2
J. Gossett, R. Srivastava / Tetrahedron Letters xxx (2017) xxx–xxx
Table 1
R
OH
OH
ZReO3
Optimization of solvents and alcohol reductants in the presence of NH4ReO4 catalysts.
+
Red
RedO + H2O
+
R
Entry
Solvent
Styrene (%)
Time (h)
1
2
3
4
5
6
7
8
Toluene
Toluene
84
99
42
17
32
19
75
10
4
5
Scheme 1. Metal-catalyzed DODH reaction.
1-Butanol
Benzene
THF
Acetonitrile
3-Octanol
Isopropanol
24
24
24
24
24
24
R
OH
OH
H2
RCH3
+
[Cp*Ru(CO)2]2
and
[RuCl2(R2SO)4]
R
R
Isolation
O
(R= methyl, tetramethylene)
NH4ReO4 (28 mg, 0.1 mmol,), (+)-diethyl tartrate (198 mg,
1 mmol), 2,4-dimethyl-3-pentanol (388 L), and anhydrous
l
Scheme 2. [Cp*Ru(CO)2]2-catalyzed hydrodeoxygenation and hydrocracking and
RuCl2(R2SO)4-catalyzed hydrogenolysis of diols and epoxides (R = methyl and
tetramethylene).
toluene (6 mL) were added to a thick-walled Ace glass reactor tube.
The reactor was placed in a heating mantle bath in the range of
165 °C for 24 h while stirring magnetically. The reaction mixture
was cooled and filtered over silica gel. Solvents were removed
using a rotary evaporator under reduced pressure. The product
was separated by column chromatography using ethyl acetate/
hexane eluent. Product yield was 73 mg, 42%.
alyst.13 [Cp⁄Ru(CO)2]2-catalyzed hydrodeoxygenation and hydroc-
racking and RuCl2(R2SO)4-catalyzed hydrogenolysis of diols and
epoxides has also been established by us (Scheme 2).14,15
The Nicholas group9c have used ammonium perrhente (APR)
catalyst for the DODH reaction of vicinal diols in the presence of
benzylic alcohol as reductant. In the pursuit to develop a new
DODH processes for the conversion of renewable cellulosic
biomass to valuable chemicals, we revisited the chemistry of
NH4ReO4 and developed a modified process, which requires a
Result and discussion
In pursuit to improve catalytic systems for DODH with better
efficiency, we prefer to use ionic ammonium perrhenate (APR,
NH4ReO4) as a suitable catalyst. APR is inexpensive, known for
DODH ability, greater hydrolytic stability compared to MeReO3,16
and its ionic nature. To test the viability of alcohols as a reductant
for the DODH of glycols, an exploratory reaction was carried out
with styrene diol, 2,4-dimethyl-3-pentanol and ammonium per-
rhenate (10 mol%) in anhydrous toluene, which produced styrene
quantitatively in 5 h at 165 °C. We began the survey with polar
and apolar solvents at various temperatures. The reaction per-
formed in anhydrous toluene produced an excellent yield of the
alkene whereas hydrated toluene and benzene resulted in a low
yield. The addition of 4 Å molecular sieve did not change the pro-
duct yield. The coordinating solvent such as THF and acetonitrile
also produced significantly lower yield of styrene, probably due
to the coordination of solvent to Re (Table 1). Our next step was
to screen the effect of temperature and we found that
160–165 °C was the optimum temperature for the model substrate
for optimum yield of alkene. We preferred secondary alcohol
(2,4-dimethyl-3-pentanol) over butanol-1,3-octanol, and iso-
propanol for DODH reductant because the higher yiled of alkenes
and the resulting ketone co-product could be easily separated from
the olefinic products in GC–MS.
small amount of
secondary
alcohol (4.28 Â 10À4 to
8.56 Â 10À4 mol) as a reductant compared to earlier reports9b,c
(Scheme 3). The reaction is clean and no byproducts except the oxi-
dized byproduct of 2,4-dimethyl-3-pentanol detected.
Experimental section
General information
All reagents were obtained commercially and used without fur-
ther purification. All solvents were ACS grade and were used
directly (unless otherwise described in the procedures). GC–MS
analyses were performed on an Agilent instrument using a Stabil-
wax capillary column. NMR spectra were recorded in CDCl3 with
tetramethylsilane (TMS) as the internal standard for 1H (Varian,
400 MHz) and for 13C (100 MHz) spectra.
Typical reaction procedure
Glycerol (0.3 mmol, 42 mg), NH4ReO4 (0.03 mmol, 8 mg), 2,4-
dimethyl-3-pentanol (0.43–0.86 mmol, 60–120 lL), and 1 mL
After optimizing reaction conditions (10 mol% APR, 0.3 mmol
glycol, 2,4-dimethyl-3-pentanol in anhydrous toluene, 140-
165 °C, 4–24 h), we determined that the representative glycols
were converted to the corresponding olefins in good to excellent
yields (Scheme 3, Table 2). All polyols subjected to catalytic
reaction are efficiently converted to the corresponding alkenes
regioselectivily as is shown in Table 2. The activated diol such as
1-phenyl-1, 2-ethanediol converted to styrene quantitatively in
5 h at 165 °C (run 1, Table 2). Long chain diols, tetradecanediol
anhydrous toluene were added to a thick-walled Ace glass reactor
tube. The Teflon seal was closed and the reactor was placed in a
heating mantle connected with a Digi Troll (Glas-Col) digital tem-
perature controller equipped with a thermocouple at 140-165 °C
for 5–48 h while stirring. After cooling to room temperature, the
solution was filtered to remove the precipitated NH4ReO4 and ana-
lyzed with GC–MS.
OH
O
R
R
NH4ReO4
Toluene
+
+
+ H2O
HO
OH
Scheme 3. Optimized DODH reaction scheme for glycol conversion to the corresponding olefins.