Synthesis of 1-(2-Furyl)-2-alkanones Eldon H. Sund and David Scott HunterJ. Heterocyclic Chem. 11, 1123-1124 (1974)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/darzen.arylalkanones.pdf)
In connection with our interest in enolizable ketones, it was found of interest to synthesize a series of 1-(2-furyl)-2-alkanones. Previously three of these ketones were prepared by Hass, et al.
3 by the condensation of 2-furaldehyde and the requisite nitroalkane with subsequent reduction of the resulting nitroalkane to yield the ketone. This method lacks generality because of the difficulty in obtaining higher homologs of the nitroalkanes.
A convenient method of preparation of these ketones is the Darzens glycidic ester condensation and subsequent hydrolysis and decarboxylation of the glycidic ester to yield the requisite ketone. The ethyl 2-bromoesters were either purchased or prepared by the method of Schwenk and Papa
4. These ethyl 2-bromoesters were condensed with 2-furaldehyde essentially as described by Ruzicka and Ehmann
5. The resulting glycidic ester was not isolated, but rather saponified and decarboxylated in the usual manner to yield the 1-(2-furyl)-2-alkanone, usually in good yield.
Experimental
Preparation of 1-(2-Furyl)-2-alkanones
A mixture of 29.8 g (0.31 mole) 2-furaldehyde and 0.31 mole of the ethyl 2-bromoester were cooled to 5-10°C. While maintaining this temperature and with stirring a solution of sodium ethoxide prepared from 13.8 g. (0.60 mole) sodium in 150 mL of ethanol was slowly added to the aldehyde-ester mixture. The reaction mixture was stirred an additional 30 minutes at this temperature and then allowed to warm to room temperature with an additional 2 hours of stirring. Approximately 30 mL of water were added to the flask and the mixture stirred on a steam bath for 3 hours. The reaction mixture was cooled to room temperature and a sufficient quantity of dilute phosphoric acid was added to the solution to bring the pH in a range of 3-4. As the acid was added a large quantity of carbon dioxide was evolved. The ketone was extracted with ether, washed with 5% sodium bicarbonate solution, water and dried over anhydrous sodium sulfate. After removal of the ether by flash distillation the ketone was distilled through a Nester-Faust annular Teflon spinning-band column under reduced pressure. These ketones are shown in Table I.References[3] H. B. Hass, A. G. Susi and R. T. Heider,
J. Org. Chem. 15, 8-14 (1950)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/nitro.alkene.derivatives.pdf)
[4] E. Schwenk and D. Papa,
J. Am. Chem. Soc. 70, 3626-3627 (1948)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/alpha-bromination.carboxylic.acids.pdf)
[5] R. Ruzicka and T. Ehmann,
Helv. Chim. Acta 15, 160 (1932)