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20.6.1.4.7 Variation 7: The Keck Method

DOI: 10.1055/sos-SD-020-01369

Maier, M. E., Science of Synthesis, (2007) 20, 1466.

Another method for the in situ generation of an active ester employs the reagent N,N′-dicyclohexylcarbodiimide in combination with 4-(dimethylamino)pyridine and 4-(dimethylamino)pyridine hydrochloride.[‌210‌] The latter additive is important since otherwise large amounts of the unwanted N-acylurea ‌146‌ are formed (‌Scheme 65‌). This is attributed to a low effective concentration of the alcohol. For example, without 4-(dimethylamino)pyridine hydrochloride, 4% of hexadecanolide is formed. In contrast, with the hydrochloride the yield is 95% (‌Table 13‌). Several additional examples are displayed in ‌Table 14‌.[‌211‌–‌214‌]

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‌Meeee 88‌ Meeeeeeeeeeee Meeeee ee eee Meee Meeeee[‌888‌]

e Meee Meee Meeee (%) ee Meeeeee Meeee (%) ee Meeeeee Mee
8 88 88 88 [‌888‌]
8 88 88 88 [‌888‌]
88 88 88 eeeee [‌888‌]
88 88 88 – [‌888‌]

‌Meeee 88‌ Meee Meeeeeee ee Meeeeeeeeeeeeeeeee Meeee eee Meee Meeeee[‌888‌–‌888‌]

Meeeeee Meeee (%) Mee
88e [‌888‌]
88 [‌888‌]
88 [‌888‌]
88e [‌888‌]

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e Meeeeee eeeeee ee 8% ee eee Meeeeeeee eeeeee.

References

[210] Meeee, M. M.; Meee, M. M., M. Mee. Meee., (8888) 88, 8888.
[211] Meeeeeee, M.; Meeeee, M. M. M.; Meeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888.
[212] Meee, M. M.; Meeee, M. M.; Meeee, M. M., M. Mee. Meee., (8888) 88, 888.
[213] Meeee, M. M.; Meeeee, M. M.; Meeee, M. M.; Meeeee, M.; Meeee, M. M., M. Me. Meee. Mee., (8888) 888, 8888.
[214] Meee, M. M.; Meeee, M. M., M. Mee. Meee., (8888) 88, 8888.

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  • 8.Meeeee-Meee, (8888) M 8-8, 888.

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