Tetrahedron Letters,Vol.28,No.44,pp 5233-5236,1987 0040-4039/87 $3.00 + .oo Printed in Great Britain Pergamon Journals Ltd. zyxwvutsrqp CHIRAL CATALYSTS FOR THE ENANTIOSELECTIVE ADDITION OF ORGANOMETALLIC REAGENTS TO ALDEHYDES E.J. Corey and Francis J.Hannon Department of Chemistry, Harvard University, Cambridge, Massachusetts, 02138 zyxwvutsrqponmlkjihg Summary : A mechanistic model for the enantioselective addition of diethylzinc to benzaldehyde with chiral tridentate lithium complexes as catalysts correctly predicts the observed direction of enantioselectivity which occurs at levels of 8595% ee. A recent paper from these laboratories described two rationally designed and effective chiral catalysts for the enantioselective conjugate addition of organocopper reagents to a$-en0nes.l Thus, the lithium salt derived from 1 (available in one step from (lR, 2S)-(-)-ephedrine) brings together 2-cyclohexenone and an organocopper reagent to generate selectively the product shown (e.g. for R=C2H5 as the R(+) form in 92% ee). The two most reasonable modes of assembly of the reactants and catalyst, A and B, both predict the same product enantiomer and, consequently, no decision between these possibilities has been made. 1 In parallel with these studies we have investigated a similar approach to the catalytic, enantioselective 1,2-addition of organometallic reagents to aldehydes. This paper describes some of the results and insights emerging from this project using four different catalysts and organozinc reagents. Organozinc reagents are the simplest to study because the rates of the uncatalyzed (i.e. spontaneous) reactions with aldehydes are low and catalytic effects can be large.2 Fair to excellent enantioselectivities have been reported previously233 using various chiral ligands, organometallic reagents and aldehydes. As in our previous work,’ the design of potential catalysts was guided by mechanistic considerations and, particularly, the idea that the assembly 2, containing a rigid chiral catalyst and the reactants, may provide the required low-energy pathway. The specific ligand 3 (oil), [CX] 23,,-33.6’, (c=O.9 in CHC13) was synthesized from 0 'LI 0 iJH CHI 5233