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The ketene formation during the deprotonation process for substrates possessing Evans' oxazolidinone is also a main side reaction for the related alkylation reactions. Development in the field of enamine chemistry and the utilization of imine derivatives of enolates managed to provide an alternative for enolate alkylation reactions.
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.
Deprotonation at the nitrogen atom generates a Schiff base, which tautomerizes to form an enamine that gets protonated via the acid catalyst, which is commonly concentrated sulfuric acid (H 2 SO 4). The second major step, which is also the rate-determining step, is the annulation of the molecule.
The Stork enamine synthesis: formation of an enamine from a ketone; addition of the enamine to an alpha, beta-unsaturated aldehyde or ketone; hydrolysis of the enamine back to a ketone; The Stork enamine reaction. The reaction also applies to acyl halides as electrophiles, which results in the formation of 1,3-diketones (Stork acylation). [2]
The mechanism of this Kröhnke-type reaction likely proceeds via a vinylogous cyanamide 23 which undergoes elimination of hydrocyanic acid, deprotonation to form enamine 24 and cyclization to form intermediate 25, which is then dehydrated to form the desired pyridine product. Figure 6
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds.These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. [1]
In organic chemistry, the Mannich reaction is a three-component organic reaction that involves the amino alkylation of an acidic proton next to a carbonyl (C=O) functional group by formaldehyde (H−CHO) and a primary or secondary amine (−NH 2) or ammonia (NH 3). [1]
In organic chemistry, the Michael reaction or Michael 1,4 addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon-carbon bond at the acceptor's β-carbon.