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H. Alinezhad et al.
LETTER
Table 2 Comparison of the Results Obtained by ZrBDC with Other Reducing Agents for the Deoxygenation of Aldehydes and Ketones
ZrBDC
Other Reagentsa–d
Entry
Substrate
Time (h)
Yield (%)
Time (h)
Yield (%)
Time (h)
Yield (%)
1
2
3
4
5
P-CNC6H4CHO
p-NO2C6H4CHO
2-Adamantanone
Cinnamaldehyde
2-Undecanone
7
80
86
84
87
83
8
6
6
3
4
<5a
–
20
2
–
6
Tracea
82a
24b
78c
0c
7.4
7.3
8
98a
–
81a
3
36d
a NaBH3CN (reagent/substrate 4:1).8,
b NaBH3CN/ZnI2 (reagent/substrate 5:1).9,
c Bis(triphenylphosphine) copper(I) tetrahydroborate (reagent/substrate 1:1).11,
d NaBH3CN/ZnCl2 (reagent/substrate 1:1).10
completion of the reaction, the mixture was diluted with H2O (20
mL) and then extracted with n-hexane (3 × 30mL). After evapora-
tion of the solvent, the product was purified by column chromato-
graphy and eluted with hexane–EtOAC 20:1 (150 mL). Evaporation
of the solvent afforded almost pure alkane. The product was identi-
fied by comparison of its spectra (1H NMR, IR) and physical data
with authentic sample.
Selective and high yield of the reductive deoxygenation of
benzaldehydes with different substituted groups was per-
formed smoothly in this reducing system. We have ob-
served that functional groups such as nitro, cyano and
C=C bond remained intact during the progress of the reac-
tion (Table 1, entries 2–4, 16, 17). The effect of the nature
of the substituted groups on the aromatic rings of the car-
bonyl compounds is quite clear. Comparing substitutent
groups on the aromatic ring show that electron-releasing
groups such as NMe2 retard the rate of reaction in relation
to electron-withdrawing groups (Table 1, entries 2–5).
Furthermore, under the same reaction conditions, a,b-un-
saturated carbonyl compounds have been deoxygenated
without allylic rearrangement (Table 1, entries 16, 17).
Acknowledgment
Financial support of this work from the Research Council of
Mazandaran University gratefully acknowledged.
References
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In order to show the advantages and drawbacks of our
method, we have compared some of our results with those
reported in the literature in Table 2.
As indicated in Table 2, our method in most cases gives
higher yields of the corresponding hydrocarbons.
In conclusion, ZrBDC is a good substitute for NaBH4,
NaBH3CN, NaBH3CN/ZnI2 and NaBH3CN/ZnCl2 for the
preparation of alkanes from carbonyl compounds. More-
over, the mildness, ease of reaction work up, efficiency,
regioselectivity, high yields, and lack of requirement of an
inert atmosphere make this reagent a useful addition to the
category of reagents used for the reductive preparation of
alkanes.
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General Procedure for the Deoxygenation of Tosylhydrazones
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ZrBDC12 and tosylhydrazones13 used in this study were prepared
according to the literature procedures. All products are known com-
pounds and yields refer to isolated products.
A solution of the tosylhydrazone (1 mmol), ZrBDC (1 mmol) and
0.3 g of p-toluenesulfonic acid in 10 mL of a 1:1 mixture of DMF–
sulfolane was heated at 110 °C. Progress of the reaction was conve-
niently followed by TLC (eluent: n-hexane–EtOAC 4:1). After
Synlett 2005, No. 1, 170–172 © Thieme Stuttgart · New York