“…Other phosphorane reagents, most significantly TsunodaÕs cyanomethylene reagents, generate basic anions during the reaction and thus provide results similar to the original Mitsunobu class [10][11][12] In contrast, our recently [6] reported phosphorane, synthesized from tributylphosphine and chlorodimethylmalonate, produces an intermediate that expels the dimethylmalonyl anion and is therefore significantly less basic than 6. This tributylphosphorane reagent was shown to promote the general condensation reaction of a wide range of carboxylic acid and alcohol partners, through generation of intermediates analogous to 5 under conditions of controlled reaction basicity, providing esters along with tributylphosphine oxide and dimethylmalonate [6]. In addition to the levels of stereocontrol achievable (vide infra), the side products produced are easily removed by aqueous base partition, eliminating the purification difficulties inherent in the use of standard Mitsunobu reagents.…”