Aerobic Oxidation of Cyclic Amines to Lactams Catalyzed by Ceria-Supported Nanogold
13
a base. In that report, an N-phenyl pyrrolidinium intermedi-
ate was proposed (Scheme 3) [55].
N-methylmorpholin-3-one (72 % yield; Eq. 7). The mecha -
nism of the Au/CeO -catalyzed oxidation of N-methylated
2
Under the optimized conditions for the current Au/CeO 2-
catalyzed oxidation of N -methylpyrrolidine into N -methyl-
cyclic tertiary amines to their lactams (Eqs. 6, 7) is clearly
different from that for the oxidation of cyclic secondary
amines (Eq. 4), since the N-methyl substituent prevents oxi-
dative dehydrogenation to form the initial imine (Scheme
2).
2-pyrrolidone, it is conceivable that the N-methylpyrrolidinium
cation III is generated, which then undergoes addition of water
to produce the hemiaminal compound IV (Scheme 4 ). The
resulting hemiaminal could then undergo oxidation to give the
N-methylated lactam product. Although this is a plausible mech-
anism, none of the proposed intermediates have been detected
or identified. However, the high yield (97%, Table 2, entry 1)
of N-methyl-2-pyrrolidone when 110 equiv of water, relative to
N-methylpyrrolidine, is added to the reaction mixture, as com-
pared with only an 8 % yield of the lactam product when no
Acknowledgments This research was partially supported by the U.S.
Department of Energy, Office of Basic Energy Sciences, Division of
Chemical Sciences, Geosciences, and Biosciences through the Ames
Laboratory (Contract No. DE-AC02-07CH11358). The authors thank
Evonik Degussa Corporation for a generous donation of Aerosil 200.
water is added (Table 2, entry 5) suggests that nucleophilic addi- References
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3