A new performance of the reaction of PCl3/AlCl3 with anisoles - One-pot and multi-step syntheses of a new fused-ring system [1,2,3]benzoxadiphospholo[2,3-b][1,2,3]benzoxadiphosphole

Article abstract of DOI:10.1002/1099-0690(200106)2001:12<2229::AID-EJOC2229>3.0.CO;2-T

Anisoles 4 react with AlCl₃ and PCl₃ to yield the new fused bicyclic system derivatives 5 and 6 as major products in a one-pot procedure. An alternative multi-step synthesis of this system is also reported in which bis(o-methoxyaryl)phosphane oxides 11 are treated with AlCl₃ and PCl₃; the diarylphosphane oxides 11 are obtained by a new simple method.

Full text of DOI:10.1002/1099-0690(200106)2001:12<2229::AID-EJOC2229>3.0.CO;2-T

FULL PAPER
A New Performance of the Reaction of PCl /AlCl with Anisoles ؊ One-Pot
3
3
and Multi-Step Syntheses of a New Fused-Ring System
1,2,3]Benzoxadiphospholo[2,3-b][1,2,3]benzoxadiphosphole
[
[
a]
[a]
[a]
Graziano Baccolini,* Michele Bazzocchi, and Carla Boga
Keywords: Phosphorus heterocycles / Phosphorylations / Domino reactions / Insertions / Lewis acids
Anisoles 4 react with AlCl
bicyclic system derivatives 5 and 6 as major products in a
one-pot procedure. An alternative multi-step synthesis of this lphosphane oxides 11 are obtained by a new simple method.
3
and PCl
3
to yield the new fused
system is also reported in which bis(o-methoxyaryl)phos-
phane oxides 11 are treated with AlCl and PCl ; the diary-
3
3
Introduction
In contrast to these reported results, in recent years, we
discovered[ that the reaction of PCl3 and AlCl3 with
thioanisoles 1 gave, unexpectedly, the new fused bicyclic
system[ 2 (fused 1,2,3-benzothiadiphosphole) in good
yields (see Scheme 2). In addition, we found that the reac-
tion is very dependent on the ratio of the reagents and on
5]
Since the last century the FriedelϪCrafts-type reaction
6]
using PCl and AlCl has been an excellent method for the
3
3
direct attachment of a phosphorus atom to an aromatic ring
to give aryldichlorophosphanes or diarylchlorophosphanes.
However, this reaction is very sensitive to the type of sub-
the quality of the AlCl , which, in this reaction, is not a
3
catalyst, but a reagent. The best yields of 2 were obtained
with freshly sublimed AlCl3 and a ratio 1:0.6:2Ϫ4 of
thioanisole 1/AlCl /PCl and final quenching with water.
[
1,2]
stituents present on the aromatic ring
and the literature
[3,4]
often gives conflicting results.
In particular, it is report-
[
4a]
3
3
ed that anisole upon treatment with phosphorus trichlor-
ide and aluminium chloride, afforded p-anisylphosphonous
dichloride (I) but in very poor yields and with large
amounts of undistillable residues, while in some cases it
gave phenylphosphorodichloridite (II) but always in poor
yields. In addition, it is reported[
4a,4b]
that this phos-
phonation reaction fails completely when thioanisoles are
used (Scheme 1).
Scheme 2. One-pot synthesis of 2
The molecular structure of 2 was determined[5a] by X-ray
analysis with the molecule adopting a butterfly-like struc-
ture with the phosphorus electron lone pairs in a cis config-
uration and in an eclipsed conformation. Recently, the
[
5c]
course of this anomalous reaction has been studied
by
1
31
H and P NMR and it was seen that the benzothiadiphos-
phole system is formed by a ‘‘domino reaction’’ as reported
in Scheme 3. Probably, because of the relative complexity
of the structure of 2, its formation from this simple and
well-known reaction was never observed. It should be noted
that the final phosphonium salt G does not give, after treat-
ment with water, the expected product of hydrolysis 3, but
gives 2a as a product of reduction. At that time, this result
was unexplained.
Scheme 1. Literature-known results from the reaction between ani-
3 3
sole or thioanisole and AlCl /PCl
To increase the yield and the selectivity of this phosphon-
ation reaction on anisoles and thioanisoles, the AlCl cata-
3
lyst has been replaced[ by SnCl and, very recently,
4a]
[4b]
4
by BiCl3.
Results and Discussion
[
a]
Dipartimento di Chimica Organica, Universit a´ ,
Viale Risorgimento 4, 40136 Bologna, Italy
Fax: (internat.) ϩ 39-051/209-3654
[4]
On analysis of the data on anisoles reported above and
our results[ on thioanisoles, we decided to reinvestigate the
reaction of anisoles 4 with the couple PCl /AlCl , in order
5]
E-mail: baccolin@ms.fci.unibo.it
3
3
Eur. J. Org. Chem. 2001, 2229Ϫ2233

WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ193X/01/0612Ϫ2229 $ 17.50ϩ.50/0
2229

G. Baccolini, M. Bazzocchi, C. Boga
FULL PAPER
ratio of 1:0.6:1, at 70Ϫ80 °C for 7Ϫ10 h under dry nitrogen
and without solvent.
Scheme 4. Results obtained from the reaction of anisole and AlCl
3
/
PCl in different ratios of the reagents
3
A suggested mechanism, depicted in Scheme 5, for this
phosphorus insertion reaction was also reported.[ The in-
sertion of a P moiety is explained by the attack of a molec-
ule of PCl on an anisoleϪAlCl complex and subsequent
7]
3
3
migration of the methyl group to the same P atom giving
the intermediate AЈ. Subsequent nucleophilic attack of free
anisole on phosphonium salt AЈ gives BЈ which, after
quenching with water, gives phosphonate 8.
Scheme 3. Pathway of the domino reaction giving the benzothiadi-
phosphole system
to verify whether the reported[3,4] large amounts of undis-
tillable residues and the conflicting reported results might
be due to the formation of heterocyclic compounds related
to 2 or of other unexpected products.
At the beginning of this study we noted by GLC-MS that
the reaction of PCl and AlCl with p-methylanisole (4a) is
3
3
indeed very complex as it gives a reaction mixture con-
taining several products. We found great variations in these
final products and in their relative ratios on varying the
ratio of the reagents and reaction conditions. However, we
noted, under some reaction conditions, the formation of
traces of heterocycle 5a among several other products. The
identification of 5a was facilitated by comparison of its
mass spectra fragmentations with the fragmentations of 2a.
Scheme 5. Pathway of the formation of 8
It should be noted that in the same reagent ratios and
Recently, after several studies on the structure of the reaction conditions thioanisoles 1 did not give formation of
other products, we found[ that, when the reaction is car- PϪMe compounds related to 8 and the single product was
ried out under appropriate reaction conditions, an unexpec- always 2. This fact may be explained as follows: In the case
ted ‘‘insertion’’ of a phosphorus moiety into the OϪMe of thioanisole the S atom can be hypervalent such as in
bond of anisole 4 occurs, to give compound 8 as the major intermediate B of Scheme 3, while in the case of anisole the
product in place of the expected FriedelϪCrafts phosphon- O atom cannot give this hypervalent coordination. In the
ation (Scheme 4). The best selective formation of 8 first step it prefers to expel the Me group which is captured
7]
(
50Ϫ70% yield) was obtained with an anisole 4/AlCl /PCl3 by a phosphorus atom giving stable intermediate AЈ (as de-
3
2230
Eur. J. Org. Chem. 2001, 2229Ϫ2233

3 3
A New Performance of the Reaction of PCl /AlCl with Anisoles
FULL PAPER
ϩ
picted in Scheme 5) thus explaining the insertion of the P compound 2a exhibits ion peaks at m/z: 306 [M ], 243 (base
moiety on the OϪMe bond.
ϩ
peak) [M Ϫ PS], 211, 197, 153, 121, 77, 63 [PS]. As a
After repeated attempts varying the reagent ratios and consequence of the assignment of 5a, the structure of 6a is
reaction conditions, we have been able to obtain the easily deduced from its mass and NMR spectra. Its mass
ϩ
ϩ
benzooxadiphosphole system as prevalent product peaks are: m/z: 290 (base peak) [M ], 243 [M Ϫ PO], and
ϩ
31
(
30Ϫ40% yield), as reported in Scheme 4 using a ratio of 227 [M Ϫ PO ], 196, 152, 121, 77, 47. The P NMR spec-
2
4
a/AlCl /PCl of 1:0.6:7 and refluxing for about 20Ϫ25 h trum of 6a contains a set of two doublets; the ones at lower
3 3
without solvent. In contrast with the reaction with thioani- field (δ ϭ 69.9, JPP ϭ 209 Hz) being assignable to the
soles 1, the reaction with anisole 4a gives a large amount OP(O)O phosphorus atom while the other as doublet of
of its monoxide 6a and only traces of the benzooxadiphos- triplets (δ ϭ Ϫ112.5, dt, JPP ϭ 209 Hz, JPH ϭ 7 Hz) charac-
phole 5a. An amount of 10Ϫ20% of 8a was also obtained. terises the phosphane phosphorus atom. The configuration
Presumably, the formation of the benzooxadiphosphole de- of 5a and 6a should be cis according to the structure of
rivatives 5a and 6a is favoured, with respect to the forma- related benzothiadiphosphole 2 determined by X-ray ana-
tion of 8, by the large excess of PCl . Thus, the concomitant lysis and as predicted by semi-empirical MM2 calculations.
3
methylation of the same phosphorus atom which attacks This predicted configuration was ascribed to easier accom-
the oxygen atom of anisole giving the intermediate AЈ (as modation of the long PϪP bond in the cis relative to the
reported in Scheme 5) is unfavourable in the first step.This trans isomer and this preference appears to be general, ac-
is because the anisoleϪAlCl complex now presumably un- cording to other fused-ring systems.[
9]
3
dergoes attack by two or more molecules of PCl , as de-
When the reaction was carried out with 4b, products 5b
3
picted in Scheme 6. The subsequent steps of the pathway and 6b were obtained in minor amounts, 20Ϫ25% yield.
for the formation of 6 are, tentatively, very similar to the The 31P NMR spectrum of 5b shows a doublet at δ ϭ 186
domino reaction reported[
5c]
for the formation of 2 (JPP ϭ 175 Hz) and a doublet of triplets at δ ϭ Ϫ13 (JPP
175 Hz, JPH ϭ 7 Hz), while 6b (as white solid, m.p.
66Ϫ167 °C) shows a doublet at δ ϭ 69.3 (JPP ϭ 211 Hz)
and a doublet of triplets at δ ϭ Ϫ114 (JPP ϭ 211 Hz, JPH
ϭ
(Scheme 3).
1
ϭ
7
2
4
Hz). The mass spectrum of 5b exhibits ion peaks at m/z:
46, 199 (base peak) [M Ϫ PO], 183, 170, 152, 107, 69,
ϩ
7, while the mass spectrum of 6b exhibits ion peaks at m/
ϩ
z: 262 (base peak), 215 [M Ϫ PO], 199, 168, 152, 107,
6
9, 47.
In order to obtain supporting evidence for a possible
pathway of this presumed domino reaction, aliquots of the
reaction mixture from 4a, AlCl and PCl were analysed by
3
3
31
P NMR spectroscopy. After 10 h and after removal of
PCl , the P( H) NMR spectrum showed several signals at
31
1
3
Scheme 6. Intermediate 7 to obtain 6
δ ϭ 178, 158, 104, 69, and 49 as broad singlets and an
intense doublet of doublets at δ ϭ 88.3 (d, JPP ϭ 262 Hz),
It should be noted that compounds 5a and 6a are very Ϫ105.0 (dt, JPP ϭ 262 Hz, JPH ϭ 7.5 Hz). At the end of
oxygen- and water-sensitive and that their prolonged the reaction we noted the prevalence of the above doublets
workup gives oxidation and decomposition products. In ad- over the singlets and after addition of water we noted the
dition, chromatographic purification cannot be performed. disappearance of the above doublets and the appearance of
The proposed structure for 5a is mainly supported by its the doublets of 6a. Very small signals of the doublets of 5a
3
1
NMR-spectroscopic data. The P NMR spectrum shows were also observed. Thus, the couple of doublets, observed
the presence of two magnetically non-equivalent phos- before quenching with water, might be assigned to the final
phorus atoms and the presence of a large coupling between intermediate 7 in Scheme 6. From these data we can affirm
them (JPP ϭ 175 Hz) indicates the presence of a PϪP bond. that the final intermediate 7 corresponds to the final inter-
The strongly deshielded doublet at δ ϭ 188.0 can be unam- mediate G (Scheme 3) observed for the same reaction with
biguously assigned to the phosphorus atom between the thioanisole 1, but the results of the treatment with water
two oxygen atoms whereas the other signal at δ ϭ Ϫ11.8 as are very different. In fact the treatment of phosphonium
a doublet of triplets (JPP ϭ 175 Hz, JPH ϭ 6 Hz) is unam- salt 7 with water gives the expected product of hydrolysis 6
biguously assigned to the other phosphorus atom. In addi- while the same treatment of phosphonium salts G gives 2
tion, these values are in good agreement with or very close as an unexpected reduction product.
to those reported for related nonfused 1,2,3-benzoxadi-
It should be noted that compounds 5 are very unstable,
phosphole derivatives obtained as decomposition products air- and moisture-sensitive compounds, while the related bi-
from the distillation of o-phosphanylphenols.[ The mass cyclic compounds 2 are very stable and air-insensitive
8]
ϩ
spectrum of 5a exhibit ion peaks at m/z: 274 [M ], 227 solids. This difference is due only to the replacement of two
ϩ
(
base peak, [M Ϫ PO]), 211, 197, 153, 121, 77, 47 [PO]. oxygen atoms with the sulfur atoms. We think that this
It should be noted that the mass spectrum of the related simple substitution might favour a quasi-aromatic structure
Eur. J. Org. Chem. 2001, 2229Ϫ2233
2231

G. Baccolini, M. Bazzocchi, C. Boga
FULL PAPER
or a more delocalised structure in the case of compounds 2 tion about the limited success in the phosphonation of ani-
in contrast to 5. This stabilization of 2 might also be re- soles obtained so far with the same reagents. In addition,
sponsible for its preferred formation with respect to the ox- we have applied the reactivity of the couple PCl /AlCl to
3
3
idized derivative 3 in the final hydrolysis of its precursor bis(o-methoxyaryl)phosphane oxides 11 to form in a one-
phosphonium salt G (Scheme 3). In contrast, the oxidised pot procedure two OϪP bonds and one PϪP bond to yield
derivative 6 is preferred in the case of 5. The quasi-aromatic 6. Finally, these findings represent a generalisation of a fa-
structure of 2 might explain also the large difference be- cile one-pot route to obtain benzo-fused systems containing
tween the 3 P NMR spectra of 5a [δ ϭ 188.0 (d, P-6); Ϫ11.8 the PϪPX unit (X ϭ S, O, etc.). It should be noted that
1
2
3
1
[11]
(
dt, P-12, J ϭ 6 Hz, J ϭ 175 Hz)] and the ones of 2a recently the fused-ring compound 2a has been used
as
PH
PP
3
1
[
δ ϭ 88.3 (d, P-6); δ ϭ 65.4 (dt, P-12, J ϭ 7.8 Hz, J
ϭ
an efficient phosphorus-donating reagent and 6a might also
PH
PP
2
11.5 Hz)] in which we have two signals for the two P atoms be an interesting PϭO donating reagent.
in the same region, indicating a possible delocalization of
the two P lone pairs.
In order to obtain other data to support the structures
of the benzo-fused compound 6 we carried out a multi-step
Experimental Section
synthesis of this system. As reported in Scheme 7, in the General Remarks: 1H, 13C, and 31P NMR spectra were recorded
first step o-bromoanisole 9 was transformed to its Grignard with a Varian Gemini spectrometer at 300 MHz, 75.46 MHz, and
3
derivative 10. In the second step 10 was transformed to di- 120.75 MHz, respectively, in CDCl . Chemical shifts are referenced
1
13
to internal standard TMS ( H NMR), to solvent (δ ϭ 77.0 for
C
arylphosphane oxide 11 by PCl in high dilution with THF
and then hydrolysis. In the last step, again using the couple
3
3
1
3 4
NMR), and to external standard 85% H PO ( P NMR); J values
are given in Hz. Ϫ IR spectra were recorded with a PerkinϪElmer
spectrophotometer model 1600 FT-IR. IR spectra of compounds
a and 6b showed typical signals: PϭO (1254 cm ), PϪOϪC
PCl /AlCl , demethylation, formation of two OϪP bonds,
3
3
and formation of one PϪP bond yield 6 in a one-pot pro-
cedure.
Ϫ1
6
Ϫ1
Ϫ1
(
1086 cm ) and PϪPh (1466 cm ). Ϫ MS data were recorded at
an ionisation voltage of 70 eV with a VG 7070 E spectrometer. GC-
MS analyses were performed with an HP-5890 gas chromatograph
equipped with a methyl silicone capillary column and an HP-5970
mass detector. Ϫ Thin-layer chromatography was performed on
Merck Kieselgel 60 F254. Melting points were measured with a
Büchi apparatus and are uncorrected. Ϫ THF was distilled from
sodium benzophenone ketyl. All reagents were commercial samples
(
Aldrich). Air- and moisture-sensitive solutions and reagents were
handled in a dried apparatus under dry nitrogen. Chemical and
physical data of compounds 8a and 8b are in agreement with liter-
ature values.[
7]
One-Step Synthesis of the [1,2,3]Benzooxadiphospholo[2,3-b][1,2,3]-
benzooxadiphosphole Systems 5a,b and 6a,b from Anisoles 4a,b and
PCl
3
/AlCl
3
. ؊ Typical Procedure: p-Methylanisole (1a) (5.04 mL,
(3.20 g, 0.024 mol), and PCl (24.26 mL, 0.28 mol)
Scheme 7. Alternative multi-step synthesis of 6
0
.04 mol), AlCl
3
3
were placed in a dried apparatus, filled with dry nitrogen. The mix-
ture was stirred at 80 °C. The reaction was monitored by GC-MS
analysis. After about 20Ϫ25 h, the reaction mixture was treated
quickly with a mixture of water and dichloromethane. After extrac-
tion with dichloromethane, the organic layer was dried with anhyd-
It should be noted that the described formation of 11
is a new and simple synthesis of this type of phosphorus
derivatives. In fact, according to the literature[ these com-
pounds are formed in a dry box under nitrogen by reaction
of aryllithium compounds with diethyl phosphite.
10]
2 4
rous Na SO and the solvent was removed giving a greasy mixture
containing 5a, 6a, and 8a in the ratio of about 1:7:2. After remov-
ing 8a by bulb-to-bulb distillation at 0.1 Torr at 200 °C, the undis-
2 2 2
tillable residue was crystallised from CH Cl /Et O giving a white
Conclusion
solid, containing compounds 5a and 6a in a 1:7 ratio. Fast recrys-
tallization of this solid gave pure 6a (2.13 g, 35%) as a white solid.
The procedure shown above was followed using the anisole 4b as
reagent. From this reaction, compound 5b was obtained in traces
and 6b in 20Ϫ25% yield.
We have reported that the ‘‘domino reaction’’ which oc-
curs when thioanisole reacts with the couple PCl /AlCl giv-
ing the fused bicyclic system 2 can occur also with anisoles
giving the related fused system 5, but with a very large
3
3
amount of its monoxide 6. However, for anisoles, the best 2,10-Dimethyl[1,2,3]benzooxadiphosphole[2,3-b][1,2,3]benzooxa-
3
1
1
diphosphole (5a): P{ H} NMR (120.75 MHz, CDCl
3
): δ ϭ 188.0
reaction conditions have been more difficult to find because
another unexpected reaction (insertion of a P moiety into
the OϪMe bond) giving diaryl methylphosphonates 8 can
also occur. We have, however, been able to control the two
(
1
d, JPP ϭ 175 Hz, P-6), Ϫ11.8 (dt, JPP ϭ 175 Hz, JPH ϭ 6 Hz, P-
2). Ϫ MS (70 eV, EI): m/z (%) ϭ 274 [M ] (95), 227 [M Ϫ PO]
ϩ
ϩ
(
100), 211 (45), 197 (26), 153 (18), 121 (20), 77 (28), 63 (35).
5
different pathways by simple control of the reagent ratios 2,10-Dimethyl-6λ -[1,2,3]benzooxadiphosphole[2,3-b][1,2,3]benzo-
and reaction conditions. These results also give an explana- oxadiphosphol-6-one (6a): M.p. 176Ϫ177 °C (from CH
2 2 2
Cl /Et O).
2232 Eur. J. Org. Chem. 2001, 2229Ϫ2233

A New Performance of the Reaction of PCl
3
/AlCl
3
with Anisoles
), 6.95Ϫ7.50 Reaction of 11a and 11b with AlCl
FULL PAPER
1
Ϫ H NMR (300 MHz, CDCl
3
): δ ϭ 2.30 (s, 6 H, CH
3
3
/PCl
3
. ؊ Typical Procedure:
(
2
m, 2 H, 3-H, 9-H), 7.10Ϫ7.18 (m, 2 H, 4-H, 8-H), 7.32Ϫ7.39 (m, Compound 11a (0.46 g, 0.0016 mol), PCl
3
(0.96 mL, 0.0075 mol),
31
1
H, 1-H, 11-H). Ϫ P{ H} NMR (120.75 MHz, CDCl
3
): δ ϭ 69.9
3
and AlCl (0.22 g) were placed in a dried apparatus filled with dry
(
d, JPP ϭ 209 Hz, P-6), Ϫ112.5 (dt, JPP ϭ 209 Hz, JPH ϭ 7.0 Hz, nitrogen. The mixture was stirred at 80 °C, and the reaction was
ϩ
ϩ
P-12). Ϫ MS (70 eV, EI): m/z (%) ϭ 290 [M ] (100), 243 [M
PO] (75), 227 (45), 196 (26), 152 (7), 121 (11), 77 (9), 47 (32). Ϫ
HRMS: calcd. for C14
7.95, H 4.17; found C 57.87, H 4.12.
Ϫ
monitored by GC-MS analysis. After 4 h, the reaction mixture was
quickly treated with a mixture of water and dichloromethane. After
H
12
O
3
P
2
: 290.0262, found 290.0266; calcd. C extraction with dichloromethane, the organic layer was dried with
anhydrous Na SO and the solvent was removed. The residue was
crystallised from CH Cl /Et O giving 6a (0.232 g, 50%). The pro-
5
2
4
2
2
2
[
1,2,3]-Benzooxadiphosphole[2,3-b][1,2,3]benzooxadiphosphole (5b):
cedure shown above was followed using compound 11b as reagent.
From this reaction compound 6b was obtained in 53% yield.
3
1
1
P{ H} NMR (120.75 MHz, CDCl
3
): δ ϭ 186.0 (d, JPP ϭ 175 Hz,
P-6), Ϫ13.0 (dt, JPP ϭ 175 Hz, JPH ϭ 7.0 Hz, P-12). Ϫ MS (70 eV,
ϩ
ϩ
EI): m/z (%) ϭ 246 [M ] (95), 199 [M Ϫ PO] (100), 183 (15), 170
18), 152 (20), 107 (16), 69 (28), 47 (25).
Reaction of p-Methylthioanisole (1a)/AlCl
lution of p-methylthioanisole (1a) (13.26 mL, 0.1 mol), PCl
8.7 mL), and AlCl (0.6 mol) (sublimed prior to use) was refluxed
3 3
/PCl (1.0:0.6:1.0): A so-
(
3
(
3
[
1,2,3]-Benzooxadiphosphole[2,3-b][1,2,3]benzooxadiphosphol-6-one
1
and stirred under dry nitrogen for 10 h. The reaction mixture was
treated with a mixture of ice and dichloromethane; the organic
layer was washed with a 5% aq. NaOH solution and twice with
water. After removal of the solvent, no traces of methylphosphoryl-
ation products were detected, only benzothiadiphosphole 2a.
(
(
7
6b): M.p. 165Ϫ166 °C (from CH
300 MHz, CDCl ) δ ϭ 7.07Ϫ7.19 (m, 4 H, 2-H, 3-H, 9-H, 10-H),
.35Ϫ7.42 (m, 2 H, 4-H, 8-H), 7.58 (dd, JPH ϭ JHH ϭ 7.1 Hz, 2
2 2 2
Cl /Et O). Ϫ H NMR
3
31
1
H, 1-H, 11-H). Ϫ P{ H} NMR (120.75 MHz, CDCl
3
): δ ϭ 69.3
(d, JPP ϭ 211 Hz, P-6), Ϫ114.0 (d, JPP ϭ 211 Hz, JPH ϭ 7.1 Hz,
ϩ
ϩ
P-12). Ϫ MS (70 eV, EI): m/z (%) ϭ 262 [M ] (100), 215 [M
PO] (72), 199 (38), 168 (48), 152 (13), 107 (15), 69 (26), 47 (24). Ϫ
HRMS: calcd. for C12
4.98, H 3.08, found C 54.83, H 3.02.
Ϫ
H
8 3
O
2
P : 261.9949, found 261.9945; calcd. C Acknowledgments
5
This investigation was supported by the University of Bologna
Two-Step Synthesis of Benzooxadiphospholes 6a,b from o-Bromoani-
(funds for selected research topics AA 1999Ϫ2001), the Ministero
soles 9a,b. ؊ Preparation of 11a and 11b. ؊ Typical Procedure: A dell’Universit a´ e della Ricerca Scientifica e Tecnologica (MURST,
solution of PCl (0.654 mL, 0.0075 mol) in THF (30 mL) was Roma), Consiglio Nazionale delle Ricerche (CNR, Roma).
placed in a dried apparatus filled with dry nitrogen. A solution of
-(4-methyl)anisylmagnesium bromide [prepared from 2-bromo-4-
3
2
[
1]
A. Michaelis, Ber. Dtsch. Chem. Ges. 1879, 12, 1009.
[2]
methylanisole (9a) (2.17 mL, 0.015 mol) and magnesium turnings
in THF (30 mL)] was added dropwise and under quick stirring, at
0
at room temperature, and the reaction was monitored by GC-MS
analysis. After 5 h the reaction mixture was hydrolysed with an
aqueous acid solution for almost 30 min. After extraction with
dichloromethane, the organic layer was dried with anhydrous
M. Fild, R. Schmutzler, Organic Phosphorus Compounds (Ed.
G. Kosolapoff, L. Maier), Wiley-Interscience, 1972, vol. 4, p.
°C for 4 h. After the addition, the mixture was left under stirring
7
9.
[
[
3] [3a]
A. Michaelis, Justus Liebigs Ann. Chem. 1896, 294, 1. Ϫ [3b]
P. Kunz, Ber. Dtsch. Chem. Ges. 1894, 27, 2559Ϫ2565.
4] [4a]
J. A. Miles, M. T. Beeny, K. W. Ratts, J. Org. Chem. 1975,
0, 343Ϫ347. Ϫ [ F. Sim e´ on, P. Jaffr e` s, D. Villemin, Tetrahed-
4b]
4
ron 1998, 54, 10111Ϫ10118.
Na
from CH
0.76 g, 70%). The procedure shown above was followed using 2-
2
SO
4
and the solvent was removed. The residue was crystallised
[5] [5a]
G. Baccolini, E. Mezzina, P. E. Todesco, E. Foresti, J.
Chem. Soc., Chem. Commun. 1988, 304Ϫ305. Ϫ [ G. Baccol-
2
Cl /Et O giving a white solid containing compound 11a
2
2
5b]
(
ini, E. Mezzina, P. E. Todesco, J. Chem. Soc., Perkin Trans. 1
bromoanisole (9b) as reagent. From this reaction compound 11b
was obtained in 70% yield.
[5c]
1
988, 3281Ϫ3283. Ϫ
G. Baccolini, M. Beghelli, C. Boga,
[5d]
Heteroatom Chem. 1997, 8, 551Ϫ556. Ϫ
Wasylishen, W. P. Power, G. Baccolini, Can. J. Chem. 1992,
2, 1229Ϫ1235.
Gang Wu, R. E.
Bis(2-methoxy-5-methylphenyl)(oxo)phosphorane (11a): R
F
ϭ 0.15
) δ ϭ 2.31 (s, 6 H, CH ),
3
), 6.77Ϫ6.85 (m, 2 H, 4-H), 7.27Ϫ7.34 (m, 2 H,
7
1
(in Et
2
O). Ϫ H NMR (300 MHz, CDCl
3
3
[6]
For a recent review on fused rings see: J. C. Tebby, ‘‘Bicyclic
Systems with Ring Junction, Phosphorus, Arsenic, Antimony,
or Bismuth Atoms’’, in: Comprehensive Heterocyclic Chemistry
II (Eds.: A. R. Katrizky, C. W. Rees, E. F. V. Scriven, G. Jones),
Pergamon Press, New York, 1996, vol. 8, p. 864Ϫ888.
G. Baccolini, C. Boga, Synlett 1999, 822Ϫ824.
3
3
5
1
.74 (s, 6 H, OCH
3
4
-H), 7.41 (dd, JPH ϭ15.3, J ϭ 2.4 Hz, 2 H, 6-H), 8.22 (d, JPH
ϭ
20 Hz, 1 H, PH). Ϫ 31P{ H} NMR (120.75 MHz, CDCl
1
3
): δ ϭ
0.0 (dt, JPH ϭ 520 Hz, JPH ϭ 15 Hz). Ϫ MS (70 eV, EI): m/z
[
[
7]
8]
ϩ
(
%) ϭ 290 [M ] (100), 259 (52), 241 (39), 135 (95), 105 (54). Ϫ
HRMS: calcd. for C16 P: 290.1072, found 290.1067, calcd. C
6.20, H 6.60; found C 66.05, H 6.45.
J. Heinicke, M. He, R. Kadyrov, P. G. Jones, Heteroatom Chem.
19 3
H O
1
998, 9, 183Ϫ193.
6
[9]
R. W. Alder, C. Ganter, M. Gil, R. Gleiter, C. J. Harris, S. E.
Harris, H. Lange, A. G. Orpen, P. N. Taylor, J. Chem. Soc.,
Perkin Trans. 1 1998, 1643Ϫ1656.
Bis(2-methoxyphenyl)(oxo)phosphorane (11b): M.p. 136 °C (ref.[
11a]
1
135Ϫ136 °C), R
F
ϭ 0.30 (in Et
2
O). Ϫ H NMR (300 MHz, CDCl
3
)
[10] [10a]
[10b]
3
3
J. L. Willans, Chem. Ind. (London) 1957, 235Ϫ236. Ϫ
R. L. Wife, A. B. Van Oort, J. A. Van Doorn, P. W. N. M. Van
Leeuwen, Synthesis 1983, 71Ϫ73.
δ ϭ 3.76 (s, 6 H, OCH
3
), 6.90 (dd, J ϭ8.5, J ϭ 6.0 Hz, 2 H, 4-
H), 7.02Ϫ7.12 (m, 2 H, 5-H), 7.46Ϫ7.56 (m, 2 H, 3-H), 7.67 (qd,
3
3
4
J ϭ7.5 Hz, JPH ϭ 15.0, J ϭ 1.8 Hz, 2 H, 6-H), 8.25 (d, JPH
ϭ
[11] [11a]
G. Baccolini, G. Orsolan, E. Mezzina, Tetrahedron Lett.
3
1
1
5
8
2
15 Hz, 1 H, PH). Ϫ P{ H} NMR (120.75 MHz, CDCl
.2 (dt, JPH ϭ 515 Hz, JPH ϭ 15 Hz). Ϫ MS (70 eV, EI): m/z (%) ϭ
62 [M ] (100), 231 [M Ϫ 31] (31), 213 (44), 121 (85), 91 (32). Ϫ
P: 262.0759, found 262.0709.
3
): δ ϭ
[11b]
1
995, 36, 447Ϫ450. Ϫ
G. Baccolini, C. Boga, U. Negri,
3
Synlett 2000, 1685Ϫ1687.
ϩ
ϩ
Received January 11, 2001
[O01012]
15 3
HRMS: calcd. for C14H O
Eur. J. Org. Chem. 2001, 2229Ϫ2233
2233