The pyrethrins and related compounds; Part XXIII:Kinetic control in the formation of pyrethroidal estersb

The unequal amounts of the two diastereomers of (RS)‐1‐(3‐phenoxyphenyl)ethyl (RS)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate, obtained from equimolar proportions of the alcohol and acyl chloride under normal conditions, imply stereoselectivity in the reaction. The extent to which this depends on the nature of the α‐substituent for arange of 3‐phenoxybenzyl esters, on the nature of the acid, and on the method of esterification is investigated. Selectivity arises from kinetic, rather than thermodynamic control.