Introduction
<P>Diphenylphosphoryl azide, originally developed by Yamada in
1972,
[
¹]
has shown significant
synthetic versatility,
[
²]
being
used in isocyanate synthesis, especially in the Curtius rearrangement,
[
¹]
stereospecific conversion
of alcohol into azide,
[
³]
as
a coupling reagent in macrolactamization,
[
4]
in
allylic amine synthesis,
[
5]
and in
aziridination reactions.
[
6]
</P><P>Diphenylphosphoryl azide, also called DPPA, diphenyl phosphorazidate
or phosphoric acid diphenyl ester azide, is a colorless liquid with
high boiling point (157 ˚C/0.17 mmHg),
and can be easily prepared by the reaction between diphenylphosphoryl
chloride and sodium azide in acetone in high yield.
[
¹]
[
7]
The
Waldvogel group developed a reliable protocol for the large-scale
(100 g) synthesis of DPPA, including purification by reduced-pressure
distillation (Scheme
[
¹]
).
[
8]
A polymer-supported form of the
reagent has also been developed using phenol resin by the Taylor
group.
[
9]
</P>
Scheme 1 Preparation of DPPA in
400 mmol scale
<P>
Abstracts
</P>
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(A) Yamada and co-workers
developed an improved method for the Curtius rearrangement reaction
using DPPA, which was later named Yamada-Curtius rearrangement.
[¹]
In 2007, the Ciufolini
group employed this method in the total synthesis of streptonigrone,
to transform a carboxylic acid group into a protected amino group
through the hydrolysis of an isocyanate intermediate.
[¹0]
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</TD>
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(B) A primary or secondary
alcohol can be easily converted into an azide group by DPPA under
mildly basic conditions or using Mitsunobu conditions
for stereochemical inversion. In the total synthesis of cribrostatin
VI, the Danishefsky group successfully employed DPPA to displace
a benzyl alcohol in high yield and ee.
[¹¹]
Another
example was demonstrated in the synthesis of Tamiflu and its phosphonate
congeners by the Wang group in 2007.
[¹²]
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</TD>
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(C) Diphenylphosphoryl
azide has also been widely used in peptide coupling reactions, particularly
in macrolactamization.
[4]
In 2005,
the Moody group completed the synthesis of thiopeptide amythiamicin D.
In the final step, after global deprotection of N-Boc
and tert-butyl groups, an α-amino
ketone was successfully coupled with a thiazole carboxylic acid
in DMF in 73% yield.
[¹³]
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</TD>
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(D) The Batey group has
developed a stereoselective synthesis of allylic amines through
a [3,3]-aza-phospha-oxa-Cope sigmatropic rearrangement.
[5]
Methylvinylcarbinol was converted
into crotylamine in 85% yield over two steps. DPPA was
used as an amine source in these reactions, and excellent selectivity
was achieved through addition of a catalytic amount of PdCl2(MeCN)2 catalyst.
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</TD>
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(E) A new catalytic aziridination
reaction using cobalt tetraphenylporphyrin [Co(TPP)] as
catalyst has been extensively studied by the Zhang group.
[6]
DPPA functioned as a nitrene source
in the reaction that proceeded in good to excellent yield.
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</TD>
