Stereochemistry of a carbonium ion rearrangement

Abstract

CONCERTED rearrangements of the carbonium ion kind (1 → 3) are usually supposed to go with stereochemical inversion at the migration terminus (C¹) and retention in the migrating group (R) (ref. 1). Many chemists have recorded one or other of these results but no one has shown both in one and the same acyclic molecule, largely because it is very difficult to find a reaction in which both centres are chiral and both survive as chiral in the product. Rigid cyclic systems do show both results at once but this is not very informative as no other outcome is conceivable in a molecule which has no opportunity for internal rotation.