Synthesis of esters by in situ formation and trapping of diazoalkanes

Article abstract of DOI:10.1021/acs.joc.6b00408

A general method has been developed for the in situ formation and trapping of diazoalkanes by carboxylic acids to form esters. The method is applicable to a large variety of carboxylic acids using diazo compounds that are formed from the hydrazones of benzaldehydes and aryl ketones. In situ reaction monitoring with IR spectroscopy (ReactIR) was used to demonstrate that slow addition of the hydrazone to a mixture of oxidant and carboxylic acid avoids the buildup of the diazo compound. This method enables the safe preparation of esters from simple precursors without isolation of diazo compounds.

Full text of DOI:10.1021/acs.joc.6b00408

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Article
Synthesis of Esters by in situ Formation and Trapping of Diazoalkanes
Richard A. Squitieri, Galen P Shearn-Nance, Jason E Hein, and Jared T. Shaw
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00408 • Publication Date (Web): 18 May 2016
Downloaded from http://pubs.acs.org on June 4, 2016
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Synthesis of Esters by in situ Formation and Trapping of
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Diazoalkanes
Richard A. Squitieri1, Galen P. Shearn-Nance1, Jason E. Hein2, Jared T. Shaw*1
1Department of Chemistry, University of California, One Shields Ave, Davis, CA 95616
2Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
*jtshaw@ucdavis.edu
O
R2
O
R2
MnO2
NH2
HO
N2
R3
R1
O
R3
R1
N
R1=Ar
R2=Ar, alkyl, H
R3=Ar, alkyl
R2
via
R1
ABSTRACT: A general method has been developed for the in situ formation and trapping of
diazoalkanes by carboxylic acids to form esters. The method is applicable to a large variety of
carboxylic acids using diazo compounds that are formed from the hydrazones of benzaldehydes
and aryl ketones. In situ reaction monitoring with IR spectroscopy (ReactIR) was used to
demonstrate that slow addition of the hydrazone to a mixture of oxidant and carboxylic avoids
the buildup of the diazo compound. This method enables the safe preparation of esters from
simple precursors without isolation of diazo compounds.
Introduction:
Diazoalkanes are useful synthetic species that have a broad number of applications due to their
ylide reactivity and utility as carbene precursors; however, use of diazoalkanes is hampered by
their toxicity and poor thermal stability.1,2 Additionally, the difficulty and hazards associated
with isolation and storage of diazoalkanes greatly reduces their practicality. Diazoalkanes are
typically prepared from a diazo transfer reagent or the base-mediated cleavage of a tosyl
hydrazone.3 Diazoalkanes have also been synthesized via the oxidation of their corresponding
hydrazones with a variety of transition metals such as HgO, Ag2O, CrO2, Ni2O3, KMnO4-Al2O3,
MnO2, and Pb(OAc)4, as well as organic oxidants such as TsNIK, TEMPO, and DMSO/oxalyl
chloride (Swern conditions).4
In order to bypass the isolation, handling and/or storage of diazoalkanes, we are interested in
developing reactions where these species are consumed at rates that are competitive with their
formation in situ. Although MnO2 has been used for the preparation and isolation of diazo
compounds that were used to form esters, there is only one example of doing so in situ so as to
avoid handling potentially explosive reagents.5 Most reactions of diazoalkanes involve separate
steps for the formation and consumption of the species, often in a single pot.6 An early example
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of the formation and simultaneous consumption of a diazoalkane demonstrated that
benzophenone hydrazone could be oxidized and used in the esterification of carboxylic acids.7 In
2004 Myers and Furrow prepared esters from N-TBS hydrazones using (difluoroiodo)benzene
and 2-chloropyridine in a one-pot oxidation-esterification sequence.8 This transformation was
notable in that the formation of azines could be successfully avoided and the reaction works well
for diazoalkanes possessing α-hydrogens that might normally eliminate. The one liability in the
Myers method lies in the use of PhIF2, which is prepared fresh from concentrated HF.9 More
recently, our group reported a one-pot oxidation of hydrazones to diazoalkanes using MnO2 in
the presence of a rhodium(II) catalyst that enables concomitant C–H insertion reactions of the
transient carbene.10 Herein, we present a one-pot synthesis of esters by the rapid capture of
diazoalkane compounds formed in situ by the cheap and commercially available oxidant, MnO2.
In addition, we use in situ FTIR spectroscopy (reactIR) to demonstrate that these conditions
avoid the buildup of the diazoalkane species.
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Results and Discussion:
Table 1: Optimization conditions for the esterification reaction.
NH2
PhCO2H
8 equiv. MnO2
N
O
Ph
conditions
Ph
Ph
Ph
O
2
Ph
1
entry
hydrazone
equiv.
yield
(%)
solvent
additive
temp
(°C)
1
2
3
4
5
6
7
8
0.83
1.5
1.0
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
EtOAc
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
none
none
none
none
none
none
none
none
none
none
8 equiv. alumina
8 equiv. Na2CO3
8 equiv. K2HPO4
25
25
25
25
25
25
0
49
72
68
70
65
57
70
43
42
48
47
0
-5
9
-10
25
25
25
25
25
25
10a
11
12
13
14
15b
28
90
77
8 equiv. KH2PO4
8 equiv. KH2PO4
a 4 equiv. of MnO2.
b Hydrazone added dropwise to a solution of acid, buffer, and oxidant.
We first attempted to form ester 2 through the oxidation of hydrazone 1 with MnO2 followed
by capture with benzoic acid (Table 1). Benzophenone hydrazone 1 was allowed to stir for 5
minutes in MnO2, rapidly oxidizing to the diazo compound, evident by the formation of a dark
pink solution. The carboxylic acid was then added, rapidly consuming the diazolkane to release a
stream of nitrogen bubbles. Our initial result afforded the ester product in 49% yield, which was
improved to 72% by using an excess of the hydrazone (Table 1, entries 1-3). Two other polar
aprotic solvents, EtOAc and CH3CN were also screened, giving no increase in yield (Table 1,
entries 4-6). Attempts at reducing the temperature did not cause an increase of yield (Table 1,
entry 7) and sub-zero temperatures reduced the formation of the ester product (Table 1, 8 and 9).
Lowering the amount of oxidant to 4 equivalents also led to a significant reduction in yield
(Table 1, entry 10).
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Given the beneficial effect of alumina on the esterification reported by Curini,7 we explored the
use of several mildly basic reagents (Table 1, entries 11-14). Alumina offered no improvement in
the reaction (Table 1, entry 11). No product formation was observed in the presence of Na2CO3
(Table 1, entry 12).11 We attribute this result to the deprotonation of the carboxylic acid, which
prevents initial protonation of the diazoalkane. The use of less basic reagents was more effective.
Addition of K2HPO4 enabled the ester product to be formed in 28% yield (Table 1, entry 13),
whereas, when KH2PO4 was employed an increase in yield to 90% was observed (Table 1, entry
14). Dropwise addition of the hydrazone to the remainder of the reagents was also explored,
showing a minor depreciation of yield to 77% (Table 1, entry 15).
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Table 2. Substrate scope of acids for the esterification reaction.
A: MnO2, KH2PO4, CH2Cl2
then acid
(acid last)
NH2
N
1
O
O
Ph
OR
Ph
Ph
R
OH
R
O
Ph
B: Acid, KH2PO4, MnO2, then
hydrazone dropwise
(hydrazone last)
3a-j
Entry
R
Yield (%)
Method A
Yield (%)
Method B
Product
84
84
49
85
87
51a
86a
80
91
74
75
30
70
68
30a
82a
28
73
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
4-OCH3C6H4
4-CNC6H4
4-OHC6H4
E-C6H5CHCH
C6H5CH2CH2
(CH3)3C
3g
3h
3i
CH3
N-Boc(Val)
3-furyl
a No KH2PO4 was added for these entries.
Both of the conditions for esterification were applied to a range of carboxylic acids. Benzoic
acids containing electron withdrawing or electron donating groups in the para position were
found to work well (Table 2, entries 1-2). When an additional O-H insertion site was present
(Table 2, entry 3) the yield for both procedures dropped significantly. Cinnamic acid and
dihydrocinnamic acid worked in high yield (Table 2, entries 4 and 5). Acetic acid and pivalic
acid were able to add to convert to their respective esters without KH2PO4, however, in the
presence of the buffer the reaction did not proceed (Table 2, entries 6 and 7). N-Boc-protected
valine and 3-furanoic acid were converted to their corresponding esters in high yields (Table 2,
entries 8 and 9).
Table 3. Substrate scope of hydrazones for the esterification reaction.
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A: MnO2, KH2PO4, CH2Cl2
then acid
(acid last)
NH2
R2
N
O
O
R2
R1
R3
OH
R3
O
R1
OR
4a-g
5a-i
B: Acid, KH2PO4, MnO2, then
hydrazone dropwise
(hydrazone last)
Product R1
R2
R3
Yield (%) Yield (%)
Method A Method B
Entry
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2
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H
76
84
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97
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68
80
77
45
92
85
94
84
80
21
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
5b
5c
5d
5e
5f
H
4-OCH3C6H4
4-CNC6H4
2,4,6-(CH3)3C6H2
C6H5
H
H
CH2CH2CH3
CH3
C6H5
5g
5h
5i
alpha-tetralone
H
C6H5
c-C6H11
C6H5
c-C6H11
H
4-OCHC6H4
The substrate scope for different hydrazones was also explored (Table 3). The hydrazones
were, in some cases, contaminated with azine that formed during their synthesis. Azine has been
known to form from both diazo compounds as well as hydrazone.8,12 Benzyl ester formation
worked well with both benzyl hydrazone and p-methoxy benzyl (PMB) hydrazone (Table 3,
entry 2). Upon addition of the carboxylic acid the reaction evolved N2 for thirty seconds
indicating the reaction occurred rapidly. The addition of an electron withdrawing group caused a
decrease in yield (Table 3, entry 3). The more sterically demanding mesityl hydrazone was able
to react with benzoic acid in high yield but did not work with cyclohexane carboxylic acid (Table
3, entry 4). The esters formed from the hydrazones of α-tetralone, propanoic acid, and
acetophenone reacting with benzoic acid were all formed in high yields showing that the reaction
tolerates the presence of α-protons (Table 3, entries 5-7). Cyclohexane carboxylic acid gave poor
yield with diphenyl hydrazone, however worked well with both benzyl hydrazone and p-
methoxy benzyl hydrazone (Table 3, entries 8 and 9).
Conducting this reaction on larger scale poses hazards associated with large quantities of the
diazo compound. A method that involved the dropwise addition of the hydrazone to the rest of
the reagents would provide access to the ester products without buildup of the diazo compound.
We investigated whether changing the order of steps could mitigate any build-up of potentially
explosive compound. A suspension of the benzoic acid, MnO2, and K2HPO4 in CH2Cl2, followed
by the dropwise addition of hydrazone furnished the ester product in 77% yield (Table 1, entry
15).
In order to prove that we were able to access ester 1 without diazo buildup, we monitored
reaction progress with in situ IR spectroscopy (aka ReactIR) using both methods of addition.
Although there is at least one case where ReactIR has been used to monitor reactions that employ
a diazo-alkane, there are no examples that examine the formation and consumption of these
species.13 We found that when the hydrazone was added first that there was a large diazo peak at
2050 cm-1 and the reaction went to completion in 25 minutes (Figure 1). Interestingly, when
method B was employed there was no peak corresponding to diazo, however, the reaction took
almost 18 hours to go to completion, indicating that the rate of diazo formation was slowed
(Figure 2).
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Figure 1. ReactIR data for the "acid last" esterification conditions (Table 1) showing buildup of
diphenyldiazomethane (blue), consumption of benzoic acid (red), and appearance of
diphenylmethyl benzoate (2, green). Note: the acid carbonyl stretch does not return to baseline
because of interference from the ester stretch that grows in.
Figure 2. ReactIR data for the "hydrazone last" esterification conditions (Table 1) showing
consumption of benzoic acid (red) and appearance of diphenylmethyl benzoate (2, green). Note:
MnO2 was added at 10 minutes. The benzophenone hydrazone was added starting at 19 minutes,
dropwise, for 10 minutes.
One final order of addition was investigated by ReactIR. Benzoic acid and benzophenone
hydrazone were allowed to stir in solvent and buffer followed by the addition of MnO2 last
(Figure 3). This sequence of addition showed similar initial kinetics as was observed when
hydrazone was added last. This indicates that if the hydrazone and acid are allowed to
equilibrate, then the oxidation reaction is slow and that dropwise addition of the hydrazone is not
necessary to prevent buildup of diphenyldiazomethane. This reaction was conducted on
preparatory scale (Eqs 1 and 2) and similar yields to the other two sets of conditions were
observed.
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Figure 3. ReactIR data for the "MnO2" esterification conditions (See Table 1) consumption of
benzoic acid (red), and appearance of diphenylmethyl benzoate (2, green). Note: MnO2 was
added at 14 minutes to a solution of benzophenone hydrazone and benzoic acid.
1) PhCO2H
NH2
CH3
O
N
CH3
KH2PO4
2) MnO2
(1)
O
Ph
H
CH2Cl2, 93%
H3C
CH3
H3C
CH3
4f
5f
1) PhCH2CH2CO2H
KH2PO4
2) MnO2
NH2
N
1
Ph
O
CH2Cl2, 77%
(2)
Ph
Ph
Ph
O
Ph
3f
These results paired with the observation that mildly basic buffer can be beneficial to the
reaction suggest that the rate of diazo compound formation and consumption is sensitive to pH
(Equation 3). When the acid is added last, the diazocompound is formed quickly and then
consumed quickly. With the acid present, it is likely that the hydrazone NH2 is at least partially
protonated and, as a result, slow to oxidize. Furthermore, partial deprotonation of the carboxylic
acid prevents it from reacting with the diazo compound, i.e. by preventing protonation on carbon
to form the requisite diazonium species. Although the process is slower and the yields slightly
lower (10-20%) on average, the "hydrazone last" procedure is still a useful method of
esterification that minimizes the buildup of the diazo compound.
NH2
NH3
H+
N2
N
N
N2
MnO2
MnO2
Slow
(3)
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Fast
Conclusion:
In summary a new method has been developed for the facile esterification of acids by in situ
oxidation of hydrazones and trapping of the produced diazo compound. The in situ production of
diazo compound followed by rapid trapping with acid allows for safe scalability of this reaction
following the dropwise protocol, reducing diazo build up.
Experimental Section:
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General Comments. Chemicals were purchased and used without further purification unless
otherwise specified. Solvents were purified and dried on a solvent system or purchased
anhydrous where required. Reactions were monitored by TLC (Merck), and detected by
examination under UV light (254 nm and 365 nm). Flash column chromatography was
performed using silica gel [230−400 mesh (40−63 µm)]. Extracts were concentrated in vacuo
using both a rotary evaporator (bath temperatures up to 40 °C) at a pressure of either 15 mmHg
(diaphragm pump) or 0.1 mmHg (oil pump), as appropriate, and a high vacuum line at room
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temperature. H and C spectra were measured in CDCl3 at 300, 400, or 600 MHz, and 101 or
151 MHz respectively. For HRMS analysis, samples were analyzed by flow-injection analysis
LTQ Orbitrap XL operated in the centroided mode. Samples were injected into a mixture of 50%
CH3OH and 0.1% formic acid/H2O at a flow of 200 ul/min. Source parameters were 5kV spray
voltage, capillary temperature of 275 °C and sheath gas setting of 20. Spectral data were
acquired at a resolution setting of 100,000 FWHM with the lockmass feature which typically
results in a mass accuracy <2ppm.
General procedure for hydrazone formation. To a solution of anhydrous hydrazine (1.1 mL,
36 mmol) in anhydrous EtOH (25.0 mL) was added the respective ketone (5.0 mmol) dropwise
or as a solution in EtOH. After the mixture was allowed to stir overnight it was poured into water
(50 mL) and extracted with CH2Cl2 (3 x 75 mL). The combined organic layers were dried over
Na2SO4, filtered, and concentrated in vacuo (0-10 °C). The hydrazones were taken onto the ester
formation reaction without further purification.
General procedure A for ester formation (acid last). To a solution of hydrazone (1.2 equiv.)
in anhydrous CH2Cl2 (0.1 M) was added MnO2 (8 equiv), KH2PO4 (8 equiv.), and finally the
respective acid (1 equiv.). After 3-16 h the reaction mixture was filtered through a plug of silica
and washed with EtOAc. The resultant filtrate was concentrated in vacuo and purified by flash
column chromatography to yield the desired ester.
General procedure B for ester formation (dropwise addition of hydrazone). To a solution of
acid (1 equiv.) MnO2 (8 equiv.), and KH2PO4 (8 equiv.) in CH2Cl2 (0.1 M) was added dropwise
over 5 minutes to a solution of hydrazone (1.2 mmol) in of CH2Cl2 (1.0 mL). After 12-16 h the
reaction mixture was filtered through a plug of silica and washed with EtOAc. The resultant
filtrate was concentrated in vacuo and purified by flash column chromatography to yield the
desired ester.
benzophenone hydrazone (1). Hydrazone 1 was recrystallized in CH3OH from the
commercially available material.
benzylidenehydrazine (4a). Hydrazone 4a (977 mg, 80%) was synthesized according to the
general hydrazone procedure using benzaldehyde (1.0 mL, 10 mmol), hydrazine (1.1 mL, 36
mmol), and EtOH (25.0 mL). 1H NMR (600 MHz, CDCl3) δ 7.75 (s, 1H), 7.54 (d, J = 8.2 Hz,
2H), 7.35 (t, J = 7.8 Hz, 2H), 7.32-7.27 (m, 1H), 5.53 (s, 2H). Proton NMR data of the crude
material was consistent with the reported literature values.14
(4-methoxybenzylidene)hydrazine (4b). Hydrazone 4b was synthesized according to the
general hydrazone procedure using p-anisaldehyde (0.30 mL, 2.5 mmol), hydrazine (0.55 mL, 18
1
mmol), and EtOH (12.5 mL). H NMR (600 MHz, CDCl3) δ 7.71 (s, 1H), 7.48 (d, J = 8.8 Hz,
2H), 6.88 (d, J = 8.8 Hz, 2H), 5.40 (s, 2H), 3.81 (s, 3H). Proton NMR data of the crude material
was consistent with the reported literature values.14
4-(hydrazonomethyl)benzonitrile (4c). Hydrazone 4c was synthesized according to the general
hydrazone procedure using p-cyanobenzaldehyde (330 mg, 10 mmol), hydrazine (1.3 mL, 43
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mmol), and EtOH (25.0 mL). 1H NMR (400 MHz, CDCl3) δ 7.70 (s, 1H), 7.61 (s, 4H), 5.87 (s,
2H). Proton NMR data of the crude material was consistent with the reported literature values.17
(E)-(2,4,6-trimethylbenzylidene)hydrazine (4d). Hydrazone 4d was synthesized according to
the general hydrazone procedure using mesitylaldehyde (0.74 mL, 5.0 mmol), hydrazine (1.1
mL, 36 mmol), and EtOH (25.0 mL). 1H NMR (400 MHz, CDCl3) δ 8.02 (s, 1H), 6.84 (s, 2H),
5.47 (s, 2H), 2.37 (s, 6H), 2.26 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 13C NMR (101 MHz,
CDCl3) δ 143.4, 137.9, 137.2, 129.6, 21.3.; m.p. 85-89 °C IR (neat): νmax 3365, 2914, 1611, 1380,
1030 cm-1; AMM (ESI) m/z calcd for C10H15O2N2Na+ [M + H]+ 163.1230, found 163.1227.
(3,4-dihydronaphthalen-1(2H)-ylidene)hydrazine (4e). Hydrazone 4e (645 mg, 87%) was
synthesized according to the general hydrazone procedure using propiophenone (0.66 mL, 5.0
mmol), hydrazine (1.1 mL, 36 mmol), and EtOH (25.0 mL). 1H NMR (600 MHz, CDCl3) δ 7.65
(d, J = 7.2 Hz, 2H), 7.36 (t, J = 7.6 Hz, 2H), 7.30 (t, J = 7.3 Hz, 1H), 5.42 (s, 2H), 2.65 (q, J =
7.7 Hz, 2H), 1.18 (t, J = 7.7 Hz, 3H). Proton NMR data of the crude material was consistent with
the reported literature values.16
(1-phenylethylidene)hydrazine (4f). Hydrazone 4f (251 mg, 37%) was synthesized according to
the general hydrazone procedure using acetophenone (0.58 mL, 5.0 mmol), hydrazine (1.1 mL,
36 mmol), and EtOH (25.0 mL). 1H NMR (600 MHz, CDCl3) δ 7.65 (d, J = 7.7 Hz, 2H), 7.36 (t,
J = 7.6 Hz, 2H), 7.30 (t, J = 7.3 Hz, 1H), 5.35 (s, 2H), 2.14 (s, 3H). Proton NMR data of the
crude material was consistent with the reported literature values.15
3,4-dihydronaphthalen-1(2H)-ylidene)hydrazine (4g). Hydrazone 4g (801 mg, 93%) was
synthesized according to the general hydrazone procedure using α-tetralone (1.0 mL, 5.0 mmol),
hydrazine (1.1 mL, 36 mmol), and EtOH (25.0 mL). 1H NMR (600 MHz, CDCl3) δ 7.95-7.94 (m,
1H), 7.21-7.18 (m, 2H), 7.12-7.10 (m, 1H), 5.30 (s, 2H), 2.73 (t, J = 6.3, 2H), 2.49 (t, J = 6.6 Hz,
2H), 1.96-1.92 (m, 2H). Proton NMR data of the crude material was consistent with the reported
literature values.15
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benzhydryl benzoate (2). Ester 2 was synthesized according to the general ester formation
procedure A using MnO2 (253 mg, 2.90 mmol), KH2PO4 (395 mg, 2.90 mmol), hydrazone 1 (86
mg, 0.44 mmol), benzoic acid (44 mg, 0.36 mmol), and CH2Cl2 (3.6 mL). The crude product was
purified by flash column chromatography (40:60 toluene/hexanes) affording ester 2 (92 mg,
90%) as a white solid. Procedure B using MnO2 (291 mg, 3.34 mmol), KH2PO4 (455 mg, 3.34
mmol), hydrazone 1 (98 mg, 0.50 mmol), benzoic acid (51 mg, 0.42 mmol), and CH2Cl2 (4.2
mL) followed by flash column chromatography as above afforded ester 2 (93 mg, 77%) as a
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white solid. H NMR (600 MHz, CDCl3) δ 8.20 (d, J = 7.6 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1H),
7.49 (dd, J = 7.9, 2.9 Hz, 6H), 7.40 (t, J = 7.5 Hz, 4H), 7.33 (t, J = 7.3 Hz, 2H), 7.18 (s, 1H).
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Proton NMR data of the crude material was consistent with the reported literature values.
benzhydryl 4-methoxybenzoate (3a). Ester 3a was synthesized according to the general ester
formation procedure A using MnO2 (256 mg, 2.94 mmol), KH2PO4 (396 mg, 2.91 mmol),
hydrazone 1 (87 mg, 0.44 mmol), p-methoxybenzoic acid (55 mg, 0.36 mmol), and CH2Cl2 (3.7
mL). The crude product was purified by flash column chromatography (50:50 toluene/hexanes)
affording ester 3a (98 mg, 84%) as a white solid. Procedure B using MnO2 (769 mg, 8.82 mmol),
KH2PO4 (1200 mg, 8.82 mmol), hydrazone 1 (262 mg, 1.33 mmol), p-methoxybenzoic acid (166
mg, 1.09 mmol), and CH2Cl2 (11.0 mL) followed by flash column chromatography as above
afforded ester 3a (256 mg, 74%) as a white solid. 1H NMR (600 MHz, CDCl3) δ 8.10 (d, J = 8.5
Hz, 2H), 7.42 (d, J = 7.6 Hz, 4H), 7.33 (t, J = 7.6 Hz, 4H), 7.26 (t, J = 7.4 Hz, 2H), 7.10 (s, 1H),
6.91 (d, J = 8.5 Hz, 2H), 3.80 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 165.4, 163.7, 140.6, 131.9,
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128.7, 128.0, 127.2, 122.7, 113.8, 77.2, 55.5; m.p. 95.7-99.1 °C IR (neat): νmax 2846, 1690, 1583,
1255 cm-1; AMM (ESI) m/z calcd for C21H18O3Na+ [M + Na]+ 341.1153, found 341.1147.
benzhydryl 4-cyanobenzoate (3b). Ester 3b was synthesized according to the general ester
formation procedure A using MnO2 (236 mg, 2.71 mmol), KH2PO4 (369 mg, 2.71 mmol),
hydrazone 1 (80 mg, 0.41 mmol), p-cyanobenzoic acid (50 mg, 0.34 mmol), and CH2Cl2 (3.4
mL). The crude product was purified by flash column chromatography (8:92 EtOAc/hexanes)
affording ester 3b (89 mg, 84%) as a white solid. Procedure B using MnO2 (253 mg, 2.91 mmol),
KH2PO4 (400 mg, 2.94 mmol), hydrazone 1 (87 mg, 0.44 mmol), p-cyanobenzoic acid (54 mg,
0.37 mmol), and CH2Cl2 (3.7 mL) followed by flash column chromatography as above afforded
ester 3b (87 mg, 75%) as a white solid. 1H NMR (600 MHz, CDCl3) δ 8.24 (d, J = 8.4 Hz, 2H),
7.76 (d, J = 8.4 Hz, 2H), 7.42 (s, 4H), 7.38 (t, J = 7.5 Hz, 4H), 7.35-7.29 (t, J = 7.3 , 2H), 7.14 (s,
1H); 13C NMR (151 MHz, CDCl3) δ 164.2, 139.8, 134.2, 132.5, 130.5, 128.9, 128.5, 127.3,
118.1, 116.8, 78.6; m.p. 87-88 °C; IR (neat): νmax 2230, 1717, 1258 cm-1; AMM (ESI) m/z calcd
for C21H15O2NNa+ [M + Na]+ 336.1000, found 336.1008..
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benzhydryl 4-hydroxybenzoate (3c). Ester 3c was synthesized according to the general ester
formation procedure A using MnO2 (244 mg, 2.81 mmol), KH2PO4 (382 mg, 2.81 mmol),
hydrazone 1 (83 mg, 0.42 mmol), p-hydroxybenzoic acid (48 mg, 0.35 mmol), and CH2Cl2 (3.5
mL). The crude product was purified by flash column chromatography (30:70 EtOAc/hexanes)
affording ester 3c (51 mg, 49%) as an amorphous solid. Procedure B using MnO2 (276 mg, 3.17
mmol), KH2PO4 (432 mg, 3.17 mmol), hydrazone 1 (94 mg, 0.48 mmol), p-hydroxybenzoic acid
(55 mg, 0.40 mmol), and CH2Cl2 (4.0 mL) followed by flash column as above afforded ester 3c
(37 mg, 30%) as an amorphous solid. 1H NMR (600 MHz, CDCl3) δ 8.04 (d, J = 9.0 Hz, 2H),
7.43 (d, J = 7.2 Hz, 4H), 7.34 (t, J = 7.7 Hz, 4H), 7.28 (t, J = 7.2 Hz 2H), 7.08 (s, 1H), 6.85 (d, J
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= 9.0 Hz, 2H), 5.55 (s, 1H); C NMR (151 MHz, CDCl3) δ 166.2, 160.8, 140.4, 132.4, 128.8,
128.2, 127.3, 122.3 115.6, 77.7; IR (neat): νmax 3311, 1725, 1165 cm-1; AMM (ESI) m/z calcd for
C20H16O3Na+ [M + Na]+ 327.0997, found 327.0993.
benzhydryl cinnamate (3d). Ester 3d was synthesized according to the general ester formation
procedure A using MnO2 (274 mg, 3.15 mmol), KH2PO4 (410 mg, 3.01 mmol), hydrazone 1 (88
mg, 0.45 mmol), trans-cinnamic acid (56 mg, 0.38 mmol), and CH2Cl2 (3.8 mL). The crude
product was purified by flash column chromatography (30:70 to 50:50 toluene/hexanes)
affording ester 3d (100 mg, 85%) as a white solid. Procedure B using MnO2 (267 mg, 3.07
mmol), KH2PO4 (413 mg, 3.03 mmol), hydrazone 1 (89 mg, 0.45 mmol), trans-cinnamic acid (56
mg, 0.38 mmol), and CH2Cl2 (3.8 mL) followed by flash column chromatography as above
afforded ester 3d (83 mg, 70%) as a white solid. 1H NMR (600 MHz, CDCl3) δ 7.82 (d, J = 15.9
Hz, 1H), 7.57 (m, 2H), 7.36-7.33 (m, 11H), 7.27 (m, 2H), 7.09 (s, 1H), 6.62 (d, J = 16.0 Hz, 1H).
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Proton NMR data of the product was consistent with the reported literature values.
benzhydryl 3-phenylpropanoate (3e). Ester 3e was synthesized according to the general ester
formation procedure A using MnO2 (261 mg, 3.00 mmol), KH2PO4 (406 mg, 2.98 mmol),
hydrazone 1 (86 mg, 0.44 mmol), phenylpropanoic acid (58 mg, 0.38 mmol), and CH2Cl2 (3.8
mL). The crude product was purified by flash column chromatography (50:50 toluene/hexanes)
affording ester 3e (106 mg, 87%) as a white solid. Procedure B using MnO2 (249 mg, 2.86
mmol), KH2PO4 (398 mg, 2.93 mmol), hydrazone 1 (90 mg, 0.46 mmol), phenylpropanoic acid
(56 mg, 0.38 mmol), and CH2Cl2 (3.8 mL) followed by flash column chromatography as above
afforded ester 3e (81 mg, 68%) as a white solid. Ester 3e was also synthesized by a third method,
MnO2 last. MnO2 (901 mg, 10.4 mmol) was added to a suspension of hydrocinnamic acid, (122
mg, 1.24 mmol), KH2PO4 (1350 mg, 9.92 mmol), and hydrazone 1 (292 mg, 1.49 mmol) in
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CH2Cl2 (12 mL). The crude product was filtered through silica and purified by flash column
chromatography (50:50 toluene/hexanes) affording ester 3e (199 mg, 77%) as a white solid. H
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NMR (600 MHz, CDCl3) δ 7.33 – 7.21 (m, 12H), 7.20 – 7.13 (m, 3H), 6.88 (s, 1H), 2.97 (t, J =
7.8 Hz, 2H), 2.74 (t, J = 7.8 Hz, 2H). Proton NMR data of the product was consistent with the
reported literature values.
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benzhydryl pivalate (3f). Ester 3f was synthesized according to the modified general ester
formation procedure A using MnO2 (1.75 g, 20.0 mmol), hydrazone 1 (589 mg, 3.0 mmol),
pivalic acid (267 mg, 2.50 mmol), and CH2Cl2 (25.0 mL). The crude product was purified by
flash column chromatography (20:80 CH2Cl2/hexanes) affording ester 3f (359 mg, 51 %) as a
white solid. Procedure B using MnO2 (1.72 g, 19.3 mmol), hydrazone 1 (582 mg, 2.97 mmol),
pivalic acid (252 mg, 2.47 mmol), and CH2Cl2 (24.7 mL) followed by flash column
chromatography as above afforded ester 3f (199 mg, 30%) as a white solid. 1H NMR (600 MHz,
CDCl3) δ 7.35-7.29 (m, 8H), 7.27-7.23 (m, 2H), 6.82 (s, 1H), 1.25 (s, 9H). Proton NMR data of
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the product was consistent with the reported literature values.
benzhydryl acetate (3g). Ester 3g was synthesized according to the modified general ester
formation procedure A using MnO2 (306 mg, 3.52 mmol), hydrazone 1 (103 mg, 0.530 mmol),
acetic acid (28 uL, 0.42 mmol), and CH2Cl2 (4.2 mL). The crude product was purified by flash
column chromatography (4:96 EtOAc/hexanes) affording ester 3g (82 mg, 86%) as a white solid.
Procedure B using MnO2 (306 mg, 3.52 mmol), hydrazone 1 (103 mg, 0.530 mmol), acetic acid
(28 uL, 0.42 mmol), and CH2Cl2 (4.2 mL) followed by flash column chromatography as above
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afforded ester 3g (81 mg, 82%) as a white solid. H NMR (300 MHz, CDCl3) δ 7.39-7.35 (m,
8H), 7.32-7.30 (m, 2H), 6.88 (s, 1H), 2.15 (s, 3H). Proton NMR data of the product was
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consistent with the reported literature values.
benzhydryl (tert-butoxycarbonyl)valinate (3h). Ester 3h was synthesized according to the
general ester formation procedure A using MnO2 (256 mg, 2.94 mmol), KH2PO4 (400 mg, 2.94
mmol), hydrazone 1 (87 mg, 0.44 mmol), Boc-val-OH (80 mg, 0.37 mmol), and CH2Cl2 (3.7
mL). The crude product was purified by flash column chromatography (10:90 EtOAc/hexanes)
affording ester 3h (113 mg, 80%) as a white solid. Procedure B using MnO2 (256 mg, 2.94
mmol), KH2PO4 (409 mg, 2.94 mmol), hydrazone 1 (87 mg, 0.44 mmol), Boc-val-OH (80 mg,
0.37 mmol), and CH2Cl2 (3.7 mL) followed by flash column chromatography as above afforded
ester 3h (41 mg, 28%) as a white solid. 1H NMR (600 MHz, CDCl3) δ 7.34-7.32 (m, 8H), 7.29-
7.27 (m, 2H), 6.90 (s, 1H), 5.02 (d, J = 9.3 Hz, 1H), 4.36 (dd, J = 9.1, 4.5 Hz, 1H), 2.22-2.19 (m,
1H), 1.43 (s, 9H), 0.92 (d, J = 6.9 Hz, 3H), 0.76 (d, J = 6.9 Hz, 3H); 13C NMR (151 MHz,
CDCl3) δ 171.5, 155.7, 139.7, 128.5, 128.1, 128.0, 127.3, 127.0, 79.7, 77.8, 58.5, 31.3, 28.3,
19.1, 17.2; IR (neat): νmax 3378, 1732, 1705, 1490, 1260 cm-1; m.p. 110-112 °C; AMM (ESI) m/z
calcd for C23H29O4NNa+ [M + Na]+ 406.1994, found 406.1998.
benzhydryl furan-3-carboxylate (3i). Ester 3i was synthesized according to the general ester
formation procedure A using MnO2 (103 mg, 1.19 mmol), KH2PO4 (162 mg, 1.19 mmol),
hydrazone 1 (35 mg, 0.18 mmol), furanoic acid (17 mg, 0.15 mmol), and CH2Cl2 (1.5 mL). The
crude product was purified by flash column chromatography (10:90 EtOAc/hexanes) affording
ester 3i (38 mg, 91%) as a white solid. Procedure B using MnO2 (181 mg, 2.08 mmol), KH2PO4
(283 mg, 2.08 mmol), hydrazone 1 (61 mg, 0.31 mmol), furanoic acid (29 mg, 0.26 mmol), and
CH2Cl2 (2.6 mL) followed by flash column chromatography as above afforded ester 3i (53 mg,
73%) as a white solid.1H NMR (600 MHz, CDCl3) δ 8.12 (s, 1H), 7.45 (s, 1H), 7.40 (d, J = 7.3
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Hz, 4H), 7.36 (t, J = 7.5 Hz, 4H), 7.30 (t, J = 7.2 Hz, 2H), 7.07 (s, 1H), 6.82 (s, 1H); C NMR
(151 MHz, CDCl3) δ 162.3, 148.2, 144.0, 140.3, 128.8, 128.2, 127.3, 119.6, 110.1, 77.1; IR
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(neat): νmax 1710, 1299, 1136 cm-1; m.p. 98-100 °C; AMM (ESI) m/z calcd for C18H14O3Na+ [M
+ Na]+ 301.0841, found 301.0838.
benzyl benzoate (5a). Ester 5a was synthesized according to the general ester formation
procedure A using MnO2 (225 mg, 2.59 mmol), KH2PO4 (353 mg, 2.59 mmol), hydrazone 4a (47
mg, 0.39 mmol), benzoic acid (39 mg, 0.32 mmol), and CH2Cl2 (3.2 mL). The crude product was
purified by flash column chromatography (7:93 EtOAc/hexanes) affording ester 5a (52 mg,
76%) as a yellow oil. Procedure B using MnO2 (234 mg, 2.69 mmol), KH2PO4 (366 mg, 2.69
mmol), hydrazone 4a (48 mg, 0.40 mmol), benzoic acid (41 mg, 0.34 mmol), and CH2Cl2 (3.4
mL) followed by flash column chromatography as above afforded ester 5a (71 mg, 80 %) as a
yellow oil.1H NMR (600 MHz, CDCl3) δ 8.11 (d, J = 7.9 Hz, 2H), 7.57 (t, J = 7.4 Hz, 1H), 7.44-
7.40 (m, 4H), 7.41 (t, J = 7.6 Hz, 2H), 7.36 (t, J = 7.3 Hz, 1H), 5.39 (s, 2H). Proton NMR data of
the product was consistent with the reported literature values.18
4-methoxybenzyl benzoate (5b). Ester 5b was synthesized according to the general ester
formation procedure A using MnO2 (227 mg, 2.61 mmol), KH2PO4 (355 mg, 2.61 mmol),
hydrazone 4b (59 mg, 0.39 mmol), benzoic acid (40 mg, 0.33 mmol), and CH2Cl2 (3.3 mL). The
crude product was purified by flash column chromatography (7:93 EtOAc/hexanes) affording
ester 5b (66 mg, 84%) as a clear oil. Procedure B using MnO2 (232 mg, 2.66 mmol), KH2PO4
(363 mg, 2.66 mmol), hydrazone 4b (60 mg, 0.40 mmol), benzoic acid (41 mg, 0.33 mmol), and
CH2Cl2 (3.3 mL) followed by flash column chromatography as above afforded ester 5b (63 mg,
77%) as a clear oil.1H NMR (600 MHz, CDCl3) δ 8.08 (d, J = 8.7 Hz, 2H), 7.55 (t, J = 7.4 Hz,
1H), 7.47-7.36 (m, 4H), 6.93 (d, J = 8.7 Hz, 2H), 5.31 (s, 2H), 3.82 (s, 3H). Proton NMR data of
the product was consistent with the reported literature values.22
4-cyanobenzyl benzoate (5c). Ester 5c was synthesized according to the general ester formation
procedure A using MnO2 (216 mg, 2.48 mmol), KH2PO4 (338 mg, 2.48 mmol), hydrazone 4c (54
mg, 0.37 mmol), benzoic acid (37 mg, 0.30 mmol), and CH2Cl2 (3.0 mL). The crude product was
purified by flash column chromatography (10:90 EtOAc/hexanes) affording ester 5c (37 mg,
52%) as a white solid. Procedure B using MnO2 (207 mg, 2.38 mmol), KH2PO4 (324 mg, 2.38
mmol), hydrazone 4c (52 mg, 0.36 mmol), benzoic acid (36 mg, 0.30 mmol), and CH2Cl2 (3.0
mL) followed by flash column chromatography as above afforded ester 5c (32 mg, 45%) as a
white solid.1H NMR (600 MHz, CDCl3) δ 8.08 (d, J = 8.0 Hz, 2H), 7.68 (d, J = 8.0 Hz, 2H), 7.60
(t, J = 7.4 Hz, 1H), 7.55 (d, J = 8.0 Hz, 2H), 7.47 (t, J = 7.7 Hz, 2H), 5.42 (s, 2H). Proton NMR
data of the product was consistent with the reported literature values.18
2,4,6-trimethylbenzyl benzoate (5d). Ester 5d was synthesized according to the general ester
formation procedure A using MnO2 (160 mg, 1.84 mmol), KH2PO4 (250 mg, 1.84 mmol),
hydrazone 4d (45 mg, 0.28 mmol), benzoic acid (27 mg, 0.23 mmol), and CH2Cl2 (2.3 mL). The
crude product was purified by flash column chromatography (3:97 EtOAc/hexanes) affording
ester 5d (57 mg, 96%) as a white solid. Procedure B using MnO2 (216 mg, 2.48 mmol), KH2PO4
(338 mg, 2.48 mmol), hydrazone 4d (60 mg, 0.37 mmol), benzoic acid (37 mg, 0.31 mmol), and
CH2Cl2 (3.1 mL) followed by flash column chromatography as above afforded ester 5d (73 mg,
92%) as a white solid. Ester 5d was also synthesized by a third method, MnO2 last. MnO2 (682
mg, 7.84 mmol) was added to a suspension of benzoic acid, (121 mg, 0.980 mmol), KH2PO4
(1067 mg, 7.840 mmol), and hydrazone 4d (191 mg, 1.18 mmol) in CH2Cl2 (10 mL). The crude
product was filtered through silica and purified by flash column chromatography (40:60
toluene/hexanes) affording ester 5d (249 mg, 93%) as a white solid. 1H NMR (600 MHz, CDCl3)
δ 8.00 (d, J = 7.8 Hz, 2H), 7.52 (t, J = 7.4 Hz, 1H), 7.39 (t, J = 7.7 Hz, 2H), 6.90 (s, 2H), 5.41 (s,
2H), 2.41 (s, 6H), 2.29 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 166.9, 138.6, 138.5, 133.0, 130.4,
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129.8, 129.2, 128.5, 61.8, 21.2, 19.8; IR (neat): νmax 1725, 1451, 1165 cm-1; m.p. 65-67 °C;
AMM (ESI) m/z calcd for C17H18O2Na+ [M + Na]+ 277.1205, found 277.1210.
1-phenylpropyl benzoate (5e). Ester 5e was synthesized according to the general ester
formation procedure A using MnO2 (237 mg, 2.72 mmol), KH2PO4 (370 mg, 2.72 mmol),
hydrazone 4e (61 mg, 0.41 mmol), benzoic acid (41 mg, 0.34 mmol), and CH2Cl2 (3.4 mL). The
crude product was purified by flash column chromatography (3:97 EtOAc/hexanes) affording
ester 5e (81 mg, 99%) as a yellow oil. Procedure B using MnO2 (251 mg, 2.88 mmol), KH2PO4
(392 mg, 2.88 mmol), hydrazone 4e (64 mg, 0.43 mmol), benzoic acid (44 mg, 0.36 mmol), and
CH2Cl2 (3.6 mL) followed by flash column chromatography as above afforded ester 5e (73 mg,
85%) as a yellow oil. 1H NMR (600 MHz, CDCl3) δ 8.10 (d, J = 7.9 Hz, 2H), 7.56 (t, J = 7.4 Hz,
1H), 7.44 (m, 4H), 7.36 (t, J = 7.6 Hz, 2H), 7.29 (t, J = 7.3 Hz, 1H), 5.93 (t, J = 6.8 Hz, 1H), 2.09
(ddq, J = 14.7, 7.4, 7.4 Hz, 1H), 1.97 (ddq, J = 14.7, 7.4, 7.4 Hz, 1H), 0.98 (t, J = 7.4 Hz, 3H).
Proton NMR data of the product was consistent with the reported literature values.25
1-phenylethyl benzoate (5f). Ester 5f was synthesized according to the general ester formation
procedure A using MnO2 (318 mg, 3.66 mmol), KH2PO4 (498 mg, 3.66 mmol), hydrazone 4f (74
mg, 0.54 mmol), benzoic acid (56 mg, 0.46 mmol), and CH2Cl2 (4.0 mL). The crude product was
purified by flash column chromatography (4:96 EtOAc/hexanes) affording ester 5f (96 mg, 93%)
as a yellow oil. Procedure B using MnO2 (256 mg, 2.94 mmol), KH2PO4 (400 mg, 2.94 mmol),
hydrazone 4f (55 mg, 0.45 mmol), benzoic acid (45 mg, 0.37 mmol), and CH2Cl2 (3.7 mL)
followed by flash column chromatography afforded ester 5f (79 mg, 94%) as a yellow oil. 1H
NMR (600 MHz, CDCl3) δ 8.14 (d, J = 7.1 Hz, 2H), 7.58-7.56 (t, J = 7.4 Hz, 1H), 7.48 (m, 4H),
7.41 (t, J = 7.6 Hz, 2H), 7.34 (t, J = 7.4 Hz, 1H), 6.20 (q, J = 6.6 Hz, 1H), 1.72 (d, J = 6.6 Hz,
3H). Proton NMR data of the product was consistent with the reported literature values.26
1,2,3,4-tetrahydronaphthalen-1-yl benzoate (5g). Ester 5g was synthesized according to the
general ester formation procedure A using MnO2 (210 mg, 2.41 mmol), KH2PO4 (329 mg, 2.41
mmol), hydrazone 4g (58 mg, 0.36 mmol), benzoic acid (36 mg, 0.30 mmol), and CH2Cl2 (3.0
mL). The crude product was purified by flash column chromatography (0:100 to 2:98
EtOAc/hexanes) affording ester 5g (72 mg, 97%) as a yellow oil. Procedure B using MnO2 (247
mg, 2.84 mmol), KH2PO4 (387 mg, 2.84 mmol), hydrazone 4g (68 mg, 0.43 mmol), benzoic acid
(43 mg, 0.36 mmol), and CH2Cl2 (3.6 mL) followed by flash column chromatography as above
afforded ester 5i (75 mg, 84%) as a yellow oil. 1H NMR (600 MHz, CDCl3) 8.10 (d, J = 7.8 Hz,
2H), 7.56 (t, J = 7.4 Hz, 1H), 7.44 (t, J = 7.7 Hz, 2H), 7.40 (d, J = 7.7 Hz, 1H), 7.27 (t, J = 7.4
Hz, 1H), 7.20 (t, J = 8.3 Hz, 2H), 6.30 (t, J = 4.8 Hz, 1H), 2.93-2.89 (m, 1H), 2.90-2.74 (m, 2H),
2.13-2.03 (m, 2H), 1.99-1.82 (m, 1H). Proton NMR data of the product was consistent with the
reported literature values.25
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benzyl cyclohexanecarboxylate (5h). Ester 5h was synthesized according to the general ester
formation procedure A using MnO2 (188 mg, 2.16 mmol), KH2PO4 (294 mg, 2.16 mmol),
hydrazone 4a (40 mg, 0.33 mmol), cyclohexane carboxylic acid (35 mg, 0.27 mmol), and
CH2Cl2 (2.7 mL). The crude product was purified by flash column chromatography (5:95
EtOAc/hexanes) affording ester 5h (56 mg, 95%) as a clear oil. The final product contained up to
17 % of the azine byproduct resulting from hydrazone condensation (1H NMR (600 MHz,
CDCl3) δ 8.69 (d, J = 1.3 Hz, 2H), 7.86-7.83 (m, 4H), 7.34-7.31 (m, 6H)). Procedure B using
MnO2 (226 mg, 2.60 mmol), KH2PO4 (354 mg, 2.60 mmol), hydrazone 4a (77 mg, 0.39 mmol),
cyclohexane carboxylic acid (42 mg, 0.33 mmol), and CH2Cl2 (3.3 mL) followed by flash
column chromatography as above afforded ester 5h (56 mg, 80%) as a clear oil.1H NMR (600
MHz, CDCl3) δ 7.37- 7.28 (m, 5H), 5.10 (s, 2H), 2.35 (tt, J = 11.7, 3.0 Hz, 1H), 1.96-1.90 (m,
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2H), 1.75 (m, 2H), 1.66-1.60 (m, 2H), 1.46 (m, 2H), 1.32-1.18 (m, 2H). Proton NMR data of the
product was consistent with the reported literature values.23
4-methoxybenzyl cyclohexanecarboxylate (5i). Ester 5i was synthesized according to the
general ester formation procedure A using MnO2 (341 mg, 3.92 mmol), KH2PO4 (533 mg, 3.92
mmol), hydrazone 4b (111 mg, 0.740 mmol), cyclohexane carboxylic acid (63 mg, 0.49 mmol),
and CH2Cl2 (4.9 mL). The crude product was purified by flash column chromatography (10:90
EtOAc/hexanes) affording ester 5i (83 mg, 68%) as a clear oil. Procedure B using MnO2 (331
mg, 3.58 mmol), KH2PO4 (487 mg, 3.58 mmol), hydrazone 4b (102 mg, 0.670 mmol),
cyclohexane carboxylic acid (57 mg, 0.45 mmol), and CH2Cl2 (4.5 mL) followed by flash
column chromatography as above afforded ester 5i (23 mg, 21%) as a clear oil.1H NMR (600
MHz, CDCl3) δ 7.27 (d, J = 8.4 Hz, 2H), 6.88 (d, J = 8.5 Hz, 2H), 5.03 (s, 2H), 3.79 (s, 3H), 2.31
(tt, J = 11.3, 3.6 Hz, 1H), 1.90(dd, J =12.4, 3.6 Hz, 2H), 1.76-1.71 (m, 2H), 1.64-1.61 (m, 1H),
1.48-1.39 (m, 2H), 1.31-1.18 (m, 3H). Proton NMR data of the product was consistent with the
reported literature values.24
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Acknowledgements:
JTS thanks the Donors of the American Chemical Society Petroleum Research Fund for partial
support of this research (53767-ND1). GPS thanks UC Davis for providing a Provost's
Undergraduate Fellowship (PUF).
Supporting Information:
1H and 13C NMR spectra of new compounds, 1H of known compounds, ReactIR experimentals,
and ReactIR data are located in the supporting info.
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