Synthesis of Triafulvene Precursors for Retro-Diels-Alder Reactions

Article abstract of DOI:10.1002/hlca.19860690410

Triafulvene precursors exo-15 and endo-15 have been prepared by addition of dibromocarbene to benzobarrelene 12 followed by a lithium-halogen exchange, methylation, and elimination of HBr (12 -> 13 -> 14 -> 15), (Scheme 2).Gas-phase pyrolysis of exo/endo-mixtures of 15 above 400 deg gave minor amounts of naphthalene (16), traces of a hydrocarbon C4H4 identified by MS (presumably triafulvene 1) and predominantly (36percent) the isomerization product 17 (Scheme 3).In a second synthetic approach the well-known cycloheptatriene-norcaradiene equilibrium of type 26->/<-27 has been utilised to prepare various endo-trans-3-(X-methyl) tricyclo<3.2.2.0^2,4>nona-6,8-dienes 31 (Scheme 5).However, numerous elimination experiments 31 -> 9 failed so far.The structure of two rearrangement products 33 and 34 (Scheme 6) has been elucidated.