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.