Scheme 6.

Ring opening of the pyrrolidin‐2‐one ring by a Grignard reagent (PhMgBr) after protection of the nitrogen atom of 1 a with a tert‐butyloxycarbonyl (Boc) group: Synthesis of acyclic allene 9 via intermediate 8.

Ring opening of the pyrrolidin‐2‐one ring by a Grignard reagent (PhMgBr) after protection of the nitrogen atom of 1 a with a tert‐butyloxycarbonyl (Boc) group: Synthesis of acyclic allene 9 via intermediate 8.