Reactions of carbene intermediates from the reaction of trialkyl phosphites with dialkyl benzoylphosphonates: Preparation and reactions of dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphosphonate and dimethyl 2-(methylamino)benzoylphosphonate

Article abstract of DOI:10.1039/a701147d

Dimethyl 2-(methylamino)benzoylphosphonate has been prepared by the thermal decomposition of dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphosphonate formed by the action of triethylamine on 1-tert-butyl-3-(dimethoxyphosphinyl)-1-methyl-2,1-benzisoxazoli

Full text of DOI:10.1039/a701147d

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Reactions of carbene intermediates from the reaction of trialkyl
phosphites with dialkyl benzoylphosphonates: preparation and
reactions of dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphos-
phonate and dimethyl 2-(methylamino)benzoylphosphonate
D. Vaughan Griffiths,*,a Jayne E. Harrisa and Belinda J. Whiteheadb
a
Department of Biological and Chemical Sciences, University of Essex, Colchester,
UK CO4 3SQ
b Department of Chemistry, University of Keele, Staffordshire, UK ST5 5BG
D imethyl 2-(methylamino)benzoylphosphonate has been prepared by the thermal decomposition of
dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphosphonate formed by the action of triethylamine on
1-tert-butyl-3-(dimethoxyphosphinyl)-1-methyl-2,1-benzisoxazolinium hexafluorophosphate. The
reactions of both benzoylphosphonates with trimethyl phosphite proceed via carbene intermediates 4 to
initially give ylidic phosphonates 5, which for 5 (X = 2-M eN H ) undergoes cyclisation and rearrangement
to give the novel 2-oxophosphorindoline 11.†
We have previously shown that dialkyl benzoylphosphonates 1
+
O
P(OMe)3
O
C
O
react with trialkyl phosphites to give anionic intermediates 2,
which in the presence of proton donors are usually trapped to
give the phosphates 3, although other products have been
observed (Scheme 1).1 We have also shown that if no electro-
philes are present to trap the intermediates 2, cleavage of the α-
C᎐O bond can occur to give carbene intermediates 4.2 If a suit-
able substituent is present at the 2-position on the benzene ring
this can react with the carbene centre to give cyclic products2–5
but if this is unfavourable the carbenes 4 will be preferentially
trapped by the trialkyl phosphite in the reaction mixture to give
ylidic phosphonates 5.
(MeO)3P
C
–
P(OMe)2
O
P(OMe)2
X
X
2
1
heat
— (MeO)3PO
HY
O
O
P(OMe)2
P(OMe)2
O
O
C
H
C
••
P(OMe)2
X
X
Dialkyl benzoylphosphonates are invariably prepared by the
reaction of a trialkyl phosphite with the appropriate carboxylic
acid chloride which in turn is usually generated by the action of
thionyl chloride on the carboxylic acid. While this approach has
proved suitable for the preparation of a wide range of substi-
tuted dialkyl benzoylphosphonates, difficulties arise with the
preparation of those benzoylphosphonates possessing basic
substituents such as amino groups. In our experience, efforts to
prepare amino-substituted benzoyl chlorides invariably lead to
the formation of their hydrochloride salts and the presence of
this additional hydrogen chloride can then act as a proton
donor when attempts are made to prepare the corresponding
benzoylphosphonates resulting in the formation of the phos-
phates 3 rather than the benzoylphosphonates 1. Moreover,
reagents such as triphenylphosphine in carbon tetrachloride6
which can convert carboxylic acids to the corresponding acid
chlorides under essentially neutral conditions are not easily
employed in the case of amino-substituted benzoic acids which
are not readily soluble in the organic solvents usually used.
The reported preparation of a phosphonate believed to be
dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphosphonate
1 (X = 2-ButMeN)7 by the reaction of the perchlorate salt
9 (Z = ClO4) with an organic base was therefore of particular
interest to us in this context and worthy of further investig-
ation.
+
MeY
3
4
O
(MeO)3P
Me
P(OMe)2
C
X
P(OMe)2
O
heat
O
6
P(OMe)2
C
–
O
X
H
+
P(OMe)3
P(OMe)2
C
5
HY
X
P(OMe)2
O
7
+
MeY
Scheme 1
Results and discussion
As previously reported 8 reaction of anthranil‡ with 2-
methylpropan-2-ol in the presence of perchloric acid led to the
formation of the anthranilium salt 8 (Z = ClO4) which on reac-
tion with trimethyl phosphite gave the anthranilium salt 9
(Z = ClO4) (Scheme 2). Treatment of this material with triethyl-
† IUPAC name for phosphorindoline: 2,3-dihydro-1H-1,2-benzaza-
phosphole.
‡ 2,1-Benzisoxazole.
J. Chem. Soc., Perkin Trans. 1, 1997
2545

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feature of this bisphosphonate is that its 31P NMR spectrum
Me3COH
HZ
O
shows two doublets [δP 22.8 (d, JPP 6 Hz) and 23.3 (d, JPP 6 Hz)]
rather than the expected singlet. This clearly indicated that
the two phosphorus atoms in this bisphosphonate are non-
equivalent on the NMR timescale and suggests that the bulky
ortho substituent on the benzene ring is restricting rotation
about the bond between the α-carbon and the benzene ring.
Preliminary modelling studies provide additional support for
this view.9 However, warming the NMR sample to 80 ЊC pro-
duced no significant broadening of the phosphorus resonances.
The steric effects of the o-(N-tert-butyl-N-methylamino) sub-
stituent can also be seen in the 1H NMR spectrum of the ben-
zoylphosphonate 1 (X = 2-ButMeN) which clearly indicates that
the carbonyl group is twisted out of the plane of the benzene
ring leading, among other things, to a marked upfield shift of
the 6-H resonance relative to its position in the benzoylphos-
phonate 1 (X = 2-MeNH).
O
N
N
–
+
Z
But
8
(MeO)3P
H
P(O)(OMe)2
O
C
O
Et3N
P(OMe)2
O
–
+
–
– Et3NH Z
+
Z
N
N
Me
But
Me
But
1 (X = 2-ButMeN)
9
Scheme 2
amine gave a moisture sensitive product which readily hydro-
lysed to 2-(N-tert-butyl-N-methylamino)benzoic acid. The
product also reacted with methanol to give methyl 2-(tert-
butylmethylamino)benzoate and dimethyl phosphite and it was
on this basis that previous workers7 had proposed the involve-
ment of dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphos-
phonate 1 (X = 2-ButMeN). By carefully excluding water from
the reaction we were able to isolate the benzoylphosphonate 1
(X = 2-ButMeN) in a reasonably good state of purity and to
confirm its structure by NMR spectroscopy. In particular, the
product gave a signal in the 31P NMR spectrum around 0 ppm,
(δP Ϫ1.6), typical of benzoylphosphonates, and a character-
istically large doublet in the carbonyl region of the 13C NMR
spectrum [δC 206.0 (d, JPC 185 Hz)]. An initial attempt to purify
the crude benzoylphosphonate 1 (X = 2-ButMeN) by distil-
lation appeared successful although subsequent analysis indi-
cated that the tert-butyl group had been lost from the nitrogen
during the distillation to give the benzoylphosphonate 1 (X =
2-MeNH). However, more seriously, a subsequent attempt to
distil some crude benzoylphosphonate 1 (X = 2-ButMeN)
resulted in an explosion, probably due to the presence of
perchlorate salts in the distillation residue. For this reason,
efforts were made to find an alternative route to the benzoyl-
phosphonate 1 (X = 2-ButMeN) avoiding the use of perchloric
acid.
The reaction of anthranil with 2-methylpropan-2-ol in the
presence of a variety of acids, including sulfuric, methanesul-
fonic, trifluoromethanesulfonic and toluene-4-sulfonic acid,
was investigated but, while results initially looked encouraging,
attempts to precipitate the anticipated anthranilium salts 8
resulted in the formation of oils highly contaminated with the
acids used in their preparation and therefore unsuitable for sub-
sequent reaction with trimethyl phosphite. In contrast, the use
of hexafluorophosphoric acid resulted in the formation of the
anthranilium salt 8 (Z = PF6) which precipitated from the crude
reaction mixture in good yield on the addition of diethyl ether.
This salt was then converted into the benzoylphosphonate 1
(X = 2-ButMeN) via the anthranilium salt 9 (Z = PF6) in an
analogous manner to that used for the corresponding perchlor-
ate salt. Attempts to distil the benzoylphosphonate 1 (X = 2-
ButMeN), formed in this way, confirmed our earlier observa-
tion that the tert-butyl group was readily lost from the nitrogen
under these conditions to give 1 (X = 2-MeNH) and that it was
difficult to avoid such decomposition even when great care was
taken during the distillation. Subsequent reactions of the ben-
zoylphosphonate 1 (X = 2-ButMeN) were therefore carried out
on this material prior to distillation.
The reaction of trimethyl phosphite with the benzoylphos-
phonate 1 (X = 2-MeNH) was also investigated to see if the
N᎐H proton would act as a proton donor and trap the initially
formed anionic intermediate 2 (X = 2-MeNH) to give a phos-
phate such as 3 (X = 2-Me2N). However, no evidence for such a
reaction was observed. Instead the reaction proceeded cleanly
to initially give an ylidic phosphonate [δP 69.0 (d, JPP 73 Hz) and
25.9 (d, JPP 73 Hz)] and trimethyl phosphate. This clearly indi-
cates that the carbanionic centre in 2 (X = 2-MeNH) is not suf-
ficiently basic to abstract the adjacent N᎐H proton, and that
this is also true for the carbanionic centre in the ylides sub-
sequently formed. It should be noted, however, that the 31P
NMR shifts of the ylidic phosphonate from 1 (X = 2-MeNH)
are significantly different from those expected for 5 (X = 2-
MeNH) based on those systems studied so far [δP ca. 54 and ca.
31].2 This suggests that the ylide 5 (X = 2-MeNH), which would
result from trapping the carbene 4 (X = 2-MeNH) with tri-
methyl phosphite, undergoes rapid cyclisation to give the ylidic
phosphonate 10 (R = Me). While it could be argued on elec-
tronegativity grounds that the replacement of an oxygen sub-
stituent on the phosphonium centre by a nitrogen one would
produce an upfield rather than a downfield shift, there is clear
evidence that steric factors are also important and that amino
substituents with two carbons β to the phosphonium centre
produce an overall downfield shift.10 The effect of ring form-
ation is more difficult to predict in this particular case but it
appears to further increase the chemical shift of the phospho-
nium centre.
As the reaction between trimethyl phosphite and the ben-
zoylphosphonate 1 (X = 2-MeNH) proceeded, the initially
observed ylide 10 (R = Me) underwent a rearrangement to give
one major isomer of the diphosphorus compound 11 (Scheme
3). Strong evidence for the presence of the P᎐N bond in the
O
O
Me
P(OMe)2
P(OMe)2
C
C
R = Me
–
O
OR
P
+
P
N
N
OMe
OR
10
11
Me
Me
Scheme 3
isomers of 11 is provided by 1H NMR spectroscopy which
shows coupling between the N-methyl group and only one of
the phosphorus atoms in both isomers. This rearrangement of
10 (R = Me) is analogous to the observed formation of the
bisphosphonates 6 on heating the ylidic phosphonates 52 and
provides further support for the structure of the precursor of 11
as being the ylidic phosphonate 10 (R = Me). It is interesting to
note that no coupling (JPP < 2 Hz) was observed between the
resonances of the two phosphorus atoms in the major isomer of
11 despite their close proximity. As with the rearrangements
The reaction of the benzoylphosphonate 1 (X = 2-ButMeN)
with trimethyl phosphite proceeded as anticipated, with the
involvement of the carbene intermediate 4 (X = 2-ButMeN)
being indicated by the formation of trimethyl phosphite and the
isolation of the bisphosphonate 7 (X = 2-ButMeN) in reason-
able yield from the reaction mixture. A particularly unusual
2546
J. Chem. Soc., Perkin Trans. 1, 1997

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of the ylidic phosphonates 5 previously studied,2 the reaction of
the benzoylphosphonate 1 (X = 2-MeNH) with triethyl phos-
phite led to the formation of the ylidic phosphonate 10 (R = Et)
which proved to be resistant to further thermal rearrangement.
In conclusion, we have shown that the reaction of triethyl-
amine with the anthranilium salt 9 (Z = PF6) provides an
unusual route to two 2-amino-substituted dialkyl benzoylphos-
phonates and that both these phosphonates react with trialkyl
phosphites to give compounds which possess novel features.
The preparation of other amine-containing benzoylphospho-
nates is being investigated.
CH), 125.1 (d, JPC 3, CH), 130.8 (d, JPC 4, Q), 131.9 (d, JPC 2,
CH), 133.8 (d, JPC 2, CH), 139.8 (d, JPC 7, Q).
Dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphosphonate 1
(X = 2-ButMeN)
1-tert-Butyl-3-(dimethoxyphosphinoyl)-1-methyl-2,1-benzisox-
azolinium hexafluorophosphate 9 (Z = PF6) (1.5 g, 3.4 mmol)
was added dropwise to a cooled solution of triethylamine
(0.6 g, 6.7 mmol) in dichloromethane (10 cm3) at 0 ЊC, en-
suring the reaction temperature did not rise above 5 ЊC. After
a few minutes, the solvent was evaporated under reduced pres-
sure (20 mmHg), and the residue extracted with diethyl ether
(3 × 10 cm3). The solvent was then removed from the extracts
to give dimethyl 2-(N-tert-butyl-N-methylamino)benzoylphos-
phonate 1 (X = 2-ButMeN) as a moisture sensitive yellow oil
(0.9 g, 88%), δP(CDCl3) Ϫ1.6; δH (CDCl3; 270 MHz) 1.06 (9H,
s, CMe), 2.84 (3H, s, NMe), 3.78 (3H, d, JPH 11, POMe), 3.81
(3H, d, JPH 11, POMe), 7.24 (1H, m, 5-H), 7.35 (2H, br d, JH H 8,
3-H, 6-H), 7.55 (1H, m, 4-H); δH ([2H6]acetone; 270 MHz) 1.06
(9H, s, CMe), 2.84 (3H, s, NMe), 3.76 (6H, d, JPH 11, POMe),
7.34 (2H, m, 5-H, 6-H), 7.47 (1H, br d, JH H 8, 3-H), 7.61 (1H,
m, 4-H); δC(CDCl3) 26.5 (s, CMe3), 37.4 (s, NCH3), 53.8 (br d,
JPC 8, MeOP), 57.2 (s, NCMe3), 125.5 (d, JPC 1.5, C-3), 127.2 (s,
C-5), 127.3 (d, JPC 3, C-6), 132.7 (s, C-4), 139.6 (d, JPC 56, C-1),
Experimental
NMR spectra were obtained on JEOL EX270 spectrometers.
J Values are given in Hz. In the assignment of 13C NMR spec-
tra, Q refers to quaternary carbon.
1-tert-Butyl-3-(dimethoxyphosphinoyl)-1-methyl-2,1-benzisox-
azolinium perchlorate 9 (Z = ClO4)
This material was prepared by a modification of the method of
Olofson et al.7 A mixture of 1-tert-butyl-2,1-benzisoxazolinium
perchlorate 8 (Z = ClO4)8 (23 g, 0.084 mol) and trimethyl phos-
phite (15.6 g, 0.126 mol) in acetonitrile (150 cm3) was stirred at
room temperature for several hours and the resulting yellow
solution then poured into diethyl ether (400 cm3). The resulting
gum was triturated with diethyl ether to leave a solid residue
which was recrystallised from acetone–diethyl ether (50:50) to
give 1-tert-butyl-1-methyl-3-(dimethoxyphosphinoyl)-2,1-benz-
isoxazolinium perchlorate as a white solid (28.4 g, 84.7%), mp
113 ЊC (lit.,7 114 ЊC decomp.); δP 14.7.
151.8 (s, C-2), 206.0 (d, JPC 185, C᎐O).
᎐
The same product was obtained by the reaction of 1-tert-
butyl-3-(dimethoxyphosphinoyl)-1-methyl-2,1-benzisoxazol-
inium perchlorate 9 (Z = ClO4Ϫ) with triethylamine using the
procedure previously reported.7
Decomposition of the dimethyl 2-(N-tert-butyl-N-methyl-
amino)benzoylphosphonate 1 (X = ButMeN) in boiling meth-
anol led to the formation of methyl 2-(N-tert-butyl-N-
methylamino)benzoate as previously reported.7
1-tert-Butyl-2,1-benzisoxazolinium hexafluorophosphate 8
(Z = PF6)
Dimethyl 2-(N-methylamino)benzoylphosphonate 1 (X = 2-
MeNH)
Hexafluorophosphoric acid (22.54 g, 0.27 mol) was added slow-
ly to a stirred mixture of anthranil (2,1-benzisoxazole) (5.0 g, 42
mmol) and 2-methylpropan-2-ol (3.1 g, 42 mmol) at 0 ЊC in a
Teflon beaker, and the resulting solution was then stirred over-
night at room temperature. After the addition of a little acetone
(ca. 5 ml), diethyl ether was added to precipitate the anthranil-
ium salt. This solid was filtered off and recrystallised from
acetone–diethyl ether (1:2) and then dried under vacuum to
give the title compound 8 as a pale yellow solid (10.1 g, 75%),
mp 143–145 ЊC (decomp.); m/z 176 [M Ϫ (PF6)ϩ] (Found: C,
41.1; H, 4.5; N, 4.2. C11H14NOPF6 requires C, 41.11; H, 4.39; N,
4.36%); δH ([2H6]acetone; 270 MHz) 2.04 (9H, s, CMe3), 7.62–
7.69 (1H, ddd, JH H 9.0, 6 and 1), 8.13–8.30 (3H, m), 10.24 (1H,
s, 3-H); δC(CDCl3) 28.4 (Me), 71.5 (Q), 112.1 (CH), 121.9 (Q),
124.5 (CH), 128.5 (CH), 141.9 (CH), 146.5 (Q), 161.8 (CH).
NB: See warning in discussion section about distillation of the
benzoylphosphonate 1 (X = 2-ButMeN) from 1-tert-butyl-3-
(dimethoxyphosphinoyl)-1-methyl-2,1-benzisoxazolinium per-
chlorate 9 (Z = ClO4Ϫ). A quantity of crude dimethyl 2-(N-tert-
butyl-N-methylamino)benzoylphosphonate 1 (X = 2-ButMeN)
(1 g), prepared as previously described, was heated in a distil-
lation apparatus under reduced pressure (0.04 mmHg). Decom-
position occurred and dimethyl 2-(N-methylamino)benzoyl-
phosphonate 1 (X = 2-MeNH) (0.65 g, 79%) distilled over as a
pale yellow oil, bp 148 ЊC at 0.04 mmHg; m/z 243 (Mϩ) (Found:
C, 49.2; H, 6.0; N, 5.55. C10H14NO4P requires C, 49.37; H, 5.8;
N, 5.76%) δP(CDCl3) 2.9; δH (CDCl3; 270 MHz) 2.96 (3H, s,
NMe), 3.90 (6H, d, JPH 11, POMe), 6.66–6.77 (2H, m, 3-H, 5-
H), 7.46 (1H, ddd, JH H 1.5, 7 and 9, 4-H), 8.43 (1H, dd, JH H 1.5
and 8, 6-H); δC(CDCl3) 29.1 (s, NMe), 53.8 (d, JPC 7, POMe),
111.2 (d, JPC 5, C-3), 114.7 (s, C-5), 117.2 (d, JPC 61, C-1), 134.5
(s, C-6), 136.7 (s, C-4), 152.9 (d, JPC 14, C-2), 196.4 (d, JPC 173,
1-tert-Butyl-3-(dimethoxyphosphinoyl)-1-methyl-2,1-benzisox-
azolinium hexafluorophosphate 9 (Z = PF6)
A mixture of 1-tert-butyl-2,1-benzisoxazolinium hexafluoro-
phosphate 8 (Z = PF6) (5.00 g, 15.5 mmol) and trimethyl phos-
phite (1.92 g, 15.5 mmol) in acetonitrile (15 ml) was stirred
overnight at room temperature in a glass vessel under an
atmosphere of dry nitrogen. The resulting solution was then
poured into diethyl ether to precipitate the product which was
filtered off and recrystallised from acetone–diethyl ether (1:1).
The title compound (5.9 g, 85%) was isolated as a pale yellow
solid, mp 112–114 ЊC (decomp.); m/z 300 (Mϩ) (Found: C, 37.9;
H, 5.4; N, 3.15. C14H23NO4P2F6 requires C, 37.74; H, 5.21; N,
3.15%); δP([2H6]acetone) 13.5 (s, MeOP), Ϫ139.6 (septet, JPF
707, PF6); δH ([2H6]acetone; 270 MHz) 1.67 (9H, s, CMe3), 3.81
(3H, d, JPH 11, MeOP), 3.93 (3H, d, JPH 11, MeOP), 4.10 (3H,
s, NMe), 6.55 (1H, s, 3-H), 7.75–7.92 (3H, m, 4-H, 5-H, 6-H),
8.03 (1H, br d, JH H 8, 7-H); δC([2H6]acetone) 24.1 (s, Me3), 53.1
(d, JPC 2, NCH3), 54.8 (d, JPC 7, MeOP), 55.1 (d, JPC 7, MeOP),
82.9 (d, JPC 165, PCH), 86.4 (d, JPC 3, NCMe3), 119.7 (d, JPC 2,
C᎐O).
᎐
Reaction of dimethyl 2-(N-tert-butyl-N-methylamino)benzoyl-
phosphonate 1 (X = 2-ButMeN) with trimethyl phosphite
The crude dimethyl 2-(N-tert-butyl-N-methylamino)benzoyl-
phosphonate 1 (X = 2-ButMeN) (2.0 g, 6.7 mmol), prepared as
previously described, was heated with trimethyl phosphite (1.65
g, 13.3 mmol) at 105 ЊC under an atmosphere of dry nitrogen
for 4 h. Volatile components were removed from the reaction
mixture by heating for 1 h under reduced pressure (70 ЊC at
0.003 mmHg) and analysis of the residue by 31P NMR spectro-
scopy indicated the major component present to be tetrameth-
yl [2-(N-tert-butyl-N-methylamino)phenyl]methane-1,1-diphos-
phonate 7 (X = 2-ButMeN). This material was isolated as a col-
ourless oil by reversed-phase HPLC using aqueous methanol
(70%) as the eluent; m/z (FAB) 394.1536 (M ϩ Hϩ); δP 22.8 (d,
JPP 6), 23.3 (d, JPP 6); δH (CDCl3; 270 MHz) 1.15 (9H, s, CMe3),
J. Chem. Soc., Perkin Trans. 1, 1997
2547

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2.61 (3H, s, NMe), 3.64 (3H, d, JPH 11, MeOP), 3.66 (3H, d, JPH
11, MeOP), 3.73 (3H, d, JPH 11, MeOP), 3.84 (3H, d, JPH 11,
MeOP), 5.56 (1H, br t, JPH 25, α-CH), 7.14–7.30 (2H, m, 4-H,
5-H), 7.39 (1H, br d, JPH 11, 3-H), 7.82 (1H, m, 6-H); δC(CDCl3)
27.8 (s, CMe3), 37.71 (br s, NMe), 37.74 (dd, JPC 134 and 137,
α-CH), 53.15 (d, JPC 7, POMe), 53.3 (d, JPC 7, POMe), 53.8 (d,
JPC 7, POMe), 53.9 (d, JPC 7, POMe), 55.3 (br s, CMe3), 125.3 (t,
JPC 2.5, C-5), 128.0 (t, JPC 3, C-3), 128.2 (t, JPC 2, C-4), 129.6
(dd, JPC 6 and 8, C-1), 130.3 (t, JPC 4, C-6), 151.3 (t, JPC 8, C-2).
(t, JPC 5, CMe), 27.3 (d, JPC 1.5, NMe), 40.4 (dd, JPC 115 and
137, C-3), 54.0 (d, JPC 7, POMe), 54.2 (d, JPC 6, POMe), 54.6 (d,
JPC 7, POMe), 108.4 (t, JPC 11, C-7), 120.6 (d, JPC 2, C-5), 124.3
(dd, JPC 6 and 8.5, C-3a), 126.3 (dd, JPC 4 and 12, C-4), 129.2 (d,
JPC 3, C-6), 143.4 (dd, JPC 7 and 25, C-7a).
Reaction of dimethyl 2-(N-methylamino)benzoylphosphonate 1
(X = 2-MeNH) with triethyl phosphite
A mixture of dimethyl 2-(N-methylamino)benzoylphosphonate
1 (X = 2-MeNH) (2 g, 6.3 mmol) and triethyl phosphite (3.15 g,
19 mmol) was heated at 105 ЊC for 3 h in an atmosphere of dry
nitrogen. Analysis of the reaction mixture by 31P NMR spec-
troscopy indicated the formation of equimolar quantities of the
ylidic phosphonate 10 (R = Et), δP(CDCl3) 25.8 [d, JPP 74,
P(OMe)2], 65.3 (d, JPP 74, PN) and triethyl phosphate.
Reaction of dimethyl 2-(N-methylamino)benzoylphosphonate 1
(X = 2-MeNH) with trimethyl phosphite
A mixture of dimethyl 2-(N-methylamino)benzoylphosphonate
1 (X = 2-MeNH) (2 g, 6.3 mmol) and trimethyl phosphite (1.6
g, 12.5 mmol) was heated at 105 ЊC in an atmosphere of dry
nitrogen and the progress of the reaction monitored by 31P
NMR spectroscopy. This indicated the initial formation of tri-
methyl phosphate and the ylide 10 (R = Me) [δP 69.0 (d, JPP 73)
and 25.9 (d, JPP 73)]. As the reaction proceeded the ylide 10
(R = Me) underwent a rearrangement to give essentially one
isomer of the diphosphorus compound 11. After 4 h the reac-
tion was complete and the volatile components in the reaction
mixture were removed by heating under reduced pressure (60 ЊC
at 0.05 mmHg) for 1 h. An analytically pure sample of the
major isomer of 11 was obtained using reversed-phase HPLC
with aqueous methanol (60%) as eluent.
3-Dimethoxyphosphinyl-2-methoxy-1,3-dimethyl-2-oxo-2,3-
dihydro-1H-1,2ë5-benzazaphosphole 11. The major isomer of 11
was isolated as a yellow oil, m/z 319 (Mϩ) (Found: C, 45.58;
H, 6.16; N, 4.39. C12H19NO5P2 requires C, 45.14; H, 5.96;
N, 4.39%); δP(CDCl3) 45.5 (s, NP), 26.3 [s, P(O)(OMe)2];
δH (CDCl3; 270 MHz) 1.82 (3H, t, JPH 16.5, CMe), 2.99 (3H, d,
JPH 8.5, NMe), 3.63 (3H, d, JPH 11, POMe), 3.79 (3H, d, JPH 11,
POMe), 3.94 (3H, d, JPH 11.5, POMe), 6.64 (1H, d, JH H 7.5, 7-
H), 6.92 (1H, t, JH H 7.5, 5-H), 7.25 (1H, tm, JH H 7.5, 6-H), 7.44
(1H, dm, JH H 7.5, 4-H); δC(CDCl3) 19.3 (t, JPC 5, CMe), 27.1 (s,
NMe), 40.4 (dd, JPC 111 and 142, C-3), 53.7 (d, JPC 7, POMe),
54.4 (d, JPC 7, POMe), 55.0 (d, JPC 6, POMe), 108.4 (t, JPC 11,
Acknowledgements
We thank the EPSRC for a studentship for J. E. H. and the
University of Keele for a studentship for B. J. W. We also
acknowledge the use of the EPSRC’s Chemical Database Ser-
vice at Daresbury.11
References
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C-7), 120.5 (d, JPC 1, C-5), 124.8 (t, JPC 6, C-3a), 125.9 (dd, JPC
and 12, C-4), 129.1 (br s, C-6), 143.4 (dd, JPC 9 and 27, C-7a).
4
10 D. V. Griffiths and P. A. Griffiths, in Handbook of Phosphorus-31
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The minor isomer of 11 was isolated in an impure form con-
taining some of the major isomer, δP(CDCl3) 45.0 (d, JPP 10,
NP), 24.8 [d, JPP 10, P(O)(OMe)2]; δH (CDCl3; 270 MHz) 1.78
(3H, t, JPH 16, CMe), 3.04 (3H, d, JPH 9, NMe), 3.57 (3H, d, JPH
11, POMe), 3.84 (3H, d, JPH 11, POMe), 3.85 (3H, d, JPH 11,
POMe), 6.66 (1H, d, JH H 7, 7-H), 6.95 (1H, t, JH H 7.5, 5-H),
7.25 (1H, m, 6-H), 7.39 (1H, dm, JH H 7.5, 4-H); δC(CDCl3) 16.7
Paper 7/01147D
Received 18th February 1997
Accepted 8th May 1997
2548
J. Chem. Soc., Perkin Trans. 1, 1997