1-Pyrrolidino-1-cyclopentene

(1; R = 1-pyrrolidino)

[7148-07-4]  · C9H15N  · 1-Pyrrolidino-1-cyclopentene  · (MW 137.25) (2; R = 4-morpholino)

[936-52-7]  · C9H15NO  · 4-Morpholino-1-cyclopentene  · (MW 153.25) (3; R = 1-piperidino)

[1614-92-2]  · C10H17N  · 1-Piperidino-1-cyclopentene  · (MW 151.28) (4; R = 1-perhydroazepino)

[7374-91-6]  · C11H19N  · 1-Perhydroazepino-1-cyclopentene  · (MW 165.31) (5; R = Me2N)

[4840-12-4]  · C7H13N  · Dimethylamino-1-cyclopentene  · (MW 111.21)

(either the enamine nitrogen or its b-carbon atom is nucleophilic, undergoing substitution or conjugate addition;1 can take part in 1,2- or 1,4-cycloadditions1)

Physical Data: (1) bp 88-92 °C/15 mmHg; n20D 1.5155; IR (C=C) 1630 cm-1. (2) bp 105-106 °C/12 mmHg; n20D 1.5118; IR (C=C) 1630 cm-1. (3) bp 90-91 °C/12 mmHg; n20D 1.5042; IR (C=C) 1634 cm-1. (4) bp 83-85 °C/1 mmHg; n20D 1.517; IR (C=C) 1630 cm-1. (5) bp 68 °C/45 mmHg; IR (C=C) 1648 cm-1.

Preparative Methods: the most commonly used method of preparation for these enamines is the acid-catalyzed condensation of a secondary amine with cyclopentanone (eq 1).1a

The use of a stoichiometric amount of Titanium(IV) Chloride makes it possible to produce highly hindered as well as ordinary enamines.2,3 More highly hindered ketones react more rapidly with dimethylamine than with heterocyclic secondary amines such as Pyrrolidine (eq 2).2

Handling, Storage, and Precautions: readily reacts with water or atmospheric oxygen; should be stored under dry nitrogen.

Alkylation.4

Alkylation of these enamines can take place with activated alkyl halides or electrophilic alkenes. A biphilic combination of these two alkylating agents has been used in an annulation sequence (eq 3).5

Acylation.6

Acylation of morpholine enamines with acyl halides can take place in a normal manner (eq 4).7

Cycloadditions.

Diethyl maleate and Methyl Propiolate rapidly add to the enamines to form [2 + 2] adducts.8,9 The propiolate adduct upon heating rearranges to a cycloheptadiene derivative (Scheme 1).9

A similar cycloaddition takes place with Dimethyl Acetylenedicarboxylate in nonpolar solvents, but a pyrrolizine is formed in the polar solvent methanol.10

Reduction.

Hydroboration of 1-morpholino-1-cyclopentene with 9-Borabicyclo[3.3.1]nonane followed by mild heating in methanol produces cyclopentene (eq 5).11

Related Reagents.

Dimethyl Acetylenedicarboxylate; (Dimethylamino)methyl Methyl Ether; Methyl Propiolate; Morpholine; Pivalaldehyde; Pyrrolidine; 1-Pyrrolidino-1-cyclohexene.


1. (a) Stork, G.; Brizzolara, A.; Landesman, H.; Szmuszkovicz, J.; Terrell, R. JACS 1963, 85, 207. (b) Szmuszkovicz, J. Advances in Organic Chemistry: Methods and Results; Interscience: New York, 1964; Vol. 4, p 1. (c) Kuehne, M. E. S 1970, 510. (d) Dyke, S. F. The Chemistry of Enamines; Cambridge: London, 1973. (e) Hickmott, P. W. T 1982, 38, 1975, 3363. (f) Pitacco, G.; Valentin, E. In The Chemistry of Amino, Nitroso, and Nitro Compounds and Their Derivatives; Wiley: New York, 1982; Part 1, p 623. (g) Granik, V. G. RCR 1984, 53, 383. (h) Enamines: Synthesis, Structure, and Reactions, 2nd ed.; Cook, A. G., Ed.; Dekker: New York, 1988.
2. White, W. A.; Weingarten, H. JOC 1967, 32, 213.
3. Carlson, R.; Nilsson, A. ACS 1984, B38, 49.
4. Whitesell, J. K.; Whitesell, M. A. S 1983, 517.
5. Nelson, R. P.; McEuen, J. M.; Lawton, R. G. JOC 1969, 34, 1225.
6. Hunig, S.; Hoch, H. Fortschr. Chem. Forsch. 1970, 14, 235.
7. Hunig, S.; Lendle, W. CB 1960, 93, 909.
8. Brannock, K. C.; Burpitt, R. D.; Goodlett, V. W.; Thweatt, J. G. JOC 1964, 29, 813.
9. Brannock, K. C.; Burpitt, R. D.; Goodlett, V. W.; Thweatt, J. G. JOC 1964, 29, 818.
10. Reinhoudt, D. N.; Verboom, W.; Visser, G. W.; Trompenaars, W. P.; Harkema, S.; Van Hummel, G. J. JACS 1984, 106, 1341.
11. Singaram, B.; Rangaishenvi, M. V.; Brown, H. C.; Goralski, C. T.; Hasha, D. L. JOC 1991, 56, 1543.

A. Gilbert Cook

Valparaiso University, IN, USA



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