Novel analgesics and molecular rearrangements in the morphine–thebaine group. Part X. Further acid-catalysed rearrangements of alcohols in the 6,14-endo-ethenotetrahydrothebaine series
Abstract
Thebaine-derived alcohols of general structure (4), showing chain branching on the carbon atom adjacent to the alcoholic centre, can be rearranged in acids in a manner different from alcohols in which there is no such chain branching, to give initially derivatives of furano[2′,3′ :6,7] codide (8 and 9) and finally, by a process that can be represented as proceeding through a bridgehead carbonium ion, derivatives of cyclopenteno[3′,2′ :6,7]codide (13 and 14). The αβ-unsaturated carbinol (22) in contrast rearranges through the codeinone (24) and pyranocodide (25) to the thebainone-A derivative (26).