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

Abstract

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 [1 s , 2 s ] sigmatropic rearrangements to give propargylbenzenes ( 28 , 29 , 30 , 38 ) and [3 s , 4 s ] sigmatropic rearrangements to give allenylbenzenes ( 24–27 , 40) (cf. schemes 2, 3, 5, 6). [3 s , 3 s ] 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 [1 s , 2 s ] sigmatropic methyl shift is observed (4%).