A Simple and Efficient Method for Transesterification of β-Keto Esters Catalyzed by Cesium Fluoride

Abstract

Cesium fluoride is found to be an efficient and reusable catalyst for the transesterification of β-keto esters with various alcohols in good to high yields.

Key words

alcohols - β-keto esters - catalysis - cesium fluoride - transesterifications

References and Notes

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• 6c Hexamethylenetetramine: Ribeiro RS. de Souza ROMA. Vasconcellos MLAA. Oliveira BL. Ferreira LC. Aguiar LCS. Synthesis  2007,  61 ; and references cited therein
• 7 Anastas PT. Warner JC. Green Chemistry: Theory and Practice   Oxford University Press; Oxford: 1998. 
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14

To the best of our knowledge, there is only one successful report⁴ on the use of this type compound in the transesterification process.

15

CsF was the best catalyst among the cesium salts examined under the identical conditions: CsCl (1%), CsBr (2%), CsI (2%).

19

Transesterification of normal esters proceeded under similar reaction conditions. The details of this result will be communicated later.

20

Typical Procedure (Table 1, entry 1): In a 65-mL test tube (2.0 × 19 cm) fitted with a Drierite drying tube, a vigorously stirred mixture of methyl acetoacetate (581 mg, 5.0 mmol), 1-octanol (846 mg, 6.5 mmol) and CsF²¹ (76 mg, 0.5 mmol) in commercial toluene without any purification (10 mL) was heated so that the toluene refluxed halfway up the tube (130-135 °C, bath temperature) for 18 h.²² After toluene had been decanted, CsF was washed with Et₂O (5 mL). The combined organic layer was evaporated under reduced pressure. The residue was chromatographed on silica gel (5% EtOAc-hexane) to afford octyl acetoacetate (997 mg, 93%).²³ CsF remained intact and was reused for the subsequent reaction.

21

Purchased from Mitsuwa Chemicals Co., Ltd.

22

The equilibrium was shifted due to the loss of the relatively volatile methyl, ethyl or isopropyl alcohol from the reaction mixture.

23

Selected spectroscopic data:
Octyl 2,2-Dimethyl-3-oxobutyrate: ¹H NMR (CDCl₃): δ = 0.88 (t, J = 7.5 Hz, 3 H), 1.22-1.66 (m, 12 H), 1.36 (s, 6 H), 2.16 (s, 3 H), 4.12 (t, J = 7.0 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.9, 21.7, 22.5, 25.5, 25.7, 28.3, 29.0, 31.6, 55.6, 65.3, 173.5, 205.6.
2-Heptynyl 3-Oxohexanoate: ¹H NMR (CDCl₃): δ = 0.91 (t, J = 7.5 Hz, 3 H), 0.93 (t, J = 7.5 Hz, 3 H), 1.36-1.44 (m, 2 H), 1.46-1.53 (m, 2 H), 1.59-1.67 (m, 2 H), 2.22 (tt, J = 2.5, 7.5 Hz, 2 H), 2.53 (t, J = 7.5 Hz, 2 H), 3.47 (s, 2 H), 4.72 (t, J = 2.5 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.4, 16.8, 18.3, 21.8, 30.3, 44.7, 48.9, 53.5, 73.3, 88.0, 166.5, 202.1.
8-Oxiranyloctyl 3-Oxohexanoate: ¹H NMR (CDCl₃): δ = 0.93 (t, J = 7.5 Hz, 3 H), 1.25-1.69 (m, 16 H), 2.47 (dd, J = 3.5, 5.0 Hz, 1 H), 2.52 (t, J = 7.5 Hz, 2 H), 2.75 (app t, J = 4.5 Hz, 1 H), 2.88-2.94 (m, 1 H), 3.43 (s, 2 H), 4.13 (t, J = 6.5 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.4, 16.8, 25.6, 25.8, 28.3, 28.9, 29.1, 29.2, 32.3, 44.7, 46.9, 49.1, 52.2, 65.3, 167.2, 202.6.
2-(Dimethylamino)ethyl 3-Oxohexanoate: ¹H NMR (CDCl₃): δ = 0.93 (t, J = 7.0 Hz, 3 H), 1.58-1.68 (m, 2 H), 2.28 (s, 6 H), 2.52 (t, J = 7.0 Hz, 2 H), 2.58 (t, J = 5.5 Hz, 2 H), 3.47 (s, 2 H), 4.24 (t, J = 5.5 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.3, 16.7, 44.7, 45.4, 49.0, 57.4, 62.6, 167.1, 202.6.
6-Chlorohexyl 3-Oxohexanoate: ¹H NMR (CDCl₃): δ = 0.93 (t, J = 7.5 Hz, 3 H), 1.35-1.82 (m, 10 H), 2.52 (t, J = 7.5 Hz, 2 H), 3.43 (s, 2 H), 3.54 (t, J = 6.5 Hz, 2 H), 4.14 (t, J = 7.0 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.4, 16.8, 25.0, 26.3, 28.2, 32.2, 44.7, 49.1, 65.0, 167.1, 202.6.