LETTER
Selective Reduction of a,b-Unsaturated Carbonyl Compounds
Typical Reduction Procedure:
1955
1,3-Diphenyl-propan-1-ol or 1,3-diphenyl-prop-2-en-1-ol
was not detected from the reaction mixture. With DMF as
the reaction solvent, while lowering the reaction tempera-
ture, the yield of 2a decreased correspondingly (Table 1,
entries 10–12).
A 100 mL three-necked flask was charged with a,b-unsaturated car-
bonyl compound (2.5 mmol), selenium (0.5 mmol), H2O (2 mL) and
DMF (20 mL). Carbon monoxide was introduced and bubbled into
the reaction mixture with vigorous stirring at 90 °C for 2–4 h. The
reaction was monitored by TLC determination. After the reaction
was complete, CO bubbling was ceased and the resultant mixture
was stirred in air at ambient temperature for 30 min. To this mixture
20 mL water was added and extracted with Et2O (3 × 40 mL). The
organic phase was dried over anhyd MgSO4, filtered and evaporated
the volatiles under reduced pressure to afford the crude product.
Further purification by column chromatography on silica gel or re-
crystallization gave the pure product. All products were identified
by NMR and/or compared with the authentic samples.
Similar reactions were investigated and the results of re-
duction of various a,b-unsaturated carbonyl compounds
are shown in Table 2. During the reduction reaction, the
chloro-, fluoro-, and methoxy group were unaffected
(Table 2, entries 2–8). However, selective reduction of 8a
was not complete under the same reaction conditions to
give 8b in only 76%. Alkyl group instead of phenyl group
was investigated; the selective reaction still could take
place in high yield (Table 2, entry 9). The carbon-carbon
double bonds of 10a and 11a underwent reduction without
affecting the furyl- and pyridyl groups. At the same time,
1,5-diphenyl-1,4-pentadien-3-one and 1,5-diphenyl-2,4-
pentadien-1-one, which possess two conjugated carbon-
carbon bonds, were completely reduced to saturated car-
bonyl compounds (Table 2, entries 12 and 13). Unfortu-
nately, cinnamonitrile would not be reactive in the current
reducing system (Table 2, entry 14). When cinnamalde-
hyde was carried out under the similar conditions, side re-
actions took place to afford a complex mixture. In
addition, styrene and 1,3-diphenyl-2-en-1-ol also did not
react at all (Table 2, entries 15 and 16), which implies that
the isolated carbon-carbon double bonds are inactive to
this reaction.
3-Anthracen-9-yl-1-pyridin-2-yl-propan-1-one (13b):
Green solid: mp 91–93 °C. 1H NMR (400 MHz, CDCl3, 23 °C): d =
8.60 (d, 1 H, CH), 8.33–8.37 (m, 3 H, CH), 8.09 (d, 1 H, CH), 7.97
(s, 1 H, CH), 7.99 (s, 1 H, CH), 7.78 (d, 1 H, CH), 7.51–7.38 (m, 5
H, CH), 3.69 (t, 2 H, CH2), 4.05 (t, 2 H, CH2). 13C NMR (400 MHz,
CDCl3, 23 °C): d = 201.92 (C=O), 153.73, 149.61, 137.51, 134.20,
132.25, 130.23, 129.86, 127.81, 126.68, 126.35, 125.50, 124.94,
122.47, 40.08 (s, CH2), 23.21 (s, CH2).
References
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Although the detail of the mechanism has not been eluci-
dated, it is likely that the selective reduction of a,b-unsat-
urated carbonyl compounds a may involve formation of
intermediate Michael adduct C6,8 by the addition of in situ
formed H2Se to the carbon-carbon double bond of a,b-un-
saturated carbonyl compounds a. Further decomposion of
C give the product b and selenium, and then the catalyst
selenium proceeds to the next cycle (Figure 1).
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RCOCH2CH2R'
CO + H2O
Se
b
CO2
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H2Se
O
SeH
R'
R
RCOCH=CHR'
c
a
R = aryl / heteroaryl R' = alkyl / aryl / heteroaryl
Figure 1 Proposed pathway to saturated carbonyl compounds b
In summary, we have developed an efficient and conve-
nient method for the selective reduction of a,b-unsaturat-
ed carbonyl compounds with CO/H2O in the presence of a
catalytic amount of selenium under atmospheric pressure
in the absence of base.
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Synlett 2004, No. 11, 1953–1956 © Thieme Stuttgart · New York