Table 1. Optimization of the Reaction Conditions for the
Electrochemical Deoxygenation of Epoxides into Alkenes in
Aqueous Mediaa
anodeꢀ
yield
[%]b
entry
cathode
electrolyte
1
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
ZnꢀZn
PtꢀPt
KNO3 (0.1 M)/THF (8:1)
sat. aq NH4HCO3/THF (8:1)
sat. aq NH4Cl/THF (8:1)
sat. aq NH4Br/THF (8:1)
sat. aq NH4Br
30
2
50
3
70
4
95
Figure 1. X-ray diffraction spectrum of Zn deposits when the
electrolysis proceeded for 40 min.
5
83
6
sat. aq NH4Br/MeCN (8:1)
sat. aq NH4Br/MeOH (8:1)
sat. aq NH4Br/DMF (8:1)
sat. aq NH4Br/THF (8:1)
sat. aq NH4Br/THF (8:1)
sat. aq NH4Br/THF (8:1)
sat. aq NH4Br/THF (8:1)
sat. aq NH4Br/THF (8:1)
20
7
40
8
30
NH4Cl. Without THF, only an 83% yield of product was
collected (Table 1, entry 5). Other organic solvents (MeCN,
MeOH, and DMF) resulted in lower yields (Table 1,
entries 6ꢀ8). Subsequent experiments that focused on inves-
tigating the effect of current density (Table 1, entries 9
and 10) revealed that an increase or decrease of the current
resulted in a decrease in the yield. The use of other metals
(Pt, Al, and Sn) instead of Zn as electrodes gave much
lower yields (Table 1, entries 11ꢀ13).
9c
10d
11
12
13
81
77
trace
<10
<10
AlꢀAl
SnꢀSn
a Standard conditions: epoxide (0.5 mmol) in electrolyte (4.5 mL) was
electrolyzed at a constant current of 30 mA in a round-bottomed flask cell
equipped with a pair of zinc electrodes (1.5 cm2) at rt. b Determined by GC
by using an internal standard technique. c 15 mA. d 45 mA.
The scope and limitation ofthe Zn-mediated deoxygena-
tion reaction were explored next. As shown in Table 2,
both the aromatic and aliphatic epoxides can be utilized in
thismethodology. For the aromaticepoxides1a, 1b, and 1c
(Table 2, entries 1ꢀ3), alkenes can be preparedsmoothly in
good to excellent yields without any additives, while for
epoxides 1dꢀ1j (Table 2, entries 4ꢀ10), acetic acid was
added to promote the reaction and the dosage of the acid
varied on different epoxides.9 Z to E isomerization oc-
curred during the deoxygenation process of cis-stilbene
and only a 30% yield of the desired product was obtained.
It was observed thatammonium salts were morepromising
for this reaction (Table 1, entries 2ꢀ4), and NH4Br was
found to be superior (95% yield) to NH4HCO3 and
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