Synthesis of Sterically Hindered β‑Diketones via Condensation of Acid Chlorides with Enolates

Bulky β-diketones have rarely
exceeded dipivaloylmethane
(DPM) in steric demand, largely due to synthetic limitations of the
Claisen condensation. This work demonstrates hindered acid chlorides
to be selective electrophiles in noncoordinating solvents for condensations
with enolates. An improved synthesis of DPM is described (90% yield),
and crowded β-diketones featuring bulky o-biphenyl
or m-terphenyl fragments were prepared in good to
excellent yields. These compounds are anticipated to have a steric
profile far greater than that of DPM. General reaction conditions
and mechanistic considerations are included.