Synthesis of polyfunctional methylphosphine oxides Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
249
Scheme 2
C(12)
Cl(1)
C(11)
C(13)
C(8)
O(1)
C(10)
C(14)
C(1)
C(9)
P(1)
N(1)
C(15)
C(2)
C(3)
C(7)
C(6)
C(4)
C(5)
Fig. 1. Structure of (diphenylphosphoryl)ꢀN,Nꢀdimethylaminoꢀ
chloromethane (3a).
(diphenyldichlorophosphorano)chloromethane (10). Then
compound 10 reacts with DMF (2a) to form compound
3a accompanied by regeneration of salt 9a.
lier.8 Toluene, CH2Cl2, and DMF were twice distilled over
CaH2; CDCl3 was distilled over P2O5. Diphenylchlorophosphine
(Aldrich), C2O2Cl2, PhP(O)Cl2, PCl5, SOCl2, and I2 (Acros
Organics) were used as received. The Xꢀray diffraction study of
compound 3a was carried out on a Smart APEX II CCD
diffractometer (MoKα radiation, graphite monochromator,
ωꢀscanning technique). All calculations were performed with
the use of the SHELXTL PLUS program package.
Synthesis of N,Nꢀdimethylamino(diphenylphosphoryl)ꢀ
chloromethane (3a). Method А. Phenylphosphonic dichloride
PhP(O)Cl2 (4) (0.03 g, 0.15 mmol) was added with stirring to
a solution of DMF (2a) (0.53 mL, 0.5 g, 7 mmol) in toluene
(3 mL) at room temperature in an inert atmosphere. After 20 min,
diphenylchlorophosphine (1) (0.4 mL, 0.5 g, 2.3 mmol) was
added. After 3 h, the reaction mixture turned redꢀbrown and
the precipitation of analytically pure compound 3a started. The
precipitation ceased within 18 h. The precipitate was filtered off,
washed with toluene (3Ѕ5 mL), and dried in vacuo. Compound
3a was obtained in a yield of 0.61 g (91%) as colorless needleꢀ
like crystals, m.p. 92—94 °C (with decomp.). Compound 3a is
hygroscopic. Found (%): C, 61.44; H, 5.79; N, 4.68; P, 10.40.
C15H17ClNOP. Calculated (%): C, 61.34; H, 5.83; N, 4.77;
P, 10.55. 31P NMR, δ: 25.9 (20%), 21.1 (80%). 1H NMR, δ: 8.2
(m, 0.2 H, P—C(H)); 7.96 (m, 4 H, oꢀHarom); 7.89 (m, 0.8 H,
P—C(H)); 7.51 (m, 6 H, mꢀHarom, pꢀHarom); 3.06 (d, 6 H,
N—CH3). M 293.74.
The 31P NMR spectra of compounds 3a,b have two
signals at δ 25.9 (80%) and 21.1 (20%) for 3a and at δ 34.9
(11%) and 25.9 (89%) for 3b. Conceivably, both comꢀ
pounds exist as equilibrium mixtures of two conformers.7
As exemplified by compound 3a, this is confirmed by the
fact that the 31P NMR spectra recorded in DMF have
only one signal at δ 26.1, which evidently corresponds to
the more stable conformation in this solvent. Analogously,
the ratio of the signals at δ 26.5 and 20.6 corresponding to
the conformers in CH2Cl2 is 1 : 1.
The structure of compound 3a was established by
Xꢀray diffraction (at 100 K, space group P21/с, Z = 4,
a = 16.217(12) Å, b = 8.136(6) Å, c = 11.127(8) Å,
β = 99.701(14)°, V = 1447.1(18) Å3, R1 = 0.0813) and is
presented in Fig. 1. It should be noted that the C(1)—Cl(1)
bond in molecule 3a is abnormally long (1.899(5) Å),
which is apparently attributed to the anomeric interaction
between the lone pair (Lp) of the nitrogen atom and
the antibonding orbital of the C—Cl bond. The stereoꢀ
electronic interaction is additionally confirmed by the
antiperiplanar orientation of Lp of the N(1) atom with
respect to the C—Cl bond (the Lp—N(1)—C(1)—Cl(1)
pseudotorsion angle is 173°) and a substantial shortening
of the N(1)—C(1) bond to 1.384(7) Å.
Method B. Oxalyl chloride C2O2Cl2 (5) (0.012 mL, 0.015 g,
0.15 mmol) was added with stirring to DMF (2a) (3 mL) in an
inert atmosphere. After the gas evolution ceased, diphenylchloroꢀ
phosphine (1) (0.4 mL, 0.5 g, 2.3 mmol) was added. After
30 min, the reaction mixture turned redꢀbrown and the precipiꢀ
tation of compound 3a started. The precipitation ceased within
8 h. The precipitate was filtered off, washed with toluene
(3×5 mL), and dried in vacuo. Compound 3a was obtained in a
yield of 0.63 g (94%).
The 1H and 31P NMR spectra were recorded on a Bruker
Avance 400 spectrometer operating at 400.13 and 161.98 MHz,
respectively. The 31P and 1H NMR spectra of the individual
compounds were measured in CDCl3. The 31P NMR spectra of
compound 1a were recorded also in DMF and CH2Cl2 with the
use of 85% H3PO4 as the external standard. NꢀFormylmorꢀ
pholine was prepared according to a procedure described earꢀ