparision
Yield/%b)
Entry
R1COOH
R2POR2
Ph2POEt
Product
8a
Yield/%
91
1
2
3
4
5
6
7
8
9
6a
6a
6a
6a
6a
6c
6c
6d
6d
1c
1d
1e
1f
85
—
90
27c)
—
—
—
—
—
Ph2POnBu
Ph2POiPr
Ph2POsBu
Ph2POtBu
Ph2POEt
8b
88
8c
93
8d
82
1g
1c
1d
1d
1e
8e
73a)
89
8f
Ph2POnBu
Ph2POnBu
Ph2POiPr
8g
85
8h
93
8i
91
10
11
6m
6m
Ph2POEt
Ph2POiPr
1c
1e
8j
76
84
34
43
8k
a) The raction mixture was refluxed for 3 h. b) Comparision of Mitsunobu reaction. See Ref. 6c. c) Mitsunobu re-
action was tried.
methane (Table 7). As a result, the corresponding benzyl
phenyl ethers were obtained in good yields under mild condi-
Table 6. Benzylation of Phenol with 1a and Quinones
tions when phenols having electron-donating or electron-with-
drawing groups were used (Table 7, entries 1–5). The corre-
sponding benzyl phenyl ether was obtained in 70% yield at
room temperature (Table 7, entry 6). Similarly, the desired
Entry
1a/equiv.
Quinone
Yield/%
products were obtained in good yields under mild conditions
when 1-naphthol and 2-naphthol were used (Table 7, entries
7 and 8).
Further, alkylations of phenol with DMBQ and several al-
koxydiphenylphosphines such as 1b, 1c, 1d, and 1e were tried
(Table 8) and the corresponding alkyl phenyl ethers were ob-
tained in good yields. When p-nitrophenol and 1g having a
bulky substituent such as t-butyl group was used, on the other
hand, the yield was 62% after refluxing them in dichloro-
methane for 10 h.
1
2
3
4
5
1.1
1.1
1.1
1.2
1.5
1,4-benzoquinone
DMBQ
DMBQ
49
85
72a)
85
DMBQ
DMBQ
92
a) To a mixꢂture of phenol and DMBQ was added 1a in
CH2Cl2 at 0 C and then reacted for 0.5 h at room tempera-
ture.
obtained in 49% yield within 0.5 h (Table 6, entry 1). When
DMBQ was used under the above conditions, the benzyl phen-
yl ether was obtained in 85% yield (Table 6, entry 2). The
yield lowered to 72% when phenol, 1.1 equivalents of DMBQ
and 1.1 equivalents of 1a were allowed to react in dichloro-
Thus, an effective method for alkylation of various phenols
was established by this new-type of oxidation–reduction con-
densation with a combination of alkoxydiphenylphosphines
having primary, secondary, or tertiary alkoxy group and
DMBQ.
One-pot Esterification of Carboxylic Acids by a New-
Type of Oxidation–Reduction Condensation Using 2,6-Di-
methyl-1,4-benzoquinone and in situ Formed Alkoxydi-
phenylphosphines from N,N-Dimethylaminodiphenylphos-
phine and Primary or Secondary Alcohols. Next, it was
thought that the present reaction would afford carboxylic acid
ꢂ
methane at 0 C and were stirred for an additional 0.5 h at
room temperature (Table 6, entry 3) whereas the desired prod-
uct was obtained in 92% yield under the above conditions
when 1.5 equivalents of 1a was used (Table 6, entry 5).
Next, the benzylation of various phenols was tried by using
1.5 equivalent of 1a and 1.0 equivalent of DMBQ in dichloro-

1650 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Table 7. Benzylation of Various Phenol with 1a and DMBQ
Table 8. Alkylation of Phenol or p-Nitrophenol with Sever-
al Alkoxydiphenylphosphines and DMBQ
Entry
1
PhOH derivative
Product
Yield/%
92
Entry
R1
Ph2POR
9a Ph2POMe
9a Ph2POEt
Product Yield/%
9a
9b
9c
9d
9e
10a
1
2
3
4
5
H
H
H
H
1b
1c
11a
11b
11c
11d
11e
88
84
87
81
62a)
2
3
4
5
10b
10c
10d
10e
82
78
88
84
9a Ph2POnBu 1d
9a Ph2POiPr
1e
1g
NO2 9d Ph2POtBu
a) The reaction mixture was refluxed for 10 h.
Table 9. Screening of Aminophosphine Derivatives on Re-
action of Benzyl Alcohol and 6a
6
9f
10f
70
Entry
Ph2P–NR2
Yield/%
76
1
2
3a
3b
7
8
9g
9h
10g
10h
81
84
70
3
4
3c
51
61
3d
5
3e
Trace
Scheme 4.
alkyl esters from the corresponding carboxylic acids and alco-
hols by one-pot procedure without isolation of alkoxydi-
phenylphosphine.
the corresponding pentavalent phosphorus compounds did not
occur.15 More importantly, the above aminophosphines were
easily converted to the alkoxy ones by the replacement of ami-
no group with the alkoxy group of alcohols.16 Then, it was
considered that the alkoxydiphenylphosphines might be
formed by alcoholysis of the corresponding aminophosphines
with alcohols. Expectedly, the desired product was obtained
in 76% yield within 0.5 h when a mixture of 1.0 equivalent
of benzyl alcohol and 1.0 equivalent of 3a was treated with
1.0 equivalent each of DMBQ and of benzoic acid in dichloro-
methane at room temperature (Table 9, entry 1).
First, chlorodiphenylphosphine (2) (132 mg, 0.6 mmol) was
dropped into a mixture of benzyl alcohol (65 mg, 0.6 mmol)
and pyridine (48 mg, 0.6 mmol) in Et2O (1.0 mL) at 0 ꢂC. Af-
ter stirring the mixture at room temperature for 1 h, salts were
filtered off and concentrated in vacuo. A reaction mixture was
again stirred at room temperature for 0.5 h after 6a and DMBQ
were added to the residue in dichloromethane. However, ben-
zyl ester 7a was not obtained when benzoic acid and DMBQ
were treated with in situ formed 1a without purification
(Scheme 4). Nor was the ester 7a obtained when 1a prepared
from 2 and benzyl alcohol by using organic bases such as
Et3N, DBU, imidazole, and 2,6-lutidine, was allowed to react
under the above conditions (Scheme 4).
These results indicated that 3a was the most preferable ami-
nodiphenylphosphine for this purpose because dimethylamine
(bp 7 ꢂC) was removed easily from the formed alkoxy-
diphenylphosphines. However, the removal of other amꢂines
ꢂ
such as diethylamine (bp 55 C), pyrrolidine (bp 87–88 C),
It was known that the phosphorus-nitrogen bond of N,N-di-
substituted diarylphosphines was thermo-stable; therefore, tau-
tomeric transformations of trivalent phosphorus compounds to
aniline (bp 184 ꢂC), and 2-pyrrolidinone (bp 245 ꢂC) from
the reaction mixture was difficult because of their higher boil-
ing points. On the contrary, when amines having lower boiling

T. Shintou et al.
Table 10. The Condensation of Benzyl Alcohol and 6a with 3a
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1651
Entry
BnOH/equiv.
3a/equiv.
6a/equiv.
DMBQ/equiv.
Time/h
Yield/%
1
2
3
4
5
6
7
8
1.0
1.0
1.0
1.5
1.0
1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.5
1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.5
1.0
0.5
1
2
1
1
1
1
1
76
82
84
81
74
89
78
82
Table 12. Screening of the Condensation of Benzyl Alcohol
and 6a with 3a
Table 11. The Preparation Ratio of in situ Formed 1a
Entry BnOH/equiv. 3a/equiv. Temp./ꢂC 1a/BnOHa)
1
2
3
4
5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.2
1.5
rt
40
reflux
40
40
16/84
87/13
86/14
88/12
86/14
Entry
BnOH/equiv.
3a/equiv.
Methoda)
Yield/%
1
2
3
4
5
6
1.0
1.0
1.1
1.2
1.5
1.5
1.0
1.0
1.1
1.2
1.5
1.5
A
B
B
B
B
C
86
90
96
95
96
94
1
a) 1a/BnOH ratios were determined by H NMR analysis.
points such as ammonia (bp ꢁ33 ꢂC) or methylamine (bp ꢁ6:3
ꢂC) were used, the compounds such as aminodiphenylphos-
phine and N-methylaminodiphenylphosphine could not be suc-
cessfully isolated because aminodiphenylphosphine, N,N-bis-
(diphenylphosphino)amine, and tris(diphenylphosphino)amine
were formed.
a) Methods A, B, C were as follows.
6a
Method A: [Ph2POBn] ꢁꢁꢁꢁꢁꢁꢁꢁ! ꢁꢁꢁꢁꢁꢁꢁꢁ! 7a
DMBQ
6a
DMBQ
Method B: [Ph2POBn] ꢁꢁꢁꢁꢁꢁꢁꢁ! ꢁꢁꢁꢁꢁꢁꢁꢁ! 7a
Method C: 6a + DMBQ ꢁꢁꢁꢁꢁꢁꢁꢁ! 7a
½Ph2POBnꢃ
Next, the reaction time and molar ratio of benzyl alcohol,
3a, 6a, and DMBQ were investigated (Table 10). Benzyl ester
7a was obtained in 89% yield after stirring it for 1 h at room
temperature when 1.5 equivalents each of benzyl alcohol and
of 3a were used.
yields where no epimerization took place (Table 13, entry 8).
Next, in order to extend the scope of the present reactions,
condensation of 6a and several alkoxydiphenylphosphines
generated from primary alcohols and 3a was tried under the
above conditions (Table 14). When benzyl alcohols having
electron-donating or electron-withdrawing groups and saturat-
ed or unsaturated aliphatic alcohols were used, the correspond-
ing esters were obtained in excellent yields (Table 14, entries
1–5 and 7). Also, the desired ester was obtained in 86% yield
when 2-pyridinemethanol having a heterocyclic moiety was
used (Table 14, entry 6).
The result above shows that the replacement of benzyloxy
group with dimethylamine group did not take place smoothly
in the preparative procedure. And the 1H NMR analysis
(Table 11) indicated that the ratio of in situ formed alkoxydi-
phenylphosphine and non-reacted benzyl alcohol was almost at
max when 1.0 equivalent each of benzyl alcohol and of 3a
ꢂ
were allowed to react for 1 h at 40 C (Table 11, entry 2).
Next, condensation of 6a and several bulky secondary alco-
hols was tried after forming an intermediate Ph2POR0 in situ.
Concerning isopropyl alcohol, the ratio of in situ formed iso-
propoxydiphenylphosphine and non-reacted isopropyl alcohol
was first examined by 1H NMR analysis (Table 15). It was re-
vealed that the replacement of isopropoxy group with di-
methylamine group did not take place smoothly under the
same conditions when dichloromethane was used as a solvent
(Table 15, entry 1). Then, the exchange reaction was tried in
refluxing dichloromethane, but no significant difference was
observed (Table 15, entry 2). A similar result was given when
toluene was used for a solvent (Table 15, entry 3). When 1,2-
dichloroethane was used, the generation of isopropoxydi-
phenylphosphine was almost completed after stirring it for 7
Product 7a was obtained in 86% yield by treating in situ
formed 1a with 6a and DMBQ (Table 12, entry 1). It was fur-
ther revealed that the desired product was obtained in 96%
yield when the reaction was carried out according to method
B by using 1.1 equivalents of benzyl alcohol and 1.1 equiva-
lents of 3a as shown in Table 12 (Table 12, entry 3).
Benzylation of various carboxylic acids with 3a and benzyl
alcohol was tried according to method B (Table 13). The ben-
zylation of benzoic acids having electron-donating or electron-
withdrawing groups, saturated or unsaturated aliphatic carbox-
ylic acids and chloroacetic acid, proceeded smoothly to afford
the corresponding carboxylic acid benzyl esters in high yields
under mild conditions. Similarly, the benzylation of N-t-but-
oxycarbonyl-L-valine gave the corresponding esters in high
ꢂ
h at 100 C (Table 15, entries 4–8, Fig. 1).

1652 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Table 13. Benzylation of Various Carboxylic Acids with 3a and Benzyl Alcohol
Oxidation–Reduction Condensation
Entry
1
RCOOH
Product
Yield/%
6a
6c
7a
7c
96
96
2
3
4
6d
6e
7d
7e
90
90
5
6
6n
7n
92
93
6m
7m
7
8
6i
7i
89a)
91
6k
7k
a) No epimerization was observed by HPLC using Daicel CHIRALPAK AF.8
Table 14. Esterification of 6a with Various Primary Alcohols
Entry
1
R0OH
Product
Yield/%
96
12a
12b
13a (7a)
2
3
13b
91
95
12c
13c
4
5
12d
12e
13d
94
96
13e (8b)
6
7
12f
13f
86
96
12g
13g
Next, the condensation of 6a and several secondary alcohols
with 3a was tried (Table 16). Alkylation of 6a proceeded
smoothly to afford the corresponding alkyl esters in high to ex-
cellent yields in 1,2-dichloroethane under the conditions
shown in Table 16. In addition, it was noted that the corre-
sponding benzoic acid alkyl esters were obtained in excellent
yields with perfect inversion of stereochemistry by SN2 re-
placement when chiral secondary alcohols were used

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1653
Table 15. The Replacement of Isopropoxy Group with Di-
methylamine Group
Entry
Solv.
Temp./ꢂC Time/h Ph2POiPr/iPrOHa)
1
2
3
4
5
6
7
8
CH2Cl2
CH2Cl2
Toluene
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
40
reflux
reflux
100
100
100
1
1
1
1
3
5
7
9
5/95
5/95
5/95
23/77
48/52
72/28
98/2
100
100
Fig. 1. The replacement isopropoxy group with dimethyl-
amine group.
99/1
a) The ratio of Ph2POiPr/iPrOH was determined by 1H NMR.
Table 16. Esterification of 6a with Various Secondary Alcohols
Entry
1
R0OH
Product
Yield/%
94d)
½ꢀꢃD
14a
14b
15a (8c)
—
2
3
15b
95
96
—
—
14c
14d
15c
15d
4
94
—
24
½ꢀꢃD ¼ þ26:6
(c 3.08, EtOH)
5a)
14e
14f
15e
15f
94
88
21
½ꢀꢃD ¼ ꢁ35:3
(c 1.10, CHCl3)
6b)
23
½ꢀꢃD ¼ þ92:0
(c 1.16, C6H6)
7c)
14g
15g
88e)
50
25
a) Isomer authentic sample 15e0: ½ꢀꢃD ¼ ꢁ28:7 (c 1.02, EtOH) (preparation from PhCOCl, Et3N, alcohol). In ad-
dition, Daicel Chiralcel OD column was used for chiral HPLC analysis. b) Isomer authentic sample 15f0:
51
22
½ꢀꢃD ¼ þ34:6 (c 1.16, CHCl3) (preparation from PhCOCl, Et3N, alcohol). c) Isomer authentic sample 15g0:
24
½ꢀꢃD ¼ ꢁ93:5 (c 1.23, C6H6) (preparation from PhCOCl, Et3N, alcohol). Diastereoselectivities determined by 1H
NMR spectroscopy.50b,52 Also, ꢂintermediate L-menthoxydiphenylphosphine was prepared by mixing 14g with 3a
and was stirred for 10 h at 100 C. d) 90% Yield by Mitsunobu reaction. e) 27% Yield by Mitsunobu reaction.

1654 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Table 17. The Replacement of tert-Butoxy Group with Di-
methylamine Group
koxydiphenylphosphines were prepared from 2 and alcohols
with nBuLi. First, into a THF (18 mL) solution of alcohol
(5.0 mmol)ꢂ was dropped a hexane solution of nBuLi (5.0
mmol) at 0 C; after it was stirred itꢂfor 1 h at room tempera-
ture, 2 (5.0 mmol) was added at 0 C. The reaction mixture
was then stirred for 1 h at room temperature and was concen-
trated in vacuo. Immediately, carboxylic acid, DMBQ, and di-
chloromethane were added to the residue and the mixture was
stirred under argon atmosphere at the temperatures between
room temperature and 40 ꢂC. The same result was alternatively
obtained by the following procedure: that is, after the above
mentioned residue was diluted with a mixed solution of hexane
(8 mL) and ethyl acetate (1 mL), lithium chloride was removed
by filtration through celite (3.0 g) after passing it through alu-
mina (activated, basic) (Wako Pure Chemical Industries, LTD)
(20 g). The diluted solution was concentrated in vacuo, and
crude alkoxydiphenylphosphine was obtained. It was then al-
lowed to react with carboxylic acid and DMBQ in dichloro-
methane by a similar procedure to that mentioned above.
When primary alcohols were used, the corresponding alk-
oxydiphenylphosphines were obtained smoothly, and the
desired esters were afforded in excellent yields by one-pot
procedure on treatment with 6a (Table 18).
The esterification of various in situ-formed secondary alk-
oxydiphenylphosphines having sterically hindered bulky alk-
oxy groups with 6a was further examined under the same
conditions (Tables 19); the corresponding esters were afforded
in high yields with perfect inversion of stereochemistry by SN2
replacement with secondary alcohols (Table 19, entries 1 and
2).
The esterification of in situ formed secondary alkoxydiphen-
ylphosphine having a sterically hindered bulky group such as
(L)-(ꢁ)-menthol with various carboxylic acids was tried under
the above conditions. Preparation of such hindered esters in
high yields under mild conditions still remains difficult be-
cause it generally needs a long reaction time (24 h) using a
Entry
Solv.
Temp./ꢂC
Ph2POtBua)
1
2
ClCH2CH2Cl
ClCH2CH2CH2Cl
100
130
N.D.
N.D.
1
a) Determined by H NMR analysis.
(Table 16, entries 5–7).
Further, the condensation of 6a and tertiary alcohols by us-
ing 3a was tried; however, replacement of tertiary alcohols did
not take place even when they were heated at higher temper-
atures than those of secondary alcohols (Table 17).
Thus, effective one-pot esterification of various carboxylic
acids was established via a new-type of oxidation–reduction
condensation using a combination of DMBQ and in situ
formed alkoxydiphenylphosphines formed from 3a and pri-
mary or secondary alcohols.
According to this procedure, 3a and 1-phenylethyl alcohol
(14h) also gave the corresponding alkoxydiphenylphosphine
smoothly; the desired ether (15h) was afforded in 82% yield
by one-pot procedure on treatment with phenol (Scheme 5).
One-pot Esterification of Carboxylic Acids by a New-
Type of Oxidation–Reduction Condensation Using 2,6-Di-
methyl-1,4-benzoquinone and Primary, Bulky Secondary,
or Tertiary in situ-formed Alkoxydiphenylphosphines
by Adding Chlorodiphenylphosphine to nBuLi-treated
Alcohols. The above experiment indicated that the key point
of the present reactions was the effective formation of
alkoxydiphenylphosphine. Then, preparation of various alk-
n
oxydiphenylphosphines from 2 and alcohols using BuLi was
tried according to Evans’s procedure.17 It was thought that
the existence of generated LiCl would not influence the oxida-
tion–reduction condensation reaction in the case when the al-
Scheme 5.
Table 18. Esterification of 6a by Using Several Primary Alcohols
Entry
1
ROH
Ph2POR
Product
Yield/%
98
1a
7a
2
16a
13g
93

T. Shintou et al.
Table 19. Esterification of 6a by Using Various Bulky Secondary Alcohols
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1655
Entry
1
ROH
Ph2POR/equiv.
Product
Time/h
3.0
Yield/%
86a)
1.1
14g
14e
17a
17b
15g
15e
2
3
1.1
1.2
1.0
3.0
93b)
85c)
14h
17c
15i
14
a) ½ꢀꢃD ¼ þ92:4 (c 1.22, C6H6). The corresponding ester was obtained with perfect inversion of stereochemistry by
23
SN2 replacement. b) ½ꢀꢃD ¼ þ27:3 (c 1.22, EtOH). c) Use of racemic compound. 58% yield by Mitsunobu reaction.
Table 20. Comparison of Esterification of Several Carboxylic Acids and (L)-(ꢁ)-Menthol by Means of Several Methods
Present reaction
Time/h Yield/%(a/%)
Mitsunobu reactionb)
Yield/%(a/%)
Tsunoda methodc)
Yield/%(a/%)
Entry
RCOOH
pKa
Product
1
2
3
4d)
5
6
7
o-NO2-PhCOOH
p-NO2-PhCOOH
m-NO2-PhCOOH
m-NO2-PhCOOH
o-MeO-PhCOOH
PhCOOH
6o
6d
6p
6p
6q
6a
6d
2.16
3.41
3.47
3.47
4.09
4.19
4.47
18a
18b
18c
18c
18d
15g
18e
3
1
3
2
3
3
1
54(>99:9)
87(>99:9)
53(>99:9)
86(>99:9)d)
53(>99:9)
86(>99:9)
88(>99:9)
33(>99:9)
84(>99:9)
55(>99:9)
—
26(0.082)
—
0
—
91(10.6)
98(>99)
27(>99:9)
17(>99:9)
p-MeO-PhCOOH
a) Inversion ratio. Diastereoselectivities determined by 1H NMR spectroscopy. Corresponding isomer (15g0, 18a0, 18b0, 18c0, 18d0,
18e0) was prepared by using RCOCl (1.0 eq.), (L)-(ꢁ)-menthol (1.0 eq.), and Et3N (1.0 eq.). b) (L)-(ꢁ)-menthol (1.0 eq.), RCOOH
(4.0 eq.), PPh3 (4.0 eq.), EtO2CN=NCO2Et (4.0 eq.), THF, rt, 24 h.6i,7c c) (L)-(ꢁ)-menthol (1.0 eq.), RCOOH (1.5 eq.), Bu3P (1.5
t
7c
eq.), Me2NOCN=NCONMe2 (1.5 eq.), benzene, 60 C, 24 h. d) (L)-(ꢁ)-menthoxydiphenylphosphine (1.5 eq.).
ꢂ
large excess amount of carboxylic acids and reagents, as
shown in the esterification of carboxylic acids with (L)-(ꢁ)-
menthol by Mitsunobu and Tsunoda methods (Table 20).
The present method using a combination of DMBQ and in
situ-formed alkoxydiphenylphosphine from lithium alkoxide
and 2 afforded the corresponding esters in good to high yields
with perfect inversion of stereochemistry by SN2 replacement
of (L)-(ꢁ)-menthol. Similarly, the esterification of 6a and ben-
zoic acids having electron-donating or electron-withdrawing
groups at p-positions, such as p-nitrobenzoic acid or p-meth-
oxybenzoic acid proceeded smoothly to afford the corre-
sponding esters in 86–88% yields under mild conditions within
1–3 h (Table 20, entries 2 and 6–7). The esterification of ben-
zoic acids having electron-donating or electron-withdrawing
groups at o-position or m-position, such as o-nitrobenzoic acid,
m-nitrobenzoic acid, or o-methoxybenzoic acid, proceeded to
afford the corresponding esters in 53–54% yields after having
been allowed to react for 3 h at room temperature (Table 20,
entries 1, 3, and 5). On the other hand, the desired ester
was obtained in 86% yield when the alkoxydiphenylphosphine,
formed from 1.5 equivalents each of lithium salt of (L)-(ꢁ)-
menthol and 2, with m-nitrobenzoic acid (Table 20, entry 4).
Interestingly, the desired ester 21a was obtained in 73%
yield by treating DMBQ and the above-mentioned crude al-

1656 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Table 21. Screening of Esterification of 6a with Tertiary
Alcohols 19a
bulky tertiary alcohols proceeded smoothly to afford the corre-
sponding alkyl esters in good yields under the conditions
shown in Table 22.
Esterifications of various in situ-formed tertiary alkoxydi-
phenylphosphines with various carboxylic acids were tried un-
der the previously mentioned conditions (Table 23). Esterifi-
cations of various aliphatic carboxylic acids smoothly
proceeded to afford the corresponding carboxylic acid bulky
alkyl esters in good yields when various bulky tertiary alcohols
were used (Table 23, entries 1–4). When an unsaturated ali-
phatic carboxylic acid was used, the corresponding ester was
also obtained in high yield (Table 23, entry 5). Similarly,
the desired products were obtained in high yields by the reac-
tions between carboxylic acids having a chlorine atom at ꢀ-po-
sition, such as chloroacetic acid, secondary and tertiary car-
boxylic acids (Table 23, entry 6).
Entry 20a/equiv. DMBQ/equiv. Temp. Time/h Yield/%
1
2
3
4
5
6
7
1.1
1.2
1.2
1.5
1.2
1.1
1.2
1.0
1.0
1.0
1.0
1.1
1.0
1.0
rt
rt
rt
rt
rt
12
7
15
15
15
3
73
78
81
81
82
64
68
reflux
reflux
3
koxydiphenylphosphine 20a with acid 6a at room temperature
for 12 h (Table 21, entry 1). The reaction condition was fur-
ther screened in order to improve the chemical yield (73%)
shown in Table 21. The ester 21a was obtained in 81% yield
when 1.2 equivalents of 20a and 1.0 equivalent of DMBQ
were treated with 6a at room temperature for 15 h (Table 21,
entry 3).
Next, the esterification of various in situ formed tertiary al-
koxydiphenylphosphines with 6a was examined under the
above conditions (Tables 22). Alkylation of 6a with various
Thus, an effective one-pot esterification of various carboxyl-
ic acids was established via a new-type of oxidation–reduction
condensation by using a combination of DMBQ and primary,
secondary, or bulky tertiary in situ formed alkoxydiphenyl-
n
phosphines by adding 2 to the BuLi-treated alcohols.
According to this one-pot procedure, secondary or tertiary
alcohols gave the corresponding alkoxydiphenylphosphines
smoothly and the desired ethers were also afforded in good
yields on treatment with p-nitrophenol (Table 24).
Table 22. Esterification of 6a Using Various Bulky Tertiary Alcohols
Entry
1
ROH
19a
Ph2POR/equiv.
Product
Condition
rt, 15 h
Yield/%
81
1.2
1.2
1.2
20a
21a
rt, 15 h
reflux, 6 h
69
79
2
3
19b
20b (1g)
21b (8e)
rt, 15 h
reflux, 6 h
69
72
19c
19d
20c
20d
21c
21d
4
5
6
1.2
reflux, 15 h
83
1.2
1.5
rt, 15 h
reflux, 3 h
23
51
19e
19f
20e
20f
21e
21f
reflux, 3 h
78
1.2
rt, 15 h
82

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1657
Table 23. Esterifications of Various Carboxylic Acids Using Various Bulky Tertiary Alcohols
Entry
ROH
Ph2POR
RCOOH
Product
Yield/%
82
1
2
3
4
5
20g
19g
6e
22a
20c
20a
20g
20f
76
85
85
92
19c
19a
6e
22b
22c
6m
19g
19f
6g
6n
22d
22e
6
7
8
20d
20d
20f
94
96
91
19d
6k
22f
19d
19f
6o
6p
22g
22h
Table 24. Alkylation of p-Nitrophenol Using nBuLi and
Several Alcohols
Mechanism for a New-Type of Oxidation–Reduction
Condensation Using 2,6-Dimethyl-1,4-benzoquinone and
Alkoxydiphenylphosphines. It is considered that 1a may
be isomerized to benzyldiphenylphosphine oxide (24) or be
oxidized to benzyloxydiphenylphosphine oxide (25). Since
thus formed compounds were thought to work as reactive spe-
cies, esterification of 6a with 24 or 25 under the present con-
ditions was tried (Scheme 6). However, the product 7a was
not detected. Thus, it was made clear that alkoxydiphenyl-
phosphines behaved as important reaction species of the pres-
ent reaction.
Entry R0OH Condition
Product
Yield/%
71
1
2
3
rt, 1 h
23a
23b
11e
reflux, 3 h
reflux, 12 h
70
72
On the other hand, esterification of 6a also proceeded to af-
ford the desired ester along with diphenylphosphinic acid 4-
hydroxy-3,5-dimethylphenyl ester (26) and its structure was
determined by the correlation of HMBC (Scheme 7).

1658 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
Scheme 6.
bon of oxygen atom of oxygen–phosphorus bond afforded the
corresponding carboxylic acid ester (15g) with perfect inver-
sion of stereochemistry by SN2 replacement along with 26.
Conclusion
A new and efficient method for the preparations of carbox-
ylic acid alkyl esters or alkyl phenyl ethers from various pri-
mary, secondary and tertiary alcohols and carboxylic acids
or phenols was established. The corresponding carboxylic
acid esters or alkyl phenyl ethers were afforded in good to high
yields by way of a new-type of oxidation–reduction condensa-
tion using alkoxydiphenylphosphines having a primary, bulky
secondary, or tertiary alkoxy group, a mild quinone type oxi-
dant such as DMBQ, and carboxylic acids or phenols. Gener-
ally, alkoxydiphenylphosphines were prepared easily from
chlorodiphenylphosphine and alcohols in the presence of pyr-
idine, and were isolated by distillation (Scheme 2, Path A). On
the other hand, the phosphines 1 were also prepared in situ
from N,N-dimethylaminodiphenylphosphine and primary or
secondary alcohols (Scheme 2, Path B) while primary, bulky
secondary, or tertiary alkoxydiphenylphosphines were alterna-
tively formed in situ by adding Ph2PCl to the nBuLi-treated al-
cohols (Scheme 2, Path C) in order to perform the above reac-
tions by one-pot procedures from alcohols and nucleophiles.
Scheme 7.
Based on the above result, a proposed reaction mechanism
of a new-type of oxidation–reduction condensation by com-
bined use of carboxylic acid, DMBQ and (L)-(ꢁ)-menthol is
shown in Scheme 8. Menthoxydiphenylphosphine (17a) was
prepared in situ with retention of stereochemistry from 3a
n
and (L)-(ꢁ)-menthol or by adding 2 to the BuLi-treated (L)-
(ꢁ)-menthol. Phosphine 17a was assumed to react with
DMBQ to form intermediate phosphonium salt (27), which
then transformed to the phosphonium carboxylate by the inter-
action with carboxylic acid. Intramolecular attack of the car-
boxylate anion of an intermediate (28) to the neighboring car-
Scheme 8.

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1659
73.7 (d, J ¼ 21:2 Hz), 24.4 (d, J ¼ 5:6 Hz).
The reaction of thus formed 1, DMBQ and carboxylic acids or
phenols afforded the corresponding alkylated products includ-
ing hindered tertiary alkylated ones, in good to high yields at
room temperature. In the case of using chiral secondary alco-
hols, the corresponding carboxylic acid alkyl esters were ob-
tained in high yields as well, with perfect inversion of stereo-
chemistry by SN2 replacement.
s-Butoxydiphenylphosphine (1f).20 Isolated as a colorless oil
(yield 45%): bp 100–103 ꢂC/0.6 Pa; 1H NMR (270 MHz, CDCl3)
ꢁ7.51–7.46 (m, 4H), 7.33–7.26 (m, 6H), 4.02–3.92 (m, 1H), 1.75–
1.51 (m, 2H), 1.26 (d, J ¼ 5:9 Hz, 3H), 0.89 (t, J ¼ 7:6 Hz, 3H);
13C NMR (68 MHz, CDCl3) ꢁ143.1 (d, J ¼ 17:3 Hz), 142.7 (d,
J ¼ 16:3 Hz), 130.3, 129.9 (d, J ¼ 6:1 Hz), 128.8, 128.7, 128.1
(d, J ¼ 7:3 Hz), 79.0, 78.7, 31.2 (d, J ¼ 5:6 Hz), 21.8 (d,
J ¼ 5:5 Hz), 10.0.
Experimental
Benzyloxydiisopropylphosphine (1h). To a stirred solution
of benzyl alcohol (6.5 g, 60 mmol) and pyridine (4.8 g, 60 mmol)
in Et2O (60 mL) under argon atmosphere was added chlorodiiso-
propylphosphine (9.2 g, 60 mmol) at 0 ꢂC. After the reaction mix-
ture was stirred at room temperature for 1 h, it was filtered, and
then concentrated in vacuo. The resulted residue was purified
by distillation under reduced pressure to afford the title compound
General. All melting points were determined on a Yanagi-
moto micro melting point apparatus (Yanaco MP-S3) and are
not corrected. Infrared (IR) spectra were recorded on a Nicolet
AVATAR360. 1H NMR spectra were recorded on a JEOL
JNM EX270L (270 MHz) spectrometer; chemical shifts (ꢁ) are re-
ported in parts per million relative to tetramethylsilane. Splitting
patterns are designated as s, singlet; d, doublet; t, triplet; q, quar-
tet; m, multiplet; br, broad. 13C NMR spectra were recorded on
EX270L (68 MHz) spectrometer with complete proton
decoupling. Chemical shifts are reported in parts per million rel-
ative to tetramethylsilane with the solvent resonance as the inter-
nal standard (CDCl3; ꢁ77.0 ppm). High resolution mass spectra
(HRMS) were recorded on a JEOL LCmate. MS spectra were re-
corded on a JEOL DX-303HF. The polarimeter used was JASCO
P-1020. Analytical high performance liquid chromatography
(HPLC) was performed on a Hitachi LC-Organizer (L-4000 UV
Detector, L-6200 Intelligent Pump, and D-2500 Chromato-Inte-
grator) equipped with a chiral column (ꢂ 4:6 ꢄ 250 mm). Analyt-
ical TLC was performed on Merck preparative TLC plates (silica
gel 60 GF254, 0.25 mm). Column chromatography was carried
out on Merck silica gel 60 (0.063–0.200 mm). Preparative thin-
layer chromatography (PTLC) was carried out on silica gel Wako-
gel B-5F. Dry solvents were prepared by distillation under appro-
priate drying agents. Carboxylic acids were purified by recrystal-
lization.
ꢂ
1
(1h) (9.4 g, 70%) as a colorless oil: bp 110 C/5.0 Pa; H NMR
(270 MHz, CDCl3) ꢁ7.38–7.34 (m, 5H), 5.08 (d, J ¼ 6:8 Hz, 2H),
2.10–1.98 (m, 2H), 1.23–1.12 (m, 12H); 13C NMR (68 MHz,
CDCl3) ꢁ137.1, 128.4 (d, J ¼ 13:4 Hz), 127.9 (d, J ¼ 5:6 Hz),
127.6, 66.2 (d, J ¼ 6:7 Hz), 26.6, 25.3, 15.8 (d, J ¼ 3:9 Hz),
15.6 (d, J ¼ 2:9 Hz).
Benzyloxydicyclohexylphosphine (1i). To a stirred solution
of benzyl alcohol (6.5 g, 60 mmol) and pyridine (4.8 g, 60 mmol)
in Et2O (60 mL) was added chlorodicyclohexylphosphine (14.0 g,
ꢂ
60 mmol) at 0 C. After the reaction mixture was stirred at room
temperature for 1 h, it was filtered and concentrated in vacuo. The
resulted residue was purified by distillation under reduced pres-
sure to afforꢂd the title compound (1i) (8.0 g, 44%) as a colorless
1
oil: bp 163 C/2.0 Pa; H NMR (270 MHz, CDCl3) ꢁ7.36–7.33
(m, 5H), 5.05 (d, J ¼ 7:0 Hz, 2H), 1.93–1.69 (m, 11H), 1.40–
1.21 (m, 11H); 13C NMR (68 MHz, CDCl3) ꢁ137.2 (d, J ¼ 5:6
Hz), 128.2, 127.7 (d, J ¼ 21:8 Hz), 66.1 (d, J ¼ 47:1 Hz), 36.7,
35.4, 26.3 (d, J ¼ 13:5 Hz), 25.8, 25.3 (d, J ¼ 3:3 Hz).
t-Butoxydiphenylphosphine (1g).19 To a stirred suspension
of potassium tert-butoxide (5.6 g, 50 mmol) in Et2O (10 mL) un-
der argon atmosphere was added a Et2O (20 mL) solution of 2
Benzyloxydiphenylphosphine (1a).18 To a stirred solution of
benzyl alcohol (6.5 g, 60 mmol) and pyridine (4.8 g, 60 mmol) in
Et2O (60 mL) under argon atmosphere was added 2 (13.2 g, 60
mmol) at 0 ꢂC. After the reaction mixture was stirred at room tem-
perature for 1 h, it was filtered and concentrated in vacuo. The
resulted residue was purified by distillation under reduced pres-
sure to afford the title compound (1a) (9.6 g, 55%) as a colorless
ꢂ
(11.0 g, 50 mmol) at 0 C. After the reaction mixture was stirred
at room temperature for 1 h, it was filtered, and concentrated in
vacuo. The resulted residue was purified by distillation under re-
duced pressure to afford the title compound (10g) (4.0 g, 31%) as
a colorless oil: bp 105–106 ꢂC/0.7 Pa; IR (ATR, cmꢁ1) 2970, 931,
738; 1H NMR (270 MHz, CDCl3) ꢁ7.51–7.46 (m, 4H), 7.31–7.28
(m, 6H), 1.40 (s, 9H); 13C NMR (68 MHz, CDCl3) ꢁ143.6 (d, J ¼
15:6 Hz), 129.9 (d, J ¼ 21:8 Hz), 128.5, 128.1 (d, J ¼ 6:7 Hz),
76.7 (d, J ¼ 12:3 Hz), 30.2 (d, J ¼ 8:4 Hz); MS (FABþ) m=z
259 [M + H]þ.
ꢂ
1
oil: bp 155–157 C/0.2 Pa; IR (ATR, cmꢁ1) 982, 735; H NMR
(270 MHz, CDCl3) ꢁ7.54–7.47 (m, 4H), 7.37–7.27 (m, 11H),
4.89 (d, J ¼ 9:2 Hz, 2H); 13C NMR (68 MHz, CDCl3) ꢁ141.7,
141.4, 130.5, 130.2, 129.2, 128.3 (d, J ¼ 6:7 Hz), 127.6, 127.4,
71.6 (d, J ¼ 20:1 Hz); MS (APCIþ) m=z 293 [M + H]þ.
Methoxydiphenylphosphine (1b)19 and Ethoxydiphenyl-
phosphine (1c).19 These reagents were purchased from Tokyo
Kasei Kogyo Co., Ltd., and were used without further purification.
n-Butoxydiphenylphosphine (1d).19 Isolated as a colorless
oil (yield 45%): bp 100–103 ꢂC/0.3 Pa; 1H NMR (270 MHz,
CDCl3) ꢁ7.51–7.45 (m, 4H), 7.34–7.27 (m, 6H), 3.88–3.80 (m,
2H), 1.69–1.61 (m, 2H), 1.43–1.35 (m, 2H), 0.89 (t, J ¼ 7:4 Hz,
3H); 13C NMR (68 MHz, CDCl3) ꢁ142.1 (d, J ¼ 17:9 Hz),
130.1 (d, J ¼ 21:8 Hz), 129.0, 128.1 (d, J ¼ 7:3 Hz), 69.9 (d, J ¼
19:0 Hz), 33.6 (d, J ¼ 7:8 Hz), 19.1, 13.9.
N,N-Dimethylaminodiphenylphosphine (3a).21 Through a
stirred solution of 2 (6.6 g, 30 mmol) in benzene (40 mL) under
argon atmosphere, dimethylamine gas was bubbled for 45 minutes
at 0 ꢂC. After the reaction mixture was stirred at room temperature
for 1 h, it was filtered and concentrated in vacuo. The resulted res-
idue was purified by distillation under reduced pressure to afford
the title compound (3a) (6.0 g, 87%) as a colorless oil: bp 129 ꢂC/
0.7 Pa (lit.21a bp 106 C/0.2 Torr); IR (ATR, cmꢁ1) 1053, 960,
ꢂ
744; 1H NMR (270 MHz, CDCl3) ꢁ7.40–7.32 (m, 10H), 2.63
(d, J ¼ 9:7 Hz, 6H); 13C NMR (68 MHz, CDCl3) ꢁ138.6 (d, J ¼
15:2 Hz), 131.9 (d, J ¼ 19:0 Hz), 128.2, 128.0 (d, J ¼ 5:6 Hz),
41.8 (d, J ¼ 14:6 Hz); MS (FABþ) m=z 229 [M]þ.
Isopropoxydiphenylphosphine (1e).19 Isolated as a colorless
oil (yield 52%): bp 98–99 ꢂC/0.8 Pa; 1H NMR (270 MHz, CDCl3)
ꢁ7.51–7.45 (m, 4H), 7.36–7.30 (m, 6H), 4.22–4.15 (m, 1H), 1.39
(d, J ¼ 6:2 Hz, 6H); 13C NMR (68 MHz, CDCl3) ꢁ142.8 (d, J ¼
16:8 Hz), 130.0 (d, J ¼ 21:2 Hz), 128.8, 128.1 (d, J ¼ 6:7 Hz),
N,N-Diethylaminodiphenylphosphine (3b).12a To a stirred
solution of 2 (6.6 g, 30 mmol) in benzene (70 mL) under argon
atmosphere was added diethylamine (5.1 g, 75 mmol) at 0 ꢂC. Af-

1660 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
ter the reaction mixture was stirred at room temperature for 1 h, it
was filtered and concentrated in vacuo. The resulted residue was
purified by distillation under reduced pressure to afford the title
compound (3b) (6.3 g, 82%) as a colorless oil: bp 122 ꢂC/1.0
Pa (lit.12a bp 138 ꢂC/0.3 Torr); IR (ATR, cmꢁ1) 1021, 742; 1H
NMR (270 MHz, CDCl3) ꢁ7.44–7.30 (m, 10H), 3.13–3.02 (m,
4H), 0.95 (t, J ¼ 7:0 Hz, 6H); 13C NMR (68 MHz, CDCl3)
ꢁ140.2 (d, J ¼ 14:5 Hz), 131.9 (d, J ¼ 19:5 Hz), 128.0, 127.9
(d, J ¼ 5:6 Hz), 44.4 (d, J ¼ 15:6 Hz), 14.6 (d, J ¼ 3:4 Hz);
MS (FABþ) m=z 257 [M]þ.
143.6, 136.1, 129.6, 129.0, 128.5, 128.1, 128.0, 127.3, 66.5,
21.7; MS (EIþ) m=z 226 [M]þ.
Benzyl 4-Methoxybenzoate (7c).24 Colorless oil; IR (ATR,
1
cmꢁ1) 1709, 1604, 1250, 1165, 1097, 768; H NMR (270 MHz,
CDCl3) ꢁ8.04–8.01 (m, 2H), 7.45–7.32 (m, 5H), 6.92–6.89 (m,
2H), 5.33 (s, 2H), 3.85 (s, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ166.0, 163.3, 136.2, 131.6, 128.4, 128.0 (ꢄ2), 122.4, 113.5,
66.4, 55.4; MS (EIþ) m=z 242 [M]þ.
Benzyl 4-Nitrobenzoate (7d).25 Yellow solid; mp 79–81 C
ꢂ
(lit.25 mp 83–84 ꢂC); IR (ATR, cmꢁ1) 1710, 1519, 1271, 743;
1H NMR (270 MHz, CDCl3) ꢁ8.21–8.30 (m, 4H), 7.47–7.36 (m,
5H) 5.40 (s, 2H); 13C NMR (68 MHz, CDCl3) ꢁ164.4, 135.4,
135.1, 130.7, 128.6, 128.5, 128.3, 123.4, 67.7; MS (EIþ) m=z
257 [M]þ.
1-(Diphenylphosphonio)pyrrolidine (3c).12a
Isolated as a
colorless oil (yield 53%): bp 128 ꢂC/1.0 Pa (lit.11a bprttf 156–
160 ꢂC/0.9 Torr); IR (ATR, cmꢁ1) 1063, 1001; 1H NMR (270
MHz, CDCl3) ꢁ7.38–7.29 (m, 10H), 3.03–3.02 (m, 4H), 1.76–
1.72 (m, 4H); 13C NMR (68 MHz, CDCl3) ꢁ139.0 (d, J ¼ 12:3
Hz), 132.0 (d, J ¼ 19:6 Hz), 128.1, 127.9 (d, J ¼ 6:1 Hz), 49.6
(d, J ¼ 12:3 Hz), 26.4 (d, J ¼ 5:6 Hz); MS (FABþ) m=z 255
[M]þ.
Benzyl 3-Phenylpropionate (7e).26 Colorless oil; IR (ATR,
cmꢁ1) 1732, 1147, 745; 1H NMR (270 MHz, CDCl3) ꢁ7.33–
7.16 (m, 10H), 5.11 (s, 2H), 2.97 (t, J ¼ 7:7 Hz, 2H), 2.68 (t, J ¼
7:7 Hz, 2H); 13C NMR (68 MHz, CDCl3) ꢁ168.8, 140.3, 135.8,
133.9, 128.4 (ꢄ2), 128.2, 128.1, 126.2, 66.3, 36.0, 31.0; MS
(EIþ) m=z 240 [M]þ.
(Phenylamino)diphenylphosphine (3d).12b
Isolateꢂd as a
12c
ꢂ
white solid (yield 56%): mp 59–61 C (lit. mp 69–71 C); IR
(ATR, cmꢁ1) 888, 738; 1H NMR (270 MHz, CDCl3) ꢁ7.48–
7.34 (m, 10H), 7.24–7.16 (m, 2H), 7.02–6.99 (m, 2H) 6.84–6.78
(m, 1H), 4.38 (d, J ¼ 7:8 Hz, 1H); 13C NMR (68 MHz, CDCl3)
ꢁ146.4 (d, J ¼ 17:3 Hz), 140.0 (d, J ¼ 11:7 Hz), 131.1 (d,
J ¼ 20:7 Hz), 129.2 (d, J ¼ 1:7 Hz), 129.0, 128.5 (d, J ¼ 6:7
Hz), 119.3, 115.8 (d, J ¼ 12:9 Hz); MS (FABþ) m=z 277 [M]þ.
Benzyl Propionate (7f).27 Colorless oil; IR (ATR, cmꢁ1
)
1735, 1170, 737; 1H NMR (270 MHz, CDCl3) ꢁ7.38–7.31 (m,
5H), 5.11 (s, 2H), 2.38 (q, J ¼ 7:6 Hz, 2H), 1.16 (t, J ¼ 7:6 Hz,
3H); 13C NMR (68 MHz, CDCl3) ꢁ174.1, 136.0, 128.4, 128.0,
66.1, 27.7, 9.2; MS (EIþ) m=z 164 [M]þ.
Benzyl Trimethylacetate (7g).27,28 Colorless oil; IR (ATR,
cmꢁ1) 1729, 1142, 735; 1H NMR (270 MHz, CDCl3) ꢁ7.38–
7.27 (m, 5H), 5.10 (s, 2H), 1.23 (s, 9H); 13C NMR (68 MHz,
CDCl3) ꢁ178.1, 136.3, 128.3, 127.5, 66.0, 38.8, 27.2; MS (EIþ)
m=z 192 [M]þ.
1-(Diphenylphosphonio)pyrrolidin-2-one (3e).13
1-(Tri-
methylsilyl)-2-pyrrolidinone (4.7 g, 30 mmol) was dropped into
2 (6.6 g, 30 mmol) at 0 ꢂC under argon atmosphere. After the re-
action mixture was stirred at room temperature for 1 h, chlorotri-
methylsilane (TMSCl) was removed in vacuo. The resulted resi-
due was purified by recrystallization from benzene to afford the
title compound (3e) (6.1 g, 76%) as a white solid: mp 123–125
ꢂC (lit.13 mp 129–132 ꢂC); IR (ATR, cmꢁ1) 1691, 1119, 742;
1H NMR (270 MHz, CDCl3) ꢁ7.40–7.35 (m, 10H), 3.17 (t,
J ¼ 7:0 Hz, 2H), 2.51 (t, J ¼ 8:1 Hz, 2H), 2.08–1.97 (m, 2H);
13C NMR (68 MHz, CDCl3) ꢁ132.3 (d, J ¼ 21:3 Hz), 129.4,
128.5 (d, J ¼ 6:2 Hz), 128.2, 46.3 (d, J ¼ 8:9 Hz), 32.2, 20.3;
MS (FABþ) m=z 269 [M + H]þ.
Typical Experimental Procedure for Esterification of Vari-
ous Carboxylic Acids by Using a Combination of 2,6-Dimeth-
yl-1,4-benzoquinone and Alkoxydiphenylphosphines (Tables 4
and 5). To a mixture of carboxylic acid (0.60 mmol) and DMBQ
(0.60 mmol) under argon atmosphere was added a solution of alk-
oxydiphenylphosphine (0.66 mmol) in dichloromethane (0.50 mL)
at room temperature. The reaction mixture was stirred for 0.5 h at
room temperature. After the reaction that was monitored by TLC
was completed, the reaction mixture was quenched by adding wa-
ter and the aqueous layer was extracted with dichloromethane.
The combined organic layer was dried over anhydrous sodium
sulfate. After filtration and evaporation, the resulted residue
was purified by preparative TLC to afford the corresponding car-
boxylic esters.
Benzyl Tetrahydrofuran-2-carboxylate (7h).29 Yellow oil;
IR (ATR, cmꢁ1) 1746, 1169, 1083, 738; 1H NMR (270 MHz,
CDCl3) ꢁ7.35 (s, 5H), 5.17 (s, 2H), 4.52–4.47 (m, 1H), 4.06–
3.87 (m, 2H), 2.31–2.20 (m, 1H), 2.07–1.88 (m, 3H); 13C NMR
(68 MHz, CDCl3) ꢁ173.0, 135.5, 128.4, 128.1, 128.0, 76.6,
69.3, 66.5, 30.2, 25.2; MS (EIþ) m=z 206 [M]þ.
N-t-Butoxycarbonyl-L-valine Benzyl Ester (7i).30 Colorless
30b
20
oil; ½ꢀꢃD ¼ ꢁ33:4 (c 1.11, MeOH) (lit.
½ꢀꢃD ¼ ꢁ33:3 (c 2,
MeOH)); IR (ATR, cmꢁ1) 1711, 1498, 1366, 1243, 1154, 734;
1H NMR (270 MHz, CDCl3) ꢁ7.35 (m, 5H), 5.16 (q, J ¼ 11:5
Hz, 2H), 5.10–5.02 (m, 1H), 4.28 (m, 1H), 2.14–2.04 (m, 1H)
1.44 (s, 9H) 0.94 (d, J ¼ 6:8 Hz, 3H), 0.85 (d, J ¼ 7:0 Hz, 3H);
13C NMR (68 MHz, CDCl3) ꢁ172.1, 155.5, 135.3, 128.4, 128.3,
128.2, 79.7, 66.9, 58.6, 31.4, 28.4, 19.1, 17.5; MS (EIþ) m=z
307 [M]þ; HPLC analysis: DAICEL CHIRALPAK AF (ꢂ
4:6 ꢄ 250 mm), hexane/isopropyl alcohol = 19/1, flow rate:
ꢂ
1.0 mL/min, Temp.: 25 C, detector: 254 nm, N-t-butoxycarbon-
yl-L-valine benzyl ester (7i) (tR ¼ 7:8 min), N-t-butoxycarbonyl-
D-valine benzyl ester (7j) (tR ¼ 9:6 min).
N-t-Butoxycarbonyl-D-valine Benzyl Ester (7j).30 Colorless
20
oil; ½ꢀꢃD ¼ þ32:1 (c 1.08, MeOH); IR (ATR, cmꢁ1) 1709, 1497,
1366, 1243, 1153, 748; 1H NMR (270 MHz, CDCl3) ꢁ7.35 (m,
5H), 5.16 (q, J ¼ 11:5 Hz, 2H), 5.05–5.02 (m, 1H), 4.29–4.25
(m, 1H), 2.19–2.09 (m, 1H) 1.41 (s, 9H) 0.40 (d, J ¼ 7:0 Hz,
3H), 0.85 (d, J ¼ 7:0 Hz, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ172.1, 155.5, 135.3, 128.4, 128.2 (ꢄ2), 79.7, 66.8, 58.6, 31.3,
28.4, 19.0, 17.5; MS (EIþ) m=z 307 [M]þ.
Benzyl Benzoate (7a).22 Colorless oil; IR (ATR, cmꢁ1) 1715,
1265, 1105, 736; 1H NMR (270 MHz, CDCl3) ꢁ8.10–8.06 (m,
2H), 7.59–7.53 (m, 1H), 7.46–7.33 (m, 7H), 5.37 (s, 2H); 13C
NMR (68 MHz, CDCl3) ꢁ166.3, 135.9, 132.9, 130.0, 129.6,
128.5, 128.3, 128.1, 128.0, 66.7; MS (EIþ) m=z 212 [M]þ.
Benzyl 4-Methylbenzoate (7b).23 Colorless oil; IR (ATR,
cmꢁ1) 1702, 1264, 1097, 750; 1H NMR (270 MHz, CDCl3)
ꢁ7.98–7.95 (m, 2H), 7.45–7.32 (m, 5H), 7.25–7.21 (m, 2H),
5.35 (s, 2H), 3.40 (s, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.3,
Benzyl 2-Chloroacetate (7k).27
Colorless oil; IR (ATR,
cmꢁ1) 1752, 1163, 740; H NMR (270 MHz, CDCl3) ꢁ7.37 (m,
5H), 5.22 (s, 2H), 4.10 (s, 2H); 13C NMR (68 MHz, CDCl3)
ꢁ166.9, 134.8, 128.5 (ꢄ2), 128.3, 67.8, 40.9; MS (FABþ) m=z
149 [M ꢁ Cl]þ.
1

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1661
Benzyl 2,2,2-Trichloroacetate (7l).27 Colorless oil; IR (ATR,
(EIþ) m=z 130 [M]þ.
Isopropyl Pentanoate (8k).34 Colorless oil; IR (ATR, cmꢁ1
1
cmꢁ1) 1763, 1222, 825; H NMR (270 MHz, CDCl3) ꢁ7.44–7.32
)
(m, 5H), 5.36 (s, 2H); 13C NMR (68 MHz, CDCl3) ꢁ161.7, 133.6,
128.9, 128.7, 128.4, 128.2, 70.7; MS (FABþ) m=z 254 [M + H]þ.
1731, 1179, 1108; 1H NMR (270 MHz, CDCl3) ꢁ5.05–4.96 (m,
1H), 2.26 (t, J ¼ 7:6 Hz, 2H), 1.66–1.54 (m, 2H), 1.41–1.28 (m,
2H), 1.23 (t, J ¼ 6:2 Hz, 6H), 0.92 (t, J ¼ 7:3 Hz, 3H); 13C
NMR (68 MHz, CDCl3) ꢁ173.2, 67.3, 34.5, 27.2, 22.3, 21.9,
13.8; MS (EIþ) m=z 129 [M ꢁ CH3]þ.
Ethyl Benzoate (8a).28,31a,31c Colorless oil; IR (ATR, cmꢁ1
)
1714, 1270, 1105; 1H NMR (270 MHz, CDCl3) ꢁ8.06–8.03 (m,
2H), 7.54–7.40 (m, 3H), 4.38 (q, J ¼ 7:1 Hz, 2H), 1.39 (t,
J ¼ 7:1 Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.4, 132.6,
130.4, 129.4, 128.2, 60.9, 14.4; MS (EIþ) m=z 150 [M]þ.
Typical Experimental Procedure for Etherification of Phe-
nols by Using a Combination of 2,6-Dimethyl-1,4-benzoqui-
none and Alkoxydiphenylphosphines (Tables 7 and 8). To a
stirred solution of phenol (0.60 mmol) and DMBQ (0.60 mmol)
in dichloromethane (0.25 mL) under argon atmosphere was added
a solution of alkoxydiphenylphosphine (0.90 mmol) in dichloro-
methane (0.25 mL) at room temperature. The reaction mixture
was stirred for 0.5 h at room temperature and was quenched with
water after completion of the reaction (detected by TLC). The
aqueous layer was extracted with dichloromethane and the com-
bined organic layer was dried over anhydrous sodium sulfate. Af-
ter filtration and evaporation, the resulted residue was purified by
preparative TLC to afford the corresponding ethers.
Butyl Benzoate (8b).22,31a,31c Colorless oil; IR (ATR, cmꢁ1
)
1716, 1270, 1107; 1H NMR (270 MHz, CDCl3) ꢁ8.06–8.02 (m,
2H), 7.54–7.39 (m, 3H), 4.32 (t, J ¼ 6:6 Hz, 2H), 1.78–1.72 (m,
2H), 1.52–1.44 (m, 2H), 0.98 (t, J ¼ 7:4 Hz, 3H); 13C NMR (68
MHz, CDCl3) ꢁ166.5, 132.6, 130.4, 129.4, 128.1, 64.8, 30.8,
19.3, 13.8; MS (EIþ) m=z 178 [M]þ.
Isopropyl Benzoate (8c).28,31b,31c Colorless oil; IR (ATR,
cmꢁ1) 1712, 1271, 1097; 1H NMR (270 MHz, CDCl3) ꢁ8.06–
8.02 (m, 2H), 7.56–7.39 (m, 3H), 5.30–5.21 (m, 1H), 1.37 (d, J ¼
6:5 Hz, 6H); 13C NMR (68 MHz, CDCl3) ꢁ165.9, 132.5, 130.7,
129.3, 128.1, 68.3, 22.0; MS (EIþ) m=z 164 [M]þ.
1-Methylpropyl Benzoate (8d).31c,32 Colorless oil; IR (ATR,
Benzyl Phenyl Ether (10a).35a,35b White solid; mp 39–41 ꢂC
(lit.35b mp 39–40 ꢂC); IR (ATR, cmꢁ1) 1234, 1011, 742; 1H NMR
(270 MHz, CDCl3) ꢁ7.45–7.24 (m, 7H), 6.99–6.93 (m, 3H), 5.06
(s, 2H); 13C NMR (68 MHz, CDCl3) ꢁ158.6, 136.9, 129.4, 128.5,
127.8, 127.4, 120.8, 114.8, 69.9; MS (EIþ) m=z 184 [M]þ.
Benzyl 4-Methylphenyl Ether (10b).36 White solid; mp 35–
36 ꢂC; IR (ATR, cmꢁ1) 1507, 1234, 1009, 806, 731; 1H NMR
(270 MHz, CDCl3) ꢁ7.42–7.28 (m, 5H), 7.08–7.05 (m, 2H),
6.87–6.84 (m, 2H), 5.01 (s, 2H), 2.27 (s, 3H); 13C NMR (68
MHz, CDCl3) ꢁ156.5, 137.1, 130.0, 129.8, 128.4, 127.7, 127.3,
114.6, 70.0, 20.5; MS (EIþ) m=z 198 [M]þ.
1
cmꢁ1) 1713, 1265; H NMR (270 MHz, CDCl3) ꢁ8.06–8.03 (m,
2H), 7.56–7.50 (m, 1H), 7.45–7.39 (m, 2H), 5.13–5.06 (m, 1H),
1.81–1.64 (m, 2H), 1.34 (d, J ¼ 6:2 Hz, 3H) 0.97 (t, J ¼ 7:6
Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.0, 132.5, 130.8,
129.3, 128.1, 72.8, 29.0, 19.6, 9.8; MS (FABþ) m=z 227 [M +
H]þ.
t-Butyl Benzoate (8e).22,28,31a,31c Colorless oil; IR (ATR,
cmꢁ1) 1710, 1288, 1112; 1H NMR (270 MHz, CDCl3) ꢁ8.01–
7.97 (m, 2H), 7.55–7.38 (m, 3H), 1.60 (s, 9H); 13C NMR (68
MHz, CDCl3) ꢁ165.6, 132.3, 131.9, 129.3, 128.0, 80.9, 28.3;
MS (FABþ) m=z 149 [M ꢁ 2Me + H]þ.
Benzyl 4-Methoxyphenyl Ether (10c).35c,35d White solid; mp
64–66 ꢂC; IR (ATR, cmꢁ1) 1503, 1221, 1032, 824, 725; 1H NMR
(270 MHz, CDCl3) ꢁ7.42–7.29 (m, 5H), 6.92–6.80 (m, 4H), 4.99
(s, 2H), 3.74 (s, 3H); 13C NMR (68 MHz, CDCl3) ꢁ153.8, 152.8,
137.2, 128.4, 127.7, 127.3, 115.7, 114.5, 70.6, 55.7; MS (EIþ) m=z
214 [M]þ.
Ethyl 4-Methoxybenzoate (8f).
Colorless oil; IR (ATR,
cmꢁ1) 1707, 1605, 1250, 1166, 1099, 769; H NMR (270 MHz,
CDCl3) ꢁ8.01–7.98 (m, 2H), 6.92–6.89 (m, 2H), 4.34 (q,
J ¼ 7:1 Hz, 2H), 3.85 (s, 3H), 1.38 (t, J ¼ 7:1 Hz, 3H); 13C
NMR (68 MHz, CDCl3) ꢁ166.2, 163.0, 131.4, 122.8, 113.4,
60.6, 55.4, 14.4; MS (EIþ) m=z 180 [M]þ.
1
Benzyl 4-Nitrophenyl Ether (10d).37 Yellow solid; mp 102–
Butyl 4-Methoxybenzoate (8g).31c Colorless oil; IR (ATR,
cmꢁ1) 1708, 1605, 1251, 1166, 1100, 769; H NMR (270 MHz,
104 C; IR (ATR, cmꢁ1) 1493, 1249, 1004, 840, 753; H NMR
(270 MHz, CDCl3) ꢁ8.22–8.18 (m, 2H), 7.42–7.36 (m, 5H),
7.04–7.01 (m, 2H), 5.16 (s, 2H); 13C NMR (68 MHz, CDCl3)
ꢁ163.5, 135.4, 133.2, 128.7, 128.4, 127.4, 125.8, 114.8, 70.7;
MS (EIþ) m=z 229 [M]þ.
ꢂ
1
1
CDCl3) ꢁ8.01–7.98 (m, 2H), 6.92–6.89 (m, 2H), 4.29 (t, J ¼ 6:6
Hz, 2H), 3.84 (s, 3H), 1.79–1.68 (m, 2H), 1.51–1.43 (m, 2H),
0.97 (t, J ¼ 7:3 Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.2,
163.0, 131.3, 122.8, 113.4, 64.5, 56.3, 30.8, 19.3, 13.8; MS
(EIþ) m=z 208 [M]þ.
Benzyl 4-Chlorophenyl Ether (10e).35b Colorless solid; mp
65–67 ꢂC; IR (ATR, cmꢁ1) 1487, 1243, 1041, 826, 731; 1H
NMR (270 MHz, CDCl3) ꢁ7.39–7.31 (m, 5H), 7.24–7.20 (m,
2H), 6.90–6.87 (m, 2H), 5.02 (s, 2H); 13C NMR (68 MHz, CDCl3)
ꢁ157.2, 136.5, 129.2, 128.5, 128.0, 127.3, 125.7, 116.1, 70.3; MS
(EIþ) m=z 218 [M]þ.
Butyl 4-Nitrobenzoate (8h).25 Colorless oil; IR (ATR, cmꢁ1
)
1721, 1526, 1271, 1101; 1H NMR (270 MHz, CDCl3) ꢁ8.30–8.19
(m, 4H), 4.39 (t, J ¼ 6:5 Hz, 2H), 1.85–1.74 (m, 2H), 1.54–1.46
(m, 2H), 1.00 (t, J ¼ 7:4 Hz, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ164.5, 150.2, 135.7, 130.5, 123.3, 65.7, 30.6, 19.2, 13.7; MS
(EIþ) m=z 223 [M]þ.
Benzyl 2,6-Dimethylphenyl Ether (10f).38 Colorless oil; IR
(ATR, cmꢁ1) 1196, 767; 1H NMR (270 MHz, CDCl3) ꢁ7.49–
7.33 (m, 5H), 7.04–6.91 (m, 3H), 4.81 (s, 2H), 2.31 (s, 6H); 13C
NMR (68 MHz, CDCl3) ꢁ155.6, 137.6, 131.0, 128.8, 128.4,
127.8, 127.6, 128.8, 73.9, 16.5; MS (EIþ) m=z 212 [M]þ.
Benzyl 1-Naphthyl Ether (10g).39a Colorless oil; IR (ATR,
cmꢁ1) 1267, 1096, 768; 1H NMR (270 MHz, CDCl3) ꢁ8.36–
8.32 (m, 1H), 7.80–7.77 (m, 1H), 7.53–7.32 (m, 9H), 6.88–6.85
(m, 1H), 5.23 (s, 2H); 13C NMR (68 MHz, CDCl3) ꢁ154.3,
137.0, 134.4, 128.5, 127.8, 127.3, 127.2, 126.3, 125.7, 125.1,
122.1, 120.4, 105.1, 70.1; MS (EIþ) m=z 234 [M]þ.
Isopropyl 4-Nitrobenzoate (8i).33 White solid; mp 104–106
ꢂC (lit.33b mp 108.5 ꢂC); IR (ATR, cmꢁ1) 1710, 1520, 1274, 1094;
1H NMR (270 MHz, CDCl3) ꢁ8.30–8.19 (m, 4H), 5.32–5.27 (m,
1H), 1.41 (d, J ¼ 6:2 Hz, 6H); 13C NMR (68 MHz, CDCl3)
ꢁ163.9, 150.2, 136.1, 130.5, 123.3, 69.7, 21.9; MS (EIþ) m=z
209 [M]þ.
Ethyl Pentanoate (8j). Colorless oil; IR (ATR, cmꢁ1) 1735,
1177; 1H NMR (270 MHz, CDCl3) ꢁ4.12 (q, J ¼ 7:1 Hz, 2H),
2.29 (t, J ¼ 7:6 Hz, 2H), 1.66–1.55 (m, 2H), 1.42–1.33 (m, 2H),
1.25 (t, J ¼ 7:2 Hz, 3H), 0.92 (t, J ¼ 7:3 Hz, 3H); 13C NMR
(68 MHz, CDCl3) ꢁ173.7, 60.1, 34.1, 27.1, 22.3, 14.3, 13.8; MS
Benzyl 2-Naphthyl Ether (10h).39 White solid; mp 96–98 ꢂC
(lit.39b mp 99–100 ꢂC); IR (ATR, cmꢁ1) 1018, 838, 743; 1H NMR

1662 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
(270 MHz, CDCl3) ꢁ7.77–7.70 (m, 3H), 7.49–7.30 (m, 7H), 7.23–
7.21 (m, 2H), 5.17 (s, 2H); 13C NMR (68 MHz, CDCl3) ꢁ156.6,
136.8, 134.4, 129.3, 129.0, 128.5, 127.9, 127.54, 127.47, 126.7,
126.3, 123.6, 119.0, 107.1, 70.0; MS (EIþ) m=z 234 [M]þ.
Methyl Phenyl Ether (11a). Colorless oil; 1H NMR (270
MHz, CDCl3) ꢁ7.33–7.24 (m, 2H), 6.97–6.88 (m, 3H), 3.80 (s,
3H); 13C NMR (68 MHz, CDCl3) ꢁ159.3, 129.3, 120.5, 113.8,
55.1.
(m, 2H), 7.57–7.51 (m, 1H), 7.44–7.37 (m, 4H), 6.93–6.89 (m,
2H), 5.30 (s, 2H), 3.81 (s, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ166.3, 159.5, 132.8, 130.1, 130.0, 129.6, 128.2, 128.1, 113.9,
66.5, 55.3; MS (FABþ) m=z 242 [M]þ.
4-Nitrobenzyl Benzoate (13c).43 White solid; mp 86–88 C
ꢂ
(lit.43 mp 88.5 ꢂC); IR (ATR, cmꢁ1) 2721, 1342, 1269, 1119;
1H NMR (270 MHz, CDCl3) ꢁ8.26–8.23 (m, 2H), 8.10–8.07 (m,
2H), 7.62–7.57 (m, 3H), 7.50–7.44 (m, 2H), 5.46 (s, 2H); 13C
NMR (68 MHz, CDCl3) ꢁ165.9, 147.5, 143.2, 133.3, 129.6,
129.3, 128.4, 128.2, 123.7, 65.1; MS (FABþ) m=z 258 [M + H]þ.
Ethyl Phenyl Ether (11b).40 Colorless oil; IR (ATR, cmꢁ1
)
1241, 1046, 750; 1H NMR (270 MHz, CDCl3) ꢁ7.31–7.23 (m,
2H), 6.95–6.86 (m, 3H), 4.03 (q, J ¼ 7:0 Hz, 2H), 1.41 (t,
J ¼ 7:0 Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ158.7, 129.3,
120.4, 114.4, 63.3, 14.9; MS (EIþ) m=z 122 [M]þ.
Phenethyl Benzoate (13d).44 Colorless oil; IR (ATR, cmꢁ1
)
1715, 1268, 1110; 1H NMR (270 MHz, CDCl3) ꢁ8.02–7.99 (m,
2H), 7.57–7.23 (m, 8H), 4.53 (t, J ¼ 7:0 Hz, 2H), 3.08 (t,
J ¼ 6:9 Hz, 2H); 13C NMR (68 MHz, CDCl3) ꢁ166.3, 137.8,
132.8, 130.2, 129.4, 128.8, 128.4, 128.2, 126.5, 65.5, 35.3; MS
(FABþ) m=z 227 [M + H]þ.
Butyl Phenyl Ether (11c).40 Colorless oil; IR (ATR, cmꢁ1
)
1242, 751; 1H NMR (270 MHz, CDCl3) ꢁ7.29–7.22 (m, 2H),
6.94–6.87 (m, 3H), 3.95 (t, J ¼ 6:4 Hz, 2H), 1.81–1.71 (m, 2H),
1.56–1.42 (m, 2H) 0.97 (t, J ¼ 7:4 Hz, 3H); 13C NMR (68
MHz, CDCl3) ꢁ158.9, 129.3, 120.3, 114.4, 67.5, 31.4, 19.3,
13.9; MS (EIþ) m=z 150 [M]þ.
2-Pyridylmethyl Benzoate (13f).45 Colorless oil; IR (ATR,
cmꢁ1) 1717, 1269, 1109; 1H NMR (270 MHz, CDCl3) ꢁ8.63–
8.61 (m, 1H), 8.14–8.10 (m, 2H), 7.75–7.69 (m, 1H), 7.61–7.55
(m, 1H), 7.48–7.43 (m, 3H), 7.27–7.22 (m, 1H), 5.49 (s, 2H);
13C NMR (68 MHz, CDCl3) ꢁ166.0, 155.8, 149.3, 136.7, 133.1,
129.7, 128.3, 122.8, 121.6, 67.2; MS (FABþ) m=z 214 [M + H]þ.
(E)-3,7-Dimethyl-2,6-octadienyl Benzoate (13g).46 Colorless
oil; IR (ATR, cmꢁ1) 1717, 1266, 1106; 1H NMR (270 MHz,
CDCl3) ꢁ8.08–8.03 (m, 2H), 7.58–7.51 (m, 1H), 7.45–7.39 (m,
2H), 5.47 (t, J ¼ 7:0 Hz, 1H), 5.13–5.07 (m, 1H), 4.84 (d
J ¼ 7:0 Hz, 2H), 2.16–2.03 (m, 4H), 1.77 (s, 3H), 1.68 (s, 3H),
1.60 (s, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.5, 142.2, 132.7,
131.7, 129.5, 129.3, 123.6, 118.3, 61.9, 39.6, 26.3, 25.8, 17.8,
16.6; MS (FABþ) m=z 259 [M + H]þ.
Isopropyl Phenyl Ether (11d).40 Colorless oil; IR (ATR,
cmꢁ1) 1239, 1117, 750; 1H NMR (270 MHz, CDCl3) ꢁ7.29–
7.23 (m, 2H), 6.94–6.87 (m, 3H), 4.56–4.52 (m, 1H), 1.33 (d, J ¼
6:2 Hz, 6H); 13C NMR (68 MHz, CDCl3) ꢁ157.7, 129.3, 120.4,
115.8, 69.7, 22.1; MS (EIþ) m=z 136 [M]þ.
t-Butyl 4-Nitrophenyl Ether (11e).41 Yellow oil; IR (ATR,
1
cmꢁ1) 1339, 1154; H NMR (270 MHz, CDCl3) ꢁ8.18–8.14 (m,
2H), 7.07–7.03 (m, 2H), 1.46 (s, 9H); 13C NMR (68 MHz, CDCl3)
ꢁ161.7, 125.1, 121.6, 80.6, 28.9; MS (FABþ) m=z 167 [M ꢁ 2Me
+ H]þ.
Typical Experimental Procedure for One-Pot Esterification
of Carboxylic Acids by a New-Type of Oxidation–Reduction
Condensation Using 2,6-Dimethyl-1,4-benzoquinone and in
situ-Formed Alkoxydiphenylphosphines from N,N-Dimethyl-
aminodiphenylphosphine and Primary Alcohols (Tables 13
and 14). To a stirred solution of primary alcohol (0.66 mmol)
in dichloromethane (0.4 mL) under argon atmosphere was added
a solution of 3a (0.66 mmol) in dichloromethane (0.4 mL) at room
temperature. The reaction was stirred for 1 h at 40 ꢂC and then the
solvent was concentrated in vacuo. To the resulted residue was
added a dichloromethane (0.7 mL) solution of carboxylic acid
(0.60 mmol) and next a dichloromethane (0.8 mL) solution of
DMBQ (0.60 mmol). The reaction was stirred for 1 h at room
temperature and was quenched with water after completion of
the reaction (detected by TLC). The aqueous layer was extracted
with dichloromethane. The combined organic layer was washed
with brine and dried over anhydrous sodium sulfate. After filtra-
tion and evaporation, the resulted residue was purified by prepara-
tive TLC to afford the corresponding esters.
Typical Experimental Procedure for One-Pot Esterification
of Carboxylic Acids by a New-Type of Oxidation–Reduction
Condensation Using 2,6-Dimethyl-1,4-benzoquinone and in
situ-Formed Alkoxydiphenylphosphines from N,N-Dimethyl-
aminodiphenylphosphine and Secondary Alcohols (Table 16).
Under argon atmosphere, a secondary alcohol (0.66 mmol) and
3a (0.66 mmol) in 1,2-dichloroethane (0.6 mL) were stirred for
7.0 h at 100 ꢂC. To a mixture of carboxylic acid (0.60 mmol)
and DMBQ (0.6 mmol) was added the above reaction solution;
then the reaction flask was washed by 1,2-dichloroethane (0.4
mL). The reaction was stirred for 1.0 h at room temperature
and was quenched with water after completion of the reaction (de-
tected by TLC).
The aqueous layer was extracted with
dichloromethane. The combined organic layer was washed with
brine and dried over anhydrous sodium sulfate. After filtration
and evaporation, the resulting residue was purified by preparative
TLC to afford the corresponding esters.
Cyclohexyl Benzoate (15b).47 Colorless oil; IR (ATR, cmꢁ1
)
Benzyl (E)-3-Phenyl-2-propenoate (7m).27 Colorless oil; IR
2935, 1712, 1273, 1110; 1H NMR (270 MHz, CDCl3) ꢁ8.07–8.03
(m, 2H), 7.58–7.51 (m, 1H), 7.46–7.40 (m, 2H), 5.08–4.99 (m,
1H), 1.93–1.65 (m, 4H), 1.61–1.32 (m, 6H); 13C NMR (68
MHz, CDCl3) ꢁ165.8, 132.5, 130.9, 129.4, 128.1, 73.0, 31.7,
25.6, 23.7; MS (FABþ) m=z 205 [M + H]þ.
1
(ATR, cmꢁ1) 1704, 1154; H NMR (270 MHz, CDCl3) ꢁ7.73 (d,
J ¼ 15:9 Hz, 1H), 7.53–7.50 (m, 2H), 7.41–7.33 (m, 8H), 6.49 (d,
J ¼ 15:9 Hz, 1H), 5.25 (s, 2H); 13C NMR (68 MHz, CDCl3)
ꢁ166.6, 145.1, 135.9, 134.2, 130.2, 128.8, 128.5, 128.2 (ꢄ2),
128.0, 117.8, 66.4; MS (FABþ) m=z 239 [M + H]þ.
2,2-Dimethyl-1-phenylpropyl Benzoate (15c).48 Colorless
oil; IR (ATR, cmꢁ1) 1708, 1275, 1108; 1H NMR (270 MHz,
CDCl3) ꢁ8.12–8.10 (m, 2H), 7.56–7.27 (m, 8H), 5.72 (s, 1H),
1.03 (s, 9H); 13C NMR (68 MHz, CDCl3) ꢁ165.4, 138.3, 132.8,
130.5, 129.5, 128.3, 127.6, 127.5, 127.4, 83.4, 35.4, 26.2; MS
(FABþ) m=z 269 [M + H]þ.
Benzhydryl Benzoate (15d).49 White solid; mp 70–72 ꢂC
(lit.49 mp 87–88 ꢂC); IR (ATR, cmꢁ1) 1711, 1262, 1107, 749;
1H NMR (270 MHz, CDCl3) ꢁ8.16–8.13 (m, 2H), 7.60–7.26 (m,
Benzyl Pentanoate (7n).31a Colorless oil; IR (ATR, cmꢁ1
)
1734, 1163, 735; 1H NMR (270 MHz, CDCl3) ꢁ7.36–7.30 (m,
5H), 5.11 (s, 2H), 2.35 (t, J ¼ 7:6 Hz, 2H), 1.69–1.57 (m, 2H),
1.41–1.28 (m, 2H), 0.91 (t, J ¼ 7:3 Hz, 3H); 13C NMR (68
MHz, CDCl3) ꢁ173.5, 136.0, 128.4 (ꢄ2), 128.0, 66.0, 34.1,
27.0, 22.3, 13.8; MS (EIþ) m=z 192 [M]þ.
4-Methoxybenzyl Benzoate (13b).42 Colorless oil; IR (ATR,
cmꢁ1) 1713, 1245, 1025; 1H NMR (270 MHz, CDCl3) ꢁ8.07–8.04

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1663
13H), 7.12 (s, 1H); 13C NMR (68 MHz, CDCl3) ꢁ165.4, 140.1,
nBuLi-treated Alcohols (Tables 18–23). Into a stirred solution
of alcohol (5.0 mmol) in THF (18 mL) was dropped a hexane
solution of nBuLi (5.0 mmol) at 0 ꢂC under argon atmosphere.
After the solution was stirred at room temperature for 1.0 h, 2
133.0, 130.1, 129.7, 128.4, 128.3, 127.8, 127.0, 77.4; MS (FABþ)
m=z 289 [M + H]þ.
(1S)-1-Phenylethyl Benzoate (15e).50 Colorless oil; ½ꢀꢃD
¼
25
23
ꢂ
þ26:6 (c 1.10, EtOH) (½ꢀꢃD ¼ þ27:3 (c 1.22, EtOH) Table 21,
(5.0 mmol) was added at 0 C. The reaction mixture was stirred
Entry 2), [lit.50a ½ꢀꢃD ¼ þ20:9 (c 2.78, EtOH)]; IR (ATR,
25
for 1.0 h at room temperature and the solvent was concentrated
in vacuo. Immediately, carboxylic acid, DMBQ, and dichloro-
methane were added to the residue and the mixture was stirred un-
der the conditions shown in Tables 18–23. The same result was
alternatively obtained by the following procedure: that is, after
the above mentioned residue was diluted with a mixed solution
of hexane (8 mL) and ethyl acetate (1 mL), lithium chloride
was removed by filtration through celite (3.0 g) after passing it
through alumina (activated, basic) (Wako Pure Chemical Indus-
tries, LTD) (20 g). The solvent was concentrated in vacuo, and
crude alkoxydiphenylphosphine was obtained. To a mixture of
carboxylic acid (0.60 mmol) and DMBQ (0.60 mmol) under argon
atmosphere was added a dichloromethane (0.50 mL) solution of
the above crude alkoxydiphenylphosphine under the conditions
shown in Tables 18–23. After the reaction that was monitored
by TLC was completed, the reaction mixture was quenched by
adding water and the aqueous layer was extracted with
dichloromethane. The combined organic layer was dried over
anhydrous sodium sulfate. After filtration and evaporation, the
resulting residue was purified by preparative TLC to afford the
corresponding carboxylic esters.
1
cmꢁ1) 1713, 1264; H NMR (270 MHz, CDCl3) ꢁ8.09–8.07 (m,
2H), 7.56–7.28 (m, 8H), 6.13 (q, J ¼ 6:5 Hz, 1H), 1.67 (d,
J ¼ 6:5 Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ165.6, 141.6,
132.8, 130.4, 129.5, 128.4, 128.2, 127.7, 125.9, 72.9, 22.5; MS
(FABþ) m=z 227 [M + H]þ; HPLC analysis: DAICEL CHIRAL-
CEL OD (ꢂ 4:6 ꢄ 250 mm), hexane/isopropyl alcohol = 1000/1,
ꢂ
flow rate: 0.5 mL/min, Temp.: 25 C, detector: 254 nm, (1S)-1-
phenylethyl benzoate (15e) (tR ¼ 34:4 min), isomer authentic
sample, (1R)-1-phenylethyl benzoate (15e0) (tR ¼ 31:2 min).
(1R)-1-Phenylethyl Benzoate (15e0).50 Isomer authentic sam-
25
1
ple; Colorless oil; ½ꢀꢃD ¼ ꢁ28:7 (c 1.02, EtOH); H NMR (270
MHz, CDCl3) ꢁ8.10–8.06 (m, 2H), 7.58–7.23 (m, 8H), 6.13 (q,
J ¼ 6:5 Hz, 1H), 1.67 (d, J ¼ 6:5 Hz, 3H); 13C NMR (68 MHz,
CDCl3) ꢁ165.6, 141.6, 132.8, 130.4, 129.5, 128.4, 128.2, 127.7,
125.9, 72.9, 22.5.
(1R)-1-Methylpropyl Benzoate (15f).51
Colorless oil;
21
½ꢀꢃD ¼ ꢁ35:3 (c 1.10, CHCl3); IR (ATR, cmꢁ1) 1713, 1269,
1096; 1H NMR (270 MHz, CDCl3) ꢁ8.06–8.03 (m, 2H), 7.56–
7.50 (m, 1H), 7.45–7.39 (m, 2H), 5.13–5.06 (m, 1H), 1.81–1.64
(m, 2H), 1.34 (d, J ¼ 6:2 Hz, 3H) 0.97 (t, J ¼ 7:6 Hz, 3H); 13C
NMR (68 MHz, CDCl3) ꢁ166.0, 132.5, 130.8, 129.3, 128.1,
72.8, 29.0, 19.6, 9.8; MS (FABþ) m=z 149 [M ꢁ Et + H]þ.
cis-2-Phenylcyclohexyl Benzoate (15i).22 Colorless oil; IR
(ATR, cmꢁ1) 2953–2842, 1699, 1254; 1H NMR (270 MHz,
CDCl3) ꢁ8.01–7.97 (m, 2H), 7.55–7.38 (m, 3H), 7.29–7.09 (m,
5H), 5.42 (s, 1H), 2.93–2.86 (m, 1H), 2.28–2.18 (m, 2H), 2.00–
1.83 (m, 2H), 1.75–1.53 (m, 4H); 13C NMR (68 MHz, CDCl3)
ꢁ165.4, 143.0, 132.5, 130.7, 129.3, 128.2, 128.0, 127.6, 126.2,
73.9, 46.8, 30.9, 26.3, 26.1, 20.4; MS (FABþ) m=z 281 [M + H]þ.
(E)-(3,7-Dimethyl-2,6-octadienyloxy)diphenylphosphine
(1S)-1-Methylpropyl Benzoate (15f0).51
Isomer authentic
22
1
sample; Colorless oil; ½ꢀꢃD ¼ þ34:6 (c 1.16, CHCl3); H NMR
(270 MHz, CDCl3) ꢁ8.07–8.03 (m, 2H), 7.57–7.51 (m, 1H),
7.46–7.40 (m, 2H), 5.13–5.06 (m, 1H), 1.78–1.64 (m, 2H), 1.34
(d, J ¼ 6:2 Hz, 3H) 0.97 (t, J ¼ 7:6 Hz, 3H); 13C NMR (68
MHz, CDCl3) ꢁ166.0, 132.6, 130.8, 129.4, 128.1, 72.8, 29.0,
19.6, 9.8.
1
(16a). Colorless oil; IR (ATR, cmꢁ1) 1226, 1129, 956, 727; H
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
(15g).50b,52
Benzoate
NMR (270 MHz, CDCl3) ꢁ7.86–7.78 (m, 4H), 7.54–7.32 (m, 6H),
5.43–5.38 (m, 1H), 5.06 (m, 1H), 4.58 (t, J ¼ 7:4 Hz, 2H), 2.06–
2.02 (m, 4H), 1.675 (s, 3H), 1.59 (s, 6H); 13C NMR (68 MHz,
CDCl3) ꢁ142.1, 131.9, 131.7, 131.5, 128.4, 128.2, 123.6, 119.2,
61.6, 39.5, 26.2, 25.8, 17.8, 16.5; HRMS (APCIþ) calcd for
C22H28OP [M + H]þ 339.1878, found m=z 339.1876.
23
Colorless oil; ½ꢀꢃD ¼ þ92:0 (c 1.16, C6H6),
14
(½ꢀꢃD ¼ þ92:4 (c 1.22, C6H6) Table 21, Entry 1); IR (ATR,
cmꢁ1) 1713, 1268, 1111; 1H NMR (270 MHz, CDCl3) ꢁ8.07–
8.04 (m, 2H), 7.58–7.41 (m, 3H), 5.46 (s, 1H), 2.11–2.06 (m,
1H), 1.85–1.48 (m, 4H), 1.26–0.78 (m, 13H); 13C NMR (68
MHz, CDCl3) ꢁ165.7, 132.6, 130.9, 129.4, 128.2, 71.7, 47.1,
39.3, 34.9, 29.5, 26.9, 25.5, 22.3, 21.1, 20.9; MS (FABþ) m=z
261 [M + H]þ.
Menthoxydiphenylphosphine (17a). Colorless oil; IR (ATR,
1
cmꢁ1) 1013, 988, 790, 739; H NMR (270 MHz, CDCl3) ꢁ7.51–
7.44 (m, 4H), 7.36–7.30 (m, 6H), 3.77–3.64 (m, 1H), 2.11–2.07
(m, 2H), 1.65–1.61 (m, 2H), 1.43–1.36 (m, 2H), 0.98–0.75 (m,
9H), 0.63 (d, J ¼ 7:0 Hz, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ143.4 (d, J ¼ 16:3 Hz), 142.6, 130.8 (d, J ¼ 22:4 Hz), 129.9
(d, J ¼ 22:4 Hz), 128.9 (d, J ¼ 31:3 Hz), 128.3, 128.1 (d,
J ¼ 2:2 Hz) 128.0 127.9, 81.3 (d, J ¼ 19:0 Hz), 49.3 (d,
J ¼ 6:7 Hz), 43.6 (d, J ¼ 5:0 Hz), 34.6 (d, J ¼ 6:1 Hz), 31.8
(d, J ¼ 12:9 Hz), 22.8 (d, J ¼ 9:5 Hz), 22.2 (d, J ¼ 8:9 Hz),
21.3 (d, J ¼ 22:9 Hz), 15.6 (d, J ¼ 1:7 Hz); HRMS (APCIþ)
calcd for C22H30OP [M + H]þ 341.2030, found m=z 341.2043.
(1R)-(1-Phenylethoxy)diphenylphosphine (17b). Colorless
oil; IR (ATR, cmꢁ1) 953, 926, 740, 728; 1H NMR (270 MHz,
CDCl3) ꢁ7.58–7.52 (m, 2H), 7.41–7.16 (m, 13H), 5.06–4.95 (m,
1H), 1.58 (d, J ¼ 6:5 Hz, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ143.5 (d, J ¼ 16:3 Hz), 129.8 (d, J ¼ 22:4 Hz), 128.5, 128.0
(d, J ¼ 7:3 Hz), 76.7, 30.2 (d, J ¼ 8:4 Hz); HRMS (APCIþ) calcd
for C20H20OP [M + H]þ 307.1248, found m=z 307.1252.
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
Benzoate
(15g0).50b,52
Isomer authentic sample; Colorless oil;
24
½ꢀꢃD ¼ ꢁ93:5 (c 1.23, C6H6); 1H NMR (270 MHz, CDCl3)
ꢁ8.06–8.03 (m, 2H), 7.57–7.40 (m, 3H), 4.94 (td, J ¼ 10:8; 3:9
Hz, 1H), 2.15–2.11 (m, 1H), 2.03–1.50 (m, 5H), 1.21–0.78 (m,
12H); 13C NMR (68 MHz, CDCl3) ꢁ165.9, 132.6, 130.7, 129.4,
128.2, 74.8, 47.3, 41.0, 34.4, 31.5, 26.5, 23.7, 22.1, 20.9, 16.6.
Phenyl 1-Phenylethyl Ether (15h).53 Colorless oil; IR (ATR,
1
cmꢁ1) 1419, 1235, 750; H NMR (270 MHz, CDCl3) ꢁ7.38–7.15
(m, 7H), 6.88–6.84 (m, 3H), 5.30 (q, J ¼ 6:4 Hz, 1H), 1.63 (d,
J ¼ 6:4 Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ157.7, 143.1,
129.2, 128.5, 127.3, 125.4, 120.5, 115.8, 75.8, 24.6; MS (FABþ)
m=z 198 [M]þ.
Typical Experimental Procedure for One-Pot Esterification
of Carboxylic Acids by a New-Type of Oxidation–Reduction
Condensation Using 2,6-Dimethyl-1,4-benzoquinone and Pri-
mary, Secondary or Bulky Tertiary in situ-Formed Alkoxydi-
phenylphosphines by Adding Chlorodiphenylphosphine to
trans-(2-Phenylcyclohexyloxy)diphenylphosphine (17c).
White solid; mp 81–83 ꢂC; IR (ATR, cmꢁ1) 2930, 1028, 964,

1664 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
752, 738; 1H NMR (270 MHz, CDCl3) ꢁ7.41–6.69 (m, 13H),
6.66–6.63 (m, 2H), 4.08–4.01 (m, 1H), 2.76–2.68 (m, 1H),
2.22–2.18 (m, 1H), 1.92–1.69 (m, 3H), 1.59–1.20 (m, 4H); 13C
NMR (68 MHz, CDCl3) ꢁ144.0, 130.4, 130.1, 129.7 (d,
J ¼ 20:7 Hz), 128.8, 128.2 (d, J ¼ 2:2 Hz), 128.0, 127.9 (ꢄ2),
127.6, 127.5, 126.1, 84.1 (d, J ¼ 19:6 Hz), 52.4 (d, J ¼ 6:7
Hz), 35.2 (d, J ¼ 5:0 Hz), 34.3, 25.6 (d, J ¼ 49:2 Hz); HRMS
(APCIþ) calcd for C24H26OP [M + H]þ 361.1717, found m=z
361.1720.
J ¼ 5:9, 1.9 Hz, 1H), 7.49–7.43 (m, 1H), 7.00–6.95 (m, 2H),
5.43 (s, 1H), 3.90 (s, 3H), 2.15–2.09 (m, 1H), 1.81–1.71 (m,
3H), 1.62–1.42 (m, 2H), 1.16–0.85 (m, 12H); 13C NMR (68
MHz, CDCl3) ꢁ165.3, 159.2, 133.2, 131.5, 120.5, 119.9, 111.8,
71.4, 55.8, 47.1, 39.2, 34.9, 29.2, 26.7, 25.4, 22.3, 21.1, 20.9;
HRMS (FABþ) calcd for C18H27O3 [M + H]þ 291.1956, found
m=z 291.1954.
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
2-Methoxy-
benzoate (18d0).6i Isomer authentic sample; Colorless oil; 1H
NMR (270 MHz, CDCl3) ꢁ7.75 (dd, J ¼ 8:0, 1.8 Hz, 1H), 7.44
(dt, J ¼ 8:5, 1.6 Hz, 1H), 6.97 (dd, J ¼ 7:8, 6.5 Hz, 2H), 4.92
(dt, J ¼ 10:8, 4.3 Hz, 1H), 3.88 (s, 3H), 2.14–2.01 (m, 2H),
1.74–1.70 (m, 2H), 1.56–1.51 (m, 2H), 1.20–0.80 (m, 12H); 13C
NMR (68 MHz, CDCl3) ꢁ165.7, 158.8, 133.0, 131.1, 120.9,
119.9, 111.9, 74.6, 55.9, 47.2, 40.9, 34.4, 31.5, 26.1, 23.3, 22.1,
21.0, 16.2.
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
2-Nitroben-
zoate (18a).6i Colorless oil; IR (ATR, cmꢁ1) 2950, 1725,
1534, 1287, 1126; 1H NMR (270 MHz, CDCl3) ꢁ7.88–7.84 (m,
1H), 7.76–7.59 (m, 3H), 5.50 (s, 1H), 2.21–2.15 (m, 1H), 1.79–
1.74 (m, 2H), 1.64–1.62 (m, 1H), 1.57–1.00 (m, 4H), 0.96–0.82
(m, 10H); 13C NMR (68 MHz, CDCl3) ꢁ164.6, 132.5, 131.4,
129.8, 127.9, 123.6, 74.0, 47.0, 38.8, 34.8, 34.7, 29.1, 26.7,
25.1, 22.3, 21.1, 20.8; MS (FABþ) m=z 306 [M + H]þ.
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
4-Methoxy-
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
2-Nitroben-
benzoate (18e).6i Colorless oil; IR (ATR, cmꢁ1) 2953–2842,
zoate (18a0).6i Isomer authentic sample; Colorless oil; 1H
1699, 1254; H NMR (270 MHz, CDCl3) ꢁ7.98 (d, J ¼ 8:9 Hz,
1
NMR (270 MHz, CDCl3) ꢁ7.91 (t, J ¼ 4:3 Hz, 1H), 7.72–7.58
(m, 3H), 4.96 (dt, J ¼ 10:8, 4.5 Hz, 1H), 2.24–2.20 (m, 1H),
1.94–1.89 (m, 1H), 1.75–1.67 (m, 2H), 1.64–1.41 (m, 2H),
1.16–0.80 (m, 12H); 13C NMR (68 MHz, CDCl3) ꢁ164.9, 132.8,
131.3, 129.5, 123.8, 76.7, 46.9, 40.0, 34.1, 31.5, 26.2, 23.3,
22.1, 20.9, 16.2.
2H), 6.90 (d, J ¼ 8:9 Hz, 2H), 5.39 (s, 1H), 3.83 (s, 3H), 2.10–
2.01 (m, 1H), 1.81–1.44 (m, 5H), 1.15–0.73 (m, 12H); 13C
NMR (68 MHz, CDCl3) ꢁ165.4, 163.0, 131.3, 123.3, 113.4,
71.2, 55.4, 47.0, 39.3, 34.9, 29.4, 26.8, 25.5, 22.3, 21.0, 20.9;
MS (FABþ) m=z 291 [M + H]þ.
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
4-Methoxy-
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
4-Nitroben-
benzoate (18e0).6i Isomer authentic sample; Colorless oil; 1H
NMR (270 MHz, CDCl3) ꢁ8.00 (td, J ¼ 9:5, 2.4 Hz, 2H), 6.90
(td, J ¼ 9:5, 2.4 Hz, 2H), 4.90 (dt, J ¼ 10:8, 4.3 Hz, 1H), 3.85
(s, 3H), 2.14–2.09 (m, 1H), 1.99–1.93 (m, 1H), 1.74–1.70 (m,
2H), 1.58–1.49 (m, 2H), 1.19–0.78 (m, 12H); 13C NMR (68
MHz, CDCl3) ꢁ165.7, 163.0, 131.4, 123.2, 113.4, 74.4, 55.4,
47.3, 41.1 34.4, 31.5, 26.5, 23.7, 22.1, 20.8, 16.6.
(1-Methyl-1-phenylethoxy)diphenylphosphine (20a). White
solid; mp 87–88 ꢂC; IR (ATR, cmꢁ1) 946, 886, 745; 1H NMR
(270 MHz, CDCl3) ꢁ7.54–7.44 (m, 6H), 7.34–7.22 (m, 9H),
1.73 (s, 6H); 13C NMR (68 MHz, CDCl3) ꢁ147.3 (d, J ¼ 2:8
Hz), 143.2 (d, J ¼ 15:6 Hz), 130.1 (d, J ¼ 22:4 Hz), 128.7,
128.1 (d, J ¼ 7:3 Hz), 126.8, 125.3 (d, J ¼ 1:2 Hz), 124.2,
79.7, 30.4 (d, J ¼ 9:5 Hz); HRMS (APCIþ) calcd for C21H22OP
[M + H]þ 321.1404, found m=z 321.1410.
zoate (18b).6i White solid; mp 85–87 C (lit. mp 93–95 C);
IR (ATR, cmꢁ1) 2960–1867, 1710, 1526, 1275; 1H NMR (270
MHz, CDCl3) ꢁ8.30 (d, J ¼ 8:9 Hz, 2H), 8.21 (d, J ¼ 8:6 Hz,
2H), 5.50 (s, 1H), 2.13–2.04 (m, 1H), 1.91–1.81 (m, 2H), 1.73–
1.62 (m, 1H), 1.55–1.43 (m, 2H), 1.24–0.75 (m, 12H); 13C
NMR (68 MHz, CDCl3) ꢁ163.8, 150.2, 136.2, 130.5, 123.5,
73.1, 46.9, 39.1 34.7, 29.5, 26.9, 25.4, 22.2, 21.0, 20.9; MS
(FABþ) m=z 306 [M + H]þ.
6i
ꢂ
ꢂ
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
4-Nitroben-
zoaꢂte (18b0).6i Isomer authentic sample; White solid; mp 58–
1
59 C; H NMR (270 MHz, CDCl3) ꢁ8.30 (td, J ¼ 7:8, 2.1 Hz,
2H), 8.21 (td, J ¼ 7:8, 2.0 Hz, 2H), 4.97 (dt, J ¼ 10:9, 4.5 Hz,
1H), 2.18–2.05 (m, 1H), 1.94–1.89 (m, 1H), 1.78–1.62 (m, 2H),
1.58–1.54 (m, 2H), 1.29–0.79 (m, 12H); 13C NMR (68 MHz,
CDCl3) ꢁ164.5, 150.7, 136.5, 131.0, 123.9, 76.6, 47.7, 41.3,
34.7, 32.0, 27.1, 24.1, 22.6, 21.3, 17.0.
(1,1-Diethylpropoxy)diphenylphosphine (20c).
Colorless
oil; IR (ATR, cmꢁ1) 929, 734; 1H NMR (270 MHz, CDCl3)
ꢁ7.55–7.49 (m, 4H), 7.32–7.23 (m, 6H), 1.70 (q, J ¼ 7:5 Hz,
6H), 0.784 (t, J ¼ 7:5 Hz, 9H); 13C NMR (68 MHz, CDCl3)
ꢁ144.0 (d, J ¼ 15:6 Hz), 130.0 (d, J ¼ 22:9 Hz), 128.5, 128.0
(d, J ¼ 7:3 Hz), 83.9 (d, J ¼ 8:4 Hz), 29.5 (d, J ¼ 7:8 Hz),
8.15 (d, J ¼ 1:1 Hz); HRMS (APCIþ) calcd for C19H26OP [M
+ H]þ 301.1717, found m=z 301.1744.
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
zoate (18c).6i Colorless oil; IR (ATR, cmꢁ1) 2968, 1721,
3-Nitroben-
1535, 1055; 1H NMR (270 MHz, CDCl3) ꢁ8.84 (t, J ¼ 1:8 Hz,
1H), 8.44–8.35 (m, 2H), 7.67 (t, J ¼ 8:0 Hz, 1H), 5.51 (s, 1H),
2.12–2.04 (m, 1H), 1.88–1.84 (m, 2H), 1.71–1.60 (m, 1H),
1.57–1.45 (m, 2H), 1.24–0.75 (m, 12H); 13C NMR (68 MHz,
CDCl3) ꢁ163.6, 135.1, 132.6, 129.5, 127.1, 124.4, 73.1, 46.9,
39.1, 34.1, 29.5, 26.9, 25.5, 22.2, 21.1, 20.9; MS (FABþ) m=z
306 [M + H]þ.
Adaꢂmantyloxydiphenylphosphine (20d). White solid; mp
1
66–68 C; IR (ATR, cmꢁ1) 1065, 974, 942, 733; H NMR (270
MHz, CDCl3) ꢁ7.52–7.46 (m, 4H), 7.36–7.28 (m, 6H), 2.16 (s,
3H), 1.97 (d, J ¼ 2:2 Hz, 6H), 1.62 (d, J ¼ 3:0 Hz, 6H); 13C
NMR (68 MHz, CDCl3) ꢁ143.8 (d, J ¼ 16:3 Hz), 129.9 (d,
J ¼ 22:4 Hz), 128.5, 128.0 (d, J ¼ 6:7 Hz), 75.7, 44.2 (d,
J ¼ 8:9 Hz), 36.2, 31.0 (d, J ¼ 1:2 Hz); HRMS (APCIþ) calcd
for C22H26OP [M + H]þ 337.1717, found m=z 337.1714.
(1-Methylcyclohexyloxy)diphenylphosphine (20e). Color-
less oil; IR (ATR, cmꢁ1) 2930, 908, 738; 1H NMR (270 MHz,
CDCl3) ꢁ7.74–7.66 (m, 1H), 7.57–7.46 (m, 5H), 7.34–7.24 (m,
4H), 1.96–1.94 (m, 3H), 1.63–1.44 (m, 7H), 1.32 (s, 3H); 13C
NMR (68 MHz, CDCl3) ꢁ143.8 (d, J ¼ 16:3 Hz), 132.5 (d,
J ¼ 3:3 Hz), 130.6 (d, J ¼ 11:2 Hz), 129.9 (d, J ¼ 22:4 Hz),
(1R; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
zoate (18c0).6i Isomer authentic sample; Colorless oil; 1H
3-Nitroben-
NMR (270 MHz, CDCl3) ꢁ8.85 (s, 1H), 8.40 (t, J ¼ 9:1 Hz,
2H), 7.70 (t, J ¼ 8:0 Hz, 1H), 5.00 (dt, J ¼ 10:9, 4.3 Hz, 1H),
2.14–2.10 (m, 1H), 1.98–1.92 (m, 1H), 1.85–1.73 (m, 2H),
1.64–1.56 (m, 2H), 1.26–0.79 (m, 12H); 13C NMR (68 MHz,
CDCl3) ꢁ163.8, 148.1, 135.2, 132.4, 129.4, 127.1, 124.4, 76.0,
47.1, 40.9, 34.2, 31.5, 26.6, 23.6, 22.1, 20.8, 16.5.
(1S; 2S; 5R)-2-Isopropyl-5-methylcyclohexyl
2-Methoxy-
benzoate (18d).54 Colorless oil; IR (ATR, cmꢁ1) 2947, 1725,
1534, 1287, 1126; 1H NMR (270 MHz, CDCl3) ꢁ7.84 (dd,

T. Shintou et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1665
128.8 (d, J ¼ 13:0 Hz), 128.3 (d, J ¼ 32:4 Hz), 127.9, 121.0, 77.9
(d, J ¼ 10:7 Hz), 38.6 (d, J ¼ 7:3 Hz), 30.0, 25.5 (d, J ¼ 17:3
Hz), 24.0, 23.0, 22.5 (d, J ¼ 8:4 Hz); HRMS (APCIþ) calcd for
C19H24OP [M + H]þ 299.1501, found m=z 299.1498.
(1-Methylcyclopentyloxy)diphenylphosphine (20f). White
solid; mp 48–49 ꢂC; IR (ATR, cmꢁ1) 922, 735; 1H NMR (270
MHz, CDCl3) ꢁ7.50–7.45 (m, 4H), 7.34–7.23 (m, 6H), 2.14–
2.08 (m, 2H), 1.75–1.53 (m, 6H), 1.46 (s, 3H); 13C NMR (68
MHz, CDCl3) ꢁ143.6 (d, J ¼ 15:6 Hz), 129.9 (d, J ¼ 22:4 Hz),
128.5, 128.1 (d, J ¼ 6:7 Hz), 87.7 (d, J ¼ 11:7 Hz), 40.3 (d, J ¼
7:1 Hz), 26.6 (d, J ¼ 10:7 Hz), 23.9; HRMS (APCIþ) calcd for
C18H22OP [M + H]þ 285.1404, found m=z 285.1467.
(1,1-Dimethyl-2-phenylethoxy)diphenylphosphine (20g).
Colorless oil; IR (ATR, cmꢁ1) 917, 740; 1H NMR (270 MHz,
CDCl3) ꢁ7.47–7.41 (m, 4H), 7.29–7.19 (m, 11H), 2.98 (s, 2H),
1.36 (s, 6H); 13C NMR (68 MHz, CDCl3) ꢁ143.3 (d, J ¼ 15:6
Hz), 137.7, 130.8, 129.9 (d, J ¼ 22:4 Hz), 128.6, 128.0 (d,
J ¼ 6:7 Hz), 127.6, 126.1, 78.9 (d, J ¼ 12:3 Hz), 49.7 (d,
J ¼ 5:0 Hz), 27.8, 27.6; HRMS (APCIþ) calcd for C22H24OP
[M + H]þ 335.1561, found m=z 335.1562.
(68 MHz, CDCl3) ꢁ171.8, 140.6, 128.3, 128.2, 126.0, 88.3, 36.9,
31.2, 26.8, 7.7; HRMS (APCIþ) calcd for C16H25O2 [M + H]þ
249.1850, found m=z 249.1844.
1-Methyl-1-phenylethyl Pentanoate (22c). Colorless oil; IR
(ATR, cmꢁ1) 1734, 1138, 763; 1H NMR (270 MHz, CDCl3)
ꢁ7.37–7.23 (m, 5H), 2.29 (t, J ¼ 7:4 Hz, 2H), 1.76 (s, 6H),
1.63–1.52 (m, 2H), 1.40–1.23 (m, 2H), 0.91 (t, J ¼ 7:3 Hz, 3H);
13C NMR (68 MHz, CDCl3) ꢁ172.3, 145.8, 128.1, 126.8, 124.1,
81.1, 35.2, 28.7, 27.1, 22.3, 13.9; HRMS (APCIþ) calcd for
C14H21O2 [M + H]þ 221.1537, found m=z 221.1529.
1,1-Dimethyl-2-phenylethyl Trimethylacetate (22d).58 Col-
orless oil; IR (ATR, cmꢁ1) 1720, 1159, 1116, 729; 1H NMR (270
MHz, CDCl3) ꢁ7.30–7.18 (m, 5H), 3.05 (s, 2H), 1.44 (s, 6H), 1.13
(s, 9H); 13C NMR (68 MHz, CDCl3) ꢁ177.7, 137.0, 130.5, 127.6,
126.2, 81.3, 46.7, 39.2, 27.1, 25.8; HRMS (APCIþ) calcd for
C15H23O2 [M + H]þ 235.1694, found m=z 235.1690.
1-Methylcyclopentyl (E)-3-Phenyl-2-propenoate (22e). Col-
orless oil; IR (ATR, cmꢁ1) 1703, 1161, 767; 1H NMR (270 MHz,
CDCl3) ꢁ7.59 (d, J ¼ 15:9 Hz, 1H), 7.53–7.49 (m, 2H), 7.38–7.36
(m, 3H), 6.38 (d, J ¼ 15:9 Hz, 1H), 2.25–2.13 (m, 2H), 1.81–1.68
(m, 6H), 1.63 (s, 3H); 13C NMR (68 MHz, CDCl3) ꢁ166.3, 143.4,
134.5, 129.9, 128.7, 127.8, 119.9, 90.0, 39.2, 24.5, 23.9; HRMS
(APCIþ) calcd for C15H19O2 [M + H]þ 231.1381, found m=z
231.1378.
1-Methyl-1-phenylethyl Benzoate (21a).55 Colorless oil; IR
(ATR, cmꢁ1) 1716, 1278, 1096, 763; 1H NMR (270 MHz, CDCl3)
ꢁ8.06–8.03 (m, 2H), 7.57–7.51 (m, 1H), 7.45–7.22 (m, 7H), 1.91
(s, 6H); 13C NMR (68 MHz, CDCl3) ꢁ164.9, 145.6, 132.5, 131.3,
129.4, 128.2 (ꢄ2), 126.9, 124.2, 82.1, 28.8; HRMS (APCIþ) calcd
for C16H17O2 [M + H]þ 241.1229, found m=z 241.1231.
1,1-Diethylpropyl Benzoate (21c).56 White solid; mp 64–65
ꢂC; IR (ATR, cmꢁ1) 2971, 1709, 1274, 1113; 1H NMR (270 MHz,
CDCl3) ꢁ8.02–7.98 (m, 2H), 7.56–7.49 (m, 1H), 7.44–7.38 (m,
2H), 1.98 (q, J ¼ 7:5 Hz, 6H), 0.88 (t, J ¼ 7:5 Hz, 9H); 13C
NMR (68 MHz, CDCl3) ꢁ165.2, 132.3, 131.7, 129.2, 128.1,
88.9, 27.0, 7.9; MS (FABþ) m=z 191 [M ꢁ Et]þ.
Adamantyl 2-Chloroacetate (22f). White solid; mp 77–78
ꢂC; IR (ATR, cmꢁ1) 1783, 1177, 1054; 1H NMR (270 MHz,
CDCl3) ꢁ3.97 (s, 2H), 2.19–2.12 (m, 9H), 1.66 (d, J ¼ 3:5 Hz,
6H); 13C NMR (68 MHz, CDCl3) ꢁ165.7, 83.1, 42.1, 41.2, 36.0,
30.9; HRMS (APCIþ) calcd for C12H18ClO2 [M
+
H]þ
229.0991, found m=z 229.0989.
Adamantyl 2-Phenylbutyrate (22g). Colorless oil; IR (ATR,
cmꢁ1) 1724, 1165, 1055; 1H NMR (270 MHz, CDCl3) ꢁ7.31–7.20
(m, 5H), 3.33 (t, J ¼ 7:7 Hz, 1H), 2.12–1.99 (m, 10H), 1.78–1.59
(m, 7H), 0.90 (t, J ¼ 7:4 Hz, 3H); 13C NMR (68 MHz, CDCl3)
ꢁ172.9, 139.7, 128.2, 127.8, 126.7, 80.5, 54.6, 41.2, 36.2, 30.8,
27.0, 12.3; HRMS (APCIþ) calcd for C20H27O2 [M + H]þ
299.2011, found m=z 299.2015.
Adamantyl Benzoate (21d).57 White solid; mp 85–87 ꢂC
(lit.57 mp 66.5–67.0 ꢂC); IR (ATR, cmꢁ1) 2907, 2848, 1704,
1270, 1048; 1H NMR (270 MHz, CDCl3) ꢁ8.01–7.97 (m, 2H),
7.55–7.49 (m, 1H), 7.44–7.37 (m, 2H), 2.26–2.22 (m, 9H),
1.72–1.65 (m, 6H); 13C NMR (68 MHz, CDCl3) ꢁ165.3, 132.2,
131.9, 129.3, 128.0, 81.0, 41.4, 36.3, 30.9; HRMS (APCIþ) calcd
for C17H21O2 [M + H]þ 257.1542, found m=z 257.1539.
1-Methylcyclopentyl Triphenylacetate (22h). White solid;
ꢂ
1
mp 73–74 C; IR (ATR, cmꢁ1) 1716, 1173, 751; H NMR (270
MHz, CDCl3) ꢁ7.27–7.23 (m, 15H), 2.02–2.00 (m, 2H), 1.60–
1.42 (m, 9H); 13C NMR (68 MHz, CDCl3) ꢁ172.3, 143.2,
130.2, 127.4, 126.5, 91.7, 67.9, 38.9, 23.8, 23.7; HRMS (APCIþ)
calcd for C26H27O2 [M + H]þ 371.2011, found m=z 371.2006.
1-Methylcyclohexyl Benzoate (21e).31c
Colorless oil; IR
(ATR, cmꢁ1) 2932, 1709, 1244, 1112; 1H NMR (270 MHz,
CDCl3) ꢁ8.04–8.01 (m, 2H), 7.53–7.40 (m, 3H), 2.37–2.32 (m,
2H), 1.61–1.49 (m, 11H); 13C NMR (68 MHz, CDCl3) ꢁ165.4,
132.3, 131.9, 129.3, 128.1, 82.4, 36.8, 25.9, 25.5, 22.2; MS
(FABþ) m=z 219 [M]þ.
1-Phenylethyl 4-Nitrophenyl Ether (23a).59
Red oil; IR
(ATR, cmꢁ1) 1494, 1334, 1250; 1H NMR (270 MHz, CDCl3)
ꢁ8.07 (dd, J ¼ 5:1, 2.0 Hz, 2H), 7.35–7.25 (m, 5H), 6.89 (dd,
J ¼ 4:9, 2.2 Hz, 2H), 5.39 (q, J ¼ 6:4 Hz, 1H), 1.67 (d, J ¼ 6:4
Hz, 3H); 13C NMR (68 MHz, CDCl3) ꢁ162.8, 141.5, 141.0,
128.7, 127.8, 125.6, 125.2, 115.5, 76.9, 24.5; HRMS (APCIþ)
calcd for C14H14NO3 [M + H]þ 244.0969, found m=z 244.0985.
1-Methyl-1-phenylethyl 4-Nitrophenyl Ether (23b).60 Red
oil; IR (ATR, cmꢁ1) 1509, 1337, 1251, 1100; 1H NMR (270
MHz, CDCl3) ꢁ7.918 (d, J ¼ 9:2 Hz, 2H), 7.38–7.25 (m, 5H),
6.66 (d, J ¼ 9:2 Hz, 2H), 1.80 (s, 6H); 13C NMR (68 MHz,
CDCl3) ꢁ161.6, 144.5, 140.9, 128.8, 127.5, 125.1, 124.8, 118.2,
81.9, 29.5; HRMS (APCIþ) calcd for C15H16NO3 [M + H]þ
257.1052, found m=z 257.1050.
1-Methylcyclopentyl Benzoate (21f). Colorless oil; IR (ATR,
cmꢁ1) 2965, 1709, 1280, 1112; 1H NMR (270 MHz, CDCl3)
ꢁ7.99 (d, J ¼ 7:3 Hz, 2H), 7.54–7.38 (m, 3H), 2.34–2.23 (m,
2H), 1.85–1.69 (m, 9H); 13C NMR (68 MHz, CDCl3) ꢁ165.7,
132.3, 131.7, 129.2, 128.0, 90.5, 39.2, 24.4, 23.9; HRMS (APCIþ)
calcd for C13H17O2 [M + H]þ 205.1229, found m=z 205.1297.
1,1-Dimethyl-2-phenylethyl 3-Phenylpropionate (22a). Col-
orless oil; IR (ATR, cmꢁ1) 1724, 1115, 730; 1H NMR (270 MHz,
CDCl3) ꢁ7.30–7.12 (m, 10H), 3.02 (s, 2H), 2.90 (t, J ¼ 7:8 Hz,
2H), 2.54 (dt, J ¼ 7:2, 1.4 Hz, 2H), 1.42 (s, 6H); 13C NMR (68
MHz, CDCl3) ꢁ172.2, 140.5, 137.1, 130.4, 128.3, 128.2, 127.8,
126.3, 126.0, 82.1, 46.5, 37.2, 31.0, 26.0; HRMS (APCIþ) calcd
for C19H23O2 [M + H]þ 283.1694, found m=z 283.1689.
1,1-Diethylpropyl 3-Phenylpropionate (22b). Colorless oil;
IR (ATR, cmꢁ1) 1724, 1131; 1H NMR (270 MHz, CDCl3) ꢁ7.31–
7.15 (m, 5H), 2.92 (t, J ¼ 7:8 Hz, 2H), 2.58 (dt, J ¼ 7:2, 1.6 Hz,
2H), 1.80 (q, J ¼ 7:5 Hz, 6H), 0.76 (t, J ¼ 7:5 Hz, 9H); 13C NMR
Benzyldiphenylphosphine Oxide (24).18b Into a methoxydi-
phenylphosphine (1.1 g, 5.0 mmol) under argon atmosphere was
dropped
a benzyl chloride (0.63 g, 5.0 mmol) at room
temperature. After the reaction mixture was stirred at 100 ꢂC
for 1 h, the reaction mixture was cooled. Crystallization of the

1666 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Oxidation–Reduction Condensation
crude product from ethanol (2 mL) gave the title compound (24)
(0.60 g, 41%) as a white needles: mp 188–189 ꢂC (lit.50b mp 189–
190 ꢂC); IR (ATR, cmꢁ1) 1180; 1H NMR (270 MHz, CDCl3)
ꢁ7.87–7.79 (m, 4H), 7.54–7.40 (m, 6H), 7.37–7.32 (m, 5H),
5.06 (d, J ¼ 6:8 Hz, 2H); 13C NMR (68 MHz, CDCl3) ꢁ136.2
(d, J ¼ 7:3 Hz), 132.1 (d, J ¼ 2:2 Hz), 132.1, 131.6 (d,
J ¼ 10:6 Hz), 130.1, 128.5 (d, J ¼ 7:8 Hz), 128.2 (d, J ¼ 12:9
Hz), 127.7, 66.3 (d, J ¼ 5:8 Hz); HRMS (APCIþ) calcd for
C19H18OP [M + H]þ 293.1091, found m=z 293.1128.
2
28, 2024 (1963).
T. Mukaiyama, I. Kuwajima, and Z. Suzuki, J. Org. Chem.,
3
(1964).
4
I. Kuwajima and T. Mukaiyama, J. Org. Chem., 29, 1385
T. Mukaiyama, R. Matsueda, and M. Suzuki, Tetrahedron
Lett., 22, 1901 (1970).
5 O. Mitsunobu, M. Yamada, and T. Mukaiyama, Bull.
Chem. Soc. Jpn., 40, 935 (1967).
6
a) O. Mitsunobu and M. Yamada, Bull. Chem. Soc. Jpn.,
Benzyloxydiphenylphosphine Oxide (25).61 Into a stirred
solution of benzyl alcohol (0.54 g, 5.0 mmol) and triethylamine
(0.51 g, 5.0 mmol) in dichloromethane (5 mL) under argon atmo-
sphere was dropped a dichloromethane (5 mL) solution of diphen-
ylphosphinic chloride (1.2 g, 5.0 mmol) at 0 ꢂC. After the reaction
mixture was stirred at room temperature for 0.5 h, diethyl ether
was added. The solution was washed with 1 mol dmꢁ3 HCl (20
mL), water (20 mL) and brine. The organic layer was dried over
anhydrous sodium sulfate. After filtration and evaporation, the re-
sulting residue was purified by column chromatography (hexane/
40, 2380 (1967). b) O. Mitsunobu and M. Eguchi, Bull. Chem.
Soc. Jpn., 44, 3427 (1971). c) O. Mitsunobu, Synthesis, 1981, 1.
d) D. L. Hughs, in ‘‘Organic Reactions,’’ ed by L. A. Paquette,
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Amos, R. W. Emblidge, and N. Havens, J. Org. Chem., 48,
3598 (1983). f) L. D. Arnold, H. I. Assil, and J. C. Vederas, J.
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Dobbs and C. M. Johnson, Tetrahedron Lett., 43, 2807 (2002).
i) J. A. Dodge, J. I. Trujillo, and M. Presnell, J. Org. Chem.,
59, 234 (1994). j) S. F. Martin and J. A. Dodge, Tetrahedron Lett.,
32, 3017 (1991).
ethyl acetate = 2/1) to afford the title compound (25) (1.4 g, 94%)
61b
ꢂ
ꢂ
as a white solid: mp 77–78 C (lit.
mp 75–76 C); IR (ATR,
cmꢁ1) 1217, 1015, 860, 729; 1H NMR (270 MHz, CDCl3)
ꢁ7.73–7.65 (m, 4H), 7.54–7.40 (m, 6H), 7.19–7.08 (m, 5H),
3.66 (d, J ¼ 13:8 Hz, 2H); 13C NMR (68 MHz, CDCl3) ꢁ132.8,
131.7 (d, J ¼ 2:8 Hz), 131.3 (d, J ¼ 19:0 Hz), 131.0 (d, J ¼ 2:8
Hz), 130.0 (d, J ¼ 5:0 Hz), 128.4, 128.3 (d, J ¼ 2:8 Hz), 126.7
(d, J ¼ 3:3 Hz), 38.1 (d, J ¼ 3:3 Hz); HRMS (APCIþ) calcd for
C19H18O2P [M + H]þ 309.1040, found m=z 309.1035.
7
a) T. Tsunoda, Y. Yamamiya, and S. Ito, Tetrahedron Lett.,
34, 1639 (1993). b) T. Tsunoda, F. Ozaki, and S. Ito, Tetrahedron
Lett., 35, 5081 (1994). c) T. Tsunoda, Y. Yamamiya, Y.
Kawamura, and S. Ito, Tetrahedron Lett., 36, 2529 (1995). d) S.
Ito, Yakugaku Zasshi, 121, 567 (2001).
8
2002, 1126.
T. Mukaiyama, T. Shintou, and W. Kikuchi, Chem. Lett.,
Diphenylphosphinic Acid 4-Hydroxy-3,5-dimethylphenyl
ꢂ
9 T. Shintou, W. Kikuchi, and T. Mukaiyama, Chem. Lett.,
32, 22 (2003).
Ester (26). Isolated as white solid; mp 144–146 C; IR (ATR,
cmꢁ1) 3309, 1182, 1133, 1017, 877, 849, 733; 1H NMR (270
MHz, CDCl3) ꢁ7.90–7.83 (m, 4H), 7.55–7.41 (m, 6H), 6.71 (s,
2H), 5.66 (br, 1H), 2.06 (s, 6H); 13C NMR (68 MHz, CDCl3)
ꢁ149.3, 132.2 (d, J ¼ 2:8 Hz), 132.1, 131.7 (d, J ¼ 10:7 Hz),
130.0, 128.4 (d, J ¼ 13:4 Hz), 124.8, 120.1 (d, J ¼ 4:5 Hz),
10 T. Mukaiyama, W. Kikuchi, and T. Shintou, Chem. Lett.,
32, 300 (2003).
11 J. Zaloom, M. Calandra, and D. C. Roberts, J. Org. Chem.,
50, 2601 (1985).
12 a) H. J. Cristau, A. Chene, and H. Christol, Synthesis, 1980,
551. b) F. Jakle, M. Mattner, T. Priermeir, and M. Wagner, J. Or-
ganomet. Chem., 502, 123 (1995). c) W. Walker, J. Chem. Soc.,
Perkin Trans. 1, 1975, 1309.
16.3; HRMS (APCIþ) calcd for C20H20O3P [M
+
H]þ
339.1146, found m=z 339.1164.
This study was supported in part by the Grant of the 21st
Century COE Program, the Ministry of Education, Culture,
Sports, Science and Technology (MEXT).
13 A. B. Ouryupin, I. A. Rakhov, V. A. Kolesova, P. V.
Petrovskii, T. A. Mastryukova, and M. I. Kabachnik, Russian
Chem. Bull., 44(11), 2157 (1995).
14 W. Voksuil and J. F. Arens, Org. Synth., Coll. Vol. e, 211
(1973).
15 G. M. Kosolapoff and L. Maier, in ‘‘Organic Phosphorus
Compounds,’’ John Wiley & Sons, New York (1973), Vol. 4,
p. 504.
The authors wish to thank Mr. Sachiki Shimizu and Miss
Mutsumi Kitabatake, Sankio Chemical Co., LTD. for their
kind help with mass spectrometry and IR analysis.
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