The synthesis and reactivity of phosphinous acid-boranes

Article abstract of DOI:10.1055/s-2005-861878

Phosphinic acid chlorides are converted directly into phosphinous acid-boranes in a process utilizing BH₃-THF complex as a reducing agent. The process is general and affords phosphinous acid-boranes in good to very high yields. Phosphinous acid

Full text of DOI:10.1055/s-2005-861878

PAPER
1279
The Synthesis and Reactivity of Phosphinous Acid-Boranes
a
a,b
S
M
ynthesis and Reactivi
a
ty of Phosp
r
hinous
A
e
cid-Borane
k
s
Stankevič, K. Michał Pietrusiewicz*
a
Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland
Department of Organic Chemistry, Maria Curie-Skłodowska University, ul. Gliniana 33, 20-614 Lublin, Poland
Fax +48(22)6326681; E-mail: kmp@icho.edu.pl
b
Received 3 January 2005
rane complexes to directly produce phosphinous acid-bo-
ranes. The synthesized phosphinous acid-boranes have
been subsequently utilized in a model reactivity study that
revealed the basic reactivity pattern of phosphinous acid-
Abstract: Phosphinic acid chlorides are converted directly into
phosphinous acid-boranes in a process utilizing BH ·THF complex
3
as a reducing agent. The process is general and affords phosphinous
acid-boranes in good to very high yields. Phosphinous acid-boranes
have been found to react readily with alkylating, acylating, reduc- boranes towards alkylating agents, halogenating agents,
ing, halogenating and deborating agents to produce the correspond- reducing agents as well as strong acids and acid chlorides.
ing phosphinous acid-borane esters, phosphinous acid-borane
In the course of our studies on phosphinous acid-boranes
and the use of borane as the mild reducing agent in phos-
anhydrides, sec-phosphine oxides, sec-phosphine boranes and
phosphinic acid halides, respectively. The efficient procedures for
these conversions have been developed and their scope has been phorus chemistry, we turned our attention to phosphinic
outlined.
acid chlorides as potential substrates. We envisaged that
reduction of their P–Cl bonds under boranating conditions
could be expected to lead directly to the formation of
phosphinous acid-boranes. The viability of this idea was
checked in a preliminary experiment utilizing tert-bu-
tylphenylphosphinic chloride as substrate. It was treated
with an excess of BH ·SMe complex (3 equiv) in THF at
Key words: phosphorus, boron, alkylation, acylation, halogenation
Phosphine-boranes of general formula R P·BH constitute
a unique class of organophosphorus compounds in respect
to their reactivity and applications in organic synthesis. A
large number of very useful preparations have been devel-
oped with phosphine-boranes as the key reagents. Espe-
cially useful in this respect proved to be borane complexes
of functionalized phosphines bearing leaving groups at
phosphorus. Among them, phosphinite-boranes which
can be formally considered as esters of phosphinous acid-
boranes have become most valuable as precursors to
3
3
1
3
2
room temperature and the reaction was found to furnish
the desired phosphinous acid-borane in excellent yield.
We selected then a short series of phosphinic acid chlo-
rides 1a–e and reacted them with three different borane
reagents (BH ·THF, BH ·SMe and BF ·NaBH ) in order
2
3
3
3
2
3
4
to generalize the synthesis and to check for possible opti-
mal conditions. The results are presented in Scheme 1 and
Table 1.
4
chiral tertiary phosphines. Despite the importance of
these derivatives of phosphinous acid-boranes, the parent
acids, their synthesis and chemistry have remained practi-
cally unexplored. Perusal of chemical literature has re-
5
vealed identification of only one sodium salt and two free
3
h,6
phosphinous acid-boranes on record.
7
In our earlier work on the use of borane complexes for the
reduction of secondary phosphine oxides we have ob-
served that the desired reduction process was sometimes
accompanied by the competitive formation of phosphi-
nous acid-boranes. This observation led consequently to
the development of the first general procedure for the syn-
thesis of phosphinous acid-boranes from secondary phos-
Scheme 1
As can be seen from Table 1, the highest yields of bo-
ranatophosphinous acids were obtained when the com-
plex BH ·THF was used as the reducing agent. BH ·SMe
8
phine oxides.
3
3
2
In this paper we wish to demonstrate that by taking advan-
tage of the reducing properties of borane, the scope of the
viable substrates for the synthesis of phosphinous acid-
boranes can also be extended to readily available phos-
phinic acid halogenides. It will be demonstrated that
readily available phosphinic acid chlorides react with bo-
complex gave good yields of phosphinous acid-boranes
only in the case of tert-butylphenylphosphinic chloride
(
1a). Other studied phosphinic halides reacted very slug-
gishly with this complex. Similarly, BF /NaBH mixture
3
4
generating BH in situ was found effective only in the case
3
of 1a. It thus appears that BH ·THF complex is the reagent
3
of choice for the synthesis of phosphinous acid-boranes
from phosphinic chlorides. The developed synthetic pro-
tocol constitutes a valuable complement to the previously
described synthesis of phosphinous acid-boranes from
SYNTHESIS 2005, No. 8, pp 1279–1290
x
x
.
x
x
.2
0
0
5
Advanced online publication: 17.03.2005
DOI: 10.1055/s-2005-861878; Art ID: Z00505SS
Georg Thieme Verlag Stuttgart · New York
©

1
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M. Stankevič, K. M. Pietrusiewicz
PAPER
Table 1 The Synthesis of Phosphinous Acid-Boranes from Phos-
phinic Acid Chlorides
as the methylating agents. The results of this screening are
displayed in Scheme 2 and Table 2.
Entry
Product R¢
R¢¢
Method
used
Isolated
yields (%)
1
2
3
4
5
6
7
8
2a
2a
2a
2b
2b
2c
2d
2d
2e
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
t-Bu
t-Bu
t-Bu
Ph
A
B
C
A
B
B
B
C
B
90
95
96
23
92
74
79
28
67
Ph
Scheme 2
PhCH2
Me
In reactions of 2a–c,g,h with trimethylsilyldiazomethane
the formation of two products was always observed. Typ-
ically, methyl esters 3a–c,g were formed as the minor
products and trimethylsilylmethyl esters 4a–c,g were
formed as the major products (Entries 1–4, Table 2), ex-
cept for acid 2h (Entry 5, Table 2), which decomposed
during the reaction. In reactions with Meerwein’s salt
Me
9
2-NpCH2a
a
Np = naphthyl.
(
Entries 6–9, Table 2) the corresponding methyl esters
secondary phosphine oxides, especially in cases where
secondary phosphine oxides are difficult to access or are
unstable.
were formed only with low to moderate yields (28–52%).
It is noteworthy to mention, that evolution of a gas, most
probably methane, was observed during these reactions.
The presence of some amounts of the corresponding sec-
ondary phosphine oxides resulting from deboration of
9
Attempted conversion of diethyl chlorophosphate into the
corresponding acid-borane under developed conditions
3
1
was unsuccessful. Inspection of the P NMR spectrum of
the crude reaction mixture revealed no trace of the desired
product. The major product formed in this case was dieth-
yl phosphite.
31
starting acid was accordingly detected in the P NMR
spectra of the crude reaction mixtures. Methylations with
diazomethane (Entries 10–14, Table 2) and with MeI/
K CO (Entries 15–18, Table 2) both gave moderate to
2
3
The developed efficient synthetic access to phosphinous very good yields of methyl esters of acids 2.
acid-boranes have made it possible to consider these com-
Encouraged by the results of methylation with the MeI/
pounds as a new class of potential synthetic intermediates
K CO system, we also checked alkylations with other
2
3
in organophosphorus chemistry. As the chemistry of
phosphinous acid-boranes was practically unexplored be-
fore, we decided to study the basic reactivity of these
compounds towards typical alkylating, acylating, reduc-
ing and halogenating agents. For this study we selected
phosphinous acid-boranes 2a–c, g and h as model sub-
strates representing diaryl-, alkylaryl-, and dialkyl-substi-
tution patterns of different steric demand (Figure 1).
Phosphinous acid-boranes 2a–c were synthesized in the
electrophiles under the same conditions using acid 2a as
the model substrate (Scheme 3, Table 3).
course of this work. 2g and 2h were available from the Scheme 3
8
previous study.
As shown in Table 3, primary alkyl halides reacted
smoothly with phosphinous acid-borane 2a to form the
corresponding esters nearly quantitatively. Even allyl es-
ter 7 could be obtained with excellent yield (Entry 3) with-
out affecting the borane and the alkenyl moieties. On the
other hand, secondary alkyl halides did not react under
these conditions at all.
Figure 1
Next, we moved to the reactions of phosphinous acid-bo-
Since the esters of phosphinous acid-boranes are valuable ranes with acylating agents in order to explore the ability
synthetic intermediates we decided to explore their syn- of phosphinous acid-boranes to form mixed anhydrides.
thesis via simple O-alkylation of the parent acids. For the First, we examined the reactivity of acids 2a–c,g,h to-
synthesis of the corresponding methyl esters of 2a–c,g,h wards carboxylic acid chlorides. The results of this
we tested TMSCHN , Me OBF , CH N and MeI/K CO
screening are presented in Scheme 4 and Table 4.
2
3
4
2
2
2
3
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Phosphinous Acid-Boranes
1281
Table 2 The Reactivity of Phosphinous Acid-Boranes toward Methylating Agents
Entry
Substrate
Substituents
Reaction conditions
Isolated yields (%)
R¢
R¢¢
3
4
1
2
3
4
5
6
7
8
9
2a
2b
2c
2g
2h
2a
2b
2c
2h
2a
2b
2c
2g
2h
2a
2b
2c
2g
Ph
t-Bu
Ph
A
A
A
A
A
B
B
B
B
C
C
C
C
C
D
D
D
D
18
25
32
25
0
55
39
40
38
0
Ph
Ph
Bn
Ph
o-An
c-Hex
t-Bu
Ph
c-Hex
Ph
52
28
47
37
83
80
58
56
89
89
71
71
49
–
Ph
–
Ph
Bn
–
c-Hex
Ph
c-Hex
t-Bu
Ph
–
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
–
Ph
–
Ph
Bn
–
Ph
o-An
c-Hex
t-Bu
Ph
–
c-Hex
Ph
–
–
Ph
–
Ph
Bn
–
Ph
o-An
–
Table 3 Synthesis of Esters of tert-Butylphenylphosphinous Acid-
Borane
drides 9 were also formed in good to excellent yields
except for acid 2b, in which case the formation of 9b was
accompanied by the generation of phosphinous acid anhy-
dride-bis(borane) 11b with overall decrease in yields. The
results of reactions of acids 2 with methyl chloroformate
were not uniformly good either. Acids 2a,g,h gave the ex-
pected mixed anhydrides 10a,g,h, respectively, in good to
excellent yields (Entries 11–15, Table 4) whereas acids
2b and 2c underwent instead conversions to phosphinous
acid anhydride-bis(borane) 11b and methyl phosphinite-
borane 3b, and phosphinous acid anhydride-bis(borane)
11c, respectively.
Entry
Substrate Electrophile
Product
Isolated
yields (%)
1
2
3
4
5
2a
2a
2a
2a
2a
PhCH Br
5
6
7
–
–
95
99
94
0
2
CH CH Br
3
2
CH =CHCH Br
2
2
c-C H Br
6
11
i-C H Br
0
3
7
The observed differences in behavior of acids 2 towards
All acids 2a–c,g,h reacted smoothly with acetyl chloride benzoyl chloride and methyl chloroformate are likely to
forming the expected mixed anhydrides 8a–c,g,h with originate from differences in stability of the resulting
good to excellent yields (Entries 1–5, Table 4). In the re- mixed anhydrides, which is dependent on the nature of 2.
action of acids 2 with benzoyl chloride, the mixed anhy- Acids with bulky groups at phosphorus like 2a,g,h, appear
Scheme 4
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M. Stankevič, K. M. Pietrusiewicz
PAPER
Table 4 The Reactivity of Phosphinous Acid-Boranes towards Carboxylic Acid Halides
Entry
Substrate
Substituents
Method used
Isolated yields
R¢
R¢¢
R¢¢¢
Me
8–10
11
0
3
–
–
–
–
–
–
–
–
–
–
1
2
3
4
5
6
7
8
9
2a
2b
2c
2g
2h
2a
2b
2c
2g
2h
2a
2b
2c
2g
2h
Ph
t-Bu
Ph
A
A
A
A
A
B
B
B
B
B
C
C
C
C
C
8a
8b
94
Ph
Me
76
76
99
98
99
20
76
74
94
99
0
0
Ph
Bn
Me
8c
0
Ph
o-An
c-Hex
t-Bu
Ph
Me
8g
0
c-Hex
Ph
Me
8h
0
Ph
9a
0
Ph
Ph
9b
25
0
Ph
Bn
Ph
9c
Ph
o-An
c-Hex
t-Bu
Ph
Ph
9g
0
1
1
1
1
1
1
0
1
2
3
4
5
c-Hex
Ph
Ph
9h
0
OMe
OMe
OMe
OMe
OMe
10a
10b
10c
10g
10h
0
0
Ph
28
53
0
27
0
Ph
Bn
0
Ph
o-An
c-Hex
74
94
0
c-Hex
0
0
to form stable sterically protected mixed anhydrides, As can be seen from Table 5 only in the case of 2a we
whereas acids with smaller substituents at phosphorus as were able to obtain the desired mixed anhydride 12a in
in 2b and 2c yield more labile mixed anhydrides which good yield (Entry 1). In all other cases either the corre-
readily enter consecutive trasformations under the reac- sponding phosphinous acid anhydride-bis(boranes) 11 or
tion conditions. It is worthy of noting, however, that the chlorophosphine-boranes 13 were isolated instead in
synthesized mixed anhydrides 8–10 and the anhydrides 11 moderate yield, except for chlorophosphine-borane 13h
exhibit remarkable stability, which allows for their routine which was isolated in excellent yield (Entry 7). It should
isolation and flash chromatography on silica gel practical- be also noted that even in the case of acid 2a the reaction
ly without any loss of the product.
could be completely driven to the selective production of
chlorophosphine-borane 13a by increasing the tempera-
ture and the concentration of the chloride ions (Entry 2).
The reactivity of phosphinous acid-boranes 2 towards sul-
fonic acid chlorides was studied next. Mesyl chloride was
chosen as a model chloride for this study. The results are Alternatively, upon changing the base and the solvent, it
collected in Scheme 5 and Table 5. could selectively lead to anhydride 11a as the sole product
Table 5 The Reactivity of Phosphinous Acid-Boranes towards Mesyl Chloride
Entry
Substrate
Substituents
Method used Reaction time (h)
Isolated yields (%)
R¢
R¢¢
11
0
12
86
0
13
0
1
2
3
4
5
6
7
2a
2a
2a
2b
2c
2g
2h
Ph
t-Bu
t-Bu
t-Bu
Ph
A
B
C
A
A
A
A
6
6
Ph
0
58
0
Ph
66
6
54
34
56
0
0
Ph
0
0
Ph
Bn
5
0
0
Ph
o-An
c-Hex
8
0
40
94
c-Hex
3
0
0
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Phosphinous Acid-Boranes
1283
Scheme 5
(
Entry 3). Other tested sulfonic acid chlorides like tosyl efficient conversion of phosphinous acid-boranes 2 into
chloride and camphorosulfonyl chloride failed to form secondary phosphine oxides 14 are presented in
mixed anhydrides even with 2a. Apparently, with the pos- Scheme 6. It is interesting to juxtapose the developed pro-
sible exception of 12a, the mixed phosphinous acid-bo- cedure to our recent finding that secondary phosphine ox-
rane sulfonic acid anhydrides are very labile compounds ides can be efficiently converted into phosphinous acid-
8
whose undergo further transformations upon formation.
boranes by treatment with NaH·BH (or BF /NaBH ).
3 3 4
The two transformations complement each other and
make the mutual conversion of these two classes of com-
pounds a synthetically reversible process.
The possibility of easy removal of protecting borane
group from phosphine-boranes to yield trivalent phospho-
rus derivatives is one of the cornerstones of their advanta-
geous use as synthetic intermediates. In the case of Another useful transformation of phosphinous acid-bo-
phosphinous acid-boranes the deprotection would lead to ranes which we wanted to develop was their reductive
secondary phosphine oxides, a valuable synthetic inter- conversion into secondary phosphine-boranes. We have
mediates per se.
tested several reducing systems to probe the susceptibility
of phosphinous acid-boranes to undergo P–O bond cleav-
age and the results of the performed representative exper-
iments are collected in Scheme 7 and Table 6.
Scheme 7
Scheme 6 The synthesis of secondary phosphine oxides from phos-
phinous acid-boranes
The reduction of acids 2 to secondary phosphine-boranes
proved to be a difficult task. Lithium aluminium hydride,
a powerful reducing agent, appeared to be completely in-
effective in the case of 2. Trichlorosilane performed
somewhat better but the yields of the obtained secondary
We found that this transformation can be conveniently
achieved by utilizing tetrafluoroboric acid as deboranat-
ing agent according to the protocol described by McKin-
1
0
stry and Livinghouse. The studied examples of highly
Table 6 Conversion of Phosphinous Acid-Boranes into Secondary Phosphine–Boranes
Entry
Compound
Substituents
Reducing agent (equiv)
Reaction conditions
Isolated yields of 15
R¢
R¢¢
1
2
2a
2a
Ph
Ph
t-Bu
t-Bu
SiHCl (5)
PhMe, reflux, 45 h
30
38
3
SiHCl (5)
NaH (1.2 equiv),
3
PhMe, PhMe, 130 °C, 5 h
3
2a
Ph
t-Bu
SiHCl (5)
NaH (1.2 equiv),
PhMe, r.t., 24 h
0
3
4
5
6
7
2a
2a
2h
2h
Ph
t-Bu
LiAlH (3)
THF, r.t., 48 h
THF, r.t., 48 h
THF, r.t., 48 h
THF, reflux, 48 h
0
11
38
13
4
Ph
t-Bu
BH ·THF (6)
3
c-Hex
c-Hex
c-Hex
c-Hex
BH ·THF (6)
3
BH ·THF (6)
3
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M. Stankevič, K. M. Pietrusiewicz
PAPER
phosphine-borane were only modest (Entries 1 and 2, They have been practically neglected before, but the un-
Table 6). Also modest yields of secondary phosphine-bo- raveled basic reactivity pattern of phosphinous acid-bo-
ranes were obtained with BH as the reducing agent (En- ranes makes them now begin to emerge as a new class of
3
tries 5–7, Table 6). Interestingly, however, somewhat phosphorus reagents of potential utility in the preparative
better yields of secondary phosphine-boranes 15 were organophosphorus chemistry. When non-symmetrically
achieved when the reduction was carried out at room tem- substituted, they are chiral at phosphorus and their synthe-
perature than when heating was applied (cf. Entries 6 and sis in the nonracemic forms and stereochemistry of their
7
).
transformations is now under active investigation.
In this paper, we have demonstrated already that phosphi-
nous acid-boranes could be readily obtained from phos- All experiments were carried under inert atmosphere. The solvents
1
13
31
phinic acid halides. We became interested in were dried prior to use. H, C and P NMR were measured with a
Varian AC-200 (200 MHz) and Bruker AM-500 (500 MHz) in
accomplishing also the reverse conversion. We chose
CDCl with Me Si or 85% H PO as internal standard. Phosphinic
acid chlorides were prepared by literature methods. Diethyl chlo-
rophosphate was commercially available.
3
4
3
4
again tert-butylphenylphosphinous acid-borane 2a as a
model substrate. The results of our screening are dis-
played in Scheme 8 and Table 7.
1
1
Phosphinous Acid-Boranes from Phosphinic Acid Chlorides
and BH ·THF; General Procedure
3
In a flask equipped with a magnetic stirrer and a reflux condenser
was placed phosphinic acid chloride (1.0 mmol) in anhyd THF (15
mL). Then, BH ·THF complex (1.5 mmol) was added through a sy-
3
ringe. After addition of borane was completed, the reaction mixture
was refluxed for 2 h and after this time it was allowed to cool to r.t.
Next, aq HCl (3 M) was added to the reaction mixture and then it
was extracted several times with CH Cl . The organic phases were
Scheme 8
2
2
combined and dried (MgSO ). The solvents were evaporated and
the residue was purified by column chromatography (silica gel; hex-
ane–EtOAc, 2:1).
4
Table 7 The Synthesis of tert-Butylphenylphosphinic Halides from
tert-Butylphenylphosphinous Acid-Borane (2a)
Entry Halogenating
agent (equiv)
Conditions
Compd Isolated
yields
tert-Butylphenylphosphinous Acid-Borane (2a)
Yield: 95%.
1
1
2
PPh (1)/CCl
CCl , reflux, 21 h 16
85
77
H NMR (200 MHz, CDCl ): d = 0.00–1.70 (br m, 3 H), 1.14 (d,
3
4
4
3
JPCCH = 14.66 Hz, 9 H), 4.52 (br s, 1 H), 7.41–7.89 (m, 3 H), 7.69–
7
CCl C(O)CCl
NaH (1.2 equiv),
16
3
3
.85 (m, 2 H).
(
5)
Et O, r.t., 3 h
2
1
3
C NMR (50 MHz, CDCl ): d = 23.85, 23.92, 31.31, 32.13, 127.82,
3
3
4
(COCl) (3)
PhH, r.t., 21 h
16
17
85
64
128.03, 131.20, 131.26, 131.46.
3
2
1
P NMR (202 MHz, CDCl ): d = 114.39 (m).
3
CBr (5)
NaH (1.2 equiv),
4
Et O, r.t., 3 h
Anal. Calcd for C H BOP: C, 61.27; H, 9.26. Found: C, 61.26; H,
10 18
2
9
.08.
5
6
(COBr) (3)
PhH, r.t., 16 h
17
18
60
90
2
Diphenylphosphinous Acid-Borane (2b)
Yield: 92%.
I2 (3)
Et O, r.t., 24 h
2
1
H NMR (200 MHz, CDCl ): d = 0.20–1.90 (br m, 3 H), 4.35 (br s,
3
Table 7 reveals a remarkably high propensity of phosphi- 1 H), 7.40–7.57 (m, 6 H), 7.70–7.86 (m, 4 H).
nous acid-boranes to undergo the transformation into
phosphinic acid halides. Each of the three phosphinic acid 130.88, 131.52, 132.40, 133.71.
13
C NMR (50 MHz, CDCl ): d = 128.35, 128.57, 130.65, 130.82,
3
halides 16–18 could be obtained in good to excellent
yields by the action of a variety of reagents including even
PPh ·CCl , which we originally hoped would secure con-
31
P NMR (202 MHz, CDCl ): d = 95.62 (m).
3
Anal. Calcd for C H BOP: C, 66.72; H, 6,53. Found: C, 66.96; H,
1
2
14
3
4
6
.70.
version of acids 2 into the corresponding chlorophos-
phine-boranes.
Benzylphenylphosphinous Acid-Borane (2c)
Yield: 74%.
We have demonstrated herein that phosphinous acid-bo-
ranes can be directly obtained from phosphinic acid chlo- 1H NMR (200 MHz, CDCl
): d = 0.07–1.65 (br m, 3 H), 3.38 (d,
JPCH = 10.22 Hz, 2 H), 4.90 (br s, 1 H), 7.01–7.13 (m, 2 H), 7.21–
.34 (m, 3 H), 7.40–7.75 (m, 5 H).
3
rides by action of BH ·THF complex in THF.
3
7
Phosphinous acid-boranes, have been shown to react
readily with alkylating, acylating, reducing, halogenating
and deborating agents to efficiently produce the corre-
sponding phosphinous acid-borane esters, phosphinous
acid-borane anhydrides, sec-phosphine oxides, sec-phos-
1
3
C NMR (50 MHz, CDCl ): d = 39.41, 40.14, 126.68, 126.74,
3
1
1
27.98, 128.03, 128.08, 128.28, 129.95, 130.04, 130.19, 130.41,
31.06, 131.13, 131.18, 131.51, 131.56, 132.32.
3
1
P NMR (202 MHz, CDCl ): d = 101.64 (m).
3
phine boranes and phosphinic acid halides, respectively. Anal. Calcd for C H BOP: C, 67.87; H, 7.01. Found: C, 68.02; H,
1
3
16
6
.95.
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Phosphinous Acid-Boranes
1285
Methylphenylphosphinous Acid-Borane (2d)
Yield: 79%.
With Potassium Carbonate in Acetone (D)
In a flask equipped with a magnetic stirrer and an argon inlet, phos-
phinous acid-borane (0.3 mmol) in acetone (15 mL) was placed.
Then, anhyd potassium carbonate (3 mmol) was added. After 5 min,
alkyl halide (2–5 equiv) was added and the reaction mixture was re-
fluxed for 3 h. Then, the reaction mixture was allowed to cool to r.t.,
inorganic salt was filtered off and the filtrate was evaporated to dry-
ness. The residue was subjected to separation (silica gel; hexane–
EtOAc, 6:1).
1
H NMR (200 MHz, CDCl ): d = 0.05–1.65 (br m, 3 H), 1.73 (d,
3
JPCH = 9.34 Hz, 3 H), 6.20 (br s, 1 H), 7.43–7.60 (m, 3 H), 7.75–7.90
(
m, 2 H).
1
3
C NMR (50 MHz, CDCl ): d = 17.31, 18.20, 128.37, 128.58,
3
1
39.73, 129.96, 131.45.
3
1
P NMR (202 MHz, CDCl ): d = 99.61 (m).
3
Anal. Calcd for C H BOP: C, 54.61; H, 7.96. Found: C, 55.04; H,
7
12
Methyl tert-Butylphenylphosphinite-Borane (3a)
Yields: 18, 52, 83 and 89%.
7
.86.
1
H NMR (200 MHz, CDCl ): d = –0.05–1.64 (br m, 3 H), 1.13 (d,
(
2-Naphthylmethyl)phenylphosphinous Acid-Borane (2e)
3
JPCCH = 14.24 Hz, 9 H), 3.73 (d, J
(
= 11.07 Hz, 3 H), 7.41–7.61
POCH
Yield: 67%.
m, 3 H), 7.61–7.77 (m, 2 H).
1
H NMR (200 MHz, CDCl ): d = 0.05–1.72 (br m, 3 H), 3.52 (d,
3
1
3
C NMR (50 MHz, CDCl ): d = 24.13, 24.19, 31.67, 32.54, 54.57,
JPCH = 9.98 Hz, 2 H), 3.60 (br s, 1 H), 7.11–7.21 (m, 1 H),7.36–7.56
3
5
3
4.74, 128.01, 128.20, 131.36, 131.41, 131.72, 131.98.
(
1
m, 5 H), 7.56–7.89 (m, 6 H)
1
3
P NMR (202 MHz, CDCl ): d = 127.62 (m).
C NMR (50 MHz, CDCl ): d = 39.64, 40.36, 125.71, 126.02,
3
3
1
1
27.39, 127.50, 127.68, 128.12, 128.25, 128.46, 128.64, 128.77,
28.89, 130,261, 130.48, 131.73, 131.77, 132.22.
+
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 233.1237;
found: 233.1235.
1
1
20
3
1
P NMR (202 MHz, CDCl ): d = 103.16 (m).
3
Methyl Diphenylphosphinite-Borane (3b)
Yields: 25, 28, 80 and 71%.
Anal. Calcd for C H BOP: C, 72.99; H, 6.48. Found: C, 73.04; H,
6
1
7
18
.53.
1
H NMR (200 MHz, CDCl ): d = 0.20–1.90 (br m, 3 H), 3.78 (d,
3
JPOCH = 12.06 Hz, 3 H), 7.44–7.62 (m, 6 H), 7.71–7.84 (m, 4 H).
13
Methylation and Alkylation of Phosphinous Acid-Boranes;
General Procedures
With Trimethylsilyldiazomethane (A)
In a flask equipped with a magnetic stirrer and an argon inlet, phos-
phinous acid-borane (0.3 mmol) in anhyd Et O (15 mL) was placed.
Then, a solution of trimethylsilyldiazomethane (0.9 mmol) was
added into the reaction mixture through a syringe. The reaction mix-
ture immediately changed color to yellow. The reaction mixture
was allowed to stay at r.t. for 24–72 h. Next, aq HCl (3 M) was add-
ed to the mixture, the biphasic mixture was extracted with CH Cl ,
C NMR (50 MHz, CDCl ): d = 54.05, 54.09, 128.43, 128.64,
3
1
3
31.03, 131.26, 132.76, 131.81.
1
P NMR (202 MHz, CDCl ): d = 109.02 (m).
3
2
+
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 253.0924;
13 16
found: 253.0947.
Methyl Benzylphenylphosphinite-Borane (3c)
Yields: 32, 47, 58 and 71%.
2
2
the organic phase was dried (MgSO ) and evaporated to dryness.
The residue was subjected to separation (silica gel, hexane–EtOAc,
1
4
H NMR (200 MHz, CDCl ): d = 0.00–1.70 (br m, 3 H), 3.35 (d,
3
JPCH = 10.30 Hz, 2 H), 3.65 (d, JPOCH = 11.86 Hz, 3 H), 6.95–7.07
(
6
:1).
m, 2 H), 7.20–7.28 (m, 3 H), 7.39–7.66 (m, 5 H).
1
3
C NMR (50 MHz, CDCl ): d = 38.63, 39.42, 54.36, 126.77,
With Meerwein Salt (B)
In a flask equipped with a magnetic stirrer and an argon inlet, phos-
phinous acid-borane (0.3 mmol) in anhyd Et O (15 mL) was placed.
3
1
1
26.82, 128.01, 128.06, 128.26, 128.46, 130.01, 130.10, 130.90,
31.12, 131.90.
2
Then, sodium hydride (0.36 mmol) was added in one portion. When
the evolution of hydrogen ceased, Meerwein salt (0.9 mmol) was
added to the reaction mixture at r.t. The mixture was allowed to
stand for 2 h, then aq HCl was added. The biphasic mixture was ex-
tracted with CH Cl , the organic phase was dried (MgSO ) and then
31
P NMR (202 MHz, CDCl ): d = 115.67 (m).
3
+
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 267.1032;
found: 267.1027.
1
4
18
2
2
4
Methyl o-Anisylphenylphosphinite-Borane (3g)
Yields: 25, 56 and 49%.
evaporated to dryness. The residue was subjected to separation (sil-
ica gel; hexane–EtOAc, 6:1).
1
H NMR (200 MHz, CDCl ): d = 0.20–1.90 (br m, 3 H), 3.67 (s, 3
3
With Diazomethane (C)
In a flask equipped with a magnetic stirrer and an argon inlet, phos-
H), 3.78 (d, JPOCH = 12.10 Hz, 3 H), 6.82–7.17 (m, 3 H), 7.22–7.34
(m, 1 H), 7.40–7.60 (m, 3 H), 7.71–7.91 (m, 2 H).
phinous acid-borane (0.3 mmol) in anhyd Et O (15 mL) was placed.
The reaction flask was cooled then to – 78 °C. In another flask
equipped with magnetic stirrer, distillation head and reflux con-
13
2
C NMR (50 MHz, CDCl ): d = 53.98, 55.53, 111.52, 111.62,
3
1
1
15.20, 120.66, 120.87, 127.93, 128.15, 129.55, 130.92, 131.16,
33.74, 133.97.
denser DIAZALD (3 mmol) was placed in Et O (30 mL) and MeOH
2
3
1
P NMR (202 MHz, CDCl ): d = 107.34 (m).
(10 mL). To this mixture, aq KOH (3 mmol) was added. After 5
3
+
min, an ethereal solution of diazomethane was distilled straight into
the flask containing phosphinous acid–borane. The reaction mixture
was maintained at –78 °C for 0.5 h, allowed to warm to r.t. and
quenched with aq HCl. The mixture was extracted with CH Cl , the
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 283.1030;
14 18 2
found: 283.1051.
2
2
Methyl Di-c-hexylphosphinite-Borane (3h)
Yields: 37 and 89%.
organic phase was dried (MgSO ) and then evaporated to dryness.
4
The residue was subjected to separation (silica gel; hexane–EtOAc,
1
H NMR (200 MHz, CDCl ): d = –0.41–1.25 (br m, 3 H), 1.15–1.60
m, 10 H), 1.60–2.00 (m, 12 H), 3.69 (d, JPOCH = 10.75 Hz, 3 H).
3
6
:1).
(
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

1
286
M. Stankevič, K. M. Pietrusiewicz
PAPER
1
3
C NMR (50 MHz, CDCl ): d = 25.06, 25.11, 26.00, 26.17, 26.43,
Ethyl tert-Butylphenylphosphinite-Borane (6)
Yield: 99%.
3
2
6.63, 26.72, 35.14, 35.92, 56.08, 56.15.
3
1
1
P NMR (202 MHz, CDCl ): d = 133.69 (m).
H NMR (200 MHz, CDCl ): d = –0.05–1.65 (br m, 3 H), 1.13 (d,
3
3
+
JPCCH = 14.44 Hz, 9 H), 1.36 (t, JHC-H = 7.10 Hz, 3 H), 3.85–4.23 (m,
2
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 265.1863;
found: 265.1853.
1
3
28
H), 7.42–7.60 (m, 3 H), 7.66–7.80 (m, 2 H).
1
3
C NMR (50 MHz, CDCl ): d = 16.59, 16.71, 24.04, 24.10, 31.51,
3
Trimethylsilylmethyl tert-Butylphenylphosphinite-Borane (4a)
32.38, 63.82, 63.90, 127.90, 128.09, 128.74, 129.57, 131.23,
Yield: 55%.
131.28, 131.63, 131.83.
1
31
H NMR (200 MHz, CDCl ): d = –0.05–1.60 (br m, 3 H), 0.17 (m,
P NMR (202 MHz, CDCl ): d = 123.80 (m).
3
3
9
3
H), 1.13 (d, J
= 14.24 Hz, 9 H), 3.60 (m, 2 H), 7.41–7.61 (m,
+
POCH
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 247.1394;
found: 247.1412.
1
2
22
H), 7.61–7.77 (m, 2 H).
Trimethylsilylmethyl Diphenylphosphinite-Borane (4b)
Yield: 39%.
Allyl tert-Butylphenylphosphinite-Borane (7)
Yield: 94%.
1
H NMR (200 MHz, CDCl ): d = 0.29–1.90 (br m, 3 H), 0.14 (m, 9
1
3
H NMR (200 MHz, CDCl ): d = –0.05–1.65 (br m, 3 H), 1.16 (d,
3
H), 3.64 (d, J
= 6.01 Hz, 2 H), 7.41–7.60 (m, 6 H), 7.69–7.82
POCH
JPCCH = 14.52 Hz, 9 H), 4.27–4.65 (m, 2 H), 5.22–5.47 (m, 2 H),
(
m, 4 H).
5
.90–6.09 (m, 1 H), 7.41–7.61 (m, 3 H), 7.68–7.81 (m, 2 H).
1
3
C NMR (50 MHz, CDCl ): d = –3.23, 60.23, 60.46, 128.34,
13
3
C NMR (50 MHz, CDCl ): d = 24.09, 24.15, 31.75, 32.61, 68.04,
3
1
28.55, 131.07, 131.29, 131.55, 131.60.
6
8.11, 117.04, 127.97, 128.17, 129.08, 130.06, 131.38, 131.43,
3
1
P NMR (202 MHz, CDCl ): d = 108.55 (m).
131.68, 131.88, 133.56, 133.69.
3
+
31
HRMS (ESI): m/z calcd for C H BONaPSi (M + Na ): 325.1319;
found: 325.1335.
P NMR (202 MHz, CDCl ): d = 126.07 (m).
1
6
24
3
+
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 259.1394;
1
3
22
found: 259.1385.
Trimethylsilylmethyl Benzylphenylphosphinite-Borane (4c)
Yield: 40%.
Mixed Phosphorus-Carboxylic Anhydrides; General Procedure
1
H NMR (200 MHz, CDCl ): d = 0.05–1.85 (br m, 3 H), 0.10 (m, 9
In a flask equipped with a magnetic stirrer and drying CaCl tube
3
2
H), 3.21–3.45 (m, 2 H), 3.51 (m, 2 H), 6.95–7.07 (m, 2 H), 7.20–
phosphinous acid-borane (0.3 mmol) in CH Cl (15 mL) was
2
2
7
.30 (m, 3 H), 7.36–7.62 (m, 5 H).
placed. Then, Et N (0.33 mmol) was added and 5 min later the
3
1
3
RC(O)Cl (0.36–0.60 mmol) was added through a syringe. Then the
reaction mixture was allowed to stand at r.t. for 2–24 h. Next, the
reaction mixture was filtered to remove the formed triethylammoni-
um salt, the filtrate was evaporated to dryness and the residue was
separated by flash chromatography (hexane–EtOAc, 2:1 or 6:1).
C NMR (50 MHz, CDCl ): d = –3.28, 38.71, 39.50, 60.55, 60.72,
3
1
1
26.65, 126.71, 127.87, 127,92, 128.15, 128.34, 129.32, 130.09,
30.17, 131.03, 131.24, 131.73, 131.78.
3
1
P NMR (202 MHz, CDCl ): d = 115.22 (m).
3
+
HRMS (ESI): m/z calcd for C H BONaPSi (M + Na ): 339.1438;
found: 339.1445.
1
7
26
Acetic tert-Butylphenylphosphinous-Borane Anhydride (8a)
Yield: 94%.
Trimethylsilylmethyl o-Anisylphenylphosphinite-Borane (4g)
Yield: 38%.
1
H NMR (200 MHz, CDCl ): d = 0.10–1.82 (br m, 3 H), 1.20 (d,
3
JPCCH = 14.72 Hz, 9 H), 2.31 (d, J
(m, 3 H), 7.63–7.78 (m, 2 H).
= 1.10 Hz, 3 H), 7.42–7.63
POCCH
1
H NMR (200 MHz, CDCl ): d = 0.20–1.92 (br m, 3 H), 0.14 (m, 9
3
H), 3.61 (dd, J
= 5.80, J
= 2.92 Hz, 2 H), 3.65 (s, 3 H), 6.82–
13
POCH
HCH
C NMR (50 MHz, CDCl ): d = 22.20, 22.25, 24.16, 24.21, 31.76,
3
6
.94 (m, 1 H), 7.04–7.16 (m, 1 H), 7.38–7.56 (m, 4 H), 7.69–7.92
3
1
2.51, 128.03, 128.15, 128.35, 131.43, 131.64, 131.88, 131.94,
66.40.
(
m, 3 H).
1
3
C NMR (50 MHz, CDCl ): d = –3.25, 55.29, 59.59, 59.75, 111.26,
31
3
P NMR (202 MHz, CDCl ): d = 126.62 (m).
3
1
1
11.36, 120.50, 120.71, 127.76, 127.97, 130.96, 131.02, 131.25,
33.76, 133.98.
Anal. Calcd for C H BO P: C, 60.54; H, 8.47. Found: C, 60.56; H,
8
1
2
20
2
.50.
3
1
P NMR (202 MHz, CDCl ): d = 107.07 (m).
3
+
Acetic Diphenylphosphinous-Borane Anhydride (8b)
Yield: 76%.
HRMS (ESI): m/z calcd for C H BO NaPSi (M + Na ): 355.1425;
found: 355.1449.
1
7
26
2
1
H NMR (200 MHz, CDCl ): d = 0.35–2.10 (br m, 3 H), 2.29 (d,
3
Benzyl tert-Butylphenylphosphinite-Borane (5)
Yield: 95%.
J = 1.24 Hz, 3 H), 7.45–7.64 (m, 6 H), 7.77–7.90 (m, 4 H).
1
3
C NMR (50 MHz, CDCl ): d = 22.30, 22.34, 128.50, 128.72,
3
1
H NMR (200 MHz, CDCl ): d = 0.10–1.65 (br m, 3 H), 1.17 (d,
JPCCH = 14.56 Hz, 9 H), 4.80–5.19 (m, 2 H), 7.32–7.64 (m, 8 H),
3
128.97, 130.19,131.52, 131.75, 132.23, 132.28.
31
P NMR (202 MHz, CDCl ): d = 106.12 (m).
3
7
.68–7.83 (m, 2 H).
+
1
3
HRMS (ESI): m/z calcd for C14H16BO NaP (M + Na ): 281.0873;
2
C NMR (50 MHz, CDCl ): d = 24.16, 24.22, 31.88, 32.74, 69.05,
9.12, 127.46, 128.02, 128.21, 128.43, 129.93, 130.83, 131.43,
31.48, 131.79, 131.98.
3
found: 281.0886.
6
1
Acetic Benzylphenylphosphinous-Borane Anhydride (8c)
Yield: 76%.
3
1
P NMR (202 MHz, CDCl ): d = 126.45 (m).
3
+
HRMS (ESI): m/z calcd for C H BONaP (M + Na ): 309.1550;
1
1
7
24
H NMR (200 MHz, CDCl ): d = 0.15–1.95 (br m, 3 H), 2.23 (d,
3
found: 309.1554.
JPOCCH = 1.18 Hz, 3 H), 3.56–3.78 (m, 2 H), 6.94–7.06 (m, 2 H),
7
.17–7.30 (m, 3 H), 7.40–7.73 (m, 5 H).
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Phosphinous Acid-Boranes
1287
1
3
+
C NMR (50 MHz, CDCl ): d = 22.22, 22.26, 36.96, 37.60, 127.12,
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 357.1186;
found: 357.1196.
3
20 20
2
1
1
27.18, 127.50, 128.14, 128.19, 128.31, 128.52, 130.01, 130.10,
30.21, 131.14, 131.36, 132.45, 132.50, 167.00, 167.16.
3
1
Benzoic o-Anisylphenylphosphinous-Borane Anhydride (9g)
Yield: 99%.
P NMR (202 MHz, CDCl ): d = 113.18 (m).
3
+
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 295.1030;
found: 295.1010.
1
5
18
2
1
H NMR (200 MHz, CDCl ): d = 0.40–2.20 (br m, 3 H), 3.61 (s, 3
3
H), 6.86–6.97 (m, 1 H), 7.11–7.22 (m, 1 H), 7.44–7.73 (m, 7 H),
7
.86–7.99 (m, 2 H), 7.99–8.18 (m, 3 H).
Acetic o-Anisylphenylphosphinous-Borane Anhydride (8g)
Yield: 99%.
1
3
C NMR (50 MHz, CDCl ): d = 55.49, 111.36, 111.45, 120.95,
3
1
121.20, 128.15, 128.38, 128.55, 129.09, 130.03, 135.35, 131.16,
1
H NMR (200 MHz, CDCl ): d = 0.30–2.10 (br m, 3 H), 2.29 (d,
3
31.41, 131.68, 131.72, 133.93, 134.25, 134.52, 160.60, 160.46.
JPOCCH = 1.24 Hz, 3 H), 3.70 (s, 3 H), 6.87–6.98 (m, 1 H), 7.08–7.20
3
1
(
m, 1 H), 7.40–7.63 (m, 4 H), 7.73–8.02 (m, 3 H).
P NMR (202 MHz, CDCl ): d = 107.45 (m).
3
1
3
+
C NMR (50 MHz, CDCl ): d = 22.21, 55.53, 111.37, 111.46,
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 373.1135;
found: 373.1154.
3
20 20
3
1
1
17.93, 120.91, 121.15, 128.02, 128.24, 129.60, 130.90, 131.03,
31.26, 131.58, 131.63, 134.09, 134.39, 134.50.
3
1
Benzoic Di-c-hexylphosphinous-Borane Anhydride (9h)
Yield: 94%.
P NMR (202 MHz, CDCl ): d = 105.37 (m).
3
+
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 311.0979;
found: 311.0997.
1
5
18
3
1
H NMR (200 MHz, CDCl ): d = –0.20–1.38 (br m, 3 H), 1.17–2.09
3
(
m, 20 H), 2.25–2.50 (m, 2 H), 7.43–7.59 (m, 2 H), 7.59–7.71 (m, 1
H), 8.00–7.13 (m, 2 H).
Acetic Di-c-hexylphosphinous-Borane Anhydride (8h)
Yield: 98%.
1
3
C NMR (50 MHz, CDCl ): d = 27.78, 25.99, 26.03, 26.37, 26.50,
3
1
26.59, 35.37, 35.95, 128.56, 130.33, 134.05, 163.02.
H NMR (200 MHz, CDCl ): d = –0.32–1.41 (br m, 3 H), 1.17–1.65
3
3
1
(
m, 10 H), 1.65–2.00 (m, 10 H), 2.05–2.31 (m, 2 H), 2.20 (d,
P NMR (202 MHz, CDCl ): d = 138.85 (m).
3
JPOCCH = 0.87 Hz, 3 H).
+
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 355.1969;
found: 355.1988.
1
9
30
2
1
3
C NMR (50 MHz, CDCl ): d = 22.19, 22.23, 25.76, 25.85, 25.90,
3
2
6.32, 26.37, 26.57, 35.09, 35.68, 167.39, 167.58.
3
1
O-Methylcarbonic tert-Butylphenylphosphinous-Borane Anhy-
P NMR (202 MHz, CDCl ): d = 137.18 (m).
3
dride (10a)
Yield: 99%.
1
+
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 293.1812;
found: 293.1821.
1
4
28
2
H NMR (200 MHz, CDCl ): d = 0.12–1.86 (br m, 3 H), 1.21 (d,
3
JPCCH = 14.92 Hz, 9 H), 3.84 (s, 3 H), 7.46–7.65 (m, 3 H), 7.65–7.82
Benzoic tert-Butylphenylphosphinous-Borane Anhydride (9a)
Yield: 99%.
(
m, 2 H).
13C NMR (50 MHz, CDCl
28.19, 128.39, 131.42, 131.64, 132.10, 132.15.
1
3
): d = 24.08, 24.16, 32.24, 32.98, 55.97,
H NMR (200 MHz, CDCl ): d = 0.15–1.93 (br m, 3 H), 1.33 (d,
3
1
JPCCH = 14.70 Hz, 9 H), 7.44–7.64 (m, 5 H), 7.64–7.83 (m, 3 H),
8
3
1
.07–8.22 (m, 2 H).
P NMR (202 MHz, CDCl ): d = 135.21 (m).
3
1
3
C NMR (50 MHz, CDCl ): d = 24.45, 24.51, 32.20, 32.95, 127.06,
Anal. Calcd for C H BO P: C, 56.73; H, 7.93. Found: C, 56.83; H,
12 20 3
7.91.
3
1
1
27.99, 128.19, 128.40, 128.75, 128.91, 130.35, 130.47, 131.32,
31.15, 131.72, 131.94, 131.99, 134.22, 162.27.
3
1
O-Methylcarbonic o-Anisylphenylphosphinous-Borane Anhy-
P NMR (202 MHz, CDCl ): d = 128.14 (m).
3
dride (10g)
Yield: 74%.
1
Anal. Calcd for C H BO P: C, 68.03; H, 7.39. Found: C, 67.91; H,
7
19
18
2
.34.
H NMR (200 MHz, CDCl ): d = 0.20–1.90 (br m, 3 H), 3.67 (s, 3
3
H), 3.83 (s, 3 H), 6.89–7.22 (m, 2 H), 7.38–7.67 (m, 4 H), 7.67–8.07
Benzoic Diphenylphosphinous-Borane Anhydride (9b)
Yield: 20%.
(
m, 3H).
13C NMR (50 MHz, CDCl
1
1
): d = 55.55, 55.79, 111.49, 111.58,
20.89, 121.13, 128.06, 128.28, 130.99, 131.23, 131.87, 134.19,
34.47, 134.81, 160.62, 160.65.
1
3
H NMR (200 MHz, CDCl ): d = 0.30–2.20 (br m, 3 H), 7.40–7.80
m, 11 H), 7.80–8.00 (m, 3 H), 8.07–8.14 (m, 1 H).
3
(
1
3
C NMR (50 MHz, CDCl ): d = 128.65, 128.85, 130.46, 131.64,
3
31
P NMR (202 MHz, CDCl ): d = 112.63 (m).
3
1
3
31.88, 132.33, 132.37, 134.27.
1
+
HRMS (ESI): m/z calcd for C15H18BO NaP (M + Na ): 327.0928;
4
P NMR (202 MHz, CDCl ): d = 107.83 (m).
3
found: 327.0946.
Benzoic Benzylphenylphosphinous-Borane Anhydride (9c)
Yield: 76%.
O-Methylcarbonic Di-c-Hexylphosphinous-Borane Anhydride
10h)
Yield: 94%.
(
1
H NMR (200 MHz, CDCl ): d = 0.15–2.00 (br m, 3 H), 3.40–3.94
3
(
m, 2 H), 6.87–7.12 (m, 2 H), 7.12–7.31 (m, 3 H), 7.45–7.82 (m, 8
1
H NMR (200 MHz, CDCl ): d = –0.29–1.41 (br m, 3 H), 1.18–1.64
3
H), 8.00–8.09 (m, 1 H), 8.18–8.26 (m, 1 H).
(
m, 10 H), 1.64–2.01 (m, 10 H), 2.01–2.26 (m, 2 H), 3.86 (s, 3 H).
1
3
C NMR (50 MHz, CDCl ): d = 37.30, 37.94, 127.13, 127.19,
3
13
C NMR (50 MHz, CDCl ): d = 25.54, 25.75, 26.09, 26.32, 26.53,
3
1
1
1
28.17, 128.22, 128.39, 128.58, 128.75, 130.10, 130.19, 130.27,
30.37, 130.40, 131.19, 131.34, 131.41, 132.49, 132.54, 134.25,
34.40, 162.98.
2
6.58, 35.22, 35.83, 55.82, 151.05.
3
1
P NMR (202 MHz, CDCl ): d = 145.60 (m).
3
3
1
P NMR (202 MHz, CDCl ): d = 114.68 (m).
3
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

1
288
M. Stankevič, K. M. Pietrusiewicz
PAPER
+
HRMS (ESI): m/z calcd for C H BO NaP (M + Na ): 309.1761;
tert-Butylphenylchlorophosphine-Borane (13a)
1
4
28
3
found: 309.1782.
Yield: 58%.
1
H NMR (200 MHz, CDCl ): d = 0.30–2.00 (br m, 3 H), 1.25 (d,
3
Diphenylphosphinous Acid Anhydride-Bis(borane) (11b)
JPCCH = 16.50 Hz, 9 H), 7.42–7.68 (m, 3 H), 7.84–7.97 (m, 2 H).
Yield: 28%.
1
3
C NMR (50 MHz, CDCl ): d = 24.50, 24.59, 35.11, 35.51, 128.19,
1
3
H NMR (200 MHz, CDCl ): d = 0.20–1.85 (br m, 3 H), 7.38–7.61
m, 6 H), 7.65–7.82 (m, 4 H).
3
1
3
28.40, 132.23, 132.28, 132.38, 132.60.
1
(
P NMR (202 MHz, CDCl ): d = 121.87 (m).
1
3
3
C NMR (50 MHz, CDCl ): d = 128.43, 128.55, 128.65, 131.59,
3
1
31.72, 131.83, 132.37.
o-Anisylphenylchlorophosphine-Borane (12g)
Yield: 40%.
3
1
P NMR (202 MHz, CDCl ): d = 114.85 (m).
3
+
1
HRMS (ESI): m/z calcd for C H B ONaP (M + Na ): 437.1548;
found: 437.1559.
H NMR (200 MHz, CDCl ): d = 0.30–1.95 (br m, 3 H), 3.71 (s, 3
2
4
26
2
2
3
H), 6.90–7.01 (m, 1 H), 7.09–7.20 (m, 1 H), 7.37–8.04 (m, 7 H).
3
1
P NMR (202 MHz, CDCl ): d = 92.20 (m).
3
Benzylphenylphosphinous Acid Anhydride-Bis(borane) (11c)
Yield: 53%.
Di-c-hexylchlorophosphine-Borane (12h)
Yield: 94%.
1
H NMR (200 MHz, CDCl ): d = 0.20–1.90 (br m, 3 H), 3.31–3.70
m, 2 H), 6.86–6.94 (m, 1 H), 6.96–7.04 (m, 1 H), 7.12–7.30 (m, 3
3
(
1
H NMR (200 MHz, CDCl ): d = –0.13–1.55 (br m, 3 H), 1.21–1.70
3
H), 7.30–7.62 (m, 5 H).
(
m, 10 H), 1.70–2.17 (m, 12 H).
1
3
C NMR (50 MHz, CDCl ): d = 39.64, 39.86, 40.33, 40.55, 127.10,
13
3
C NMR (50 MHz, CDCl ): d = 25.40, 25.46, 25.67, 26.14, 26.26,
3
1
1
28.15, 128.23, 128.36, 128.45, 130.21, 130.31, 130.41, 131.17,
31.28, 131.40, 131.52, 132.50, 132.61.
2
6.35, 26.53, 36.56, 36.96.
3
1
P NMR (202 MHz, CDCl ): d = 129.54 (m).
3
1
3
P NMR (202 MHz, CDCl ): d = 122.21 (m).
3
Anal. Calcd for C H BClP: C, 54.49; H, 9.60; Cl, 13.50. Found:
+
10 14
HRMS (ESI): m/z calcd for C H B ONaP (M + Na ): 465.1749;
found: 465.1764.
2
6
30
2
2
C, 54.34; H, 9.52; Cl, 13.59.
Conversion of Phosphinous Acid-Boranes into Secondary Phos-
phine Oxides; General Procedure
Reaction Between Phosphinous Acid-Boranes and Mesyl Chlo-
ride; General Procedure
In a flask equipped with a magnetic stirrer and an argon inlet, phos-
phinous acid-borane (0.3 mmol) in CH Cl (15 mL) was placed.
In a flask equipped with a magnetic stirrer and a drying CaCl tube,
2
2
2
phosphinous acid-borane (0.3 mmol) was placed in CH Cl or
2
2
Then, ethereal complex of tetrafluoroboric acid (1.5 mmol) was
added through a syringe. The reaction mixture was allowed to stand
at r.t. for 1.5 h. Then, aq sodium carbonate was added, and after 10
min the reaction mixture was extracted with CH Cl , the organic
MeCN (15 mL). Then, Et N (0.36 mmol) or anhyd K CO (3 mmol)
3
2
3
was added and after 5 min mesyl chloride (0.60 mmol) was added
through a syringe. The reaction mixture was allowed to stand at r.t.
for 3–66 h or was refluxed for 6 h. Then, the reaction mixture was
filtered to remove triethylammonium salt, the filtrate was evaporate
to dryness and residue was separated by flash chromatography (hex-
ane–EtOAc, 6:1).
2
2
phase was dried (MgSO ), evaporated to dryness and the residue
4
was purified by flash chromatography (EtOAc–MeOH, 20:1).
tert-Butylphenylphosphine Oxide (14a)
Yield: 96%.
Methanesulfonic tert-Butylphenylphosphinous-Borane Anhy-
dride (12a)
Yield: 86%.
1
H NMR (200 MHz, CDCl ): d = 1.16 (d, J = 16.62 Hz, 9 H),
PCCH
3
7
.04 (d, JPH = 454 Hz, 1 H), 7.42–7.80 (m, 5 H).
1
3
1
C NMR (50 MHz, CDCl ): d = 23.48, 23.52, 31.34, 32.71, 127.86,
H NMR (200 MHz, CDCl ): d = 0.16–1.94 (br m, 3 H), 1.22 (d,
3
3
1
28.21, 128.27, 128.51, 130.70, 130.90, 132,33, 132.38.
JPCCH = 15.62 Hz, 9 H), 3.49 (s, 3 H), 7.48–7.68 (m, 3 H), 7.78–7.92
(
m, 2 H).
31
P NMR (202 MHz, CDCl ): d = 47.72.
3
1
3
C NMR (50 MHz, CDCl ): d = 23.94, 24.01, 33.46, 34.13, 47.17,
+
3
HRMS (ESI): m/z calcd for C H ONaP (M + Na ): 205.0777;
10 15
found: 205.0755.
1
26.22, 127.17, 128.28, 128.48, 131.69, 131.90, 132.62, 132.67.
3
1
P NMR (202 MHz, CDCl ): d = 144.69 (m).
3
Diphenylphosphine Oxide (14b)
Yield: 91%.
Anal. Calcd for C H BO PS: C, 48.20; H, 7.35; S, 11.70. Found:
11
20
3
C, 48.09; H, 7.37; S, 11.57.
1
H NMR (200 MHz, CDCl ): d = 7.44–7.64 (m, 6 H), 7.65–7.80 (m,
3
6
H), 8.08 (d, J = 481 Hz, 1 H).
tert-Butylphenylphosphinous Acid Anhydride-Bis(borane)
PH
(
11a)
13
C NMR (50 MHz, CDCl ): d = 128.64, 128.90, 130.28, 130.45,
3
Yield: 54%.
1
30.67, 132.29, 132.42, 132.47.
1
H NMR (200 MHz, CDCl ): d = –0.10–1.60 (br m, 3 H), 1.26 (dd,
31
3
P NMR (202 MHz, CDCl ): d = 22.73.
3
JPCCH = 15.39, J
= 15.34 Hz, 9 H), 7.35–7.60 (m, 3 H), 7.65–
PCCH
+
HRMS (ESI): m/z calcd for C H ONaP (M + Na ): 225.0440;
found: 225.0449.
1
2
11
7
.90 (m, 2 H).
1
3
C NMR (50 MHz, CDCl ): d = 24.70, 24.83, 33.92, 34.69, 127.57,
3
1
1
27.68, 127.79, 127.97, 128.17, 132.34, 132.45, 132.55, 132.83,
32.94, 133.05.
Benzylphenylphosphine Oxide (14c)
Yield: 78%.
3
1
P NMR (202 MHz, CDCl ): d = 137.00 (m) and 138.83 (m).
1
3
H NMR (200 MHz, CDCl ): d = 3.29–3.60 (m, 2 H), 7.50 (dt,
3
+
JPH = 476 Hz, 1 H), 7.03–7.15 (m, 2 H), 7.23–7.33 (m, 3 H), 7.40–
.64 (m, 5 H).
HRMS (ESI): m/z calcd for C H B ONaP (M + Na ): 397.2163;
found: 397.2183.
2
0
34
2
2
7
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Phosphinous Acid-Boranes
1289
1
3
31
C NMR (50 MHz, CDCl ): d = 38.15, 39.39, 127.03, 127.11,
P NMR (202 MHz, CDCl ): d = 18.94 (m).
3
3
1
1
28.39, 128.63, 128.69, 129.53, 129.64, 129.83, 130.04, 132.41,
32.46.
Anal. Calcd for C H BP: C, 67.95; H, 12.35. Found: C, 68.21; H,
1
2
23
1
2.35.
3
1
P NMR (202 MHz, CDCl ): d = 35.49.
3
+
tert-Butylphenylphosphinic Halides; General Procedure
HRMS (ESI): m/z calcd for C H ONaP (M + Na ): 239.0596;
found: 239.0608.
1
3
13
In a flask equipped with a magnetic stirrer, an argon inlet and a re-
flux condenser (if needed), phosphinous acid-borane (0.3 mmol) in
solvent (15 mL) was placed. Then halogenating agent (0.9–1.5
mmol) was added to the reaction mixture (in Entries 2 and 4 after
addition of base). Then, the reaction mixture was allowed to stand
at r.t. or at reflux for 3–24 h. The reaction was quenched by addition
of aq HCl (3 M), then the mixture was extracted with CH Cl , the
o-Anisylphenylphosphine Oxide (14g)
Yield: 96%.
1
H NMR (200 MHz, CDCl ): d = 3.80 (s, 3 H), 6.87–6.99 (m, 1 H),
.07–7.19 (m, 1 H), 7.43–7.61 (m, 4 H), 7.70–7.89 (m, 3 H), 8.19
d, JPH = 499 Hz, 1 H).
3
3
7
(
2
2
organic phase was dried (MgSO ) and evaporated to dryness. The
residue was purified with flash chromatography (hexane–EtOAc,
4
1
C NMR (50 MHz, CDCl ): d = 55.45, 110.66, 110.78, 120.92,
3
2
:1).
1
1
20.16, 128.30, 130.23, 130.47, 131.91, 131.97, 132.85, 132.99,
34.32, 134.36.
tert-Butylphenylphosphinic Acid Chloride (16)
Yields: 85, 77 and 85%.
3
1
P NMR (202 MHz, CDCl ): d = 14.51.
3
+
HRMS (ESI): m/z calcd for C H OP (M + H ): 233.0726; found:
2
1
1
3
14
H NMR (200 MHz, CDCl ): d = 1.26 (d, J
= 19.10 Hz, 9 H),
3
PCCH
33.0731.
7
.45–7.70 (m, 3 H), 7.79–7.96 (m, 2 H).
1
3
C NMR (50 MHz, CDCl ): d = 24.12, 38.15, 39.70, 128.12,
Di-c-hexylphosphine Oxide (14h)
Yield: 67%.
3
1
3
28.37, 132.35, 132.55, 132.79, 132.84.
1
1
P NMR (202 MHz, CDCl ): d = 74.25.
H NMR (200 MHz, CDCl ): d = 1.13–1.51 (m, 10 H), 1.55–2.10
3
3
(
m, 12 H), 6.33 (dm, J = 438 Hz, 1 H).
PH
tert-Butylphenylphosphinic Acid Bromide (17)
Yields: 66 and 60%.
1
3
C NMR (50 MHz, CDCl ): d = 24.84, 24.91, 25.69, 25.84, 25.99,
3
2
6.09, 26.29, 33.95, 35.23.
1
H NMR (200 MHz, CDCl ): d = 1.29 (d, J
.46–7.68 (m, 3 H), 7.84–7.98 (m, 2 H).
= 19.70 Hz, 9 H),
3
1
3
PCCH
P NMR (202 MHz, CDCl ): d = 53.87.
3
7
13
+
HRMS (ESI): m/z calcd for C H ONaP (M + Na ): 237.1379;
1
2
23
C NMR (50 MHz, CDCl ): d = 24.31, 40.07, 41.46, 128.10,
3
found: 237.1389.
1
28.35, 132.41, 132.61, 132.85, 132.92.
3
1
P NMR (202 MHz, CDCl ): d = 73.73.
Reduction of Phosphinous Acid-Boranes into Secondary Phos-
phine-Boranes; General Procedure
3
tert-Butylphenylphosphinic Acid Iodide (18)
Yield: 90%.
In a flask equipped with a magnetic stirrer, an argon inlet and a re-
flux condenser (if needed), phosphinous acid-borane (0.3 mmol) in
solvent (15 mL) was placed. Then, reducing agent (0.9–1.8 mol)
was added (in Entries 2 and 3 after addition of base) and the reaction
mixture was refluxed or was allowed to stand at r.t. for 5–48 h.
Then, aq HCl (3 M) was added and the resulting biphasic mixture
was extracted with CH Cl , the organic phase was dried (MgSO )
1
H NMR (200 MHz, CDCl ): d = 1.26 (d, J
.47–7.66 (m, 3 H), 7.82–7.96 (m, 2 H).
= 20.34 Hz, 9 H),
3
PCCH
7
1
3
C NMR (50 MHz, CDCl ): d = 24.33, 41.52, 42.71, 127.91,
3
1
3
28.16, 132.07, 132.27, 132.76, 132.82.
1
2
2
4
and then evaporated to dryness. The residue was purified by flash
chromatography (hexane–EtOAc, 6:1).
P NMR (202 MHz, CDCl ): d = 63.13.
3
Acknowledgment
tert-Butylphenylphosphine-Borane (15a)
Yields: 30, 38 and 11%.
Financial support of this study by the State Committee For Scienti-
fic Research, Poland, through the grant 3 T09A 119 26 is gratefully
acknowledged.
1
H NMR (200 MHz, CDCl ): d = –0.05–1.65 (br m, 3 H), 1.21 (d,
3
JPCCH = 14.8 Hz, 9 H), 5.13 (dq, JPH = 368 Hz, 1 H), 7.41–7.73 (m,
5
H).
1
3
C NMR (50 MHz, CDCl ): d = 26.51, 26.57, 28.14, 124.24,
3
References
1
25.26, 128.44, 128.64, 131.47, 131.52, 133.80, 133.95.
3
1
(1) (a) Brunel, J. M.; Faure, B.; Maffei, M. Coord. Chem. Rev.
P NMR (202 MHz, CDCl ): d = 31.99 (m).
3
1
998, 178-180, 665. (b) Ohf, H.; Holz, J.; Quirmbach, M.;
Anal. Calcd for C H BP: C, 66.71; H, 10.08. Found: C, 66.83; H,
1
10
15
Börner, A. Synthesis 1998, 1391.
0.21.
(
2) (a) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.;
Sato, K. J. Am. Chem. Soc. 1990, 112, 5244. (b) Imamoto,
T.; Oshiki, T.; Onozawa, T.; Matsuo, M.; Hikosaka, T.;
Yanagawa, M. Heteroat. Chem. 1992, 3, 563. (c) Imamoto,
T.; Tsuruta, H. Chem. Lett. 1996, 707. (d) Muci, A. R.;
Campos, K. R.; Evans, D. A. J. Am. Chem. Soc. 1995, 117,
Di-c-hexylphosphine-borane (15h)
Yields: 38 and 13%.
1
H NMR (200 MHz, CDCl ): d = –0.45–1.50 (br m, 3 H), 1.20–1.59
m, 10 H), 1.64–2.02 (m, 12 H), 4.15 (dq, JPH = 348 Hz, 1 H).
3
(
1
9075.
3
C NMR (50 MHz, CDCl ): d = 25.65, 26.21, 26.43, 26.63, 27.60,
3
2
8.48, 29.15, 29.21, 29.27.
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York

1
290
(
M. Stankevič, K. M. Pietrusiewicz
PAPER
1990, 63, 3719. (e) Oshiki, T.; Hikosaka, T.; Imamoto, T.
Tetrahedron Lett. 1991, 32, 3371. (f) Imamoto, T.; Tsuruta,
H.; Wada, Y.; Masuda, H.; Yamaguchi, K. Tetrahedron Lett.
1995, 36, 8271.
3) (a) Lam, H.; Aldous, D. J.; Hii, K. K. Tetrahedron Lett.
003, 44, 5213. (b) Longeau, A.; Durand, S.; Spiegel, A.;
Knochel, P. Tetrahedron: Asymmetry 1997, 8, 987.
c) Jugé, S.; Stephan, M.; Laffitte, J. A.; Genêt, J. P.
2
(
Tetrahedron Lett. 1990, 31, 6357. (d) Jugé, S.; Stephan, M.;
Merdès, R.; Genêt, J. P.; Halut-Despartes, S. J. Chem. Soc.,
Chem. Commun. 1993, 531. (e) Jugé, S.; Stephan, M.; Achi,
S.; Genêt, J. P. Phosphorus, Sulfur Silicon Relat. Elem.
(5) Schmidbaur, H. J. Organomet. Chem. 1980, 200, 287.
(6) (a) Köster, R.; Tsay, Y.-H.; Synoradzki, L. Chem. Ber. 1987,
120, 1117. (b) Uziel, J.; Stéphan, M.; Kaloun, E. B.; Genêt,
J. P.; Jugé, S. Bull. Soc. Chim. Fr. 1997, 134, 379.
(7) Stankevič, M.; Pietrusiewicz, K. M. Synlett 2003, 1012.
(8) Stankevič, M.; Andrijewski, G.; Pietrusiewicz, K. M. Synlett
2004, 313.
1
990, 49/50, 267. (f) Ramsden, J. A.; Brown, J. M.
Tetrahedron: Asymmetry 1994, 5, 2033. (g) Bauduin, C.;
Moulin, D.; Kaloun, E. B.; Darcel, C.; Jugé, S. J. Org. Chem.
2
003, 68, 4293. (h) Nagata, K.; Matsukawa, S.; Imamoto, T.
(9) See, for example: Pietrusiewicz, K. M.; Wiśniewski, W.;
Zabłocka, M. Tetrahedron 1989, 45, 337.
J. Org. Chem. 2000, 65, 4185.
(
4) (a) Hoge, G. J. Am. Chem. Soc. 2003, 125, 10219.
(10) McKinstry, L.; Livinghouse, T. Tetrahedron Lett. 1994, 35,
9319.
(11) (a) Maier, L.; Dietl, P. J. Phosphorus, Sulfur, Silicon Relat.
Elem. 1996, 115, 723. (b) Korpiun, O.; Lewis, R. A.;
Chickos, J.; Mislow, K. J. Am. Chem. Soc. 1968, 90, 4842.
(
b) Oshiki, T.; Imamoto, T. J. Am. Chem. Soc. 1992, 114,
975. (c) Nettekoven, U.; Widhalm, M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. Tetrahedron: Asymmetry 1997, 8,
185. (d) Oshiki, T.; Imamoto, T. Bull. Chem. Soc. Jpn.
3
3
Synthesis 2005, No. 8, 1279–1290 © Thieme Stuttgart · New York