mild and selective, offering the possibility to perform the
transformation enantioselectively when feasible.
Table 1. Reaction Scope with Alcohols
As mentioned, Cu(I), Cu(II), and Rh(II) salts or com-
plexes are particularly efficient for the decomposition of
diazo derivatives. However, other metal sources are active,
and ruthenium complexes have become an interesting
alternative to these moieties,8 including CpRu derivatives.9
More specifically, [CpRu(PPh3)3Cl2] was shown by Del
Zotto and collaborators to promote N-H and S-H inser-
tions into ethyldiazoacetate or the transformation of tertiary
amines into ammonium ylides that underwent [1,2]-Stevens
shifts or sigmatropic rearrangements.10 Recently, our group
has shown that combinations of [CpRu(CH3CN)3][PF6] 1
and pyridine-imine/pyridine-oxazoline ligands (L1-L4) are
effective catalysts for the enantioselective decarboxylative
rearrangements of allylic β-ketoesters and carbonates.11 In
a different context, R-diazo-β-ketoesters 2 (Figure 1) were
reacted with cyclic ethers in the presence of dirhodium
complexes to yield original 16- to 18-membered macro-
cycles.12 Having access to complex 1, ligands L ,and reagents
2, it was therefore tempting to study their interactions, and
this in the context of electrophilic metal carbene chemistry.
The occurrence of reactivity was established using a classi-
cal reaction of diazo reagents, i.e., the insertion in the O-H
bond of alcohols.13 The results are summarized in Table 1.
Ethyl 2-diazo-3-acetoacetate 2a was dissolved in various
alcohols (R1OH) along with 1 (2.5 mol %) and 1,10-phenan-
throline L1 (2.5 mol %).14 After 45 min at 60 °C, full
conversion was achieved in all cases, and products of inser-
tion 3a-3d (R1 = Et, allyl, t-Bu, benzyl) were obtained in
good to excellent isolated yields (entries 1-4, 75-90%). No
entrya
1
L1
R1
Et
3
t (h)
conv (yield %)b,c
1
2
3
4
5
6
7
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
-
3a
3b
3c
3dd
3a
3a
3a
0.75
0.75
0.75
0.75
24
>97 (90)
>97 (78)
>97 (85)
>97 (75)
<3
allyl
t-Bu
Bn
Et
-
2.5
-
2.5
Et
1
>97
2.5
Et
1
>97
a Catalyst combination 1 (x mol %) and ligand L1 (x mol %), 60 °C,
[diazo] 0.5 M in R1OH. b Conversion determined by 1H NMR (400
MHz). c Isolated yield after column chromatography. d Purified by bulb
to bulb distillation.
Scheme 1. Reaction Scope with Nitriles
conversion of 2a was detected after 24 h at 60 °C in the
absence of 1 (entry 5). Reactions were also performed in
EtOH with and without L1. Whereas only 15 min was
necessary to reach full conversion with the ligand, 1 h was
required to reach the same result without it (entries 6 and 7).15
With this result in hand, other classical transformations
were investigated and condensation reactions with nitrile16,17
or carbonyl18,19 moieties in particular.
For instance, diazoacetoacetate 2a was dissolved in
nitriles R2CN in the presence of 1/L1 (2.5 mol %). After
1 h at 60 °C, full conversion of the starting material was
achieved and oxazoles 4a-4d (R2 = Me, Et, i-Pr, Ph) were
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