Direct Elimination of Epoxides to Dienes with Phosphonium Anhydrides

A Straightforward Hetero‐Diels–Alder Approach to (2‐ambo,4′R,8′R)‐α/β/γ/δ‐4‐Thiatocopherol

“…These three steps occurred with very good yields and can be carried out without purification of the intermediates. Eventually, epoxide 13 reacted with freshly prepared Hendrickson reagent (or POP) [22] to give the expected 1,3-diene 8 isolated in 40 % yield (Scheme 5). This methodology required more steps than those initially envisaged and the yield of the last step was not brilliant.…”

Triphenylphosphonium Anhydride Trifluoromethanesulfonate

“…The facile elimination of secondary (in the presence of K 2 CO 3 ) and tertiary alcohols with the aid of the Hendrickson reagent has been previously reported. 8, 24 Further examples of its reactivity, such as that with epoxides, demonstrate the versatility of this reagent. A range of cyclic, acyclic, and 1,2disubstituted acyclic epoxides were converted to derived dienes by refluxing in 1,2-dichloroethane, in the presence of 1 equiv of reagent and excess triethylamine.…”

“…A range of cyclic, acyclic, and 1,2disubstituted acyclic epoxides were converted to derived dienes by refluxing in 1,2-dichloroethane, in the presence of 1 equiv of reagent and excess triethylamine. 24 Reaction monitoring via 31 P NMR indicated initial attack by the epoxide oxygen on the phosphonium species (which is reversible, as the epoxide was recovered on addition of water). This intermediate then rearranges to a 1,2-bis-phosphonium ether that undergoes double elimination to the diene on the addition of base.…”

“…Indeed, the facile conversion of an alkene to a diene can also be envisaged, after initial conversion of the alkene to an epoxide (eq 10). 24 OH OH 1 equiv POP, base O 1 equiv POP, base (10) Amide Activation in Heterocycle Synthesis. The ability of the reagent to activate amide bonds has been exploited in the synthesis of thiazolines from protected N-acyl cysteine precursors.…”

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

“…Table 8 in yields ranging from 50-85%. 11 The elimination reactions were performed in one pot where a prepared suspension of the phosphonium anhydride reagent 1 was treated with an equimolar amount of the epoxide, followed by five equivalents of Et 3 N at 0 o C. The white precipitate was immediately discharged and the mixtures were heated at reflux from 6-48 hrs. Table 8 shows a selection of examples that illustrate the range of substrates that were converted successfully to the corresponding dienes.…”