Formation of a dimeric camphor derivative with an unusually stable 3-exo substituent

The reductive dimerization of E-3-benzylidenecamphor with sodium proceeds w ith homoacyloin regiochemistry to give a complex mixture of products from w hich two major products have been isolated by chromatography. The major pro duct is formed by dimerization of the E radical anion through the re face o f one radical anion to the si face of the other. This compound lacks a true inversion center of symmetry, but the atoms of the 1,2-diphenylethane moie ty, as well as the camphor oxygen atoms and C(1)-C(4) and C(10) of the camp hor groups, are related by a local inversion center of symmetry. One of the camphor moieties carries an exo substituent, but the compound does not rea dily equilibrate to the epimeric compound where both camphor moieties carry an endo substituent. (C) 2000 Elsevier Science Ltd. All rights reserved.