Direct conversion of secondary phosphine oxides and h-phosphinates with [Di(acyloxy)iodo]benzenes to phosphinic and phosphonic amides

Article abstract of DOI:10.1002/hc.20514

The reaction of [di(acyloxy)iodo]- benzene with secondary phosphine oxides or H-phosphinates in the presence of primary or secondary amines allows one to obtain phosphinic or phosphonic acids amides in the one-pot process. We take advantage of the strong acylating system DAIB/R2P(O)H to phosphinylation of amines. However, the reaction mechanism is multipathway and causes yields of phosphinic or phosphonic acids amides to be moderate. When the concentration of amines is low, the intermolecular process plays a main role leading to the formation of carboxylic amides through mixed phosphoric-carboxylic anhydride, and also in the low concentration of amines, tetrahydrofuran effectively competes with the amines in the nucleophilic attack on the acylating intermediates.

Full text of DOI:10.1002/hc.20514

Heteroatom Chemistry
Volume 20, Number 2, 2009
Direct Conversion of Secondary Phosphine
Oxides and H-Phosphinates with
[Di(acyloxy)iodo]benzenes to Phosphinic
and Phosphonic Amides
Anna Hubacz and Slawomir Makowiec
Department of Organic Chemistry, Faculty of Chemistry, Gdansk University of Technology,
Narutowicza 11/12; Gdan`sk 80-952, Poland
Received 30 December 2008
used in organic transformations [2,3], reactiv-
ABSTRACT: The reaction of [di(acyloxy)iodo]-
ity of hypervalent organoiodine compound with
benzene with secondary phosphine oxides or
organophosphorus reagents is still considerably
H-phosphinates in the presence of primary or sec-
unexplored area. There are only a few publica-
ondary amines allows one to obtain phosphinic or
tions concerning reactions of usual hypervalent
phosphonic acids amides in the one-pot process.
organoiodine regents as [di(acetoxy)iodo]benzene,
We take advantage of the strong acylating system
[bis(trifluoroacetoxy)iodo]benzene, iodozobenzene,
DAIB/R2P(O)H to phosphinylation of amines. How-
or dichloroiodobenzene with phosphorus nucle-
ever, the reaction mechanism is multipathway and
ophiles. In 1978, Foss published work concerning
causes yields of phosphinic or phosphonic acids
oxidation of diphosphines and trialkyl phosphites
amides to be moderate. When the concentration of
with iodozobenzene [4]. Lopusinski carried out a set
amines is low, the intermolecular process plays a
of experiments between phosphor organic reagents
main role leading to the formation of carboxylic
such as triphenylphosphine, trialkyl phosphites,
amides through mixed phosphoric–carboxylic anhy-
triarylphosphites with iodozobenzene and iodoxy-
dride, and also in the low concentration of amines,
benzene in the presence of montmorylonite or in
tetrahydrofuran effectively competes with the amines
the absence of such a catalyst [5]. Garreg et al. tried
in the nucleophilic attack on the acylating intermedi-
to use [di(acetoxy)iodo]benzene as a mild reagent
ꢀ
C
ates.
2009 Wiley Periodicals, Inc. Heteroatom Chem
for oxidation of H-phosphonates to phosphates in
oligonucleotide synthesis [6]. An interesting aspect
of the reactivity of hypervalent iodine organic com-
pounds with phosphorus nucleophiles is the direct
arylation of phosphorus acid salts [7], trialkyl phos-
phites [8], or phosphines [9] using aryliodonium
salts.
Phosphorus analogs of Koser reagent [hy-
droxy((phosphoryl)oxy)iodo]benzenes and their
reactivity exemplify an interesting aspect of hyper-
valent iodine and phosphor organic chemistry, par-
ticularly α-phosphoryloxylation of ketones [10,11]
and preparation of alkynyl dialkyl phophates [12].
20:81–86, 2009; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20514
INTRODUCTION
Despite the fact that first hypervalent organoiodine
compound was synthesized by Wilgerodt in 1886
[1], and hypervalent iodine reagents are widely
Correspondence to: Slawomir Makowiec; e-mail: mak@chem.
pg.gda.pl.
2009 Wiley Periodicals, Inc.
c
ꢀ
81

82 Hubacz and Makowiec
In our research, we focused on the subject of
the reactivity of hypervalent iodine compounds
with phosphorus nucleophiles, such as dialkyl
phosphites, trialkyl phosphites, secondary phos-
phine oxides, and aryl H-phosphinates, as well as
on the problem of reactivity of hypervalent iodine
compounds with aforementioned phosphorus nucle-
ophiles in the presence of additional nucleophiles,
for example, alcohols [13,14].
As we previously reported, the system
[di(acyloxy)iodo]benzene and R2P(O)H is a strong
acylating agent, which is able to acylate various
oxygen nucleophiles as alcohols or carboxylic acids
[13,14]. Moreover, the system of the Koser reagent
Ph(OTs)OH/R2P(O)H in the absence of other better
nucleophiles is able to acylate even ethers like THF,
which demonstrates the acylating power of this
system [15].
So far, our research in exploring properties of hy-
pervalent iodine/organophosphorus nucleophile as
an acylating system considers only acylation of oxy-
gen species as sufficiently resistant to oxidation by
hypervalent iodine compounds to ensure a clean
route of reaction. However, now we would like
to present results of research in which we exam-
ined the acylating properties of the hypervalent io-
dine/organophosphorus nucleophile system toward
acylation of aliphatic amines, an alternative for the
Todd–Atherton reaction [16].
However after workup and separation of the
reaction mixture, we did not obtain any traces of
N-isobutyl diphenylphosphinic acid amide 9; in-
stead, we isolated diphenylphosphinic acid 5 with
50% yield and O-(diphenylphosphinoyl)-Oꢁ-acetyl-
1,4-butanediol 8 with 12% yield as a product of
THF ring opening. In further experiments, we used
[di(benzoyloxy)iodo]benzene as a hypervalent io-
dine reagent to facilitate isolation of carboxylic
amides.
We performed
a set of experiments with
[di(benzoyloxy)iodo]benzene and diphenylphospine
oxide or dibenzylphosphine oxide. The results of
these experiments are presented in Table 1. From
the reactions mixtures, we isolated THF ring open-
ing products 8, phosphinic acids 5, and carboxylic
amides 6, and we did not isolate phosphinic acids
amides 9. On the basis of these experiments, and tak-
ing into consideration our previous works [14,15],
we have proposed tentative mechanism of this reac-
tion presented in Scheme 1.
At the first stage, the trivalent form of
phosphorous nucleophiles reacts with the
[di(acyloxy)iodo]benzene and forms intermedi-
ate 3, which may undergo reactions in two ways.
The first possibility pathway (a) is intermolecular
collapse of 3 into phosphoric–carboxylic mixed
anhydride, which undergoes further reaction with
amine and produces as a final product carboxylic
amide. Such a reaction of mixed anhydrides with
amines is a well-known fast process [17], so we did
not isolate mixed anhydride since it was immedi-
ately consumed in the reaction with amine. The
second possibility pathway (b) is reaction of the
intermediate 3 with THF, which is present in a large
excess as a solvent leading to oxonium salt 7, which
undergoes reaction with carboxylic acid anion and
produces O-(phosphinoyl)-Oꢁ-acyl-1,4-butanediol 8.
Surprisingly, we did not isolate any product of
the nucleophilic attack of amine on the phosphorus
atom in the intermediate 3, meaning phosphinic acid
amide, which we might expect, taking into consid-
eration much higher nucleophilicity of amines com-
pared with THF, but we had already noticed that
RESULTS AND DISCUSSION
At first, we performed an experiment with com-
mercially available [di(acetoxy)iodo]benzene 2 and
diphenylphosphine oxide 1 in the presence of
isobutyl amine. To take into consideration the higher
nucleophilicity of amines compared with the nu-
cleophilicity of alcohols and ethers, we performed
first experiments with only 3 equiv of amine in the
tetrahydrofuran (THF) solution. We had expected
that because of the high nucleophilicity of amine, we
would obtain mainly N-isobutyl diphenylphosphinic
acid amide 9.
TABLE 1 Reaction of R1R2P(O)H with [Di(benzoyloxy)iodo]benzene in the Presence of Amines R4R5NH in THF As a Solvent
Yields (%)
Run
R1, R2
R4
R5
5
6
8
1
2
3
4
Ph
Bzl
Bzl
Ph
H
H
Et
Et
iBu
iBu
Et
66
45
50
77
62
21
60
29
16
10
20
14
Et
Heteroatom Chemistry DOI 10.1002/hc

Reaction of [Di(acyloxy)iodo]benzene with Secondary Phosphine Oxides or H-Phosphinates 83
SCHEME 2
ate amine with [di(benzoyloxy)iodo]benzene. From
the reaction mixtures, we isolated phosphinic acid
amides 9, carboxylic amides 6, and phosphinic acids
5. The results are presented in Table 2.
Because of higher concentration of amines, we
were able to push the reaction via pathway (c)
Scheme 2 so as to produce phosphinic acid amide.
However, intermolecular pathway (b) Scheme 1,
which led to mixed phosphoric–carboxylic anhy-
dride and in the further reaction with amine to car-
boxylic amide, was still present. It must be pointed
that the formation of 9 may result by the pathway
(c), besides the nucleophilic attack on the phospho-
rus atom in the intermediate 3, we have to consider
SCHEME 1
alternative pathway (d) with ligand exchange acy-
loxy group with amine with the formation of inter-
mediate 3a and subsequent intermolecular reaction
leading to amide 9 and PhI. However, at this mo-
ment we do not have rational arguments to exclude
or confirm one of them.
To confirm proposed mechanism and to ex-
clude possibility that carboxylic amide is formed
in the reaction [di(acyloxy)iodo]benzene) with
amine, we run an independent experiment with
[di(benzoyloxy)iodo]benzene) in the excess of
isobutylamine as a solvent without 1 in which we did
not observe the formation of any traces of 6. Despite
the cited reactions of mixed phosphorus–carboxylic
anhydrides with amines [17], to additionally confirm
the species type of 3 is an extremely reactive acy-
lating agent, which we were able to observe only
in 31P NMR but were not able to isolate [14]. So,
if this compound is extremely reactive, its selectiv-
ity is poor and probably it reacts quickly in solvent
cage with any nucleophile whose concentration is
higher. In typical experiment, the molar ratio of THF
to amine is about 30:1, which explains why we could
not isolate phosphinic acid amide.
Because we did not isolate phosphinic acid
amides, we run experiments in amines as a solvent
to make nucleophilic attack of amine on 3 possi-
ble and to exclude THF opening ring process. We
performed experiments in which we treated the so-
lution of R1R2P(O)H phosphorus acids in appropri-
TABLE 2 Reaction of R1R2P(O)H with [Di(benzoyloxy)iodo]benzene in the Presence of Amines As Solvents
Yields (%)
Run
R1, R2
R4
R5
5
6
9
5
6
7
Ph
Ph
n-Hex
Et
H
Et
Et
iBu
Et
34
38
43
29
60
18
34
34
11
Heteroatom Chemistry DOI 10.1002/hc

84 Hubacz and Makowiec
TABLE 3 Reaction of R1R2P(O)H with [Di(acetoxy)iodo]benzene in the Presence of Amines As Solvents
Yields (%)
Run
R1
R2
R4
R5
5
9
8
9
10
11
12
13
Ph
Bzl
Ph
Ph
n-Hex
Ph
Ph
Bzl
iPrO
Ph
n-Hex
iPrO
H
H
H
n-Bu
n-Bu
n-Bu
33
54
55
53
20
46
34
30
16
19
22
17
(CH2)2O(CH2)2
(CH2)2O(CH2)2
H
iBu
that in case of our model of anhydride only 6
is produced in the reaction of mixed phosphinic–
carboxylic anhydride with amine, we performed an
experiment, using diphenylphosphinic-benzoic an-
hydride obtained on the independent way (from
diphenylphosphinic acid salt and acetyl chloride)
with N,N-diethylamine, and in this reaction we ob-
served formation of only carboxylic amide without
any traces of phosphinic amide.
Taking into consideration that in performed
experiments, phosphorus amides were produced
in one-top process directly from secondary phos-
phine oxides or H-phosphinates. Similarly as
in the Todd–Atherton reaction, we ran a set
of experiments between commercially available
[di(acetoxy)iodo]benzene and R1R2P(O)H acids in
the excess of amines to check the possibility of using
the explored reaction for the quick preparation of
phosphinic or phosphonic acids amides. The results
are presented in Table 3. From the reactions mix-
tures, we have isolated phosphoric acids amides and
also phosphinic or phosphonic acids, which confirm
the competition of both processes by the pathways
(a) and (c) and cause yields of phosphinic or phos-
phonic acids amides to be moderate.
total of 10 mmol of [di(acetoxy)iodo]benzene and
20 mmol of benzoic acid was dissolved in 40 mL of
CHCl3 followed by five times repeated slow evapo-
ration under reduced pressure. Residue was finally
crystallized from CHCl3/Hexane. Yield 70%, 3.12 g,
mp = 155–157◦C.
General Procedure for the Reactions of
R1 R2P(O)H with [di(benzoyloxy)iodo]benzene
in the Presence of Amines in THF As a Solvent
[Runs 1–4]
To a solution of 1 (2 mmol) in THF (20 mL)
and amine (8 mmol), [di(benzoyloxy)iodo]benzene
(2 mmol, 0892 g) was added. Reaction mixture was
stirred under argon at room temperature for 15 h.
The solvent was removed under reduced pressure,
and the residue was dissolved in Et2O (50 mL); Et2O
was washed off with 5% NaHCO3 (3 × 5 mL) and 2 M
HCl (2 × 5 mL), dried with MgSO4, the solvent was
removed under reduced pressure, and the residue
was purified by column chromatography over sil-
ica gel (chloroform–acetone, 15:1) to obtain 6 and
8. Alkaline water layer was acidified with concen-
trated HCl and extracted with AcOEt (3 × 30 mL)
and dried with MgSO4, the solvent was removed un-
der reduced pressure, and the residue was crystal-
lized from AcOEt–Hexane to obtain 5.
EXPERIMENTAL
Run 1: O-(Diphenylphosphinoyl)- Oꢁ-benzoyl-
1,4-butanediol (126 mg, 16%).1H NMR (200MHz,
CDCl3) δ: 1.9 (m, 4H), 4.05–4.15 (m, 2H), 4.3–4.4 (m,
2H), 7.35–7.6 (m, 9H), 7.75–7.9 (m, 4H), 8–8.08 (m,
2H); 31P NMR (300MHz, CDCl3) δ: 34.38; N-isobutyl
benzamide (220 mg, 62%); Diphenylphosphinic acid
(292 mg, 66%) mp = 189–191◦C. 31P NMR (300MHz,
CDCl3) δ: 34.18.
All reactions were carried out under argon at-
mosphere in dry solvents (THF was dried over
potassium, chloroform over P2O5, alcohols over
magnesium). Chromatography was carried out on
®
Silica Gel 60 (0.15–0.3 mm) Macherey Nagel .
31P NMR and 1H NMR spectra were recorded
with a Varian apparatus at 200 or 500 MHz.
[Di(acetoxy)iodo]benzene was purchased from
Avocado (Karlsruhe, Germany).
Run 2: O-(Dibenzylphosphinoyl)-Oꢁ-benzoyl-
1,4-butanediol (80 mg, 10%).1H NMR (200 MHz,
CDCl3) δ: 1.53–1.78 (m, 4H), 3.05 (t, JPH = 15 Hz, 4H),
3.85 (t, 2H), 4.25 (t, 2H), 7.1–7.7 (m, 15H); 31P NMR
(300MHz, CDCl3) δ = 51.26; N-isobutyl benzamide
(70 mg, 21%); Dibenzylphosphinic acid (220 mg,
[Di(benzoyloxy)iodo]benzene
[Di(benzoyloxy)iodo]benzene was obtained by the
modification method described in literature [18]. A
Heteroatom Chemistry DOI 10.1002/hc

Reaction of [Di(acyloxy)iodo]benzene with Secondary Phosphine Oxides or H-Phosphinates 85
45%) mp = 187–189◦C, 31P NMR (300 MHz, CDCl3)
vent was removed under reduced pressure, and the
residue was dissolved in Et2O (50 mL), Et2O was
washed off with 5% NaHCO3 (3 × 5 mL) and 2 M
HCl (2 × 5 mL), dried with MgSO4, the solvent was
removed under reduced pressure, and the residue
was purified by column chromatography over sil-
ica gel (chloroform–acetone, 15:1) to obtain 9. Al-
kaline water layer was acidified with concentrated
HCl and extracted with AcOEt (3 × 30 mL) and dried
with MgSO4, the solvent was removed under re-
duced pressure, and the residue was crystallized
from AcOEt–Hexane to obtain 5.
δ: 52.36.
Run 3: O-(Dibenzylphosphinoyl)-Oꢁ-benzoyl-
1
1,4-butanediol (160 mg, 20%). H NMR (200 MHz,
CDCl3); N,N-diethyl benzamide (212 mg, 60%);
dibenzylphosphinic acid (246 mg, 50%).
Run 4: O-(diphenylphosphinoyl)-Oꢁ-benzoyl-
1,4-butanediol (110 mg, 14%).; N,N-diethyl benza-
mide (102 mg, 29%); diphenylphosphinic acid (335
mg, 77%).
General Procedure for Reactions of R1 R2P(O)H
with [Di(acyloxy)iodo]benzene in the Presence
of Amines As Solvents
Run 8: N-n-Butyl diphenylphosphinic acid
1
amide (185 mg, 34%). H NMR (200 MHz, CDCl3)
δ: 0.85 (t, 3H), 1.32 (m, 2H), 1.53 (m, 2H), 2.93 (m,
3H), 7.41 (m, 6H), 7.88 (m, 4H), 31P NMR (300 MHz,
CDCl3) δ: 24.72; diphenylphosphinic acid (143 mg,
33%).
Run 9: N-n-Butyl dibenzylphosphinic acid amide
(180 mg, 30%).1H NMR (500 MHz, CDCl3) δ: 0.85 (t,
3H), 1.23 (m, 2H), 1.36 (m, 2H), 2.85 (q, 2H), 3.09 (m,
4H), 7.26 (m, 6H), 7.33 (m,4H), 31P NMR (300 MHz,
CDCl3) δ = 38.42; dibenzylphosphinic acid (265 mg,
45%).
Runs 5–7. To a solution of 1 (2 mmol) in amine
(100 mmol), [di(benzoyloxy)iodo]benzene (2 mmol,
0,892 g) was added. Reaction mixture was stirred
under argon at room temperature for 15 h. The sol-
vent was removed under reduced pressure, and the
residue was dissolved in Et2O (50 mL); Et2O was
washed off with 5% NaHCO3 (3 × 5 mL) and 2 M
HCl (2 × 5 mL), dried with MgSO4, the solvent was
removed under reduced pressure, and the residue
was purified by column chromatography over sil-
ica gel (chloroform–acetone, 15:1) to obtain 6 and
9. Alkaline water layer was acidified with concen-
trated HCl and extracted with AcOEt (3 × 30 mL)
and dried with MgSO4, the solvent was removed un-
der reduced pressure, and the residue was crystal-
lized from AcOEt–Hexane to obtain 5.
Run 10: N-n-Butyl O-isopropyl phenylphospho-
1
nic acid amide (82 mg, 16%). H NMR (500 MHz,
CDCl3) δ: 0.85 (t, 3H), 1.26 (m, 2H), 1.29 (d, 3H),
1.36 (d, 3H), 1.42 (m, 2H), 2.84 (m, 3H), 4.74 (m,
1H), 7.44 (m, 3H), 7.80 (m, 2H), 31P NMR (300 MHz,
CDCl3) δ = 22.56; isopropyl phenylphosphonate (224
mg, 56%).
Run 11: 4-Diphenylphosphinoyl-morpholine
Run 5: N,N-Diethyl diphenylphosphinic acid
amide (185 mg, 34%). 1H NMR (200 MHz, CDCl3) δ:
1.09 (t, 6H), 3.11 (m, 4H), 7.34–7.56 (m, 6H), 7.78–
7.94 (m, 4H); N,N-diethyl benzamide (113 mg, 32%);
diphenylphosphinic acid (148 mg, 34%).
1
(109 mg, 19%). H NMR (500 MHz, CDCl3) δ: 3.07
(m, 4H), 3.70 (m, 4H), 7.47 (m, 6H), 7.87 (m, 4H),
31P NMR (300 MHz, CDCl3) δ: 30.25; diphenylphos-
phinic acid (239 mg, 55%).
Run 12: 4-(Di-n-hexylphosphinoyl)-morpholine
Run 6: N-Isobutyl diphenylphosphinic acid
1
(133 mg, 22%). H NMR (500 MHz, CDCl3) δ: 0.87
1
amide (185 mg, 34%). H NMR (200 MHz, CDCl3)
(t, 6H), 1.25–1.31 (m, 12H), 1.58–1.66 (m, 8H), 3.04
(m, 4H), 3.66 (m, 4H), 31P NMR (300 MHz, CDCl3) δ:
49.28; di-n-hexylphosphic acid (34 mg, 20%).
Run 13: N-Isobutyl O-isopropyl phenylphospho-
δ: 0.9 (d, 6H), 1.8 (m, 1H), 2.8 (t, J = 7.14 Hz, 2H),
3.1–3.45 (bs, 1H), 7.32–7.73 (m, 6H), 7.95–8.14 (m,
4H); 31P NMR (300 MHz, CDCl3) δ: 27.45; N-isobutyl
benzamide (212 mg, 60%); diphenylphosphinic acid
(165 mg, 38%).
Run 7: N,N-Diethyl di-n-hexylphosphinic acid
amide (64 mg, 11%).1H NMR (200 MHz, CDCl3)
δ: 0.8–1.75 (m, 32H), 2.9–3.17 (m, 4H); 31P NMR
(300MHz, CDCl3) δ = 50.72; N,N-diethyl benzamide
(64 mg, 18%); di-n-hexylphosphinic acid (201 mg,
43%); 31P NMR (300 MHz, CDCl3) δ: 52.36.
1
nic acid amide (85 mg, 17%). H NMR (200 MHz,
CDCl3) δ: 0.85 (dd, 6H), 1.35 (dd, 6H), 1.62 (m, 1H),
1.36 (d, 3H), 2.65 (t, 2H), 2.96 (bs, 1H), 4.72 (m, 1H),
7.44 (m, 3H), 7.80 (m, 2H); isopropyl phenylphos-
phonate (184 mg, 46%).
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Heteroatom Chemistry DOI 10.1002/hc

86 Hubacz and Makowiec
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