Synthesis of enantiopure C-2-symmetric VERDI disulfonamides and their application to the catalytic enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes
La. Paquette et Rj. Zhou, Synthesis of enantiopure C-2-symmetric VERDI disulfonamides and their application to the catalytic enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes, J ORG CHEM, 64(21), 1999, pp. 7929-7934
The enantiopure disulfonamides 7a-c have been prepared from the Ct-symmetri
c diketone 2, a starting material conveniently accessible from the "dimeriz
ation" of (+)-verbenone. These ligands, when treated with titanium isopropo
xide and diethylzinc, function as catalysts for the enantioselective alkyla
tion of aldehydes. Stereoselectivity levels ranging from 72 to 98% ee are s
een depending on the structural characteristics of the aldehyde. In all cas
es, the absolute configuration of the carbinol product is R. A working mech
anistic model is advanced for the purpose of rationalizing the high levels
and direction of asymmetric induction exhibited by these VERDI catalysts.