Die Dienol‐Benzol‐Umlagerung von Propargylcyclohexadienolen: aromatische [1,2]‐, [3,3]‐ und [3,4]‐sigmatropische Umlagerungen

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Abstract
The acid catalysed dienol‐benzene rearrangement of methyl substituted o‐ and p‐propargylcyclohexadienols (18–22, 34 and 35) was investigated. In the first step water is eliminated to yield the corresponding methyl propargyl benzonium ions (cf. scheme 6, a), which undergo [1s, 2s] sigmatropic rearrangements to give propargylbenzenes (28, 29, 30, 38) and [3s, 4s] sigmatropic rearrangements to give allenylbenzenes (24–27, 40) (cf. schemes 2, 3, 5, 6). [3s, 3s] sigmatropic rearrangements occur only to a small extend. In the rearrangement of 2‐propargyl‐2,4,6‐trimethylcyclohexa‐3,5‐dien‐1‐ol (18) a [1s, 2s] sigmatropic methyl shift is observed (4%).