Cyclic Analogues of the Hendrickson ‘POP’ Reagent

Abstract

The Hendrickson reagent, triphenylphosphonium anhydride trifluoromethanesulfonate, ‘POP’ 1, is a powerful dehydrating agent. Five-, six-, and seven-membered cyclic analogues of the ‘POP’ reagent 2–4 have been prepared and their use for ester and amide synthesis investigated. A kinetic comparison of the cyclic analogues 2–4 revealed that a considerable increase in the rate of esterification could be achieved when the five-membered ring analogue 2 was used, presumably due to the ease of formation of the putative phosphorane intermediate. The rate of ester formation from a primary alcohol using the Hendrickson reagent 1 was shown to be significantly faster when non-polar solvents were employed.