Asymmetric activation of tropos catalysts in the stereoselective catalytic conjugate additions of R 2Zn to α,β-enones: an efficient synthesis of (−)-muscone

Abstract

The preparation of a new phosphoramidite starting from ( R)-BINOL and a biphenylamine is presented. In such a compound the chirality is due only to atropisomerism and this molecule possesses a flexible biphenylamine residue. Therefore it can work as a tropos catalyst. The catalytic efficiency of this new phosphoramidite has been tested in some asymmetric conjugate additions of dialkylzinc reagents to α,β-enones and compared with that of an analogous already known non-tropos ligand. Interestingly, while comparable results were obtained in the addition of ZnEt 2 to chalcone and cyclohexenone, in the case of the addition of ZnMe 2 to ( E)-cyclopentadec-2-en-1-one, the new ligand provides (−)-muscone, a valuable ingredient of the perfume industry, in 84% ee, while the non-tropos ligand gives a much lower (57%) ee value.