Acetylenecarboxylic esters

N-Unsubstituted pyrazoles and imidazoles add to unsaturated compounds in Michael reactions, for example acetylenecarboxylic esters and acrylonitrile readily form the expected addition products. Styrene oxide gives rise, for example, to 1-styrylimidazoles (76JCS(P1)545). Benzimidazole reacts with formaldehyde and secondary amines in the Mannich reaction to give 1-aminomethyl products. 

R.M. Acheson u. N.F. Elmore, Reactions of Acetylenecarboxylic Esters with Nitrogen-Containing Heterocycles, Adv. Heterocycl. Chem. 23, 263, 335-348 (1978). 

Additional information about the effect of amine structure and solvent on the steric course of the reaction of amines with acetylenecarboxylic esters has recently been reported by Huisgen [93]. 

Pyrazolinones and isoxazolinones are prepared from (3-keto esters and hydrazine or hydroxylamine by reactions such as (34 — 35) similar to those in (i) above. Diketene behaves as a masked (3-keto ester. Acetylenecarboxylic esters can be used in place of (3-keto esters to give pyrazolinones such as (36) and (37) and the corresponding isoxazolinones. (3-Chloro-a,(3-unsaturated acid chlorides react similarly (cf. 38 — 39). 

Reactions of Acetylenecarboxylic Esters with Nitrogen-containing Heterocycles R. M. 

Sec. II.A] ACETYLENECARBOXYLIC ESTERS AND N-HETEROCYCLES II. Three-Membered Ring Nitrogen-Containing Heterocycles... 

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