reducing reagent, an impressive change of selectivity
was accomplished in one case (entries 7 and 8). This
was explained by precoordination of DIBAL-H to the
carbonyl group, thus disfavoring58or59for steric
reasons.
31a
A similar picture is obtained when analyzing
nucleophilic additions toR-chiral epoxyaldehydes and
ketones (Scheme 23, Table 11).
34
Again, there seems
to be quite a delicate balance between chelation