No abstract

A systematic study on hippuric acid substituents was performed in order to better understand the influence of stereoelectronic factors on the Erlenmeyer reaction rate. In addition, two reaction systems were evaluated: Hünig’s base solvent free conditions and catalytic sodium acetate in 2-methyl-THF. The effect on reaction rate of electron withdrawing and electron donating groups are reported. Specifically, the study led to the conclusion that stereoelectronic factors have significant influence in one of our key Erlenmeyer reaction by affecting its reaction rate.

An exothermic decomposition was observed during a metalation/acylation of 3,4-difluoroanisole (5), resulting in a significant thermal hazard. The lithiated anion 6 was found to decompose exothermically at temperatures above −47 °C showing an adiabatic temperature rise at a peak rate of 120 °C/min. A literature search revealed similar observations for metalation/acylation in analogous aromatic difluoro compounds. This sequence of reactions was evaluated thermochemically. Control experiments at −55 °C over 2 h indicated anion 6 was stable at temperatures below −55 °C under dilute reaction concentrations. This runaway hazard could be addressed using MgCl2 to stabilize the reactive species and thereby decrease its decomposition rate. Thermochemical experiments suggested MgCl2 forms a weak interaction with lithiated species 6, rather than via complete lithium−magnesium exchange. The process was successfully piloted on a multikilo scale by use of MgCl2 as an additive.