DBU-Promoted [4 + 4] Domino Cycloaddition of Ynones with Benzylidenepyrazolones To Access Eight-Membered Cyclic Ethers

An efficient DBU-promoted [4 + 4]
domino annulation reactions of
ynones and benzylidenepyrazolones has been developed. This process
resulted finally in the formation of eight-membered cyclic ethers
in moderate to good yields. The easy availability of starting materials
and the simple cyclization procedure make this approach suitable for
the preparation of a wide range of useful oxocino [2,3-c] pyrazoles.