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The general structure of an enamine. An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. [1] [2] Enamines are versatile intermediates. [3] [4] Condensation to give an enamine. [5] The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine.
The term "imine" was coined in 1883 by the German chemist Albert Ladenburg. [6] Usually imines refer to compounds with the general formula R 2 C=NR, as discussed below. [7] In the older literature, imine refers to the aza-analogue of an epoxide. Thus, ethylenimine is the three-membered ring species aziridine C 2 H 4 NH. [8]
The reaction depicted in Scheme 2 illustrates the Povarov reaction with an imine and an enamine in the presence of yttrium triflate as the Lewis acid. [5] This reaction is regioselective because the iminium ion preferentially attacks the nitro ortho position and not the para position.
enamine – imine: H−N−C=C ⇌ N=C−C−H. cyanamide – carbodiimide; guanidine – guanidine – guanidine: With a central carbon surrounded by three nitrogens, a guanidine group allows this transform in three possible orientations
Depending on reaction conditions, reactive intermediate imines can also undergo attack by amine products to afford secondary and tertiary amines: 2 R-C≡N + 4 H 2 → (R-CH 2) 2 NH + NH 3 3 R-C≡N + 6 H 2 → (R-CH 2) 3 N + 2 NH 3. Such reactions proceed via enamine intermediates. [8]
General structure of an imine. Schiff bases are imines in which R 3 is an alkyl or aryl group (not a hydrogen). R 1 and R 2 may be hydrogens General structure of an azomethine compound. In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure R 1 R 2 C=NR 3 (R 3 = alkyl or aryl, but not hydrogen).
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Stork enamine reaction with alkyl halides. In this method a carbonyl compound is condensed to a Schiff base. The imine then reacts with a Grignard reagent to the corresponding Hauser base. This species' negative charge enables displacing a less reactive alkyl halide, including methyl, ethyl, and other nonactivated halides.