[76524-71-5] · C7H12O3 · 2-Ethoxyallyl Acetate · (MW 144.17)
Alternate Name: 3-acetoxy-2-ethoxy-1-propene.
Preparative Methods: by reaction of a-lithioethyl vinyl ether with Paraformaldehyde (40-50%) followed by acetylation (Acetic Anhydride, Pyridine).1
Handling, Storage, and Precautions: use in a fume hood.
2-Ethoxyallyl acetate (1) is a useful reagent for the preparation of enol ethers by way of palladium-catalyzed allylic alkylations. Reaction of the p-allylpalladium intermediate generated from (1) with several types of nucleophiles has been studied. Aryl,2 vinyl,2 and enol stannanes2,3 all give satisfactory reactions (eqs 1-3).
For enol stannanes where regioisomers are possible, the product obtained is that arising from reaction of the more stable enolate (cf. eqs 4 and 5).3 Active methylene compounds, such as b-diketones or b-keto esters, can be alkylated in the presence of a base (eqs 6 and 7).1
The enol ethers arising from palladium-catalyzed allylic alkylations can be transformed into cyclopentenones. Several methods for cyclization have been developed. For simple ketones, acidic hydrolysis of the enol ether followed by base-promoted aldol condensation provides the annulated product (eq 8).3 More complex ketones require the use of an intramolecular Wittig reaction to effect cyclization (eqs 9 and 10).1 In the event, enol ether hydrolysis with N-Bromosuccinimide and H2O provides the a-bromo ketone. Reaction with Triphenylphosphine yields a phosphonium salt which, upon treatment with base, undergoes cyclization. A useful application of this method is seen in the synthesis of several analogs of the Wieland-Miescher ketone (eq 9).1
David L. Clark
University of California, Berkeley, CA, USA