Reagent‐Controlled Synthesis of Syn‐β‐hydroxy‐α‐aryl Carboxylic Acid Esters

A systematic investigation into the steric effects of boron reagents on the diastereoselectivity of the enolboration–aldolization of methyl phenylacetate has led to an efficient synthesis of syn ‐β‐hydroxy‐α‐aryl carboxylic acid esters. The use of less sterically hindered, 9‐borabicyclo[3.3.1]nonyl triflate (9‐BBNOTf), in the presence of diisopropylethylamine as an enolizing reagent, consistently provided high yields and excellent diastereoselectivities in a shorter enolboration–aldolization time.