Phosphorylation of phenols and naphthols by phenylmethylenephosphine oxide generated by the thermolysis of a 2-phosphabicyclo[2.2.2]octa-5,7-diene 2-oxide

Article abstract of DOI:10.1081/SCC-100104403

A simple method utilising a low-coordinate phosphorus species is described for the phosphorylation of a series of phenols and naphthols to afford aryl methylphenylphosphinates in reasonable yields.

Full text of DOI:10.1081/SCC-100104403

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PHOSPHORYLATION OF
PHENOLS AND NAPHTHOLS BY
PHENYLMETHYLENEPHOSPHINE
OXIDE GENERATED BY THE
THERMOLYSIS OF A 2-
PHOSPHABICYCLO[2.2.2]OCTA-5,7
DIENE 2-OXIDE
Gy. Keglevich a , H. Szelke a , A. Dobó , Z. Nagy &
L. Toke a
a Department of Organic Chemical Technology ,
Budapest University of Technology and
Economics , Budapest, 1521, Hungary
Published online: 09 Nov 2006.
To cite this article: Gy. Keglevich , H. Szelke , A. Dobó , Z. Nagy & L. Toke (2001)
PHOSPHORYLATION OF PHENOLS AND NAPHTHOLS BY PHENYLMETHYLENEPHOSPHINE
OXIDE GENERATED BY THE THERMOLYSIS OF A 2-PHOSPHABICYCLO[2.2.2]OCTA-5,7-
DIENE 2-OXIDE, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 31:11, 1737-1741, DOI: 10.1081/
SCC-100104403
To link to this article: http://dx.doi.org/10.1081/SCC-100104403
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SYNTHETIC COMMUNICATIONS, 31(11), 1737–1741 (2001)
PHOSPHORYLATION OF PHENOLS
AND NAPHTHOLS BY PHENYL-
METHYLENEPHOSPHINE OXIDE
GENERATED BY THE THERMOLYSIS OF A
2-PHOSPHABICYCLO[2.2.2]OCTA-5,7-DIENE
2-OXIDE
Gy. Keglevich,1, H. Szelke,1 A. Dobo,2 Z. Nagy,3
*
and L. Toke1
1Department of Organic Chemical Technology,
Budapest University of Technology and Economics,
1521 Budapest, Hungary
2Hungarian Academy of Sciences, Chemical Research
Center, 1525 Budapest, Hungary
3Gedeon Richter Ltd., 1475 Budapest, Hungary
ABSTRACT
A simple method utilising a low-coordinate phosphorus
species is described for the phosphorylation of a series of
phenols and naphthols to afford aryl methylphenylphos-
phinates in reasonable yields.
The functionalised derivatives of 2-phosphabicyclo[2.2.2]octa-5,7-
diene and 2-phosphabicyclo[2.2.2]oct-5-ene oxides (1) are useful in the UV
* Corresponding author.
1737
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1738
KEGLEVICH ET AL.
light-mediated phosphorylation of alcohols and primary amines
(Scheme 1).1–4
1–3
Scheme 1.
Methylenephosphine oxides (2) were assumed to be the intermediates
of the phosphorylations.1,2 It was, however, pointed out that in certain
cases, the phosphorylations may also proceed through a concurrent reaction
path involving a pentacoordinated species formed by the addition of the
nucleophile on the P ¼ O group of the precursor.3–5
The phosphorylation of non-volatile aromatic hydroxy compounds
cannot be achieved by photolysis. The thermolysis of phosphabicycloocta-
dienes, having a more strained skeleton as compared to the phosphabicy-
clooctenes,6 seemed to be
a good choice for the generation of
methylenephosphine oxides to phosphorylate the phenol derivatives. In
this paper, we describe our results on the preparation of aryl methylphenyl-
phosphinates utilizing phenyl-methylenephosphine oxide (2, Y ¼ Ph) gener-
ated from a suitable phosphabicyclooctadiene precursor on heating.
Thermal examination (TG and DTG) of P-phenyl phosphabicyclooc-
tadiene oxide 41 consisting of two configurational isomers suggested that the
bridging moiety is ejected in the range of 190–265ꢀC.7 To ensure fast frag-
mentation, a temperature above 200ꢀC had to be applied. A series of phe-
nols including hydroxy-, methyl-, chloro- and nitro derivatives, as well as
naphthols were efficiently phosphorylated by adding their samples neatly to
the precursor (4) prior to the thermolysis (Scheme 2). The optimum con-
ditions included the heating of cycloadduct 4 at 240ꢀC in the presence of a
threefold excess of the aromatic hydroxy compound for 10 min. After
removing the excess of the phenol/naphthol by extraction using a 5%
sodium carbonate solution (or – in one case – a 2% sodium hydroxide
solution), a purification by column chromatography furnished the aryl
methylphenylphosphinates (6a–h) in 51–73% yields, in a purity of
95–98% (Table 1). The phosphorylated phenols/naphthols (6a–h) were char-
acterised by 31P NMR shifts, mass spectral data and HR-MS peak match
(Table 1).

PHOSPHORYLATION OF PHENOLS AND NAPHTHOLS
1739
Scheme 2.
Table 1. Phosphorylation of Phenols/Naphthols by PhP(O)CH2 Generated from
Precursor 4
Yield
Comp. [%] (CDCl3) (rel. int.)
dP
MS, m/z
Mþ
Formula
Mþ
cal
found
6a
6b
73
61
43.1
37.8
248 (M+, 75)
247 (87),
139 (M–ArO, 100)
248 (M+, 49),
247 (100),
248.0601 C13H13O3P
248.0602
248.0604 C13H13O3P
248.0602
139 (M–ArO, 67)
248 (M+, 65),
139(M–ArO, 100)
290 (M+, 100),
275(8),
6c
6d
63
69
37.7
41.7
248.0610 C13H13O3P
290.1085 C16H19O3P
248.0602
290.1072
139 (M–ArO, 48)
334 (M+, 13),
333 (15),
139 (M–ArO, 100)
277 (M+, 23),
276 (73),
139 (M–ArO, 100)
282 (M+, 50),
281 (23),
139 (M–ArO, 100)
282 (M+, 47),
281 (45),
6e
6f
54
51
65
60
45.1
43.5b
44.1
39.5
333.9471a C13H10Cl3O2P 333.9484a
6g
6h
282.0821 C17H15O2P
282.0824 C17H15O2P
282.0810
282.0810
139 (M–ArO, 100)
b
a For the species containing 35Cl isotopes; dP (lit8) 44.7 (CDCl3).

1740
KEGLEVICH ET AL.
The efficiency of the phosphorylations were somewhat decreased by
the inevitable polmerisation of the methylenephosphine oxide (2, Y ¼ Ph) at
240ꢀC. GC-MS analyses of the crude reaction mixtures showed the presence
of phthalate 5 (MS, m/z (rel. int.) 242 (Mþ, 4), 211 (100), 152 (59)).
According to our experiences, the other regioisomer of the precursor (40),1
also consisting of two configurational isomers, could be used in the phos-
phorylations similarly as the isomers represented by structure 4. Moreover,
there was no need to separate the isomers 4 and 40 at all; their mixture
formed in the synthesis1 was also a suitable source for PhP(O)CH2. There
was no observable difference between the reactivity of the isomers of phos-
phabicyclooctadienes 4 and 40.
The method described here is of general applicability. The extension to
other methylenephosphine oxide derivatives also seems to be possible and
we plan to carry out such experiments soon. Our procedure is the alternative
of the classical phosphorylations using phosphinic chlorides. The reaction of
phenol and 4-nitrophenol by methylphenylphosphinic chloride also gave the
corresponding phosphinates in good yields,9,8 but preparation of the phos-
phinic chloride from phosphorus trichloride requires four steps and was
accomplished only in 48% yield.10,11
EXPERIMENTAL
General Procedure: 0.2 g (0.53 mmol) of phosphabicyclooctadiene 41
consisting of a 59–41% mixture of two isomers (with dP 44.3 and 44.8,
respectively) and 1.59 mmol of the phenol or the naphthol derivative were
measured into a vial. The components of the vial were kept at 240ꢀC for 10
min then the crude mixture was taken up in 5 mL of chloroform and filtered
through a 5 cm layer of silica gel using 3% methanol in chloroform as the
eluent. After evaporation, the main fraction was dissolved in 30 mL of
chloroform and extracted using 10 mL of 5% Na2CO3 solution. (During
the phosphorylation of 3,4,5-trichlorophenol, 10 mL of 2% NaOHsolution

PHOSPHORYLATION OF PHENOLS AND NAPHTHOLS
1741
was used.) The organic phase was dried (Na2SO4) and the oily residue
obtained after evaporation was purified by column chromatography (silica
gel, 3% methanol in chloroform). A repeated refinement of the main frac-
tion led to the corresponding phosphinate (6a–h) in an average purity of
96% (Table 1).
ACKNOWLEDGMENTS
We are grateful for the FKFP and OTKA supports of the above
research (Grant numbers are 363/1999 and T 029039, respectively).
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Accepted in the Netherlands August 24, 2000