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9.9.4.1.6 Method 6: Introduction of Aminoalkyl Groups (Mannich Reaction)

DOI: 10.1055/sos-SD-009-00244

König, B.Science of Synthesis, (20019243.

Alkyl-substituted furans 281 react with formaldehyde and amines 282 in the presence of acids as catalysts to give 1-(aminoalkyl)furans 284 (Mannich reaction; Scheme 92).[‌511‌‌513‌] As in all electrophilic substitution reactions of furans, reaction at the α-position is favored. The best yields are reported for Mannich reactions using secondary amines. Aminomethylation of unsubstituted furan is not successful under these conditions.[‌511‌] However, if preformed iminium salts 283 are used in aprotic solvents, the reaction proceeds with 6575% yield.[‌514‌] Iminium salts have also been generated in situ for aminomethylation of furans in aprotic solvents from N,O-acetals and chlorotrimethylsilane.[‌515‌,‌516‌]

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