The zwitterionic aza‐Claisen rearrangement of optically active N‐allylpyrrolidines and α‐phenoxyacetyl fluorides proceeds with complete simple diastereoselectivity (internal asymmetric induction) and complete 1,2‐asymmetric induction to generate a new C–C bond adjacent to a chiral C‐N‐Boc functionality. The resulting γ,δ‐unsaturated amides were cyclised to give the corresponding pyrrolizidinones, which enabled the determination of the relative configuration of the stereotriads. Vinyl group degradation and a final lactam reduction gave an optically active analogue of (+)‐petasinine (a pyrrolizidine alkaloid). Furthermore, the stereotriad‐containing amides should be useful key intermediates for the total synthesis of optically active elaeocarpin (an indolizidine alkaloid).