A simple entry to sugar derived bispiropyrrolidines through non-stabilized azomethine ylides

1,3-Dipolar cycloaddition reaction of a carbohydrate-derived exocyclic olefin with in situ generated non-stabilized azomethine ylides, formed by the reaction of sarcosine (a secondary α-amino acid) with isatins, acenaphthenedione and cycloalkanones in refluxing toluene afforded bispiropyrrolidine derivatives in 78–92% yield, when DIPEA was used as a base. However, using Et3N/DBU, the reaction of the olefin precursor with azomethine ylide (derived from the condensation of cyclopentanone and sarcosine) furnished the product in 51–53% yield. On the other hand, in the absence of a base the yield of the cycloaddition product was dramatically decreased to 10–22%.