TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2037–2038
a-Nitrohydrazones: versatile intermediates for phosphonate
derivatives formation from primary nitro compounds
L. El Ka ¨ı m,* L. Grimaud, N. K. Jana and C. Tirla
Laboratoire Chimie et Proc e´ d e´ s, Ecole Nationale Sup e´ rieure de Techniques Avanc e´ es, 32 Bd Victor, 75015 Paris, France
Received 27 August 2001; revised 25 January 2002; accepted 28 January 2002
Abstract—Primary nitro compounds can be easily converted into hydrazonophosphonate derivatives through coupling with
aryldiazonium salts followed by an Arbuzov-type reaction with phosphite. © 2002 Elsevier Science Ltd. All rights reserved.
NHAr
NO2
NHAr
Although the first additions of aryldiazonium salts to
nitro compounds have been described at the end of the
nineteenth century, the resulting a-nitrohydrazones
N
N
P(OEt)3 1.5 eq
toluene, reflux
1
OEt
OEt
R
R
P
have found relatively few synthetic uses. Most of the
described applications of these compounds stem from
Huisgen’s studies on the generation and [3+2] cycload-
dition of nitrilimines derived from a-nitrohydrazones
1
2
O
Scheme 1.
2–9
under basic conditions. Our interest in both hydra-
zone chemistry and Umpolung reactions of nitro
derivatives led us to examine the potential of various
nucleophilic additions involving such nitrohydrazones.
We now describe a new transformation allowing an
easy access to functionalised phosphonates.
preparation of functionalised keto-phosphonate 2c, 2d,
e without any cyclisation to pyridazine. Indeed, start-
ing hydrazone 1e readily cyclises into pyridazine 3 by a
mere treatment with potassium carbonate under phase-
transfer catalysis (Scheme 2).
2
a-Aminophosphonic compounds are useful analogues
of a-aminoacids which can be easily prepared by an
Arbuzov-type reaction of phosphites on acid chlorides
followed by oxime formation and reduction. We
assumed that similar reaction of a-nitrohydrazones
with triethyl phosphite would give phosphonohydra-
zones. As the reduction of hydrazonophosphonates has
This new phosphonate formation probably involves an
Arbuzov-type reaction with co-production of ethyl-
nitrite; the low boiling point of the latter allows its easy
removal from the reaction mixture as well as ensuring
the absence of oxidation products.
10,11
In contrast to the Nef reaction, the potential of a-nitro-
hydrazones as an entry into carbonyl derivatives has
been largely underestimated.1 Apart from their
been already described,
the overall transformation
would give an easy entry to aminophosphonic deriva-
tives from primary nitro compounds.
2
behaviour towards hydrolysis, their use as elec-
trophiles has only been reported in a study on the
Indeed when various a-nitrohydrazones 1 were heated
with triethyl phosphite in toluene hydrazonophospho-
nates 2 were easily obtained in moderate yields (Scheme
13
preparation of sulfur heterocycles. In preliminary
experiments, these authors present several simple nucle-
ophilic additions (amine, thiol, cyanide) but no yields
were given to ascertain the efficiency of the latter
1, Table 1).
13
additions.
The reaction appears to be compatible with a variety of
functional groups. It is also interesting to note that the
reaction conditions are smooth enough to permit the
In view of the importance of nitro compounds in CꢀC
bond forming reactions (Michael, Henry reactions) and
the ease with which nitronates react with diazonium
salts, we believe that this approach offers a flexibility
not available by other routes.
*
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00208-3
El Ka?m
