Reactions of tert-Butyl Phosphoramidites with Carbon Tetrachloride and Chloroform

Article abstract of DOI:10.1023/A:1025624116438

The reactions of 2-tert-butoxy-3-phenyl-1,3,2-oxazaphospholane and di-tert-butyl diethylphosphoramidite with carbon tetrachloride and chloroform were studied. These reactions proceed via formation of an intermediate quasiphosphonium compound. In the proce

Full text of DOI:10.1023/A:1025624116438

Russian Journal of General Chemistry, Vol. 73, No. 4, 2003, pp. 533 535. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 4, 2003,
pp. 566 568.
Original Russian Text Copyright
2003 by Sal’keeva, Nurmaganbetova, Kurmanaliev.
Reactions of tert-Butyl Phosphoramidites
with Carbon Tetrachloride and Chloroform
L. K. Sal’keeva, M. T. Nurmaganbetova, and O. Sh. Kurmanaliev
Buketov Karaganda State University, Karaganda, Kazakhstan
Received April 10, 2001
Abstract The reactions of 2-tert-butoxy-3-phenyl-1,3,2-oxazaphospholane and di-tert-butyl diethylphos-
phoramidite with carbon tetrachloride and chloroform were studied. These reactions proceed via formation
of an intermediate quasiphosphonium compound. In the process, carbon tetrachloride acts as a source of
positively charged halogen, and chloroform, as a C H acid.
It is known that dialkyl dialkylphosphoramidites
react with CCl4 by two pathways: with the formation
of alkyl N,N-dialkyltrichloromethylphosphonoamidate
(major pathway, 1) and alkyl dialkylphosphoramido-
chloridate (pathway 2). Alkyl tetraalkylphosphorodi-
amidites react with carbon tetrachloride and chloro-
form to give tetraalkylphosphorodiamidic chloride
[1]. In these reactions, carbon tetrachloride and
chloroform presumably act as sources of positively
charged chlorine [1, 2].
OR1
OR1
P+
O
R2
R2
R2
R2
1
POR1 + CXCl3
CXCl2
P+
PCXCl2 + R1Cl
Cl
CXCl2
R23N
R23N
R23N
R23N
Cl
O
R2
2
PCl + R1CXCl2
R23N
R2 = OR1, X = Cl; R2 = NR32, X = H, Cl.
The reactions of tert-butyl phosphoramidites with
carbon tetrachloride and chloroform were studied in
detail in [3]. Because of the high rate of the second
stage of the reaction (quasiphosphonium salts contain-
ing tert-butoxy group at phosphorus decompose very
rapidly by the SN1 mechanism [4, 5]), it could be
expected that the process would yield compounds in
which the bonds formed in the initial stage would be
preserved. Indeed, it was found that tert-butyl tetra-
ethylphosphorodiamidite I reacts with carbon tetra-
chloride with the heat evolution to give tetraethyl-
phosphorodiamidic chloride II, chloroform, and iso-
butylene. Carbon tetrachloride evidently acts as the
source of positively charged chlorine [1, 2].
O
OBu-t
(Et2N)2P+ CCl3
+
(Et2N)2PCl + [CMe3 + CCl3
Me2C=CH2 + CHCl3]
(Et2N)2POBu-t + CCl4
II
I
Cl
It was interesting to perform the reaction of CCl4
with cyclic amido esters, which were not tested in this
process previously. For this purpose, we prepared
2-tert-butoxy-3-phenyl-1,3,2-oxazaphospholane III by
amide interchange of phosphite I according to the
following scheme:
1070-3632/03/7304-0533$25.00 2003 MAIK Nauka/Interperiodica

534
SAL’KEEVA et al.
phoramidite VI and isobutylene. Acid phosphite VI is
Ph
evidently formed by fast decomposition of the P-pro-
tonated intermediate with the evolution of isobutylene
and regeneration of chloroform.
N
NHPh
OH
+ I
POBu-t + 2Et2NH
O
III
OBu-t
I + CHCl3
(Et2N)2P+ CCl3
The released diethylamine was collected quantita-
tively. Phosphite III is a viscous liquid decomposing
during attempted distillation with the evolution of iso-
butylene and formation of a phosphorus-containing
viscous substance. Therefore, the purity of III was
checked by TLC. Its structure was determined by IR
H
O
+
(Et2N)2PH + [CMe3 + CCl3
VI
Me2C=CH2 + CHCl3].
1
and H NMR spectroscopy. The IR spectrum con-
1
tained the absorption bands ( , cm ) characteristic of
Phosphite III reacts with CHCl3 under more
rigorous conditions (prolonged refluxing, TLC moni-
toring of the reaction progress). It evidently confirms
the lower reactivity of phosphite III arising from the
stability of phospholane ring due to the presence of
the phenyl group, on the one hand, and steric hind-
rance to the formation of the intermediate quasiphos-
phonium compound, on the other. The reaction is also
accompanied by evolution of isobutylene and regenera-
tion of CHCl3.
phenyl (1450, 1470, 1580), P N (1350), C N (1300),
P O C (1010, 1030), and C O (1080) groups. The
protons of the tert-butoxy group give a strong singlet
1
at 1.45 ppm (9H) in the H NMR spectrum. The
methylene protons of the ring are observed as two
doublets at 2.95 [ (CH2N)] and 3.62 ppm [ (CH2O)].
Contrary to phosphite I, phosphite III reacts with
CCl4 only on heating, and the reaction is accompanied
by evolution of isobutylene and chloroform.
Ph
Ph
O
N
P
O
+ CHCl3
O
N
P
O
III + CCl4
Me2C=CH2
III + CHCl3
Cl
+ CHCl3
Me2C=CH2
H
IV
Ph
VII
2Et2NH
O
N
P
2Et2NH, CCl4
+ Et2NH HCl
NEt2
O
V
V
It is known that 3-phenyl-1,3,2-oxazaphospholane
2-oxide VII is a light yellow oil usually decomposing
during distillation [6]; therefore, compound VII was
characterized in the form of 2-diethylamino-1,3,2-
oxazaphospholane 2-oxide V obtained by treatment
of VII with diethylamine and carbon tetrachloride
under the conditions of the Todd Atherton reaction.
The IR spectrum of crude VII contains a strong band
The IR spectrum of crude IV contains the absorp-
tion bands ( , cm ) characteristic of P=O (1225), Ph
1
(1475, 1510, 1600), P O C (990), P Cl (540), and
N Ph (1325) groups. Treatment of the reaction mix-
ture with 2 mol of diethylamine in petroleum ether
gives 2-diethylamino-3-phenyl-1,3,2-oxazaphospho-
lane 2-oxide V, mp 85 86 C. Diethylamine hydro-
chloride was also isolated quantitatively, mp 221 C.
1
of phosphoryl group at 1270 cm and a band at
1
2440 cm characteristic of P H stretching vibrations.
From the reaction of di-tert-butyl diethylphosphor-
amidite with carbon tetrachloride, we also isolated
chloroform, isobutylene, and tert-butyl diethylphos-
phoramidochloridate (
products. H NMR spectrum of the latter compound
Thus, 2-tert-butoxy-3-phenyl-1,2,3-oxazaphospholane
III and di-tert-butyl diethylphosphoramidite react
with carbon tetrachloride to form the corresponding
phosphorochloridates, whereas chloroform in reaction
with III plays the role of a C H acid, converting the
substrate to oxazaphospholane VII.
9 ppm) as the reaction
P
1
3
contains the signal of CH3 (1.4 ppm, t, 6H, JHH
7 Hz), CH2 (3.2 ppm, m, 4H), and tert-butyl group
(1.67 ppm, s, 9H) groups. It decomposes during
attempted distillation.
EXPERIMENTAL
It is known that phosphite I reacts with CHCl3 on
refluxing for 3 h to give hydrogen tetraethylphos-
The IR spectra were recorded on a Specord M-75
spectrometer in the range 400 4000 cm 1 (KBr pellets,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003

REACTIONS OF tert-BUTYL PHOSPHORAMIDITES
535
1
mulls in mineral oil). The H NMR spectra were ob-
mp 85 86 C. Published data [7]: mp 85 87 C. Found,
%: C 56.45; H 7.97; N 10.78; P 12.51. C12H19N2O2P.
Calculated, %: C 56.69; H 7.48; N 11.02; P 12.20.
ained on a Tesla BS-587 spectrometer (80 MHz) in
C6D6 relative to internal HMDS. The 31P NMR spec-
tra were measured on a KGU-4 custom-made NMR
spectrometer (10.2 MHz) against 85% H3PO4. The
melting points were measured on a Boetius heating
stage.
Reaction of 2-tert-butoxy-3-phenyl-1,3,2-oxaza-
phospholane III with chloroform. A mixture of
6.0 g of III and 3.0 g of chloroform was refluxed for
5 6 h. The reaction was accompanied by evolution of
isobutylene (400 ml, 71.4%). Distillation of the re-
action mixture gave 2.4 g (82%) of chloroform. A
solution of 3.6 g of diethylamine and 3.9 g of carbon
tetrachloride in 50 ml of petroleum ether was added at
room temperature with stirring. Diethylamine hydro-
chloride was filtered off, and the solvent was removed
to give 4.0 g (63.2%) of 2-diethylamino-3-phenyl-
1,3,2-oxazaphospholane 2-oxide V, mp 85 86 C.
Reaction of phosphite I with phenylamino-
ethanol. A mixture of 12.4 g of I and 6.9 g of phenyl-
aminoethanol was heated in a distillation flask at a
bath temperature of 80 90 C. Evolution of 3.4 g of
diethylamine (93%) was observed. The purity of the
resulting
2-tert-butoxy-3-phenyl-1,3,2-oxazaphos-
pholane was checked by TLC. Found, %: C 60.88; H
7.18; N 5.23; P 12.68. C12H18NO2P. Calculated, %:
C 60.25; H 7.23; N 5.85; P 12.97.
REFERENCES
Reaction of 2-tert-butoxy-3-phenyl-1,3,2-oxaza-
phospholane III with carbon tetrachloride. Phos-
pholane III, 6.0 g, was placed in a flask equipped
with a reflux condenser connected with a gasometer,
and 3.9 g of carbon tetrachloride was added with stir-
ring at 0 5 C. No heat evolution and no noticeable
changes were observed. The reaction mixture was
heated at 90 100 C (bath temperature), and active
evolution of isobutylene was observed (490 ml, 87%).
After the reaction completion, a solution of 3.7 ml of
dry diethylamine in 50 ml of petroleum ether was
added. A white precipitate of diethylamine hydro-
chloride formed. It was filtered off (2.2 g, 82%), the
solvent was removed, and the residue was recrystal-
lized from benzene to give 4.6 g (72.3%) of 2-diethyl-
amino-3-phenyl-1,3,2-oxazaphospholane 2-oxide V,
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