Introduction <P>Phosphorus pentoxide is a white, flammable, and extremely deliquescent solid. Its
structure consists of each P atom linked with five valence electrons to three oxygen
atoms.</P>
<P>P
2 O
5 reacts violently with water to produce phosphoric acid and is therefore a versatile
acidic dehydrating agent. It is a very well-known and much-used reagent and has many
applications in organic synthesis. Recently, its use has been reported in several
types of reactions, mostly in order to improve reaction methods. The advantages are
that it is an inexpensive and selective reagent, which gives high yields in simple
operations under solvent-free conditions and short reaction time.
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It is used in the synthesis of nitriles
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2 ]
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from aldoximes,
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for oxidation of alcohols to ketones and aldehydes.
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Is a highly efficient reagent for the acetylation of a variety of alcohols, phenols
and amines with acetic anhydride under solvent-free conditions. Primary, secondary,
allylic and benzylic alcohols, diols and phenols with electron-donating or -withdrawing
substituents can be easily acetylated in high yield.
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In addition, it is used to synthesize phosphorus compounds
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and polymers.
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</P><P>Abstracts</P>
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(A) New types of concerted domino acylation-cycloalkylation reactions promoted by
methanesulfonic acid-phosphorus pentoxide, provide efficient, elegant, and expeditious
routes for biologically active naturally occurring diterpenoids, namely ()-ferruginol
(3a ), ()-nimbidiol (3b ), ()-nimbiol (3c ) (75-90%).
[8
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(B) Microwave irradiation of oximes, semicarbazones, phenylhydrazones and tosylhydrazones
of various aldehydes in the presence of phosphorus pentoxide provides a fast, efficient
and simple method for regeneration of aldehydes in high yield (68-98%).
[9
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(C) Microwave irradiation of phosphorus pentoxide supported in alumina was found to
be an efficient reagent for the synthesis of 1,5-benzodiazepine derivatives from phenylenediamine
and ketones. This method is an easy, rapid, solvent-free and high-yielding reaction
for the synthesis of 1,5-benzodiazepines (75-85%).
[10
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(D) Bromination of hydroxyheteroarenes using P2 O5 /Bu4 NBr proceeds under mild conditions to afford high yields of various bromoheteroarenes.
In general, these compounds have been prepared with PBr3 or POBr3 , but those bromination procedures have some disadvantages such as handling of hazardous
reagents, exact reaction-temperature control and evolution of toxic HBr. The P2 O5 procedure is successfully applied to large-scale synthesis of bromoheteroarenes
(75%).
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