Chemistry Letters 2001
923
unsaturated ketone was selectively afforded in high yield
(Entries 15 and 16). The primary benzylic alcohols were effec-
tively converted into the corresponding arylaldehydes in high
yields (Entries 17 and 18).12 It should be pointed out here that
any by-product such as carboxylic acid was not detected. Each
reaction shown in Table 2 was monitored by TLC or GC analy-
sis to confirm that the reaction proceeded with high selectivity.
It is noted that the selective oxidation of various alcohols
to the corresponding ketones or aldehydes was effectively cat-
alyzed by the dioxoruthenium porphyrin complex employing
nitrous oxide (N2O) as a terminal oxidant. The reaction pro-
ceeded smoothly with secondary and benzylic alcohols to give
the corresponding ketones and aldehydes in high yields with
high selectivity. It is expected that nitrous oxide could be a
new terminal oxidant producing only N2 gas as a by-product to
provide a less wasteful process. A mechanistic study of the
present reaction and further application of this oxidation system
to other organic compounds are currently under investigation.
References and Notes
1
2
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E. I. Eager, II, “Nitrous Oxide/N2O,” Elsevier, New York (1985).
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4
For example: a) P. Ciambelli, A. Di Benedetto, E. Garufi, R. Pirone,
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N2O oxidation of benzene to phenol using V2O5 / SiO2 zeolite: M.
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T. Yamada, K. Hashimoto, Y. Kitaichi, K. Suzuki, and T. Ikeno,
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10 The optimum result using 1,2-dichloroethane was interesting for us
because fluorobenzene was a suitable solvent for the N2O epoxidation
of olefins (fluorobenzene, 63% yield; dichloroethane, 40% yield of
epoxide obtained, see Ref. 7). The reason for these observations is
not quite obvious, though nitrous oxide is soluble in 1,2-
dichloroethane the same as in other aromatic solvents.
11 Typical procedure is as follows: To 1,2-dichloroethane solution of
Ru(tmp)(O)2 (13 mg, 0.015 mmol) in autoclave, a solution of 1-(2-
naphthyl)ethanol (50 mg, 0.29 mmol) was added under a nitrous
oxide atmosphere. After the solvent amount was controlled to be 14
ml, reaction mixture was heated to 120 °C under 10 atm of N2O for
7.5 h. The produced ketone was obtained through silica-gel column
with hexane/ether (10 : 1) mixture as the eluant (94% yield).
12 When primary alcohols such as cinnamyl alcohol and 1-dodecanol
were subjected to the oxidation, the corresponding aldehydes were
obtained in 25–38% yields.