[62639-97-8] · C23H24IOP · (2-Ethoxy-1-propenyl)triphenylphosphonium Iodide · (MW 474.29)
(precursor for 2-ethoxyallylidenetriphenylphosphorane, which is a three-carbon annulation reagent1)
Physical Data: mp 163-165 °C.
Preparative Methods: by the condensation of Ethyl Iodide with 1-triphenylphosphoranylidene-2-propanone.2
Purification: recrystallization from methanol-ethyl acetate.
Handling, Storage, and Precautions: should be dried in vacuo for best results.
Deprotonation of (2-ethoxy-1-propenyl)triphenylphosphonium iodide1 with n-Butyllithium in hexanes gives 2-ethoxyallylidenetriphenylphosphorane (1) (eq 1).2 This reagent has been used2 to donate three carbon atoms in a [3 + 3] annulation of cyclohexenones onto enones for the construction of six-membered carbocyclic systems.3
Thus the in situ generated ylide (1) reacts in a tandem Michael addition Wittig reaction with a variety of a,b-unsaturated ketones (2) to provide the 2-ethoxy-1,3-cyclohexadienes (3). These intermediates are subsequently hydrolyzed on workup with 1 N HCl to give the cyclohexenones (4) in 26-61% overall chemical yield (eq 2).4 This reaction sequence has been used for the construction of monocyclic, fused bicyclic, and spiro bicyclic ring systems.2
David M. Armistead
Vertex Pharmaceuticals, Cambridge, MA, USA