Nazarov Cyclization of Bis([2.2]paracyclophane-1,9-dienyl) Ketone: First Synthesis of a Bis([2.2]paracyclophane)-Annelated Cyclopenta-1,4-diene
The annelation of five-membered rings onto the bridges of [2.2]paracyclophane-1,9-diene (1) can be achieved via Nazarov cyclization. Depending on the reaction conditions, bis([2.2]paracyclophane-1,9-dienyl) ketone (4) yielded the cy-clopentenone 8 or the α-substituted cyclopentanones 3–7 with two annelated [2.2]paracyclophane units. The synthesis of 1:2-(1:2-[2.2]paracyclophane-1,9-dieno)-4:5-(9:10-[2.2]paracyclophane-1-eno)cyclopenta-1,4-diene (10) from 8 as a potential ligand for metallocene complexes and generation of its anion 11 is also described.