Chiral Organometallic Reagents, VI. Diastereomeric α‐Phenylseleno Alkyllithium Compounds, Generation and Reactions

The selenoacetals 4 having a chiral center in the β‐position were subjected to selenium/lithium exchange by butyllithium in ether. The resulting α‐phenylseleno alkyllithium compounds 5 undergo rapid epimerization at −78°C. Trapping of these organolithium compounds by ketones or aldehydes appears to be faster than the epimerization. The ratio of the trapping products therefore reflects the equilibrium ratio of the diastereomeric α‐phenylseleno alkyllithium compounds. The dependence of this equilibrium on various structural parameters has been evaluated.