Asymmetric Induction in Carbonyl Analogues: Comments on Models

Article abstract of DOI:10.1021/jo00179a008

Organometallic reagent additions to certain carbonyl analogues are reported.The compounds in question have C=C(CN)2 or C=C(CO2R)2 in place of CO.The ground-state conformation of these analogues is quite specific.Some of the additions obey the Cram et al. rules for asymmetric induction but require that approach of the organometallic reagent occurs over the L group in the ground-state conformation.This is taken as an indication that the ground-state conformation is not relevant, in agreement with the Curtin-Hammett principle.In other cases, little asymmetric induction is observed.A third type of behavior concerns opposite modes of addition to the dicyanide vs. the diester substrates.The variability of the data are discussed in terms of the validity of rules for asymmetric induction.Secondary isotope effects are explored in an attempt to resolve the dichotomy between additions to cyclic vs. acyclic ketones.The suggestion is made that the dichotomy in stereochemistry of addition may be related to a kinetically significant conformational change in cyclohexanones vs. acyclic substrates or cyclopentanones.