Other Fused Azetidines, Azetines and Azetes

The interest for 4-membered unsaturated nitrogen-containing bicyclic systems has been very limited owing to their difficult access that limits their use, and they therefore rather remain lab curiosities. In stark contrast, fused and spirocyclic azetidines have been more extensively investigated for they find applications in medicinal chemistry in the context of lead optimization. Because traditional syntheses are lengthy and low yielding, this has in addition triggered a resurge of interest from the synthetic community to develop novel and efficient strategies to access them. These will be overviewed in this chapter together with representative theoretical studies on these systems and key structural data.