Enantioselective synthesis of chiral dispiro-bisoxindole alkaloids via [3+2]-cycloaddition reaction in both enantiomeric form

In this research, a highly diastereo- and enantioselective 1,3-dipolar cycloaddition of isatin-derived azomethine ylides with new chiral 3-arylidene-oxindoles, was described. Initially, we synthesized new chiral derivative of 3-arylidene-oxindoles equipped with (S)-Oppolzer,s sultam chiral auxiliary for the first time and used it as dipolarophile in above asymmetric [3+2] cycloaddition reactions. The synthesis affords the desired chiral dispiro-bisoxindole alkaloids scaffold in excellent yields with high diastereo- and enantioselectivity under mild conditions. The other enantiomer of cycloadducts could be obtained utilizing (R)-Oppolzer,s sultam and confirmed by HPLC analysis (Fig. 1). The stereochemistry of products was determined by single-crystal X-ray analysis.1

Keywords:

Asymmetric 1 , 3-dipolar cycloaddition , Azomethine ylides , Enantioselective synthesis , Dispiro-bisoxindole alkaloids , Oppolzer , s sultam chiral auxiliary