Routes to 3aH-indenes. Deprotonation and methylation of some indenones bearing ring junction substituents

Abstract

The trienones (1), (2), and (3) have been converted into the corresponding enolate anions by reaction with potassium hydride below –10 °C. Methyl fluorosulphonate was added to each solution: with the trienones (1) and (3), transient 3aH-indenes (4a) and (14) were detected and were intercepted by reaction with 4-phenyl-triazolinedione. The tetraenol ether (4a) was also intercepted by N-phenylmaleimide. In all cases the products were the result of [8 + 2] rather than of [4 + 2] addition to the 3aH-indenes. The enolates and enol ethers derived from the trienones (1) and (2) were found to rearrange, by a [1,5] shift of the ring junction phenyl substituent, at or below room temperature.