Aziridines with acetylenic esters

Developments in aziridine chemistry, including the synthetic applications of their cycloadditions, have recently been reviewed by Lown and Matsumoto.35-37 Many investigators have added aziridines to acetylenic esters. Russian workers38 treated aziridine in the cold with various esters and then heated the mixtures to 40°-60° for 3 hours. They obtained 59% of compound 16 with EP, and 71 % of 17 with EPP, no stereochemistry being defined. Diethyl acetylenedicarboxylate gave 24% of the maleate 18 (R = Et) and 16% of the fumarate 19 (R = Et). 

The essential aspects of reaction (25) are depicted in Fig. 6. Huisgen et al. (1967) have provided a beautiful example of an odd electrocyclic change in (26). The aziridine opens up to a dipolar four-electron allylic species. Since the HOMO is b (Fig. 1), the thermal change is conrotatory and the excited state process is disrotatory. To avoid equilibration of the dipolar ions, these workers trap them with an acetylenic ester in a stereospecific cycloaddition, which we shall discuss presently. 

Dolfini [89] found that, when equimolar ratios of aziridine (ethylenimine) reacts with dimethyl acetylene dicarboxylate in methanol at room temperature, a 67 % yield of the trans and a 33 % yield of the cis product are obtained. In dimethyl sulfoxide solvent, 95% of the cis and 5% of the trans ester are obtained (Eq. 32). 

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