Chiral catalysts organocatalysed

The use of C2-symmetric A,Ai -dioxide amides in a wide variety of chiral ligand-/metal-catalysed or organocatalysed asymmetric reactions has been reviewed. Other reviews include chiral spiro catalysts and the organic and carbohydrate chemistry relevant to biomass. " ... 

The organocatalysed asymmetric cycloaddition reaction of a,p-unsaturated ketones and aldehydes is scarcely studied, especially for fluorine-containing substrates. In this area, Liu et al. have reported unusual inverse-electron-demand oxa-Diels-Alder reactions of a,p-unsaturated trifluoromethyl ketones with aldehydes catalysed by chiral a,a-diphenylprolinol trimethylsilyl ether. It was shown that the addition of pura-fluorophenol and silica gel along with this catalyst was necessary, otherwise the reaction was very slow and a poor yield was obtained. Under these optimal conditions, the expected cyclic adducts were obtained in good yields and high fl n-diastereo- and enantioselectivities, as shown in Scheme 6.11. 

In 2010, Alexakis and Quintard reported a tandem reaction beginning with a copper-catalysed 1,4-addition of diallqrlzincs to a, 3-unsaturated aldehydes which was followed by an organocatalysed Michael reaction with vinyl sul-fone. ° As shown in Scheme 7.68, this simple procedure, using two chiral entities, such as a chiral copper complex of (I )-BINAP as the first catalyst. 

Jacobsen has also developed an organocatalysed asymmetric addition of nucleophiles with iV-acyl-iminium ions (Pictet-Spengler) and oxocarbe-nium ions, potentially useful reactions in medicinal chemistry (Scheme 14.97). The mechanism involves the formation of an anionic catalyst-chloride complex which acts as a chiral counter ion directing the approach of nucleophiles to one face of the cationic species. 

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