The 1,2-Didehydronaphthalene to 1H-Indenylidenecarbene Rearrangement: Formation of 7-Methyl-1H-Indenylideneethenone and Its Rearrangement to Acenaphthylen-4-Ol in a Flash Vacuum Pyrolytic Reaction

Abstract

7-Methyl-1 H- indenone was trapped as the cyclopentadiene adduct endo* 8-methyl-1,4,4a,9a tetrahydro-1,4-methano-9H-fluoren-9-one (11) which was converted into the E- and Z-isomers (15) and (16) of endo (8'-methyl-l',4',4a',9a'-tetrahydro-1',4'-methano-9'H-fluoren-9'-ylidene) ethanoic acid by addition of methoxyethyne, rearrangement and hydrolysis. Both acids yielded the anhydride (17) of the E-acid on treatment with trifluoroacetic anhydride. Flash vacuum pyrolysis of this anhydride at 650º gave acenaphthylen-4-ol.

7-Methyl-1 H- indenylideneethenone (7) is proposed as an intermediate in this reaction and the results are discussed in relation to the rearrangement described in the title.

The X-ray crystal structure of methyl endo (E)-(8'-methyl-l',4',4a',9a'-tetrahydro-l',4'-methano-9'H-fluoren-9'-ylidene) ethanoate (13) is reported.