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.