Eine Synthese methylierter Epoxyhydroazulenone durch intramolekulare [4 + 3]‐Cycloaddition einer aus 1,1‐Dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐on erzeugten Oxyallyl‐Zwischenstufe

A synthesis of Methylated Epoxyhydroazulenones by Intramolecular [4 + 3] Cycloaddition of an Oxyallyl Intermediate, Generated from 1,1‐Dichloro‐6‐(3‐methyl‐2‐furyl)hexan‐2‐one ( Z )‐3‐Methylpent‐2‐en‐4‐yn‐1‐ol ( 7 ) was transformed to 2‐(4‐chlorobutyl)‐3‐methylfuran ( 4b ) and 2‐(but‐3‐enyl)‐3‐methylfuran ( 10a ) by C‐alkylation and 5‐exo‐dig cyclization. The Grignard derivative formed from 4b gave 1,1‐dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐onc ( 1b ) on reaction with dichloroacetyl chloride. This dichloromethyl ketone undergoes a base‐induced cyclization to form diastereoisomeric 7‐chloro‐1,2,3,6,7,8a‐hexahydro‐4‐methyl‐8H‐3a,6‐epoxyazulen‐8‐ones ( 3bα and 3bβ ) by way of an intramolecular [4+3] cycloaddition of an oxyallyl intermediate 2b. By dechlorination and hydrogenation of 3bβ , the tricyclic hydroepoxyazulenones 18 and 19 have been synthesized.