Energy Michael additions

Michael additions to benzotriazole-stabilized carbanions have been reviewed. review of the structural dependence of heterolytic bond dissociation energy of carbon-carbon a-bonds in hydrocarbons has summarized the synthesis and behaviour of molecules in which highly stable cationic and anionic hydrocarbon moieties have apparently been combined. 

Fig. 8 Oiganocatalytic Michael-addition Energy profiles of paths A and B, both leading to (t )-configurated product, as obtained from gas phase calculations (B3LYP/6-311G(d,p)// B3LYP/6-310(d))...

The electrochemical acylation reaction45-49 produces the equivalent of RC—O, which (formally) couples with the substrate. In some cases the substrate is reduced to its anion-radical which might transfer an electron to the acylation agent, and in other cases the acylating agent is reduced. Activated olefins are attacked at the site where a Michael addition would have taken place [Eq. (22)]. Aromatic rings with low resonance energy may be attacked similarly.47... 

Figure 5 Schematic free-energy profile for two modes offormation of 94 from the reaction of 90 with 91 (a) conventional sequence of independent Michael addition-crotonic condensation via formation of covalent 92a (b) a one-pot Robinson annulation without proton quenching of carbanionic intermediate 92...

Michael addition of azoles on acrylamide affords A-azolylpropanamides <88JHC225>. In this way derivatives of pyrazole (7), indazole, 5-chloroindazole, and 5-nitroindazole have been prepared and characterized by H and C NMR spectroscopy. In the case of indazoles, both isomers are formed which isomerize to the most stable 1//-derivative with activation energies high enough to observe both isomers but not to prevent their equilibration. 

Scheme 5.37. AT3 strain raises the energy of the transition structure for Michael addition of the less substituted secondary enamine [179]. The dashed lines in the transition structures indicate the primary MO interactions, according to Scheme 5.34c.

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