B. Zhou, Y. Li et al.
Table 3. 2-(Methylthio)benzaldehyde substrate scope.[a]
(3c), were tolerated, providing the desired amides in good
to excellent yields. An aliphatic sulfonyl azide (2d) reacted
equally well, giving the corresponding product (3d) in good
yield. The substrate scope was further extended to a broad
variety of aryl azides. Phenyl azides substituted with elec-
tron-withdrawing or -donating groups at the para-, meta- or
ortho-position (2e–2q) were tolerated, with good to excel-
lent yields of 3e–3q obtained, irrespective of the electronic
nature or position of the substituents on the phenyl ring.
Moreover, the reaction showed good functional group com-
patibility. For example, phenyl azides with ester (2e and
2p), nitro (2j), nitrile (2l), ketone (2k), ethyl (2h), methoxy
(2n and 2q), and chloro (2g and 2m) groups were effective
coupling partners under the optimized conditions. Notably,
the tolerance of the ester, nitro, nitrile, ketone and chloro
groups offers the opportunity for further functionalization.
In addition, 2-naphthyl and 1-naphthyl azides (2r and 2s)
were readily converted to the corresponding products in
good yields. Particularly remarkable is the participation of
alkyl azides in this reaction, providing the corresponding n-
hexyl and phenylmethane amide products (3t and 3u, re-
spectively) in excellent yields. It was found that the elec-
tronic nature of the substituents on the quinoline ring did
not play a key role in this catalytic reaction. Aldehydes with
either electron-donating or -withdrawing groups (1v–1aa)
were readily converted to the corresponding products in
good yields.
[a] Reaction conditions:
4 (0.2 mmol), 2e (0.24 mmol), Rh catalyst
(0.024 mmol), and solvent (0.3 mL) at 1058C for 24 h under argon. Yield
of isolated product; yield in parentheses is based on recovered starting
material.
and mass spectrum analysis of 7 pointed to cyclometalation.
Encouraged by the successful amidation of 8-quinolinecar-
baldehyde, we turned our attention to additional substrates
bearing synthetically useful directing groups. To our delight,
Although a number examples of acyl–rhodium
plexes have been isolated by starting from RhI catalysts,[22]
reports of stable isolated organorhodium(III) intermedi-
ates from RhIII catalysts by deprotonation are still limit-
ed,[14c,16c,e,19a,23] particularly for acyl–rhodium
(III) intermedi-
ACHTUNGTRENN(UNG III) com-
AHCTUNGTRENNUNG
2-(meACHTUNGTRENNUNGthylthio)benzaldehyde also underwent direct amida-
tion with aryl azides (Table 3). Aromatic groups bearing
electron-donating or -withdraw-
ing groups were tolerated (5a–
d) and good yields were ob-
tained, despite the need for a
relatively high catalyst loading.
To obtain further insight into
ACHTUNGTRENNUNG
this catalytic transformation,
preliminary mechanistic experi-
ments were carried out. When
benzaldehyde (6a) was utilized
as the substrate, the corre-
sponding amide was not formed
(Scheme 2a). Therefore, the
presence of a directing group in
the substrate seems to be criti-
À
cal to the initial C H bond-
functionalization event. No
product formation was ob-
served in the presence of
[(Cp*RhCl2)2] or AgSbF6 alone
(Scheme 2b). The stable cyclo-
metalated RhIII complex 7 was
obtained upon treatment of 1a
with [(RhCp*Cl2)2] and NaOAc
(Scheme 2c). 1H and 13C NMR Scheme 2. Preliminary mechanistic studies.
&
4
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