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.

Triphenylphosphonium Anhydride Trifluoromethanesulfonate

“…Treatment with Trifluoromethanesulfonic Anhydride in the usual manner generates 1,1,3,3-tetraphenyl-2-oxa-1,3-phospholanium bis(trifluoromethanesulfonate), 1,1,3,3-tetraphenyl-2-oxa-1,3-phosphinanium bis(trifluoromethanesulfonate), or 1,1,3,3-tetraphenyl-2-oxa-1,3phosphepanium bis(trifluoromethanesulfonate), respectively. 36 The advantage over the classical Hendrickson reagent is the increased polarity of the bis-phosphine oxide side-product, which aids chromatographic separation. In addition, the fivemembered cyclic POP reagent (1,1,3,3-tetraphenyl-2-oxa-1,3phospholanium bis(trifluoromethanesulfonate)) is reported to offer a faster rate of esterification than even the Hendrickson reagent.…”

The Hendrickson ‘POP’ reagent and analogues thereof: synthesis, structure, and application in organic synthesis

“…81 With the latter reagent, the release of two moles of triphenylphosphine oxide exacerbates the problem of separation of the product by chromatography. On the other hand, the bisphosphine oxide byproducts produced from the cyclic analogues are considerably more polar than triphenylphosphine oxide because of the two phosphine oxide moieties, thus rendering purification much more facile.…”

Reactions of Trivalent Iodine Reagents with Classic Iridium and Rhodium Complexes

“…Experimental details, 1 H, 31 P NMR spectra, and mass spectra are available on the Journal's website.…”

“…[16,31] Compounds 22 and 23 were shown to be in approximate ratio of 4 : 1 by 31 P NMR, bearing in mind the semiquantitative nature of 31 P NMR. A battery of efforts to selectively precipitate 22 to obtain an analytically pure sample unfortunately failed.…”