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Braverman, S.; Cherkinsky, M., Science of Synthesis Knowledge Updates, (2014) 3, 263.
Phosgenation of N-silylated amines has some advantages over phosgenation of free amines in terms of high yields and mild reaction conditions and is particularly suitable for the preparation of acid-sensitive and/or thermally unstable isocyanates. The reaction proceeds via formation of unstable intermediate N-silylcarbaminoyl chlorides, which undergo intramolecular β-elimination at relatively low temperatures and afford the corresponding isocyanates in high yields. This procedure has been applied to the preparation of a wide range of isocyanates, including isocyanates of the furan, thiophene, and fluorophenyl and polyfluorophenyl series.[166] Solutions of N-trimethylsilyl derivatives of tetrahydrofurfurylamine, furfurylamine, substituted thiophen-2-amines, and polyfluoroanilines are first prepared by silylation of the starting amines with hexamethyldisilazane or chlorotrimethylsilane in toluene or diglyme. Next, treatment of the mixture with a 25% toluene solution of phosgene in a 10% excess at 5–20 °C provides the corresponding isocyanates 59 after isolation by vacuum distillation (Scheme 66). Similarly, aliphatic, carbocyclic, and arylalkyl isocyanates can be prepared from the corresponding N-silyl derivatives.[167] The yield of isocyanates decreases when going from aliphatic amines to benzylamines and rises as the length of the alkyl chain in (arylalkyl)amines is extended.
Meeeee 88 Meeeeeeee ee Meeeeeeeeee ee Meeeeeeeeeee ee M-Meeeeeeee Meeeee[888,888]
M8 | Meeee (%) | Mee |
---|---|---|
88 | [888] | |
88 | [888] | |
8-MM8M8 | 88 | [888] |
8-MM8M8 | 88 | [888] |
8-MM8M8 | 88 | [888] |
8,8-M8M8M8 | 88 | [888] |
8-M8MM8M8 | 88 | [888] |
8-M8MM8M8 | 88 | [888] |
8-MeM8MMM8M8M8 | 88 | [888] |
8-MeM8MM8M8 | 88 | [888] |
8-MeM8MM8M8 | 88 | [888] |
8-MeM8MM8M8 | 88 | [888] |
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Meeeeeeeeeee Meeeeeeee
Meeeeeeeeee 88; Meeeeee Meeeeeeee:[888]
MMMMMMM: Meeeeeee ee e eeeeee eeeeeeeeeee eeeeeeee eee eeee eeeee ee eeeeeeeeee.
Me e eeee ee eeeeeeee (88.8 e, 8.88 eee) ee eeeeeee (88 eM) ee 88–88 °M e eeee ee eee eeeeeeeeeeeee M-eeeeeeeeee (8.8 eee) ee eeeeeee (88–88 eM) eee eeeee eeeeeeee eeeee eeeeeeeeeee eee eeeeeeeeeee eeeee (8–88 °M). Mee eeeeeee eee eeee eeeeeee eee 8 e ee eee eeeee eeeeeeeeeee, eeeee eeeee eeeeee eeeeeeee, MMMMe, eee eeeeeee eeee eeeeeeeee eee ee ee e eeeee eeeeeeeeeee ee 888 °M. Mee eeeeeee eee eeeeeeeee eeeee eeeeeee eeeeeeee eee eee eeeeeeee eeee eeeeeeeee ee eee eeee eeeeeeee; eeeee: 88–88%.
References
[166] | Meeeeee, M. M.; Meeeeeee, M. M.; Meeeeeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M., Meee. M. Mee. Meee. (Meee. Meeeee.), (8888) 88, 888. |
[167] | Meeeeee, M. M.; Meeeeeee, M. M.; Meeeeeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M., Meee. M. Mee. Meee. (Meee. Meeeee.), (8888) 88, 888. |
[168] | Meeeeee, M. M.; Meeeeeee, M. M.; Meeeeeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M.; Meeeeeee, M. M., Meee. M. Mee. Meee. (Meee. Meeeee.), (8888) 88, 8888. |