Cyclohexanone enamine catalysis

Chen and coworkers have reported a new domino Michael-Michael addition reaction between a,a-dicyanoalkene [26] derived from cyclohexanone and benzyli-deneacetone, resulting in a stepwise [4 + 2]-type cycloaddition to afford almost enantiopure bicyclic adduct 15. In contrast to the completely inert function of secondary ammonium salt, a primary amine, 9-amino-9-deoxyepiquinine lo [27], in combination with trifluoroacetic acid, was found to be highly efficient in the activation of the a, 3-unsaturated ketone by tandem iminium-enamine catalysis (Scheme 10.21) [28],... 

Cordova et al. demonstrated in 2005 that the aldol condensation between 4-nitrobenzaldehyde (5 R=p-N02) and cyclic ketones or butanone in the presence of acyclic primary amino acids led to the antz-isomer 6 (Scheme 12.3). One year later, this author described the structure-activity relationship between acyclic amino acids and the aldol derivatives, the synthetic scope of catalysis by acyclic amino acids in aqueous media and water, and studies concerning the reaction mechanism. Excellent enan-tioselectivities (ee up to >99%) were achieved in several cases. As an example of the anh -induction, the (E)-enamine arising from cyclohexanone and the acyclic amino acid could display a proton transfer from the carboxylic acid function to the alkoxide, giving a six-membered chair-like conformation. The favoured approach of the aldehyde would then lead to an anfi-isomer. 

Toste and cmworkers reported an asymmetric fluorination of a-branched cyclohexanones (252) involving a eombination of chiral anion (254) phase-transfer catalysis to activate Selectfluor (253) and enamine activation cycle, using a protected amino acid (255) as organocatalyst (Scheme 67). ... 

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