[7175-49-7]  · C14H27N  · Dicyclohexyl(ethyl)amine  · (MW 209.37)

(highly basic, nonnucleophilic amine; useful in alkylation of amines3 and in dehydrohalogenations;6 proton acceptor in esterifications7)

Physical Data: bp 132-134.2 °C/10 mmHg; d 0.909 g cm-3; fp 230 °C; absorbs CO2 from the air.

Solubility: sol acetone, cyclohexane, 1,2-dichloroethane, dichloromethane.

Preparative Method: although commerically available in small quantities, the reagent can be conveniently prepared from dicyclohexylamine and diethyl sulfate.1,2

Alkylation of Amines.

Dicyclohexyl(ethyl)amine is an excellent hindered (Hünig's) base. Compatible alkylating agents include alkyl halides, dialkyl phosphates, and trialkyloxonium species.

Dialkylation of aniline with butyl bromide in the presence of dicyclohexyl(ethyl)amine proceeds in high yield (90-180 °C, 3 h, 97%).3 Alkylation of amine hydrochlorides can be effected using this base and Dimethyl Sulfate, as demonstrated in the final step of the total synthesis of (±)-terramycin.4 The alkylation of 2-methylbenzimidazole with trialkyloxonium tetrafluoroborate in the presence of dicyclohexyl(ethyl)amine yields 1,3-dialkyl-2-methylbenzimidazolium tetrafluoroborates (0 °C, 70-90%).5


Dehydrohalogenation of alkyl halides proceeds in high yields in the presence of dicyclohexyl(ethyl)amine. n-Dodecyl bromide yields 1-dodecene (190 °C, 20 h, 98%). The reaction is applicable to the dehydrohalogenation of a-halo ethers to yield the corresponding enol ethers. Similar results can be obtained with other hindered amines, although yields are often inferior.6

Proton Acceptor.

Dicyclohexyl(ethyl)amine has been used as a proton acceptor, or proton sponge, in the preparation of esters of carboxylic acids. The reaction is applicable to the derivatization of low-melting fatty acids as their highly crystalline phenacyl bromides. Phenacyl esters are rapidly prepared in high yields (60 °C, 5 min, ~90%.7 Similarly, methyl and ethyl esters of carboxylic acids can be prepared on micro or preparative scale by alkylation with a dialkyl sulfate: EtCy2N + ROS(O2)OR (5 min, steam bath, 84-97%).8 The procedure is particularly useful as an alternative to Diazomethane esterification when the latter is inappropriate. The present amine is advantageous over more commonly available alternatives, such as tris(hydroxypropyl)amine, in that it does not remove dimethyl sulfate as the quaternary ammonium salt, and hence can be used in excess. The proton scavenging ability of dicyclohexyl(ethyl)amine is also exploited in the Friedel-Crafts silylation of ferrocene, where it suppresses the protodesilylation reaction and hence allows maximal yields to be achieved (80 °C, 4 h, 36%).9

Acylation of alkenes by acetyl hexachloroantimonate yields b,g-unsaturated ketones. As a buildup of acid is detrimental to the outcome of the reaction, a proton scavenger is necessary. The present amine maximizes yield of the desired product (-50 °C to -25 °C, 1 h, 83%).10

Arylated alkenes can be obtained, in good yield, by reaction of aroyl chlorides with activated alkenes in the presence of a hindered amine, such as dicyclohexyl(ethyl)amine, and a catalytic quantity of Palladium(II) Acetate.11

Dicyclohexyl(ethyl)amine favors the organopalladium arylation of allylic alcohols by suppressing the formation of halides from the allylic alcohols and hydrogen chloride generated during the course of the reaction.12 Similar effects are observed in the arylation of crotyl acetate.13 Yields are in any case modest.


Alkoxycarbonylation of alkyl halides, sulfates, and sulfonates can be carried out, in modest yields, in the presence of Carbon Monoxide, an alcohol, a hindered base such as dicyclohexyl(ethyl)amine, and a catalytic quantity of Sodium Tetracarbonylcobaltate (50 °C, 1 atm, 16-20 h, 20-56%).14 More nucleophilic bases yield instead the corresponding amides by competitive nucleophilic attack.

Similarly, reaction of trimethylene oxide, carbon monoxide, and tetracarbonylhydridocobalt followed by treatment with dicyclohexyl(ethyl)amine yields g-butyrolactone (0 °C, 3 h).15

Related Reagents.

Diisopropylethylamine; 2,6-Lutidine; Triethylamine.

1. Hünig, S.; Kiessel, M. CB 1958, 91, 380.
2. Stodola, F. H. Microchem J. 1963, 7, 389.
3. Hünig, S.; Kiessel, M. CB 1958, 91, 380.
4. Muxfeldt, H.; Hardtmann, G.; Kathawala, F.; Vedejs, E.; Mooberry, J. B. JACS 1968, 90, 6534.
5. Reichardt, C.; Kaufmann, N. CB 1985, 118, 3424.
6. Hünig, S.; Kiessel, M. CB 1958, 91, 380.
7. Stodola, F. H. Michrochem J. 1963, 7, 389.
8. Stodola, F. JOC 1964, 29, 2490.
9. Olah, G. A.; Bach, T.; Surya Prakash, G. K. NJC 1991, 15, 571.
10. Hoffmann, H. M. R.; Tsushima, T. JACS 1977, 99, 6008.
11. Blaser, H.-U.; Spencer, A. JOM 1982, 233, 267.
12. Heck, R. F. JACS 1968, 90, 5526.
13. Heck, R. F. JACS 1968, 90, 5518.
14. Heck, R. F.; Breslow, D. S. JACS 1963, 85, 2779.
15. Heck, R. F. JACS 1963, 85, 1460.

Paul Ch. Kierkus

BASF Corporation, Wyandotte, MI, USA

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