Directed diastereoselectivity in the asymmetric claisen/metathesis reaction sequence

The Claisen/metathesis sequence is a versatile synthetic tool for the synthesis of quaternary hydroxy and amino acid carbocycles. By correctly choosing both the configuration of the allylic alcohol and the double bond geometry, specific access to any one of four possible stereoisomers is possible in good yield and excellent diastereoselectivity. The enantiomerically pure allylic alcohols are easily obtained by addition of terminal alkynes to aldehydes. Controlled reduction of the triple bond then gives the desired double bond geometry.