Intramolecular Cycloaddition of Imines of Cysteine Derivatives

The intramolecular 1,3-dipolar cycloaddition is an important method for the construction of ring fused heterocycles. The prototropic generation of azomethine ylides from imines of a-amino acids esters is an example of this type of process.[1] We have previously reported the synthesis of tetrahydro-1H-thieno[3,4-b]pyrrole 2 through an intramolecular 1,3-dipolar cycloaddition of the azomethine ylide which was generated from the Schiff base 1 by proton transfer.[2] The structure of compound 2 was established by X-ray crystallography. Grigg and colleagues have also reported two examples of intramolecular dipolar cycloaddition of azomethine ylides derived from Schiff bases of S-allylcysteine methyl ester.1 We decided to further study this cycloaddition reaction in order to extend it as a methodology of synthesis of thieno[3,4-b]pyrrole derivatives.