Asymmetric Epoxidation of Dihydronaphthalene with a Synthesized Jacobsen's
Chem 250 GG
Abstract. 1,2 diaminocyclohexane was reacted with L-(+)-tartaric acid to yield
(R,R)-1,2-diaminocyclohexane mono-(+)-tartrate salt. The tartrate salt was then
reacted with potassium carbonate and 3,5-di-tert-butylsalicylaldehyde to yield
(R,R)-N,N'-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, which was
then reacted with Mn(OAc)2*4H2O and LiCl to form Jacobsen's catalyst. The
synthesized Jacobsen's catalyst was used to catalyze the epoxidation of
dihydronaphthalene. The products of this reaction were isolated, and it was
found that the product yielded 1,2-epoxydihydronaphthalene as well as
In 1990, professor E.N. Jacobsen reported that chiral manganese
complexes had the ability to catalyze the asymmetric epoxidation of
unfunctionalized alkenes, providing enantiomeric excesses that regularly
reaching 90% and sometimes exceeding 98% . The chiral manganese complex
Jacobsen utilized was [(R,R)-N,N'-Bis(3,5-di-tert-butylsalicylidene)-1,2-
cyclohexanediaminato-(2-)]-manganese (III) chloride (Jacobsen's Catalyst).
(R,R) Jacobsen's Catalyst Jacobsen's catalyst opens up short pathways to
enantiomerically pure pharmacological and industrial products via the
synthetically versatile epoxy function .
In this paper, a synthesis of Jacobsen's catalyst is performed (Scheme
1). The synthesized catalyst is then reacted with an unfunctional alkene
(dihydronaphthalene) to form an epoxide that is highly enantiomerically enriched,
as well as an oxidized byproduct.
Jacobsen's work is important because it presents both a reagent and a
method to selectively guide an enantiomeric catalytic reaction of industrial
and pharmacological importance. Very few reagents, let alone methods, are
known to be able to perform such a function, which indicates the truly
groundbreaking importance of Jacobsen's work.
General Protocol. 99% L-(+)- Tartaric Acid, ethanol,
dihydronaphthalene and glacial acetic acid were obtained from the Aldrich
Chemical Company. 1,2 diaminocyclohexane (98% mix of cis/trans isomers) and
heptane were obtained from the Acros Chemical Company. Dichloromethane and
potassium carbonate were obtained from the EM Science division of EM Industries,
Inc. Manganese acetate was obtained from the Matheson, Coleman and Bell
Manufacturing Chemists. Lithium chloride was obtained form the JT Baker
Chemical Co. Refluxes were carried out using a 100 V heating mantle (Glas-Col
Apparatus Co. 100 mL, 90 V) and 130 V Variac (General Radio Company). Vacuum
filtrations were performed using a Cole Parmer Instrument Co. Model 7049-00
aspirator pump with a B'chner funnel. For Thin Layer Chromatography (TLC)
analysis, precoated Kodak chromatogram sheets (silica gel 13181 with
fluorescent indicator) were used in an ethyl acetate/hexane (1:4) eluent.
TLC's were visualized using a UVP Inc. Model UVG-11 Mineralight Lamp (Short-wave
UV-254 nm, 15 V, 60 Hz, 0.16 A). Masses were taken on a Mettler AE 100. Rotary
evaporations were performed on a B'chi Rotovapor-R. Melting points were
determined using a Mel-Temp (Laboratory Devices, USA) equipped with a Fluke 51
digital thermometer (John Fluke Manufacturing Company, Inc.). Optical rotations
([a]D) were measured on a Dr. Steeg and Renter 6mbH, Engel/VTG 10 polarimeter.
Solid IR's were run on a Bio-Rad (DigiLab Division) Model FTS-7 (KBr:Sample
10:1, Res. 8 cm-1, 16 scans standard method, 500cm-1 - 4000cm-1). Flash
Chromatography was carried out in a 20 mm column with an eluant of ethyl acetate
(25%) in hexane.
(R,R)-1,2 Diaminocyclohexane mono-(+)-tartrate salt. 99% L-(+)-Tartaric
Acid (7.53g, 0.051mol) was added in one portion to a 150 mL beaker equipped
with distilled H2O (25 mL) magnetic stir bar, and thermometer. Once the
temperature had dropped to 17.8 'C, 1,2 diaminocyclohexane (11.89 g, 12.5 mL,
0.104 mol) was added with stirring in one portion. To the resultant amber
solution was added glacial acetic acid (5.0 mL, 0.057 mol). The frothy orange
product was cooled in an ice water bath for 30 minutes. The product was washed
with 5 'C distilled H2O (5.0 mL) and ambient temperature methanol (5.0 mL) and
isolated by vacuum filtration. 8.37 grams of an orange slush were obtained.
The product was further purified by recrystallization of the salt from H2O (1:10
w/v, 84 mL of H2O) and again isolated by vacuum filtration, yielding an off-
white crystalline product (1.2015g; 0.00415 mol; 8.9 % yield; mp=270.4-273.8 '
C Lit. Value mp=273 'C )
Distilled H2O (6.0 mL), (R,R)-1,2 diaminocyclohexane mono-(+)-tartrate salt
(1.1087 g, 0.0042 mol) and K2CO3 granules (1.16 g, 0.0084 mol) were added to a
100 mL RB flask equipped with a magnetic stir bar. The mixture was stirred
until complete dissolution occurred, and then ethanol (22 mL, 0.376 mol) was
added. The solution was then brought to reflux, and then a solution of 3,5-di-
tert-butylsalicylaldehyde (2.0g, 0.0037 mol) dissolved in ethanol (10 mL,
0.1713 mol) was added with a Pasteur pipette. The solution refluxed for 45
minutes. H2O (6.0 mL) was added to the yellow solution, and the mixture cooled
in an ice bath for 30 minutes. The resultant yellow solid was collected by
vacuum filtration and washed with ethanol (5 mL, 0.856 mol). The yellow solid
was dissolved in CH2Cl2 (25 mL, 0.4 mol) and washed with H2O (2 x 5.0 mL) and
saturated aqueous NaCl (5.0 mL) The organic layer was dried (Na2SO4) and then
decanted into an RB flask. Methanol was removed in vacuo, yielding a yellow
crystalline powder (1.56g; 0.00285 mol; 77 % yield; mp=202.9-205.4 'C, Lit.
Value mp=205-207 'CIII; IR (KBr) 2800, 2100, 1631.7, 1506.7, 1173.5, 828,
545cm-1; [a]D20 =-314', Lit. Value [a]D20 =-315'III)
(2-)]-manganese (III) Chloride. Absolute ethanol (25 mL, 0.429 mol) was added
to (R,R)-N,N'-bis (3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine (1.01 g,
0.001788 mol) in a 50 mL RB equipped with a magnetic stirrer, mantle, claisen
adapter and reflux condenser. The pale yellow mixture was brought to reflux,
and MnO(OAc)2*4H2O (2.0 equivalents, 0.881 g, 0.0036 mol) was added. The
orange mixture refluxed for 30 minutes, and then the reaction flask was equipped
with a glass bleed tube allowing air to bubble through at a slow rate. The
progress of the reaction was monitored by TLC until the starting material
((R,R)-N,N'-bis (3,5-di-tert-butylsalicylidene)-1,2 cyclohexane diamine)) faded
from the TLC readings (Rf=0). At this point, the air was ...
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