ja311889v_si_001.pdf (4.89 MB)
A Theoretical Investigation on the Mechanism and Stereochemical Course of the Addition of (E)‑2-Butenyltrimethylsilane to Acetaldehyde by Electrophilic and Nucleophilic Activation
journal contribution
posted on 2013-03-27, 00:00 authored by Larry M. Wolf, Scott E. DenmarkThe
diastereoselectivity of the addition of (E)-2-butenyltrimethylsilane
to acetaldehyde under electrophilic (BF3, H3O+) and nucleophilic (F–) activation
is investigated using density functional theory (M06-2X). The interaction–distortion/activation–strain
model of reactivity is used to rationalize the origin of the selectivity.
Consistent with experimental model systems, the synclinal transition
states are determined to be preferred over the antiperiplanar transition
states in the electrophilic-activated manifolds and vice versa for
the fluoride-activated manifold. The selectivity for the syn diastereomer
in the electrophilic activation manifolds is accounted for by increased
electrostatic and orbital interactions for a synclinal transition
state (syn-T3) at the expense of increased steric interactions
relative to antiperiplanar transition states. The enhanced orbital
interactions for the synclinal (syn-T3) versus antiperiplanar
transition states can be attributed to increased π→π*
interactions. The selectivity for the anti diastereomer in the nucleophilic
manifold is explained by the lesser electrostatic repulsion in the
antiperiplanar transition states which are favored relative to the
synclinal transition states. Additionally, the diastereoselectivity
is partly attributed to variation in the distortion of the crotylsilane.