Enamine salts reactions with nucleophilic reagents

B. Reactions of Enamine Salts with Nucleophilic Reagents. . 286... 

Reactions at the carbon-nitrogen double bond of iminium salts are analogous to nucleophilic reactions at the carbonyl group of aldehydes and ketones. This is why free enamines do not react with nucleophilic reagents, whereas their salts can undergo such reactions. 

Enamine salts react with many nucleophilic reagents. The reaction with the cyanide ion is noteworthy. l-Methyl-2-ethyl-2-cyanopyrrolidine (170) is formed on treatment of alkali cyanide with l-methyl-2-ethyl-.d -pyrrolin-ium perchlorate (242). The reduction of the tertiary nitrile (170) with... 

From the preparative point of view, reactions of heterocyclic aromatic compounds with nucleophilic reagents are very important, especially the reactions of their quaternary salts containing a formal enamine grouping in the molecule. 

B. Reactions of enamine salts with nucleophilic reagents. 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

Nucleophilic addition takes place at C-1, and this is considerably enhanced if the reaction is carried out upon an isoquinolinium salt. Reduction with lithium aluminium hydride [tetrahydroaluminate(III)] in THF (tetrahydrofuran), for example, gives a 1,2-dihydroisoquinoline (Scheme 3.15). These products behave as cyclic enamines and if isoquinolinium salts are reacted with sodium borohydride [tetrahy-droboronate(III)] in aqueous ethanol, further reduction to 1,2,3,4-tetrahydroisoquinolines is effected through protonation at C-4 and then hydride transfer from the reagent to C-3. 

Alkyllithium compounds and alkali cyanides, mercaptides, and alkoxides,322,323 etc. have been used as nucleophilic reagents in reactions with the enamine salts. Nitrile groups can be removed by reduction or by treatment with acids. Treatment of cotarnine (100)... 

A wide range of nucleophilic substrates of different reactivity were trifluoromethylated with these reagents. The substrates include carbanions, activated aromatics, heteroaromatics, enol silyl ethers, enamines, phosphines, thiolate ions and iodide anions. " (Scheme 3.8) The least reactive substrates, such as triphenylphosphine, aniline and phenols, require the use of the most reactive dinitro derivative. Most of the reactions can be conveniently performed with the unsubstituted 5-trifluoromethyl dibenzothiophenium salt (35). The least reactive sulfonium salts are the acyclic sulfonium compounds which reacted only with the sodium thiolates.55,59... 

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