Synthesis of trivalent phosphorus derivatives by light-induced dibromophosphination of akenes

Article abstract of DOI:10.1134/S1070363217070131

Light-induced dibromophosphination of alkenes was studied. Dehydrobromination of the synthesized bromoalkylphosphonous dibromides gave the corresponding dibromophosphinoalkenes which were converted into alkenylphosphonous acids and their cyclic esters, benzo[1,3,2]dioxaphospholes.

Full text of DOI:10.1134/S1070363217070131

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 7, pp. 1527–1530. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © M.N. Krivchun, A.V. Khramchikhin, 2017, published in Zhurnal Obshchei Khimii, 2017, Vol. 87, No. 7, pp. 1134–1137.
Synthesis of Trivalent Phosphorus Derivatives
by Light-Induced Dibromophosphination of Akenes
M. N. Krivchun* and A. V. Khramchikhin
St. Petersburg State Institute of Technology (Technical University), Moskovskii pr. 26, St. Petersburg, 190013 Russia
*e-mail: maxim1960@mail.ru
Received May 30, 2017
Abstract—Light-induced dibromophosphination of alkenes was studied. Dehydrobromination of the
synthesized bromoalkylphosphonous dibromides gave the corresponding dibromophosphinoalkenes which
were converted into alkenylphosphonous acids and their cyclic esters, benzo[1,3,2]dioxaphospholes.
Keywords: P(III) acid derivatives, phosphines, dibromophosphination of alkenes, dehydrobromination, benzo[1,3,2]-
dioxaphospholes
DOI: 10.1134/S1070363217070131
Light-induced reactions of unsaturated compounds
are presently a well-studied practical synthetic approach
to phosphonous acid dibromides [1, 2]. Along with the
unusually facile Р–С bond formation, the advantage of
this approach consists in that P(III) acid bromides,
unlike corresponding chlorides, are quite resistant to
oxidation, and, at the same time, their bromine atoms
exhibit a high reactivity in substitution reactions. Thus,
alkylphosphonous dibromides obtained from alkynes
undergo facile alcoholysis under the action of saturated
and unsaturated alcohols and react with alkynyllithium
[3]. The light-induced addition of phosphorus
tribromide to alkenes is a reversible reaction, and the
position of equilibrium depends on the temperature.
atom to form 1-(dibromophosphino)-1-phenyl-2-bromo-
ethane 2j. The reactions of haloalkylethenes 1b and 1с
occur in high yields but with a slightly lower
selectivity than in the case of styrene. 3,3,3-(Tri-
chloromethyl)propene 1d and 1,1-dichloroethene 1k
could not be reacted. At the same time, (trichlorosilyl)-
ethene 1e undergoes a fairly facile dibromophos-
phination to form regioisomeric dibromophosphines 2e
and 2e' with a total yield of 40% (Scheme 2).
The regioisomer ratio determined from the integral
intensity of their signals in the 31Р NMR spectrum is
1
2e : 2e' = 4 : 1. The Н NMR spectrum the 2e' isomer
contains two multiplets of the CHPBr2 (3.31 ppm, 2JHP
18.7, JHН = 7.5 Hz) and CH2Br protons (3.65 ppm,
3JHP = 6.5 Hz). The spectral pattern is complicated by
the exchange Cl3Si chlorine for bromine exchange.
=
3
To gain a deeper insight into the preparative
potential of this important reaction of organophos-
phorus compounds with alkenes and prepare novel
P(III) and P(IV) derivatives, in the present work we
studied the dibromophosphination of alkenes 1а–1v
under UV irradiation (Scheme 1).
Scheme 1.
hν
R1R2C=CR3R4 + PBr3 → R1R2C(PBr2)CBrR3R4
1а–1v
2а–2v
It was found that the yield of adducts 2 depends on
the steric factor. Thus, the yield of the adduct decreases
in the series CH2=CH2, MeCH=CH2, Me2C=CH2,
Me2C=CHMe, Me2C=CMe2, PhMeC=CH2, Ph2C=CH2,
PhCH=CHPh [4]. It can be suggested that the steric
factor strongly affects the position of equilibrium.
R2 = R3 = R4 = H, R1 = Br (1а), CH2Br (1b), CH2Cl (1c),
Cl3C (1d), Cl3Si (1e), Cl2CH3Si (1f), (CH3)3Si (1g), Bu (1h),
PhOCH2 (1i), Ph (1j); R3 = R4 = Н, R1 = R2 = Cl (1k), R1 =
Cl, R2 = CH2Cl (1l); R1 = R2 = CH3 (1m), R1 = R2 =
BuOCH2 (1n), R1 = CH3, R2 = Ph (1o), R1 = R2 = Ph (1p);
R1 = R2 = CH3, R3 = Br, R4 = H (1q); R1 = R2 = R3 = CH3,
R4 = H (1r); R1 = R3 = H, R2 = R4 = Ph (1s); R1 = R3 = H,
R2 = R4 = CH2Br (1t); R1 = R2 = R3 = R4 = CH3 (1u);
cyclohexene (1v).
As known [2], the light-induced addition of PBr3 to
styrene 1j occurs in a regioselective manner: the
bromine atom attaches to the least shielded carbon
1527

1528
KRIVCHUN, KHRAMCHIKHIN
2g and 2-bromo-2-(trimethylsilyl)-1-(dibromophos-
Scheme 2.
phino)ethane 2g', as determined from the intensity
Cl3SiCH=CH2 + PBr3
1
ratios of the corresponding signals in the Н and 31Р
1e
NMR spectra, is 10 : 3.
The 1Н NMR spectra of the reaction products
contain signals of dibromophosphine 2g' as a weakly
hν
→ Cl3SiCH(PBr2)CH2Br + Cl3SiCHBrCH2PBr2
2e 2e'
coupled АВСХ system: δHA = 4.12 ppm, JHA B = 10,
H
Scheme 3.
JHA C = 3.5, JHA = 8.5 Hz; δHB = 3.61 ppm, JHB C =
H
P
H
9.0, JHB = 3.0; δHC = 2.25 ppm, JHC = 14.5 Hz. The
(CH3)3SiCH=CH2 + PBr3
P
P
1g
value of the JHB vicinal constant of 3.0 Hz is
P
hν
indicative of preferential realization of a partially
eclipsed molecular conformation. The methyl groups
on silicon appear as a doublet at 0.4 ppm
→ (CH3)3SiCH(PBr2)CH2Br + (CH3)3SiCHBrCH2PBr2
2g
2g'
Scheme 4.
The synthesized dibromophosphines enter various
reactions involving both the dibromophosphino and
bromoalkyl groups: dehydrobromination, alcoholysis,
reactions with Grignard reagents to form phosphines,
and hydrolysis to form an alkylphosphonous acid (see
table). Thus, the bromophosphination of bromoethene
results in exclusive formation of 1,2-dibromo-1-(di-
bromophosphino)ethane 2а whose dehydrobromina-
tion under the action of trimethylamine provides 1-
bromo-1-(dibromophosphino)ethene 3а (Scheme 4).
hν
BrCH
BrCH
PBr2
2a
CH2 + PBr3
CH2Br
1a
NEt3
_HBr
BrC CH2
PBr2
3
1
The structure of compound 3а was proved by Н, 31Р,
and 13С NMR spectroscopy. Similarly, the dehyd-
robromination of dibromophosphine 2b leads to 3-
bromo-2-(dibromophosphino)propene 3b.
The reaction of (dichloromethylsilyl)ethene 1f with
PBr3, leading to 2-bromo-1-(dichloromethylsilyl)-1-(di-
bromophosphino)ethane 2f and its regioisomeric 1-bromo-
1-(dichloromethylsilyl)-2-(dibromophosphino)ethane
2f' in a 1 : 4 ratio, occurs in a similar way. The region-
isomer ratio was determined from the intensities of the
31Р NMR signals at δP 180.5 and 172.2 ppm
Cyclohexene 1v actively reacts with PBr3 under UV
irradiation (cf. [4]) to form 2-bromo-1-(dibromo-
phosphino)cyclohexane 2v. The dehydrobromination
of the latter gives rise to 1-(dibromophosphino)cyclo-
hexene 4 (Scheme 5). The hydrolysis of compound 2v
with water in dioxane forms (2-bromocyclohexyl)
phosphonous acid 6. The reaction of compound 4 with
phenylmagnesium bromide leads to 1-(diphenylphos-
phino)cyclohexene 5. A similar diphenylphosphine 8
The highest yield in the series of the silicon-
containing alkenes was obtained with (trimethylsilyl)-
ethene 1g (Scheme 3). Therewith, the reaction
proceeds with the highest regioselectivity: the ratio of
1-bromo-2-(trimethylsilyl)-2-(dibromophosphino)ethane
Scheme 5.
Br
P
Br
P
Et3N
2PhMgCl
Br
Br
Br
P
4
5
hν
Br
O
+ PBr3
P
Br
H2O
H
OH
3
Br
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 7 2017

SYNTHESIS OF TRIVALENT PHOSPHORUS DERIVATIVES
1529
Physicochemical characteristics, elemental analyses, and 31P NMR data for dibromoalkyl(alkenyl)phosphonites and their
derivatives
bp, °С
(mmHg)
mp, °С
Found, %
Calculated, %
Comp. Yield,
d420, g/mL
nD20
Formula
δP, ppm
no.
%
P
Br
P
Br
2а
2b
2c
30
60
58
107 (2)
43
2.6383
1.6745
8.20
7.91
8.93
84.64
81.60
69.04
C2H3Br4P
C3H5Br4P
C3H5ClBr3P
8.01
7.82
8.92
84.78
88.69
69.04
150.4
176.4
179.5
–
–
–
–
110 (1)
28
2h
2i
40
65
60
98 (2)
1.8767
1.5853
8.73
7.82
8.26
67.55
60.55
63.95
C6H12Br3P
C9H10Br3OP
C8H8Br3P
8.57
7.82
8.18
67.45
60.55
64.08
187.8
179.8
179.9
165 (0.1)
–
–
–
–
2j
90 (0.5)
45
2m
2n
2v
3a
3b
4
40
60
50
53
50
60
90
30
50
70
73 (1)
106 (0.1)
125 (2)
51 (2)
2.0950
–
1.6118
–
9.48
6.58
73.35
50.89
67.94
80.79
77.14
58.77
–
C4H8Br3P
C12H24Br3O2P
C6H10Br3P
C2H2Br3P
C3H4Br3P
C6H9Br2P
C18H19P
9.31
6.58
73.38
50.89
67.85
80.63
77.22
58.84
–
191.6
193.6
198.0
137.5
150.0
157.5
–2.02
32.06
158.9
–5.23
2.0316
2.4711
2.3124
1.8332
–
1.6283
1.6651
1.6496
1.6166
–
8.78
8.81
10.44
9.97
10.26
9.85
65 (1)
97 (2)
11.39
11.63
21.10
11.31
11.54
11.32
11.49
21.05
11.20
11.58
5
155 (0.1)
79
6
–
–
–
C6H12O2P
C6H11Br2P
C18H21P
–
7
63 (2)
1.6414
1.0700
1.5668
1.5786
58.33
–
58.40
–
8
70 (0.1)
forms from 2-(dibromophosphino)hex-1-ene 7 ob-
tained by dehydrobromination of 1-bromo-2-(dibromo-
phosphino)hexane 2h (see table).
Dibromophosphine 4 readily reacts with pyro-
catechol in the presence of pyridine as a base to form
the corresponding cyclic phosphonate 9 because of the
fast oxidation with air oxygen (Scheme 6). An
analogous reaction of styryldibromophosphine 10
gives 2-(1-phenylvinyl)benzo[1,3,2]dioxaphosphole 11.
For structural assessment compound 5 was oxidized
with air oxygen into the corresponding phosphine oxide.
Scheme 6.
Br
P
O
P
HO
O
Py
Br
+
+
O
[O]
HO
HO
4
9
O
O
Py
P
PhC
CH2
PhC
CH2
HO
PBr2
10
11
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 7 2017

1530
KRIVCHUN, KHRAMCHIKHIN
The structures of all the products were confirmed
was then filtered off. The solvent was distilled off, and
the residue was fractionated in a vacuum.
by 1Н, 13С, and 31Р NMR spectroscopy. Their principal
physicochemical characteristics and elemental analyses
are listed in the table.
Dehydrobromination of dibromophosphines
(general procedure). A solution of 0.15 mol of
dibromophosphine in 0.4 mol of dry benzene was
treated under stirring with a solution of 0.16 mol of
pyridine in benzene, and the reaction mixture was then
heated under reflux for 2 h. The precipitate of pyridine
hydrobromide was then filtered off, the solvent was
distilled off, and the residue was fractionated in a
vacuum.
Thus, the light-induced bromophosphination of
alkenes, while being a reversible reaction, allows
preparation of bromoalkylphosphonous dibromides.
Making use of the ability of the bromine atoms in the
dibromophosphino group, as well as the ability of the
bromoalkyl group to undergo dehydrobromination one
can prepare a wide range of organophosphorus
compounds.
Reactions of dibromophosphines with Grignard
reagents. A solution of 0.15 mol of dibromophosphine
in ether was added dropwise to a stirred and cooled
solution of 0.305 mol of Grignard reagent in dry ether.
The reaction mixture was stirred for 0.5 h and excess
Grignard reagent was decomposed with saturated
aqueous NH4Cl. The ether layer was dried with
MgSO4. The solvent was then distilled off, and the
residue was fractionated in a vacuum. All operations
were performed under argon.
EXPERIMENTAL
The 1Н, 13С, and 31Р NMR spectra were obtained on
a Bruker Avance III spectrometer (400 MHz) in
CDCl3.
Synthesis of dibromophosphines (general proce-
dure). A tubular quartz reactor equipped with a
magnetic stirred was charged with 0.32 mol of PBr3
and 0.11 mol of alkene at a constant temperature (with
low-boiling alkenes, a reverse trap cooled with an
acetone–dry ice mixture was used). The mixture was
irradiated at 10°С with UV light by means of a DRSh-
1000 lamp (λ 253.7 nm). The reaction progress was
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1
monitored by Н NMR. The irradiation time was 0.5–
3 h. After completion of the reaction, PBr3 was
distilled off at 1 mmHg, and the residue was
fractionated in high vacuum.
Esterification of dibromophosphines (general
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dropwise to a stirred and cooled solution of 0.107 mol
of pyridine and 0.05 mol of dibromophosphine in
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