Asymmetric Epoxidation of Dihydronaphthalene with a Synthesized Jacobsen's Catalyst
Chem 250 GG
TA: Andrea Egans
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 naphthalene.
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 Büchner 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 Büchi 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...
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