Base mediated 5i style="mso-bidi-font-style: normal"-endo-dig/i cyclization of i style="mso-bidi-font-style:normal"N/i-propargyl proline derivatives: A facile entry to pyrrolizidine scaffolds

摘要

A simple, base facilitated 5i style="mso-bidi-font-style: normal"-endo-dig/i cyclization strategy has been exploited for the assembly of bicyclic core of pyrrolizidine alkaloids. This unprecedented protocol allows access to a diverse range of alkyl and aryl substituted pyrrolizidine scaffolds in moderate yields from readily available i style="mso-bidi-font-style:normal"N/i-propargyl-L-proline ester derivatives under mild conditions. No catalyst or alkyne activator is required to effect this atom economical transformation.