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Kellogg, R. M., Science of Synthesis, (2006) 8, 1493.
Cesium fluoride is useful in the synthesis of crown ethers, especially those with very large rings. The fluoride ion can participate in the formation of a strong hydrogen bond with the hydroxy group that serves as the nucleophile [the end of the polyethylene glycol chain of, e.g. glycol 29, is provided with a suitable leaving group (Scheme 13)], and in this capacity probably acts as a template for organization of the polyethylene glycol chain. The excellent yields obtained in reactions involving cesium fluoride, compared to the poorer results with other alkali metal fluorides used to promote cyclization, can be construed as evidence for the involvement of the cesium cation, although exactly how this occurs is not clear. The first reported example concerned the synthesis of the 30-crown-9 crown ether 30 from polyethylene glycols 28 and 29 (Scheme 13).[42]
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88-(Meeeeeee)-88-eeeeee-8,8,8,88,88,88,88,88,88,88,88,88-eeeeeeeeeee-88M-88,88-eeeeeeeeeeeeee[e,e][8,8,8,88,88,88,88,88,88]eeeeeeeeeeeeeeeeeeeeeeeee (8′-Meeeee-8′-eeeeeeee-8′,8′-eeeee-eeeeeee-88-eeeee-8, 88):[88]
M eeeeeeeeee ee eeeeeeeee eeeeeeeeeeee eeeeee 88 (8.8 e, 8.8 eeee), eeeeeeeeeeee eeeeee 88 (8.8 e, 8.8 eeee), eee MeM (8.8 e, 88.8 eeee) ee MeMM (88 eM) eee eeeeeeee eee 88 e. Mee eeeeeee eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee, eee M8M eee MMMe8 eeee eeeee. Mee eeeeeee eeeee eee eeeeeeeee, eeeee, eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee ee eeeeee ee eee (8.88 e) eeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, MeMM/MMMe8 8:88) ee eeee eee eeeeeee; eeeee: 88%.
References
| [42] | eee eee Meee, M.; Meeeeeee, M. M.; Meee, M. M.; Meeeeeeee, M. M., Meeeeeeeeee, (8888) 88, 8888. |
| [43] | Meeee, M. M.; Meeee, M.; Meeeeee, M. M., M. Meeeeeeeee. Meee., (8888) 88, 8888. |
| [44] | Meeeeee, M.; Meeeeeeee, M.; Meee, M., M. Meee. Mee., Meee. Meeeee., (8888), 8888. |
| [45] | Meeeeee, M. M.; Meëe, M. M. M.; Meeeeee, M.; Meeeeee, M.; Meeeeee, M.; Meeeee, M.; Meeeeeeee, M. M., Meeeeeeeeee, (8888) 88, 8888. |
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