2-Cyclohexenone ammonium salt

Corey employed a cinchona alkaloid-derived ammonium salt 5 for the solid-liquid phase transfer catalyst, and attained 99% ee in the addition of a glycine-derived imine to 2-cyclohexenone (Scheme 6) [13,14]. 

Cheap and readily available L-proline has been used numerous times for the intermediate and reversible generation of chiral iminium ions from a,/ -unsaturated carbonyl compounds. For example, Yamaguchi et al. reported in 1993 that the rubidium salt of L-proline catalyzes the addition of di-iso-propyl malonate to the acyclic Michael acceptors 40a-c (Scheme 4.13), with enantiomeric excesses as high as 77% [22], With 2-cycloheptenone and 2-cyclohexenone as substrates ca 90% yield and ee of 59% and 49% were obtained. Later the enantioselectivity of this process was increased to a maximum of 88% ee in the addition of di-tert-butyl malonate to the E-pentenone 40a in the presence of 20 mol% Rb-L-prolinate and 20 mol% CsF [23], Taguchi and Kawara employed the L-proline-derived ammonium salts 41a and... 

The Michael addition of cyclohexenone to ascorbic acid was carried out in water in presence of an inorganic acid (rather than a base) (Scheme 28)/ The reaction" of active nitriles with acetylenes can be catalysed by quaternary ammonium salts (PTC) (Scheme 29). 

Zhang FY, Corey EJ. Highly enantioselective Michael reactions catalyzed by a chiral quaternary ammonium salt. Illustration by as3fmmetric syntheses of (S)-omithine and chiral 2-cyclohexenones. Org. Lett. 2000 2(8) 1097-1100. 

The infrared spectra of hydroiodides and perchlorates of such enamines indicate O-protonation one or two strong maxima occur in the 1600 cm-1 region and there is no absorption in the 1650-1800 cm-1 region as would be expected for the ammonium or immonium compounds. 2,5,5-Trimethyl-3-pyrrolidino-2-cyclohexenone and 5,5-dimethyl-3-pyrrolidino-2-cyclohexenone (41) are examples of compounds which form salts by O-protonation. In contrast,... 

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