Stereoregulations of Pyrimidinone Based Chiral Auxiliary in Aldol and Alkylation Reactions: A Convenient Route to Oxyneolignans

(<i>S</i>)-4-Isopropyl-1-phenyltetrahydropyrimidin-2(1<i>H</i>)-one was synthesized and evaluated as a chiral auxiliary for asymmetric acetate and propionate aldol reactions, by generation of titanium and lithium enolates, affording excellent yields and stereoselectivities for <i>syn</i> and <i>anti</i> aldol diastereomers, respectively. High stereoselectivities were also obtained in lithium mediated alkylation reactions. The application of the auxiliary was exemplified in the asymmetric synthesis of a natural oxyneolignan, (+)-(7<i>S</i>,8<i>S</i>)-4-hydroxy-3,3′,5′-trimethoxy-8′,9′-dinor-8,4′-oxyneoligna-7,9-diol-7′-oic acid.