Sigmatropische Umlagerungen von Aryl‐propargyläthern; Synthese von 1, 5‐Dimethyl‐6‐methylen‐tricyclo[3, 2, 1, 0 2,7 ]‐oct‐3‐en‐8‐on‐Derivaten. Vorläufige Mitteilung

2, 6‐Dimethylphenyl propargyl ether ( 10 ) and its derivatives 12–15 rearrange thermally to 1, 5‐dimethyl‐6‐methylene‐tricyclo [3.2.1.0 2,7 ]oct‐3‐en‐8‐one ( 9 ) and related compounds 16–19 . The ethers undergo first an aromatic [3, 3]‐sigmatropic rearrangement to ortho ‐allenyldienones 11 , which then undergo ring closure to the tricyclic products by an electrocyclic reaction. Only in the case of the γ‐methylpropargyl ether 13 , the ortho ‐dienone 11 is further rearranged in low yield to the para ‐butynylphenol 20 , but the tricyclic ketone 17 is again the main product. New data show that the known thermal cyclisation of aryl propargyl ethers to chromenes (e. g. 4 → 8 ) involves a preliminary [3, 3]‐sigmatropic rearrangement.