Chalcones Et2Zn addition

Et2Zn addition to 4,4-dimethyl-2-cyclohexenone and chalcone with 81% ee and 90% ee, respectively. 

Phosphoramidites 13, derived from 2,2 -binaphthol, proved to be versatile ligands for copper-catalyzed 1,4-additions of Et2Zn to chalcone and 2-cyclohexenone (Scheme 7.9) [37]. 

Although the presence of BINOL in the ligands so far discussed has shown itself to be particular effective, modification of the diol moiety provides new classes of ligands for this addition reaction. Alexakis, screening a number of chiral phosphites in the Cu(OTf)2-catalyzed 1,4-addition, showed that an ee of 40% could be obtained for the addition of Et2Zn to 2-cyclohexenone and of 65% for addition to chalcone, by using cyclic phosphites derived from diethyl tartrate [51]. 

The copper-catalysed enantioselective 1,4-conjugate addition of Et2Zn to chalcones was investigated in the presence of a catalytic amount of Af,P-ferrocenyl ligand (179) with central and planar chirality under mild conditions (0 °C to room temper- ature). Chalcones with ortho-substituents (from ortho-substituted benzaldehydes and acetophenones) exhibited a dramatic improvement in the enantioselectivities (<92% ee).229... 

On a similar note, conjugate addition of Et2Zn to chalcones (266), catalysed by a complex of (TfO)2Cu and (269), generates zinc enolate (267), which can be captured by nitrostyrenes (259) to produce y-nitro ketones (268) with >20 1 dr and <95% ee " ... 

Ricci and coworkers [64] studied oxazoline moiety fused with a cyclopenta[P]thio-phene as ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone. The structure of the active Cu species was determined by ESI-MS. Evans and coworkers [65] studied C2-symmetric copper(II) complexes as chiral Lewis acids. The catalyst-substrate species were probed using electrospray ionization mass spectrometry. Comelles and coworkers studied Cu(II)-catalyzed Michael additions of P-dicarbonyl compounds to 2-butenone in neutral media [66]. ESI-MS studies suggested that copper enolates of the a-dicarbonyl formed in situ are the active nucleophilic species. Schwarz and coworkers investigated by ESI-MS iron enolates formed in solutions of iron(III) salts and [3-ketoesters [67]. Studying the mechanism of palladium complex-catalyzed enantioselective Mannich-type reactions, Fujii and coworkers characterized a novel binuclear palladium enolate complex as intermediate by ESI-MS [68]. 

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