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DOI:10.15227/orgsyn.071.0022

Organic Syntheses, Coll. Vol. 9, p.387 (1998); Vol. 71, p.22 (1993).

(1R,2R)-(+)- AND (1S,2S)-(−)- 1,2-DIPHENYL-1,2ETHYLENEDIAMINE[1,2-Ethanediamine, 1,2-diphenyl-, [R-(R,R)]- and [S-(R,R)]-]

Submitted by S. Pikul1 and E. J. Corey2.
Checked by Scott C. Jeffrey and James D. White.

1. Procedure
CAUTION! Parts A and B of this procedure should be carried out in an efficient hood to avoid
exposure to noxious vapors (acetic acid, ammonia).
A. 2,2-Spirocyclohexane-4,5-diphenyl-2H-imidazole (Note 1). A 2-L, three-necked, round-bottomed
flask equipped with a mechanical stirrer and a reflux condenser is charged with 1.0 L of glacial aceticacid (Note 2), 158 g (0.75 mol) of benzil (Note 2), 400 g of ammonium acetate (Note 2) and 80 mL(0.77 mol) of cyclohexanone (Note 2). The mixture is stirred and heated at reflux temperature for 1.5 hr(Note 3) and then, while hot, poured into 3 L of vigorously stirred water. The mixture is left overnight
to cool to ambient temperature, the crystals are collected by filtration, washed 4 times with 300 mL ofwater, crushed in a mortar and dried under reduced pressure to give 205–210 g (95–97%) of theimidazole as yellowish-green crystals, mp 105–106°C, lit.3 mp 107–108°C (Note 4).
B. (±)-1,2-Diphenyl-1,2-ethylenediamine. A 2-L, four-necked, round-bottomed flask equipped witha mechanical stirrer, thermometer and dry ice condenser is charged with 72.0 g (0.250 mol) of 2,2spirocyclohexane-4,5-diphenyl-2H-imidazole. The flask is flushed with argon, and 400 mL oftetrahydrofuran (Note 5) is added. The mixture is stirred until all solids dissolve, cooled to −78°C (dryice/acetone bath) and treated with a stream of gaseous ammonia (Note 6) until the volume of liquidincreases by about 400 mL (Note 7). One of the side necks is then equipped with a solids addition
funnel and 6.94 g (1.00 mol) of lithium (Note 8) is slowly introduced by cutting the wire with scissors ina gentle stream of argon. The rate of lithium addition is such that the temperature does not rise above−65°C. Following the addition of lithium, the mixture is stirred for 30 min and 30 mL (1.0 mol) ofethanol (Note 9) is slowly added. The mixture is stirred for an additional 20 min and 70 g of ammonium
chloride is added. The cooling bath is removed, the mixture is allowed to warm to 0°C, 400 mL of wateris carefully introduced, and the phases are separated. The aqueous phase is washed 3 times with 300 mLof ether and the combined organic extracts are washed with brine, dried over anhydrous sodium sulfate,filtered and concentrated with a rotary evaporator to about 200 mL. The solution is transferred to a1-L, one-necked, round-bottomed flask equipped with a mechanical stirrer, cooled to 0°C and treatedwith 300 mL of 2 N aqueous hydrochloric acid. The biphasic mixture is vigorously stirred at ambient
temperature for 1 hr, 500 mL of water is added and phases are separated. The organic phase is washedwith 150 mL of water and the combined aqueous phases are extracted with 300 mL of dichloromethane.
The aqueous solution is then carefully treated with 300 mL of 2 N aqueous sodium hydroxide and themixture is extracted 4 times with 150 mL of methylene chloride. The combined organic extracts are
washed with brine, dried over anhydrous sodium sulfate, and filtered. Removal of volatile material
under reduced pressure (water aspirator) gives 47–50 g (89–94%) of racemic diamine as a pale yellow
solid, mp 81–82°C, lit.4 mp 82°C corr. (Note 10).
C. (1S,2S)-(−)- and (1R,2R)-(+)-1,2-Diphenyl-1,2-ethylenediamine (Note 11). A 1-L, roundbottomed flask equipped with a mechanical stirrer is charged with 42.5 g (0.200 mol) of the racemic
diamine and 230 mL of ethanol (Note 9). The solids are dissolved by heating the mixture to 70°C
whereupon a hot (70°C), homogeneous solution, of 30.0 g (0.200 mol) of L-(+)-tartaric acid (Note 12)
in 230 mL of ethanol is added (Note 13). The tartrate salts precipitate immediately, and after the mixture
is cooled to ambient temperature, the crystals are collected by filtration, washed twice with 60 mL ofethanol, and dried under reduced pressure. The solids are dissolved in 230 mL of boiling water, 230 mLof ethanol is added and the homogeneous solution is allowed to cool slowly to room temperature. Thecrystals are collected by filtration, washed with 40 mL of ethanol and dried under reduced pressure. The
recrystallization procedure is then repeated twice using the same volumes of solvents (230 mL of waterand 230 mL of ethanol) to give 23–25 g (63–69%) of the tartrate salt as colorless crystals, [α]D23 −10.8 ±
0.2° (H2O, c 1.3), lit.5 [α]D23 −11° (H2O).
The salt is transferred to a 1-L, one-necked, round-bottomed flask equipped with a magnetic stirring
bar and suspended in 300 mL of water. After the mixture is vigorously stirred and then cooled to 0–5°C,
23 mL of 50% aqueous sodium hydroxide is added dropwise followed by 150 mL of dichloromethane,and stirring is continued for 30 min. The phases are separated, the aqueous phase is washed twice with
50 mL of dichloromethane and the combined organic extracts are washed with brine, dried overanhydrous sodium sulfate and filtered. Removal of the volatile material under reduced pressure gives acolorless solid that is recrystallized from hexane to yield 12–14 g (57–66%) of (S,S)-(−)-diamine ascolorless crystals, [α]D23 −106 ± 1° (MeOH, c 1.1) lit.6 [α]D23 −106.5° (MeOH, c 1.09) (Note 14).
The filtrates from all crystallizations are combined and the solvent is evaporated on a rotary
evaporator under vacuum (water aspirator). The residual solid is transferred to a 1-L, one-necked,
round-bottomed flask equipped with a magnetic stirring bar, and suspended in 250 mL of water. To thisvigorously stirred mixture is slowly added 25 mL of aqueous 50% sodium hydroxide followed by 200mL of dichloromethane and the stirring is continued for 30 min. The phases are separated, the aqueous
phase is washed twice with 50 mL of dichloromethane and the combined organic extracts are washedwith brine, dried over anhydrous sodium sulfate and filtered. Removal of volatile material under
reduced pressure gives 24–27 g of the enriched (R,R)-diamine as pale yellow crystals. This material istreated with D-(−)-tartaric acid (Note 12) and the resulting salt is recrystallized in exactly the samemanner as described for the other enantiomer to give 29–31 g (80–85%) of colorless crystals, [α]D23 +4± 0.5 ° (H2O, c 1.3). (The checkers found that the salt from (−)-tartaric acid was optically impure evenafter five recrystallizations. However, this did not affect the optical purity of the (R,R)-(+)-diamine.)
Treatment with sodium hydroxide, as described above, followed by crystallization from hexane gives
11.5–13 g (54–61%) of (R,R)-(+)-diamine as colorless crystals, [α]D23 +106 ± 1° (MeOH, c 1.1) (Note14).

2. Notes
1. Step A is a modified literature procedure.3
2. Glacial acetic acid (99.8%), benzil (99%), anhydrous ammonium acetate (A.C.S.) and cyclohexanone(99.8%) were obtained from the Aldrich Chemical Company, Inc., and used as received.
3. As the reaction progresses there is a change of color from light yellow to dark green.
4. This material is pure enough for use in the next step. If necessary, it can be recrystallized fromhexane or methanol-water. The properties of 2,2-spirocyclohexane-4,5-diphenyl-2H-imidazole are asfollows: Rf = 0.48 (hexane-ether 1:1, v/v; 1H NMR (CDCl3) δ: 1.65–1.92 (m, 6 H), 1.95–2.00 (m, 4 H),
7.33–7.53 (m, 10 H); 13C NMR (CDCl3) δ: 24.1, 25.7, 34.7, 104.1, 128.3, 128.9, 129.9, 133.1, 164.0.
5. Reagent grade tetrahydrofuran purchased from J. T. Baker Chemical Co., was freshly distilled fromsodium metal and benzophenone.
6. Anhydrous ammonia (99.98%) was obtained from Matheson Gas Products, Inc., and used asreceived.
7. The mixture stays homogeneous when cooled to −78°C.
8. Lithium wire (99% with 1% of sodium) was purchased from the Aldrich Chemical Company, Inc.
The mineral oil is wiped off with a paper towel before use.
9. Absolute ethanol (200 proof) was obtained from Aaper Alcohol and Chemical Co. and used asreceived.
10. The racemic diamine contains 5–10% of an impurity (by 13C NMR analysis) that does not interferewith the subsequent resolution. The product has the following spectral properties: 1H NMR (400 MHz,CDCl3) δ: 1.59 (bs, 4 H), 4.10 (s, 2 H), 7.2–7.3 (m, 10 H); 13C NMR (100 MHz, CDCl3) δ: 61.9, 126.8,126.9, 128.2, 143.4.
11. This resolution procedure is essentially the same as described in the literature.5
12. L-(+)- and D-(−)-Tartaric acids (99+ and 99%, respectively) were obtained from the Aldrich
Chemical Company, Inc., and used as received.
13. The tartaric acid solution should be added slowly to avoid spontaneous boiling of ethanol.
14. The spectral properties of this product are the same as that of the racemate (see (Note 10)). The
optical purity is higher than 98% as confirmed by 1H NMR of its salt with L-mandelic acid.7

Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory";
National Academy Press; Washington, DC, 1995.

3. Discussion
Enantiomerically pure (+)- and (−)-diphenylethylenediamines have recently been used for highly
stereoselective Diels-Alder,8 aldol,8 allylation,9 osmylation,10 and epoxidation11 reactions. Othersynthetic applications involve enantioselective Michael addition12 and asymmetric hydrogenation.13
The present two-step procedure for preparation of the racemic diphenylethylenediamine issignificantly shorter and more suitable for scale-up than that described in the literature.4 The resolutionof the racemate has also been reported using the commercially available enantiomers of mandelic acid.6
This preparation is referenced from:zOrg. Syn. Coll. Vol. 9, 67

References and Notes
Miami Valley Laboratories, The Procter & Gamble Company, Cincinnati, OH 45239.
Department of Chemistry, Harvard University, Cambridge, MA 02138.
Weiss, M. J. Am. Chem. Soc. 1952, 74, 5193.
Williams, O. F.; Bailar, J. C., Jr. J. Am. Chem. Soc. 1959, 81, 4464.
Lifschitz, I.; Bos, J. G. Recl. Trav. Chim. Pays. Bas. 1940, 59, 173.
Saigo, K.; Kubota, N.; Takebayashi, S.; Hasegawa, M. Bull. Chem. Soc. Jpn. 1986, 59, 931.
Benson, S. C.; Cai, P.; Colon, M.; Haiza, M. A.; Tokles, M.; Snyder, J. K. J. Org. Chem. 1988,53, 5335.
8. Corey, E. J.; Imwinkelried, R.; Pikul, S.; Xiang, Y. B. J. Am. Chem. Soc. 1989, 111, 5493.
9. Corey, E. J.; Yu, C.-M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495.
10. Corey, E. J.; Jardine, P. D.; Virgil, S.; Yuen, P.-W.; Connell, R. D. J. Am. Chem. Soc. 1989, 111,9243.
1.
2.
3.
4.
5.
6.
7.

11. Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. J. Am. Chem. Soc. 1990, 112, 2801.
12. Brunner, H.; Hammer, B. Angew. Chem. 1984, 96, 305; Angew. Chem., Inter. Ed. Eng. 1984, 23,312.
13. Fiorini, M.; Giongo, G. M. J. Mol. Cat. 1979, 5, 303.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);(Registry Number)brine
2,2-Spirocyclohexane-4,5-diphenyl-2H-imidazole(1R,2R)-(+)- AND (1S,2S)-(−)- 1,2-DIPHENYL-1,2-ETHYLENEDIAMINE
1,2-Ethanediamine, 1,2-diphenyl-, [R-(R,R)]- and [S-(R,R)](1S,2S)-(−)- and (1R,2R)-(+)-1,2-Diphenyl-1,2-ethylenediamine(S,S)-(−)-diamine(R,R)-diamine
D-(−)-tartaric acid(−)-tartaric acid
(R,R)-(+)-diamine
L-(+)- and D-(−)-Tartaric acids(+)- and (−)-diphenylethylenediamines
ethanol (64-17-5)hydrochloric acid (7647-01-0)
acetic acid (64-19-7)
ammonia (7664-41-7)
methanol (67-56-1)
ether (60-29-7)
ammonium acetate (631-61-8)
ammonium chloride (12125-02-9)

sodium hydroxide (1310-73-2)
Mandelic acid,L-mandelic acid (90-64-2)
Cyclohexanone (108-94-1)
sodium sulfate (7757-82-6)
Benzil (134-81-6)
Benzophenone (119-61-9)
sodium (13966-32-0)
tartaric acid,L-(+)-tartaric acid (87-69-4)
methylene chloride,
dichloromethane (75-09-2)
lithium (7439-93-2)
Tetrahydrofuran (109-99-9)
Imidazole (288-32-4)
hexane (110-54-3)
argon (7440-37-1)(±)-1,2-Diphenyl-1,2-ethylenediamine
diphenylethylenediamine
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