1-(N,N-Dimethylamino)-2-methyl-1-propene

(1; R = Me)

[6906-32-7]  · C6H13N  · 1-(N,N-Dimethylamino)-2-methyl-1-propene  · (MW 99.20) (2; R,R = -(CH2)4-)

[2403-57-8]  · C8H15N  · 1-Pyrrolidino-2-methyl-1-propene  · (MW 125.24) (3; R,R = -(CH2)2O(CH2)2-)

[2403-55-6]  · C8H15NO  · 1-Morpholino-2-methyl-1-propene  · (MW 141.24) (4; R,R = -(CH2)5-)

[673-33-6]  · C9H17N  · 1-Piperidino-2-methyl-1-propene  · (MW 139.27) (5; R,R = -(CH2)6-)

[94167-75-6]  · C10H19N  · 1-Perhydroazepino-2-methyl-1-propene  · (MW 153.30)

(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-cycloaddition1)

Physical Data: (1) bp 89-90 °C; n20D 1.4221; IRC=C 1680 cm-1. (2) bp 50 °C/14 mmHg; n20D 1.4739; IRC=C 1674 cm-1. (3) bp 59-60 °C/17 mmHg; n20D 1.4676; IRC=C 1675 cm-1. (4) bp 65-67 °C/12 mmHg; n20D 1.4676; IRC=C 1675 cm-1. (5) bp 85-86 °C/12 mmHg; n20D 1.4845; IRC=C 1667.

Preparative Methods: the usual method of preparation for these enamines is the condensation of a secondary amine with isobutyraldehyde (2-methylpropanal) (eq 1).2

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

Alkylation.

Enamines derived from b-disubstituted aldehydes are alkylated on nitrogen by alkyl halides. Activated alkyl halides provide easier access to C-alkylated products, but the increased activity also results in greater amounts of dialkylation products. Allyl, benzyl, and propargyl halides give C-alkylated products with these enamines. However, in some cases (e.g. crotyl bromide, eq 2),3 N-alkylation may occur initially, followed by isomerization to the C-alkyl isomer (e.g. via [3,3]-sigmatropic rearrangement). High dielectric solvents favor C-alkylation in these reactions. Ternary iminium ions can alkylate acyclic enamines (eq 3).4

Acylation.

Addition of Acetyl Chloride to the morpholine enamine of isobutyraldehyde gives normal C-acylation which upon hydrolysis produces a keto aldehyde (eq 4).5

Cycloaddition.

The initial product formed when an electrophilic alkene such as Methyl Vinyl Ketone is allowed to react with an acyclic enamine is a dihydropyran (eq 5).6

[2 + 2] Cycloaddition takes place to form thermally stable cyclobutane products when acyclic enamines with no b-hydrogens are treated with dimethylketene,7 Methyl Acrylate,2b fumaronitrile,2c and Dimethyl Fumarate or diethyl fumarate.2c,8 The thermal and the photochemical fumarate reactions give different stereoisomeric products (eqs 6 and 7).8

Acid-catalyzed hydrolysis effects aldol cyclization to give 4,4-dimethyl-2-cyclohexenone.6b

Related Reagents.

Crotyl Chloride; Methyl Acrylate; Methyl Vinyl Ketone; Morpholine; Piperidine; Pyrrolidine; 1-Pyrrolidino-1-cyclohexene; 1-Pyrrolidino-1-cyclopentene.


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 University Press: London, 1973. (e) Hickmott, P. W. T 1982, 38, 1975, 3363. (f) Pitacco, G.; Valentin, E. 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. (a) Benzing, E. AG 1959, 71, 521. (b) Brannock, K. C.; Bell, A.; Burpitt, R. D.; Kelly, C. A. JOC 1961, 26, 625. (c) Brannock, K. C.; Bell, A.; Burpitt, R. D.; Kelly, C. A. JOC 1964, 29, 801.
3. Brannock, K. C.; Burpitt, R. D. JOC 1961, 26, 3576.
4. Böhme, H.; Osmers, K.; Wagner, P. TL 1972, 2785.
5. Inukai, T.; Yoshizawa, R. JOC 1967, 32, 404.
6. (a) Fleming, I.; Karger, M. H. JCS(C) 1967, 226. (b) Chan, Y.; Epstein, W. W. OSC 1988, 6, 496.
7. Hasek, R. H.; Martin, J. C. JOC 1963, 28, 1468.
8. Lewis, F. D.; Ho, T.-I.; DeVoe, R. J. JOC 1980, 45, 5283.

A. Gilbert Cook

Valparaiso University, IN, USA



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