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Rianelli, de Souza, and Ferreira
chemistry for the synthesis of a variety of complex molecules.[1] Base-
catalyzed transfer of the diazo moiety to a methylene group adjacent to one or
more electron-withdrawing groups is a well established and powerful
synthetic tool. The most known protocol involves the reaction of an alkyl or
arylsulfonyl azide with the methylene group[2,3] usually named diazo transfer
reaction (the reaction described here, a transfer of an intact diazo moiety to an
anionic site, is labelled as diazo transfer reaction to distinguish it from
diazotization, a process in which the N22N bond is created in the reaction[4]).
Several diazo transfer reagents based on these sulfonyl azides have been used
for preparing diazo compounds, (for the use of sulfonyl azides as diazo-
transfer reagents, see Ref.[5]) but some of then are potentially hazardous due to
their propensity for explosive decomposition under various reaction
conditions (e.g. tosylazide). In addition, several author have found that
formylation and benzoylation followed by diazo transfer are useful processes
to diazo synthesis.[6,7]
Base-catalyzed diazo transfer reactions are catalyzed mainly by alkyl
amines, but other solid bases such KF-alumina have been reported.[8]
Due to environmental demands, there has been considerable interest in
developing new catalysts for organic reactions based on inorganic solids,
which can be recovered and reused again.
In this regard, layered clay catalysts have received increasing attention in
many areas of organic chemistry, including organic synthesis,[9–12] mainly
due to their chemo- and regio-selective properties, availability, low cost, mild
reaction conditions, nonvolatility, noncorrosiveness, easy recovery, and
reuse.[13] Indeed, we recently reported a mild and efficient transesterification
process using three natural clays, which are very appropriate to be used in
reactions involving carbohydrate derivatives without their degradation.[14]
Herein, we wish to report our studies on the reaction of 1,3-dicarbonyl
compounds with mesyl azide to produce several 2-diazo-1,3-dicarbonyl
compounds by using three natural clays previously treated with sodium
hydroxide.[15] The advantage of mesyl azide is that it is easily separated from
the desired product upon washing the organic phase with 10% aqueous NaOH
solution. Several other variations conditions were examined with a view to
simplifying product isolation. To the best of our knowledge, there is no report
of diazo transfer reaction using clays as catalyst.
In the general reaction procedure an excess of clay (1.5 w/w) and mesyl
azide with an excess of 1.5 mmol was used for the 1,3-dicarbonyl compounds
(1a–h) in acetonitrile at room temperature (Sch. 1). The time of the
reaction varied from 3–72 hr (see Table 1) depending on the 1,3-dicarbonyl
compounds, but was less dependent of sulfonyl azide. The diazo compounds
were purified by column chromatography and identified by spectroscopic
methods. In some experiments the pure products (entries 8, 9, 10, 12, 13) were
Rianelli, Renata De S.
