The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part V. Rearrangements of 1,2-trimethylenenorbornanes initiated by regioselective formation of carbocation centers at C(2) and C(6)

✍ Scribed by Alfred Michael Klester; Camille Ganter

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 691 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680323

✦ Synopsis

Abstract

The behaviour of the regioselectively generated carbocation centers at C(2) and C(6) in 1,2‐trimethylenenorbornanes was investigated in order to study the occurrence or absence of a degenerate rearrangement E⇄M in the adamantane rearrangement of both 1,2‐endo‐ (1) and 1,2‐exo‐trimethylenenorbornane (2) to 2‐endo,6‐endo‐trimethylenenorbornane (3). A degenerate rearrangement E⇄M is inevitably involved inasmuch as a 1,2‐trimethylenenorborn‐2‐yl cation E not only is formed directly as manifested by the conversions of the reactants 4 (C(2), C(3)‐olefin) and 6 (C(2), C(3′)‐olefin), but also indirectly (via F→E) if the leaving group at C(6) to be ionized occupies the endo‐position (6‐endo‐alcohol 8). No degenerate rearrangement E⇄M is operative starting from reactants that lead directly to a 2,6‐trimethylenenorborn‐2‐yl cation G; this is the case with both the ionization of the 6‐exo‐alcohol 10 having the leaving OH‐group in a stereoelectronically favoured configuration to undergo simultaneous C(1), C(2)‐bond migration (→G) as well as the protonation of the olefin 13 which is followed by same reaction pathway.