A novel [2+3] cycloaddition reaction: Singlet oxygen mediated formation of1,3-dipole from iminodiacetic acid dimethyl ester and its addition to maleimides

Sensitized photolysis of iminodiacetic acid methyl ester and maleimides fol lows a [2 + 3] cycloaddition pathway yielding pyrrolidine derivatives. This is similar to the photochemical reaction between C-60 and amines. A series of pyrrolidine derivatives are prepared by the method including multipyrro lidines from bis- and tris-maleimide starting materials. The yields range f rom 13% to 85%. The reaction is highly stereoselective. All the isolated pr oducts have the 1,3-dimethoxycarbonyl groups in the cis configuration. Vari ous sensitizers may be used with slightly different yields. A plausible mec hanism is proposed that involves the singlet oxygen abstraction of two alph a hydrogen atoms from the iminodiacetate and formation of a 1,3-dipole with a structure similar to the classical thermally generated 1,3-dipole.