Congratulations to Professor Sarah Reisman at the California Institute of Technology
for having been chosen as the first recipient of the Dr. Margaret Faul Award for Women
in Chemistry
Abstract
The mechanisms by which the complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages
are probed by DFT methods. The outcomes corroborate experimental results and provide
energetic and structural details of the trajectories leading to 3-(oxacyclopentyl
or cycloalkyl)furans via the intermediacy of isolable CpCo-η
4-dienes. They comprise initial stereoselective complexation of one of the double bonds
and the triple bond, rate-determining oxidative coupling to a triplet 16e cobalta-2-cyclopentene,
and terminal double bond docking, followed by stereocontrolled insertion to assemble
intermediate cis- and trans-fused triplet cobalta-4-cycloheptenes. A common indicator of the energetic facility
of the latter is the extent of parallel alignment of the alkene moiety and its target
Co–Cα bond. The cobalta-4-cycloheptenes transform further by β-hydride elimination–reductive
elimination to furnish CpCo-η
4-dienes, which are sufficiently kinetically protected to allow for their experimental
observation. The cascade continues through cobalt-mediated hydride shifts and dissociation
of the aromatic furan ring. The findings in silico with respect to the stereo-, regio-, and chemoselectivity are in consonance with
those obtained in vitro.
Key words
DFT - enynes - β-hydride elimination - cobalt - cycloisomerization - furans
