Thermisches Verhalten von Mesitylallenen; Beispiel einer aromatischen [1, 5s]-sigmatropischen H-Verschiebung. Vorläufige Mitteilung

Mesitylallene ( 6a ), 1-mesityl-3-methyl-allene ( 6b ) and 1-mesityl-3, 3-dimethylallene ( 6c ) were prepared via dienol-benzene-rearrangements. At 170° 6a isomerises to give 5, 7-dimethyl-1, 2-dihydronaphthalene ( 8 ). Under the same conditions 6b rearranges to give 2, 5, 7-trimethyl-1, 2-dihydronaphthalene ( 10 ; 60%) and cis-1-mesitylbuta-1, 3-diene ( 11 ; 40%) while 6c gives only cis-1-mesityl-3-methyl-buta-1, 3-diene ( 13 ). The allenes undergo first an aromatic 1, 5 s]-sigmatropic H-shift to the o-xylylene derivatives 7, 9 and 12 , which then exhibit disrotatory ring closure to the dihydronaphthalenes or aromatic 1, 7 a]-sigmatropic H-shift to the 1-mesitylbuta-1, 3-dienes.