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DOI: 10.1002/cplu.201402191
Magnetic Fe3O4 Nanoparticle-Supported Phosphotungstic
Acid as a Recyclable Catalyst for the Kabachnik–Fields
Reaction of Isatins, Imines, and Aldehydes under Solvent-
Free Conditions
Mohd Nazish, S. Saravanan, Noor-ul H. Khan,* Prathibha Kumari, Rukhsana I. Kureshy,
Sayed H. R. Abdi, and Hari C. Bajaj[a]
Magnetic-nanoparticle-supported phosphotungstic acid has
been used to efficiently catalyze the hydrophosphonylation re-
action of isatins, imines, and aldehydes using dimethyl and di-
ethyl phosphite as a nucleophile to give the corresponding a-
hydroxy and a-amino phosphonates in excellent yields for
a wide range of substrates. The reaction conditions were
simple, green, and efficient. The catalyst was recycled up to
five times with retention of its activity. Based on the NMR spec-
troscopy studies, a probable catalytic cycle was proposed.
Introduction
The addition of a phosphorus–hydrogen bond to electrophilic
centers like C=O or C=N is considered to be one of the most
interesting topics in synthetic organic chemistry owing to its
widespread application and intriguing biological activities.
Among organophosphorus compounds, a-hydroxy and a-
amino phosphonic acids have received considerable interest in
the pharmaceutical industry, as biophosphate mimics, as anti-
biotics, as antivirals, and as antitumor agents.[1] Various at-
tempts have been made to develop efficient catalytic systems
for this versatile reaction like ZrCl4,[2] TiO2,[3] LiClO4,[4] ionic liq-
uids,[5] montmorillonite KSF,[6] lanthanide triflate,[7] samarium
diiodide,[8] indium chloride,[9] TaCl5-SiO2,[10] (bromodimethyl)sul-
fonium bromide,[11] alumina-supported reagents,[12] oxalic
acid,[13] Amberlite IR120,[14] and KHSO4.[15] Ghosh et al. studied
the one-pot synthesis of a-amino phosphonates using In(OTf)3
as a catalyst (10 mol%) and achieved good conversion ranging
from 16 to 99%.[16] Wu et al. used N-bromosuccinimide (NBS)
or CBr4 (5 mol%) as a catalyst for the three-component synthe-
sis of a-amino phosphonates and found that both catalysts
showed good catalytic activity under solvent-free conditions.[17]
Heydari et al. reported the hydrophosphonylation of aldehydes
using guanidine hydrochloride as a catalyst with water as a sol-
vent and achieved good conversion (60–95%).[18] Chakraborti
et al. studied the catalytic activity of Mg(ClO4)2 for the three-
component reaction of aldehydes and ketones using different
phosphites with solvent-free conditions and found that it is ef-
ficient and resulted in excellent conversion for a wide range of
substrates.[19] Rezaei et al. used FeCl3 as a catalyst for the syn-
thesis of simple and bis(a-amino phosphonates) with good
conversion (80–95%) using tetrahydrofuran (THF) as a solvent
and also studied its cytotoxic activity.[20] Petrini et al. studied
the hydrophosphonylation of unsaturated systems using CaO
and found that the system worked well under solvent-free
conditions with good conversions (49–91%) at room tempera-
ture.[21] Wang et al. reported Yb(PFO)3 as a catalyst for the hy-
drophosphonylation of aldimines at room temperature.[22]
Jeong et al. used BF3·SiO2 as a catalyst in an ionic-liquid
medium for the one-pot hydrophosphonylation of aldimines
and achieved good conversions (80–97%) of a-amino phos-
phonates.[23] Although it is gratifying to acknowledge the pio-
neering advances in the hydrophosphonylation reaction,[24–27]
most of the catalytic protocols need hazardous organic sol-
vents, expensive and moisture-sensitive catalysts, suffer from
high catalyst loading, longer reaction time, and limited sub-
strate scope. Heydari et al.[28] used H3PW12O40 as a catalyst for
the hydrophosphonylation of aldimines using dichloromethane
as a solvent. But most of the reported catalysts are not recycla-
ble making the process industrially nonviable. As part of our
ongoing development of recyclable and solvent-free catalytic
systems for organic transformations,[29] herein we report a sup-
ported heteropoly acid (phosphotungstic acid) as a recyclable
catalyst for the hydrophosphonylation reaction. The heteropoly
acid type of catalyst is well known for its catalytic activity in di-
verse organic transformations like CÀC bond-formation reac-
tions. As a result of being impressed by its catalytic per-
formance, we wished to further explore the catalytic activity of
phosphotungstic acid and also to demonstrate its extensive
application in the one-pot hydrophosphonylation reaction of
[a] M. Nazish, S. Saravanan, Dr. N.-u. H. Khan, P. Kumari, Dr. R. I. Kureshy,
Dr. S. H. R. Abdi, Dr. H. C. Bajaj
Discipline of Inorganic Materials and Catalysis
and
Academy of Scientific and Innovative Research
CSIR-Central Salt and Marine Chemicals Research Institute
G.B. Marg, Waghawadi Road, Bhavnagar, Gujarat 364 002 (India)
Fax: (+91)0278-2566970
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