A facile and efficient synthetic route for indenoquinoxalinone spiro-oxacyclic systems
with small to medium ring sizes has been developed via an efficient ring-closing enyne metathesis (RCEYM) as a key step. The starting material
O-alkylated propargylic alcohol of indenoquinoxalinone is synthesized via a two-step
protocol: 1. propargylation of ketone followed by 2. alkenylation of the resulting
propargyl ethers with alkenyl bromides. Upon being subjected to RCEYM using Grubbs
II catalyst, the resulting O-alkenylated propargyl derivative furnished the spiro-ethereal products in good yield.
Spectroscopic data and single-crystal XRD analysis characterized the structures of
the products. A plausible mechanism is provided.
Key words
ring-closing enyne metathesis - indenoquinoxalinone - alkenyl ether - Grubbs II catalyst
- oxacyclic spiro compounds