Highly Diastereoselective Construction of Acyclic Systems with Two Adjacent Quaternary Stereocenters by Allylation of Ketones

摘要

Diastereoselective construction of acyclic systems bearing multiple stereogenic centers is one of the most challenging areas in organic synthesis. Reaction of allylmetals with unsymmetrical carbonyl compounds is a major approach to this challenge. Recently much attention has been paid to diastereoselective allylation of ketones with various γ-mono-substituted allylmetals such as organoboron, silicon, tin,'' zinc,' titanium,' indium, vanadium, and samarium species. A much more arduous task is the stereoselective construction of acyclic systems having two adjacent quaternary carbon atoms, and only most recently highly stereoselective construction of such systems by the allylation of ketones has been achieved by Knochel and co-workers' and Marek and co-workers using Y,Y-disubstituted allylzinc reagents. The approach by Marek and co-workers enjoys a synthetic advantage in that the reaction is stereospecific and both the diastereomers are obtained by using the different geometrical isomers of allylzinc reagents generated in situ from terminal alkynes, organocopper reagents, and the Simons-Smith-Furukawa zinc carbenoid. The allylation, however, has only been applied to aryl, hetaryl, and styryl ketones, and the allylation of aliphatic ketones has not been elucidated yet.