Ketones, conjugated model

Here a model conjugate ketone, i.e. cw-acrolein, was adopted. From the dimeric precursor 40, the four-center reaction path was traced but could not be accomplished. The... 

Conjugated aldehydes, ketones and esters may be modeled by acrolein, methylvinyl ketone and methyl acrylate, respectively. Their LUMOs are shown below ... 

For conjugated ketones, the factors controlling the relative amounts of 1,2- and 1,4-product have been extensively studied in model systems (for example, substituted cyclohex-3-enones) [6 10 Eqs. (1) and (2)]. 

If the carbonyl group is conjugated with a n bond, as in a,/3-unsaturated ketones, the fraction of positive charge on the carbon atom is shared with the n bond, and the (3 carbon becomes partly cationic in nature, as symbolised in Figs. 2.3 and 2.4 by the relatively small p orbitals on the (3 carbon atom in Li and ip2 of acrolein as a model for a Z-substituted alkene. Looking again at those pictures, it is clear that the sum of the coefficients of the filled p orbitals on the carbonyl carbon is smaller than the sum at the (3 carbon, and that... 

This chapter begins with a detailed examination of the evolution of the theory of nucleophilic attack on a chiral aldehyde or ketone, from Cram s original rule of steric control of asymmetric induction to the Felkin-Anh-Heathcock formulation. Then follows a discussion of Cram s simpler rigid model (chelate rule), then carbonyl additions using chiral catalysts and chiral (nonenolate) nucleophiles. The chapter concludes with asymmetric 1,4-additions to conjugated carbonyls and azomethines. 

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