Transformation of 6-Methyliden-tricyclo[3.2.1.02.7]oct-3-en-8-ones into Norcaradiene/Cycloheptatriene-Derivatives. -Summary. Tricyclic ketones of type 1,5-dimethyl-6-methpliden-tricyclo[3.2.1.0~~7]oct-3-en-8-one (1) [l] rearrange on heating with sodium methylate mainly to methyl-7-methyl-bicyclo[4.1 .0]hepta-2, 4-dien-7-carboxylates = methyl-7-methyl-norcaradien-7-carboxylates (4). Moreover, the formation of methyl 2-aryl-propionate ( 5 ) is observed. Thus, tricyclic 1 gives a mixture of norcaradiene derivatives 2 and 4 in 50% yield together with 13% of methyl 2-(2', 3'-dimethylphenyl)-propionate ( 5 ) (Scheme I). Similarly the tricyclic ketone 7 rearranges to norcaradienes 8 and 9 (31,574) and methyl 2-(2', 3', 5'-trimethylphenyl)-propionate (10, 4%). I n this case, the reduction products of 7, i.e. the alcohols 11 (24%) and 12 (8%) as well as other products derived from 11 are observed; heating of the endo-alcohol 11 with sodium methylate leads to the 2-arylpropan-1-01s 13 and 14 (Scheme 2). Under the same conditions the ketone 18 affords the norcaradiene ester 20 (Scheme 3). Scheme 4 shows the rearrangement of the pentacyclic ketone 21 to the cycloheplatriene derivative 22 and the base catalysed isomerisation o f 22 to 23.The structure elucidations were achieved with the help of UV.-, IR.-and mainly NMR . spectra. The carboxy or methoxycarbonyl group assumes the exo-position in all the norcaradiene derivatives (NMR., also in the presence of NMR. shift reagents). The cycloheptatriene-norcaradiene-equilibrium is shifted to the norcaradiene side to > 95% in compounds 2, 4, 8 and 9 and to > 90% in 19 and 20. This is due to the 7-em-carboxy or 7-exo-methoxycarbonyl group and the methyl groups in positions 2 and 3 (cf. KZavner [9], chapter 4). On the other hand, in the case of 22 the cycloheptatriene structure is almost exclusively predominant.The most probable mechanism for the rearrangement of tricyclic ketones of type 1 to methylnorcaradien-7-exo-carboxylates or to the corresponding carboxylic acids is depicted in Scheme 5. Thus, the reaction path leads from 1 through a, c, f, g and h to 4. The aromatization reaction of 1 to 5 and 3 proceeds preferentially through a, c (Scheme 5) and k (Scheme 6 ) . The conversation of the tricyclic endo-alcohol 11 to 2-aryl-propan-1-01s 13 and 14 using sodium methylate occurs to ca. 90% viu m + n and ca. loo/, via m + p (Scheme 7 ) ; the primarily formed 2-aryl-propanals are reduced under the reaction conditions. The Pxo-isomer 12 shows no similar reaction.
