a-Methacrolein N-t-Butylimine

(s-cis)

[81569-06-4]  · C8H15N  · a-Methacrolein N-t-Butylimine  · (MW 125.24) (structure unspecified)

[90554-32-8]

(a,b-unsaturated aldimine or 1-aza-1,3-diene; useful building block for heterocyclic synthesis as a heterodiene or a functionalized imine and alkene1-4)

Physical Data: bp 28-30 °C/10 mmHg.

Solubility: sol most organic solvents such as ether, alcohol, carbon tetrachloride, chloroform, dichloromethane, benzene, hexane.

Form Supplied in: colorless liquid.1

Analysis of Reagent Purity: 1H NMR (CDCl3): d 1.22 (s, 9H, t-Bu), 1.93 (s, 3H, Me), 5.28 (m, 1H, =CHH), 5.50 (m, 1H, =CHH), 7.84 (s, 1H, N=CH).1,6

Preparative Methods: by dehydrohalogenation of a-haloaldimines, which are prepared by halogenation of the corresponding aldimine with N-halosuccinimide (eq 1).5,6 Alternatively, prepared by condensation of N-t-butylmethanimine and 1-piperidino-1-propene (eq 2).1,2 Preparation of this type of g-unsubstituted azadiene by direct condensation of an a,b-unsaturated aldehyde with an amine usually suffers from low yields due to side reactions.7,8

Handling, Storage, and Precautions: hygroscopic and should be handled in a dry atmosphere. It neither hydrolyzes in the absence of acid nor polymerizes upon heating and can be stored in a refrigerator for many months. Use in a fume hood.

Introduction.

a-Methacrolein N-t-butylimine (1) is known to be a heterodiene with considerable stability and versatile utility in organic synthesis as an electron-deficient alkene and an alkenyl imine, as well as an azadiene which has no substituent on the terminal carbon and the s-cis structure favorable for 1,4-cycloaddition leading to nitrogen-containing heterocycles. Another feature of the compound is the t-butyl group that often eliminates upon thermal or acidic treatment.

Polymerization.

While polymerization of imine (1) is not reported, analogous N-alkylmethacroleinimines such as N-cyclohexyl-3-methyl-1-aza-1,3-butadiene are known to polymerize by anionic catalysts but not by cationic or radical initiators. The polymerization proceeds through double bond addition and reactivity of this type with aldimines is less than that of methyl methacrylate.8

Oxidation.

Although oxidation of imine (1) itself is not reported, conversion of its analogs to alkenyloxaziridines with m-Chloroperbenzoic Acid occurs readily (eq 3).3 Reaction of (1) with singlet oxygen does not proceed, while g-substituted analogs are oxidized to 1,2-dioxolanes (eq 4).9,10

Reduction.

Selective reduction of N-alkylazadienes including imine (1) is a facile method for synthesis of secondary allylic amines (eq 5).5

Cycloaddition Leading to Heterocycles.

Methacrolein imines and their analogs react with various 1,3-dipoles, enophiles, and dienophiles to give four-, five-, and six-membered heterocyclic compounds; some representative examples are given below.

1,2-Cycloaddition of 1-Aza-1,3-dienes.

b-Alkenyl-b-lactams are synthesized by addition of ketenes across the C=N bond (eq 6). Formation of five-membered heterocycles from analogs via nitrilium ylide dipolar cycloaddition to the C=N or C=C bond (eqs 7 and 8) is reported.3

1,4-Cycloaddition of 1-Aza-1,3-dienes.

Formation of 3,5-disubstituted pyridines via [4 + 2] cycloaddition/cycloelimination of enamines to 1-aza-1,3-butadiene intermediates including (1) is known (eq 9).1,2 This process is an inverse electron demand Diels-Alder reaction and can be performed with the isolated 1-azadienes to give various unsymmetrical 3,5-disubstituted pyridines (eq 10).1,2

Dihydropyridones (d-lactams) are also prepared by Michael addition of ester enolates and subsequent cyclization (eq 11).4

Related Reagents.

Acrolein; 3-Ethoxyacrolein; Methacrolein Dimethylhydrazone; Propionaldehyde t-Butylimine.


1. Komatsu, M.; Takamatsu, S.; Uesaka, M.; Yamamoto, S.; Ohshiro, Y.; Agawa, T. JOC 1984, 49, 2691.
2. Komatsu, M.; Ohgishi, H.; Takamatsu, S.; Ohshiro, Y.; Agawa, T. AG 1982, 94, 214; AG(E) 1982, 21, 213.
3. Ohshiro, Y.; Komatsu, M.; Uesaka, M.; Agawa, T. H 1984, 22, 549.
4. Komatsu, M.; Yamamoto, S.; Ohshiro, Y.; Agawa, T. TL 1981, 38, 3769.
5. De Kimpe, N.; Stanoeva, E.; Verhé, R.; Schamp, N. S 1988, 587.
6. De Kimpe, N.; Verhé, R.; De Buyck, L. Hasma, H.; Schamp, N. T 1976, 32, 2457.
7. De Kimpe, N.; Zi-Peng, Y.; Schamp, N. BSB 1989, 98, 481.
8. Sato, H.; Tsuruta, T. J. Macromol. Sci. Chem. 1970, A4, 295.
9. Akasaka, T.; Takeuchi, K.; Misawa, Y.; Ando, W. H 1989, 28, 445.
10. Akasaka, T.; Takeuchi, K.; Ando, W. TL 1987, 28, 6633.

Yoshiki Ohshiro & Mitsuo Komatsu

Osaka University, Japan



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