2-Ethoxyallyl Acetate

[76524-71-5]  · C7H12O3  · 2-Ethoxyallyl Acetate  · (MW 144.17)

(preparation of enol ethers via the corresponding allylpalladium complexes;1 cyclopentenone annulation1)

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.

Preparation of Enol Ethers.

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

Cyclopentenone Annulation.4

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

Related Reagents.

Bromoacetone; 2,3-Dibromopropene; 2,3-Dichloropropene; Ethyl Chloroformate; 2-Methoxyallyl Bromide; 2-Nitro-1-propene; Tetrakis(triphenylphosphine)palladium(0).

1. Trost, B. M.; Curran, D. P. JACS 1980, 102, 5699.
2. (a) Kosugi, M.; Ohashi, K.; Akuzawa, K.; Kawazoe, T.; Sano, H.; Migita, T. CL 1987, 1237. (b) Kosugi, M.; Miyajima, Y.; Nakanishi, H.; Sano, H.; Migita, T. BCJ 1989, 62, 3383.
3. Trost, B. M.; Keinan, E. TL 1980, 21, 2591.
4. For a review on cyclopentannulation methods, see: Ramaiah, M. S 1984, 529.

David L. Clark

University of California, Berkeley, CA, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.