(2-Ethoxy-1-propenyl)triphenylphosphonium Iodide

[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.

Annulation of Cyclohexanones.

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

1. Ramirez, F.; Dershowitz, S. JOC 1957, 22, 41.
2. Whitesell, J. K.; Fellman, S. W. JOC 1977, 42, 1664.
3. For a review of annulation, see: (a) Jung, M. E. T 1976, 32, 3. (b) Gawley, R. E. S 1976, 777.
4. For a review of the intramolecular Wittig reaction, see: (a) Becker, K. B. T 1980, 36, 1717. (b) Becker, K. B. HCA 1977, 60, 68.

David M. Armistead

Vertex Pharmaceuticals, Cambridge, MA, USA

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