C O M M U N I C A T I O N S
Selective formation of the Z isomer is due to the strong H-bonding
between the amino proton and the oxygen atom of the carbonyl group.
The reactions of substituted 1-indanones with methoxyacetonitrile gave
the corresponding ketoenamines 3 (entry 2). Importantly, the C-H
activation of ketones can be extended to esters. Thus, the reaction of
2-benzofuranone with methoxyacetonitrile or phenylsulfonylnitrile gave
4a and 4b, respectively (entry 3). Note that the reaction tolerates
functional groups. Typically, the reaction of 4-hydroxybenzofran-2-
one with methoxyacetonitrile and 2-franacarbonitrile gave the amino-
nitrile 5a and 5b, respectively, in excellent yields (entry 4). Under
similar conditions, the direct addition of six-membered cyclic ketones
and esters to nitriles also proceeded efficiently to give the corresponding
enamines 6 and 7, respectively (entries 5 and 6). The effectiveness of
the reaction was demonstrated by the direct addition of less-reactive
amides to nitriles. Thus, the reaction of indol-2-one with methoxyac-
etonitrile gave (Z)-3-(1′-amino-2′-methoxy)ethylindene indol-2-one (8)
(entry 7). Moreover, the direct addition of cyclopentanone gave (Z)-
2-(1′-amino-2′-methoxy)ethylindenecyclopentanone (9) (entry 8). The
Re-catalyzed reaction of aliphatic ketones gave the corresponding
enaminones, which are useful for synthesis of heterocyclic compounds.
Typically, the Ru-catalyzed reaction of N-(2-cyanophenyl)-3-oxobu-
tanamide gave 3-acetyl-4-amino-2-(1H)quinolinone.
The direct catalytic reaction of ketones with nitriles under neutral
conditions has an advantage in view of atom economy over the
conventional Blaise reaction. In the latter reaction carbonyl
compounds have to be halogenated R to carbonyl, followed by a
Zn-promoted Reformatsky reaction with the nitrile. This two-step
process is not atom economical, and the products were obtained in
low overall yields.
The unique property of the Re catalyst 1 for the C-H activation
of carbonyl compounds in the presence of nitrile was proved by
the reaction of 2-indanone with ethyl cyanoacetate (eq 2). In the
presence of catalyst 1 the C-H activation of the ketone took place
to give ethyl (Z)-2-amino-2-(2′-indanoylidene)propanoate (2d)
(59%) exclusively, while in the presence of IrH(CO)(PPh3)3 catalyst
the C-H activation of the nitrile took place to give diethyl (Z)-3-
amino-2-cyano-2-pentanedione (10) (79%) exclusively.
Re2H8(PPh3)4 under heating conditions.10 However, we confirmed
that Re2H8(PPh3)4 is not effective to the present catalytic reactions;
i.e., 2a was obtained in only 7% yield. It may be reasonable to
assume that oxidative addition of the R-C-H bonds of carbonyl
compounds to a low-valent Re species affords an R-keto alkylrhe-
nium intermediate. Insertion of a nitrile to a Re-C bond of the
intermediate followed by reductive elimination and 1,3-H shift may
give the ketonenamine product. It is noted that addition of carbon-
bound rhenium enolate to a carbon-nitrogen triple bond of a
coordinated nitrile has been reported to form a rhenium imino
complex in a stoichiometric reaction.11
In conclusion, we have found a novel and efficient Re-catalyzed
reaction of carbonyl compounds with nitriles by chemoselective
R-C-H activation of carbonyl compounds and subsequent insertion
of nitriles. The reaction is highly useful and will provide scope for
finding new types of catalytic reactions for the synthesis of fine
chemicals.
Acknowledgment. This work was supported by the Research
for the Future Program of the Japan Society for the Promotion of
Science.
Supporting Information Available: Experimental details of the
preparation and characterization of the products. This material is
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An active Re catalyst may be a low-valent Re species
ReHm(PPh3)2 (m < 7) derived from losing hydrogen from
ReH7(PPh3)2.10 It is known that ReH7(PPh3)2 is converted to
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