Generation of 3-methoxy-3a-methyl-3aH-indene and study of its cycloaddition reactions

Abstract

The title compound (1) has been prepared form indan-1-one by Birch reduction and methylation followed by the introduction of a further double bond, enolisation of the ketone, and O-methylation. The tetraenol ether (1) is the first 3aH-indene derivative to be isolated. It is shown to be oxidised by air to the Z-cinnamic ester (5), and to undergo ready rearrangement to the 1H-indene (7). Cycloadditions of N-phenyltriazolinedione, diethyl azodiformate, and dimethyl acetylenedicarboxylate to the termini of the tetraene are observed. These formal [8 + 2] cycloadditions are in contrast to the [4 + 2] addition which is observed with N-phenymaleimide. The [4 + 2] adduct rearranges on heating to give a mixture of [8 + 2] adducts: it is suggested that this process involves dissociation of the adduct into its components and their re-combination.