PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
SHORT COMMUNICATION
Synthesis of organophosphates starting from a-hydroxyphosphonates
a
a
b
b
b
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Nora Z. Kiss , Zita Radai , Reka Szabo , Youness Aichi , Laila Laasri , and Said Sebti
b
aDepartment of Organic Chemistry and Technology, Budapest University of Technology and Economics, Budapest, Hungary; Laboratoire de
Chimie Physique Catalyse et Environnement (LCPCE), Faculty of Sciences Ben M’sik, Hassan II University of Casablanca, Casablanca, Morocco
ABSTRACT
ARTICLE HISTORY
Received 29 September 2018
Accepted 9 November 2018
a-Hydroxyphosphonates were successfully converted to the corresponding phosphates applying
the phospha-Brook rearrangement under phase transfer catalytic conditions. Among several pos-
sible catalysts tested, K2CO3, Cs2CO3, as well as modified Moroccan phosphates were found to
be suitable.
KEYWORDS
a-Hydroxyphosphonates;
phosphates; Moroccan
phosphates; rearrangement
GRAPHICAL ABSTRACT
Results and discussion
We have previously synthesized a series of a-hydroxyphospho-
nates (1), an important class of compounds by a benign method
starting from substituted benzaldehydes and dialkyl phosphites
applying triethylamine[1] or sodium-modified natural phos-
Scheme 1. The rearrangement reaction of a-hydroxyphosphonate (1).
phates (Na-NP)[2] as the catalyst. We aimed at applying these
catalysts for the synthesis of organophosphates by the rearrange-
ment of a-hydroxyphosphonate (1) into phosphate (2).
Table 1. The a-hydroxyphosphonate (1) ! phosphate (2) rearrangement.
Entry Base TEBAC T [ꢀC] t (min) Conversion [%] Yield [%] Product
For this, a preliminary study on the rearrangement reac-
tion of dimethyl 1-hydroxy-1-phenylmethylphosponate (1a)
was attempted in the presence of different bases in aceto-
nitrile (Scheme 1).
1
2
3
4
5
6
Et3N
DBU
K2CO3
–
–
10%
10%
25
25
25
D
25
D
60
40
60
40
40
0
79a
5
93
100
71
–
–
–
67
74
61
2a
2a
2a
2a
2a
2a
K2CO3
Applying 1 equivalent of triethylamine at 25 ꢀC for 1 h,
there was no reaction (Table 1, entry 1). 1,8-
Diazabicyclo[5.4.0]undec-7-ene (DBU) enhanced the reaction,
but significant decomposition was observed. The addition of
solid bases in the presence of benzyltriethylammonium chlor-
ide (TEBAC) as the phase transfer catalyst resulted in the
selective formation of the desired product (2a). K2CO3 was
less effective as compared to Cs2CO3 (Table 1/entries 5 vs 3).
While natural Moroccan phosphate (NP) and sodium-modi-
fied NP (Na-NP) were completely inactive, modification with
potassium[3] resulted in a suitable catalyst when boiling the
reaction mixture in acetonitrile (Table 1/entry 6). Altogether,
Cs2CO3 was chosen for our further experiments. The effect of
substituents was also investigated (Table 2), and it was found
that electron-withdrawing substituents increase, while elec-
tron-donating substituents decrease the reactivity.
Cs2CO3 10%
K-NPb
10%
120
aDecomposition was observed.
bIn the presence of NP and Na-NP, the conversion was 0%.
Table 2. Effect of substituents in the rearrangement (1!2) in the presence of
10% TEBAC and 1 eq. of Cs2CO3.
Entry
Y
T [ꢀC]
t [min]
Conversion [%]
Yield [%]
Product
1
2
3
4
5
H
4-Cl
4-F
4-Me
2-MeO
25
25
25
D
40
15
75
125
180
100
100
100
100
100
74
74
93
70
75
2a
2b
2c
2d
2e
D
In conclusion, we have developed a clean and easy
method for the phase transfer catalytic rearrangement of
a-hydroxyphosphonates to phosphates.
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CONTACT Nora Z. Kiss
ß 2018 Taylor & Francis Group, LLC
Kiss, Nóra Z.
