Alternative Modes of Addition of Electrophilic Olefins to the Vinylcyclopropane Systems in 2,2‐Ethano‐1‐Methylene‐1,2,3,4‐Tetrahydronaphthalene and 1,1‐Ethano‐2‐Methylene‐1,2,3,4‐Tetrahydronaphthalene

The title compounds 2,2‐ethano‐1‐methylene and 1,1‐ethano‐2‐methylene‐1,2,3,4‐tetrahydronaphthalene ( 13 and 14 respectively) were synthesized by the Wittig reaction from the corresponding ethano‐tetralones ( 16 ) and ( 19 ) which were, in turn, prepared from the respective α‐ and β‐tetralones ( 15 ) and ( 18 ). It is shown that the reaction of ( 13 ) with TCNE at 0° yields the corresponding [2 + 2] cycloaddition adduct ( 20 ), isomerizing thermally to the formal [2 + 5] cycloaddition adduct ( 21 ). Compound ( 13 ) reacts with N‐tosylisocyanate (TIC) and with N‐phenylsulfonylisocyanate (PSI) to a 4:1‐isomeric mixture of (Z)‐ and (E)‐acryloamides ( 24 ) and ( 26 ), respectively. The reaction of ( 14 ) with TCNE at 0° leads to the [2 + 5] cycloadduct ( 30 ), while with (TIC) and (PSI) the corresponding tricyclic adducts ( 28a ) and ( 28b ) result. Bromination of ( 16 ) with NBS yielded the respective 4‐bromo‐2,2‐ethano‐1‐tetralone ( 31 ) which gave, upon dehydrobromination with the aid of DBU, the naphtho‐dihydrofurane derivative ( 34 ). The latter was formed most likely via facile cyclopropylketone upon dihydrofurane rearrangement of an initially formed 2,2‐ethano‐1‐oxo‐1,2‐dihydronaphthalene ( 32 ) which was desired for the formation of ( 33 ). Structures of all new compounds were assigned on basis of analytical and spectroscopic data (IR, UV, mass spectra, 1 H‐NMR).