Claisen rearrangements of tropolone ethers. Part I
Abstract
2-Allyloxy-3,5,7-trimethyltropone rearranges smoothyl at 160° giving initially 7-allyl-3,5,7-trimethylcyclohepta-3,5-diene-1,2-dione. Further thermal isomerisation of this product gives two tricyclic α-diketones, whereas photolysis induces ring-collapse to a bicyclo[3,2,0]heptanedione. Rearrangement of the prop-2-ynyl ether affords a single tricyclic α-diketone, which readily undergoes acid-catalysed ring cleavage.