Catalytic Enantio­selective Hetero-dimerization of Acrylates and 1,3-Dienes

1,3-Dienes are ubiquitous and easily
synthesized starting materials
for organic synthesis, and alkyl acrylates are among the most abundant
and cheapest feedstock carbon sources. A practical, highly enantio­selective
union of these two readily available precursors giving valuable, enantio-pure
skipped 1,4-diene esters (with two configurationally defined double
bonds) is reported. The process uses commercially available cobalt
salts and chiral ligands. As illustrated by the use of 20 different
substrates, including 17 prochiral 1,3-dienes and 3 acrylates, this
hetero-dimerization reaction is tolerant of a number of common organic
functional groups (e.g., aromatic substituents, halides, isolated
mono- and di-substituted double bonds, esters, silyl ethers, and silyl
enol ethers). The novel results including ligand, counterion, and
solvent effects uncovered during the course of these investigations
show a unique role of a possible cationic Co­(I) intermediate in these
reactions. The rational evolution of a mechanism-based strategy that
led to the eventual successful outcome and the attendant support studies
may have further implications for the expanding use of low-valent
group 9 metal complexes in organic synthesis.