Direct Synthesis of 6‐Azabicyclo[3.2.1]oct‐6‐en‐2‐ones and Pyrrolizidines from Divinyl Ketones and Observation of Remarkable Substituent Effects

Substituents create access to molecular diversity. Under basic conditions, 6‐azabicyclo[3.2.1]oct‐6‐en‐2‐ones 3 and pyrrolizidines 4 are efficiently synthesized, respectively, in a single step from ethyl isocyanoacetate 2 and divinyl ketones 1 bearing an aryl or alkyl group at the 2‐position. For comparison, only the corresponding pyrrolizidines 4 ′ can be obtained from divinyl ketones 1 ′ bearing a methoxycarbonyl group at the 2‐position.