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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)
Author(s) -
Klester Alfred Michael,
Ganter Camille
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680323
Subject(s) - chemistry , carbocation , protonation , regioselectivity , adamantane , cope rearrangement , olefin fiber , stereochemistry , rearrangement reaction , vicinal , medicinal chemistry , ion , organic chemistry , polymer , catalysis
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.