OCH
3
PCl
3
OCH
3
PCl
2
A
PCl
3
OPCl
2
B
fresh AlCl
3
undistillable
products
+
comm. AlCl
3
+
undistillable
products
SMe
X
2) H
2
O
S
P
P
S
X X
1
a, X = Me
b, X = H
1) AlCl
3
, PCl
3
2 (50%)
TETRAHEDRON
LETTERS
Tetrahedron Letters 42 (2001) 6121–6124 Pergamon
One-pot synthesis of unsymmetrical aryl methylphosphinates by
insertion of dichlorophosphines into the OMe bond of anisoles
Graziano Baccolini* and Carla Boga
Dipartimento di Chimica Organica, Universita ` , Viale Risorgimento 4, I -40136 Bologna, Italy
Received 21 June 2001; accepted 4 July 2001
Abstract—This letter describes a new one-pot method for the synthesis of unsymmetrical aryl methylphoshinates by insertion of
phosphorus moiety into the OMe bond of anisoles. These products are very difficult to obtain with other reported methods
requiring several steps. © 2001 Elsevier Science Ltd. All rights reserved.
Since the last century, the Friedel–Crafts type reaction
using PCl
3
and AlCl
3
has been an excellent method for
the direct attachment of a phosphorus atom to an
aromatic ring to give aryldichlorophosphines or
diarylchlorophosphines. However, this reaction is very
sensitive to the type of substituents present on the
aromatic ring
1,2
and often the literature gives conflicting
results.
3,4
In particular, it is reported
4a
that anisole,
upon treatment with phosphorus trichloride and alu-
minum chloride, afforded p -anisylphosphonous dichlo-
ride (A) but in very poor yields and with large amounts
of undistillable residues while in some cases it gave
phenyl dichlorophosphite (B) but always in poor yields.
In addition, it is reported
4a,b
that this phosphonation
reaction fails completely when thioanisoles are used
(Scheme 1).
In contrast to these reported results, in the past years,
we discovered
5
that the reaction of PCl
3
and AlCl
3
with
thioanisoles 1 gave, unexpectedly, the new fused-
bicyclic system
6
2 (fused 1,2,3-benzothiadiphosphole) in
good yields (see Scheme 2).
Recently, analyzing the above reported
4
data on
anisoles and our results
5
on thioanisoles we decided to
reinvestigate the reaction of anisoles with the couple
PCl
3
/AlCl
3
, in order to verify whether the reported
3,4
large amounts of undistillable residues and the conflict-
uality of the reported results might be due to the
formation of heterocyclic compounds related to 2 or of
other unexpected products. In fact, we found that
varying the reagent ratios and the reaction conditions
we have been able to obtain, as prevalent product
(30–40% yield), the benzooxadiphosphole systems 4 and
5 (Scheme 3) using a ratio of 3a:AlCl
3
:PCl
3
of 1:0.6:7
Scheme 1.
Scheme 2.
Keywords : phosphorylations; insertions; Lewis acids.
* Corresponding author. Tel.: 390512093616; fax: 390512093654;
e-mail: baccolin@ms.fci.unibo.it
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII:S0040-4039(01)01197-2